Early metallurgy in the persian gulf

EARLYMETALLURGY OF THE PERSIAN GULF Technology, Trade, and the Bronze Age World

A M E R I C A N S C H O O L OF PREHISTORIC RESEARCH M O N O G R A P H SERIES

Series Editors

C. C. L A M B E R G - K A R L O VSKY, Harvard University DAVID PILBEAM, Harvard University OFE R BAR-YOSEF, Harvard University Editorial Board STE V E N L. K U H N , University of Arizona, Tucson D A N I E L E. LIEBE R M AN, Harvard University R I C H A R D H. M E A D 0 W, Harvard University M A R Y M. V O I G T , The College of William & Mary H E N R Y T. W R I G H T , University of Michigan, A n n Arbor Production Editor W R E N F 0 U R N I ER, Harvard University

The American School of Prehistoric Research (ASPR) Monographs in Archaeology and Paleoanthropology present a series of documents covering a variety of subjects in the archaeology of the Old World (Eurasia, Africa, Australia, and Oceania). This series encompasses a broad range of subjects-from the early prehistory to the Neolithic Revolution in the Old World, and beyond including: hunter-gatherers to complex societies; the rise of agriculture; the emergence of urban societies; human physical morphology, evolution and adaptation, as well as; various technologies such as metallurgy, pottery production, tool making, and shelter construction. Additionally, the subjects of symbolism, religion, and art will be presented within the context of archaeological studies including mortuary practices and rock art. Volumes may be authored by one investigator, a team of investigators, or may be an edited collection of shorter articles by a number of different specialists working on related topics.

Technology, Trade, and the Bronze Age World

Lloyd R. Weeks

Brill Academic Publishers, Inc. Boston Leiden 2003

Library of Congress Cataloging-in-Publication Data

Weeks, Lloyd R., 1970Early metallurgy of the Persian Gulf : technology, trade, and the Bronze Age World 1 Lloyd R. Weeks. p. cm. - (American school of prehistoric research monograph series ;vol. 2) Includes bibliographical references and index. ISBN 0-391-04213-0 1. Bronze age-Persian Gulf. 2. Metal-work, Prehistoric-Persian Gulf. 3. Mines and mineral resources, Prehistoric-Persian Gulf. 4. Excavations-(Archaeology)-Persian Gulf. 5. Bronze-Persian Gulf-Metallurgy. 6. Tin bronze-Persian Gulf. 7. Persian Gulf-Antiquities. I. Title. 11. Series.

ISSN 1543-0529 ISBN 0-391-04213-0 O Copyright 2004 by Brill Academic Publishers, Inc., Boston

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Contents

Foreword vii Preface ix Acknowledgments xi List of Figures xiii List of Tables xvii lntroduction 1 Outline and Genesis of the Project

1

Copper Production and the Bronze Age Economy of Southeastern Arabia

4

Alloying Practices in Bronze Age SoutheasternArabia 5 Investigation of the Bronze Age Tin Trade 5 Analytical Techniques 6 Outline of Chapters 6

Geology and Early Exploitationof Copper Deposits in Southeastern Arabia

7

Geology of Northern Oman and Masirah

7

Copper Deposits in Southeastern Arabia

12

Early Research into Ancient Copper Production in the Oman Peninsula

14

German Mining Museum Project in Oman

22 Periodicity in Copper Production in Prehistoric Southeastern Arabia

33

Organization of Early Copper Production

43

Copper-Base Objects in Bronze Age Southeastern Arabia Summary

54 57

Analyzed Artifacts: Contexts and Chronology AI Sufouh Unarl

61

Unar2

63

59

59

Tell Abraq

64

Results of CompositionalAnalyses lntroduction

71

71

Elemental Concentrations

73

Elemental Relationships: Rank-CorrelationAnalyses Principal Components Analyses (PCA) Summary

Discussion of Compositional Results lntroduction

105

Arsenic, Nickel and Cobalt

109

121

Alloy Use in Different Object Categories Summary

105

105

Iron and Sulfur Tin-Bronze

99

102

127

124

96

Lead lsotope Analysis in Archaeology

129

Theoretical Basis of the Lead lsotope Technique LIA in Archaeology

129

131

Issues for Archaeological LIA in the Gulf Region Summary

134

143

Lead lsotope Data from the Gulf (L. R. Weeks and K. D. Collerson) lntroduction

145

145

Radiogenic Outliers in the Analyzed Umm al-Nar Period Objects

145

Isotopic Differences by Site

147

Differences by Composition (Alloy Group) 150 lsotopic Comparisons with Bronze Age Objects from the Gulf

152

Absolute Provenance

155

Tin-Bronze in Wider Western Asia: Important Lead lsotope Studies

160

LIA: Summary of the Main Findings

163

Tin and Tin-Bronze in Early Western Asia lntroduction

165

l65

Tin Deposits in Western Asia and Surrounding Regions 166 Archaeological Evidence for Early Tin-Bronzes

173

Texts Referringto the Bronze Age Use and Trade ofTin Summary of Archaeological, Geological and Textual Evidence

180

Tin-Bronze in the Gulf: Patterns of Acquisition Reconsidering the "Tin Problem"

Summary and Conclusions Aims Reiterated

197

Summary of Major Results

l98 200

Prospects for Future Research

Appendix Analytical Techniques and Data Treatment

References 209 Index

247

187

197

203

181

178

Foreword

Mesopotamia, as has often been stated, lacked resources. Its lack of metal ores required this world of, at times, independent city-states and, at other times, empire, to look to distant lands in order to procure its metauores. Mesopotamian technology, however, was not a form of administrative or scribal concern. When it came to metal technology written texts offer limited information and are all but silent on the training, organization, and recruitment of metal smiths. Similarly, the texts are vague, or more typically silent, as to the geographical provenience from whence they obtained their metallore, its quantity, quality, price, or techniques of fabrication. It is left to the archaeologist and the recovered metal artifacts, workshops, associated tools, and mines, to address these questions. As important as the recovery of the metal object is its analysis. Analyses are especially helpful with regard to elucidating the sources of the metauore, the techniques of their manufacture, and the uses to which they were put. Recently there has been a trend in historical narrative to focus upon a given item and build upon it a regional, even global, history of the world. Thus, we have the history of the world according to spices, salt, cod-fish, homespun, maps, the banana and the potato, clocks, tobacco, and of course slaves, to mention but a few volumes that have produced a macrohistory according to a single item. Archaeologists have long been practitioners of such an approach. The study of metals, archaeometallurgy, has long had pride-of-place in such an approach. This monograph attests to the contribution of both archaeology and our arsenal of new analytical techniques in the study of metallurgy. Decades ago V. G. Childe placed metallurgy on the top of his list of important crafts. He maintained that the development of early civilizations was a consequence of the invention of metallurgy (Childe 1930). Bronze-working, he believed, encouraged the manufacture of tools, which in turn led to more productive agriculture, and the growth of cities. Seventyfive years ago, Childe (1930:39) could point out that "Other documents from Mesopotamia, also written in the wedge-like characters called cuneiform, refer to the importation of copper from the mountainous region east of the Tigris and of metal and stones from Magan (probably Oman on the Persian Gulf)". As demonstrated in this volume Childe's location of Magan as an important source of copper is shown to be entirely correct. In this volume Lloyd Weeks adds a significant chapter to our study of archaeometallurgy. His initial focus is the

vii

Arabian Peninsula where he introduces us to a new corpus of metal artifacts from the United Arab Emirates. Surprisingly, a significant percentage of these metals, recovered from the site of Tell Abraq, are tin-bronzes. Importantly, these artifacts, and others from near-by sites, are subject to Proton-Induced X-ray Emission analysis (PIXE). With these results in hand his horizon widens and takes on a review of metallurgy within the Bronze Age of the entirety of the Arabian Peninsula, where an extensive amount of archaeometallurgical work has been undertaken within the past few decades. Finally, his volume offers an up-to-date review of the enduring "tin-problem" within the context of the greater Near East. Again, Childe (1928:157) confronted the problem: "The Sumerians drew supplies of copper from Oman, from the Iranian Plateau, and even from Anatolia, but the source of their tin remains unknown". Today we have answers, even if they must still be regarded as partial ones. With a full appreciation of the complexity of interactions that characterized the third millennium throughout the Near East the author is not reticent to offer conclusions. Thus, he states that ". . . the absolute source of the metal [tin-bronze] is likely to have been far to the north and east in Afghanistan or central Asia". The central Asian source has been given reality by the recent discovery in Uzbekistan and Tadzhikistan of Bronze Age settlements and mines involved in tin production (Parzinger and Boroffka 2003). How is it then that if central Asian tin was reaching the Arabian Peninsula that there is a paucity, indeed a very great poverty, of contemporary tin-bronzes on the Iranian Plateau? The question does not allude the author. In fact, nothing within the data base, either bibliographic nor artifactual, escapes his lens. With careful attention to detail, a comprehensive appreciation of the evidence at hand, while subjecting the relevant evidence to laboratory analysis, Hercule Poirot would be in agreement that Lloyd Weeks' study adds both substantial evidence and clues that point toward an emerging solution of the century long case of the "tin-problem". Finally, thanks are due to Mr. Landon T. Clay whose generous support over the years include some of the metals analysis reported upon in this volume. C. C. Lamberg-Karlovsky

viii

Preface

This volume examines the production and exchange of copper and its alloys in the Bronze Age Persian Gulf. During the third and second millennia BCE, the Gulf was a critical long-distance trade route by which prestige goods such as lapis lazuli, carnelian and ivory reached wider western Asia. Additionally, the Gulf functioned as a major metal supply route for Mesopotamia and southwestern Iran, and abundant cuneiform sources testify to the flourishing copper trade between the urban centers of southern Mesopotamia and the Bronze Age Gulf polities of Dilmun and Magan. Multiple aspects of the Bronze Age Gulf trade network are investigated in this research program, which is based upon the archaeometallurgical analysis of copperalloy objects from four third millennium BCE sites in the United Arab Emirates. The data generated by compositional and lead isotope analyses are integrated with geological information from southeastern Arabia and technological studies of early copper smelting in the region, and provide important insights into a number of issues of archaeological significance. These range from technological aspects of early copper-base alloy production in southeastern Arabia, to more anthropologicallyinformed research regarding the interaction of specialized copper production, exchange, and social complexity in early Arabia. The broader archaeological issue of the Bronze Age tin trade is also investigated in detail. The trade in this metal linked vast areas of western Asia, from the IndoIranian borderlands to the Aegean, through a series of overland and maritime trade routes and exchange relationships that are only hazily understood. The discovery of tin and tin-bronze objects in third millennium BCE contexts in the U.A.E., demonstrated conclusively in the present volume, provides important new evidence for the discussion of the tin trade, a long-standing problem of Bronze Age western Asian archaeology.

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AcknowledgmentS

This book began its life as a doctoral dissertation undertaken at the University of Sydney, Australia. Although subsequent periods of research have resulted in the substantial reworking of the original text, as well as many additions, the ideas and approaches contained within it remain those which were shaped so strongly by my thesis supervisors, Dan Potts (University of Sydney) and Richard Thomas (University of Western Sydney). I would like to express my gratitude for their guidance during that critical and seemingly endless period, and in particular to Dan Potts for his practical and intellectual input into so many aspects of the work. My thesis was assessed by Andreas Hauptmann (Deutsches Bergbau-Museum, Bochum), Roger Moorey (Ashmolean Museum, Oxford), and Vincent Pigott (Institute of Archaeology, London), and this volume has been greatly improved by their constructive comments and criticisms. Of course, this volume has reached its present form since my arrival at the Peabody Museum and is funded through the good graces of the American School of Prehistoric Research (ASPR). I would like to sincerely thank the ASPR and in particular Karl Lamberg-Karlovsky and Ofer Bar-Yosef for the opportunity to produce this study, and for shepherding the manuscript when it threatened to stray. Great thanks must also be extended to Wren Fournier, who acted as production editor for the volume and oversaw all aspects of the editorial and production processes, including some particularly time-consuming adaptations of images. The volume is based upon a large number of material analyses, for which the assistance of numerous scholars and institutions must be acknowledged. The PIXE analyses were conducted by Grahame Bailey, Philip Johnson and Ed Stelcer at the Australian Nuclear Science and Technology Organisation, Lucas Heights, N.S.W., and Rainer Siegele provided important information on the accuracy and precision of the data. The TIMS lead isotope analyses of artifacts from Tell Abraq were conducted at the Department of Earth Sciences, University of Queensland, by Ken Collerson and Immo Wendt. The more recent MC-ICP-MS isotopic analyses of material from A1 Sufouh, Unarl, and Unar2 were also conducted at the University of

Queensland facilities under the direction of Ken Collerson, and were undertaken by Balz Kamber and Arildo Oliveira. I would like to express my gratitude t o all of these people for their diligence, and for taking the time to discuss various aspects of the analytical techniques and data for my enlightenment. Of course, analyses could never have proceeded without material to analyze. For allowing access to archaeological samples, I would particularly like to thank Sabah Jasim (Sharjah Archaeological Museum, U.A.E.), Christian Velde and Derek Kennet (Ras al-Khaimah Museum, U.A.E.), Hussein Qandil (Dubai Museum, U.A.E.), Dan Potts (Sydney University Excavations at Tell Abraq), and Jodie Benton (Sydney University Excavations at A1 Sufouh). A number of these scholars have also provided important unpublished contextual information on the samples, for which I am grateful. The volume benefited greatly from advice generously given during its formulation, and from editorial corrections. For general discussions regarding statistical approaches, and for confusing me by not thinking in the same way (apparently there is more than one), I would like to thank John Clegg (University of Sydney). Advice on the application of multivariate statistics to the PIXE data was kindly provided by Richard Wright (University of Sydney) and Peter Grave (University of New England). Large chunks of the volume were read and constructively commented upon by Peter Magee (Bryn Mawr College), Alastair Paterson (University of Western Australia) and Cameron Petrie (Somerville College, Oxford), a terrific help. The ideas that they read about benefited from wideranging archaeological discussions with Phi1 Kohl (Wellesley College), A. Bernard Knapp (University of Glasgow), and Mike Barbetti (University of Sydney). My doctoral research was financially supported by an Australian Commonwealth government Australian Postgraduate Award scholarship, three grants for PIXE analyses from the Australian Institute of Nuclear Science and Engineering (AINSE), a Carlyle Greenwell bequest for isotopic analyses of material from the United Arab Emirates, and a grant from the British School of Archaeology in Iraq (BSAI)for isotopic analyses of material from Saar, Bahrain. New isotopic analyses of objects from the U.A.E. presented in this volume were supported by a grant from the ASPR.

Finally, I would like to acknowledge my friends and family, who have been there for the duration. N o part of this work could have been completed without their support and it is therefore to them, individually and in their collective role as my personal safety net, that I owe my greatest thanks.

List of Figures

2.10 2.11 2.12 2.13 2.14 2.15 2.16 3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 3.9 3.10

xiii

Major archaeological sites of the U.A.E. Geological units comprising the Oman Mountains Major copper deposits and metallurgical sites of southeastern Arabia Slag heaps at Samdah, Oman Slag fields at Tawi 'Arja, Oman Settlement at Maysar 1, the mining area M2, and the cemetery M3 Evidence for Umm al-Nar Period mining at Maysar 2, Oman Hammer and anvil stones from Maysar 1, Oman Fragments of the base of a smelting furnace from Maysar 1, Oman Slag typology for Umm al-Nar Period copper production at Maysar 1 Iron Age smelting remains from Oman Iron Age copper slag from 'Arja in Oman Periods of copper production in southeastern Arabia Slag-filled planoconvex copper ingot from Al-Aqir in Oman Hoard of planoconvex copper ingots found at Maysar 1 in House 4 Third millennium BCE copper-smelting settlement of Zahra 1, Oman Iron Age slag heap at Raki 2, Oman Chronology of the excavated tomb assemblages A1 Sufouh Tomb I after excavation (from west) Fragments of copper-base objects from A1 Sufouh analyzed in this study Unarl Umm al-Nar Period tomb Fragments of copper-base objects from Unarl analyzed in this study Unar2 tomb after excavation, showing chamber designations (from north) Fragments of copper-base objects from Unar2 analyzed in this study Tell Abraq tomb after excavation (from north) Two copper-base rings from the Tell Abraq tomb, as excavated in position on phalanges Copper-base objects from Tell Abraq analyzed in this study

4.17 Tin concentrations in all Urnm al-Nar Period objects analyzed by PIXE 4.1 8 Negative correlation between tin and cobalt in the Urnm al-Nar objects analyzed by PIXE 4.19 Arsenic and nickel in Urnm al-Nar Period objects analyzed by PIXE 4.20 Nickel and cobalt in the Urnm al-Nar Period objects analyzed by PIXE 4.21 Arsenic and cobalt in the Urnm al-Nar Period objects analyzed by PIXE 4.22 Tin and silver in the Urnm al-Nar Period objects analyzed by PIXE 4.23 Element Correlations as found in a PCA of the unmodified PIXE compositional data and PIXE data converted to rank-order 4.24 PCA scattergram of untransformed PIXE data for objects from Tell Abraq and A1 Sufouh 4.25 PCA scattergrams of ranked PIXE data for all Umm al-Nar Period objects 4.26 PCA scattergrams of Urnm al-Nar Period copper objects only 4.27 PCA scattergrams of Urnm al-Nar Period tinbronzes only 4.28 Alloy use in the four Urnm al-Nar Period tomb assemblages Iron and sulfur levels in finished objects in comparison to secondary refining waste from the settlements of Saar and Muweilah Nickel, arsenic, and tin concentrations in Umm al-Nar Period objects Tin concentrations in Urnm al-Nar Period objects analyzed by PIXE, and previously analyzed Iron Age objects from southeastern Arabia Alloy use in different object categories Lead isotope data for massive sulfide deposits from Oman, in comparison to mid-ocean ridge basalts (MORB) Isotopic variability of copper ores from individual ore deposits in Oman LIA data for copper ores from Oman Isotopic composition of Omani ores, in comparison to copper ingots and finished objects from southeastern Arabia and Bahrain

3.1 1 Spearhead TA21 83 from the Tell Abraq Urnm al-Nar Period tomb 3.12 Daggerlknife blade TA2268 from the Tell Abraq Urnm al-Nar Period tomb 3.13 Daggerlknife blade TA2270 from the Tell Abraq Urnm al-Nar Period tomb 3.14 Daggerlknife blade TA2315 from the Tell Abraq Urnm al-Nar Period tomb 3.15 Daggerlknife blade TA2440 from the Tell Abraq Urnm al-Nar Period tomb 3.16 Socketed spearhead TA2757 from the Tell Abraq Urnm al-Nar Period tomb 4.1 Sulfur concentrations in A1 Sufouh, Unarl, Unar2 and Tell Abraq objects 4.2 Sulfur concentrations in all Urnm al-Nar Period objects analyzed by PIXE 4.3 Iron concentrations in AI Sufouh, Unarl, Unar2 and Tell Abraq objects 4.4 Iron concentrations in all Urnm al-Nar Period objects analyzed by PIXE 4.5 Cobalt concentrations in AI Sufouh, Unarl, Unar2 and Tell Abraq objects 4.6 Cobalt concentrations in all Urnm al-Nar Period objects analyzed by PIXE 4.7 Nickel concentrations in A1 Sufouh, Unarl, Unar2 and Tell Abraq objects 4.8 Nickel concentrations in all Urnm al-Nar Period objects analyzed by PIXE 4.9 Arsenic concentrations in A1 Sufouh, Unarl, Unar2 and Tell Abraq objects 4.10 Arsenic concentrations in all Urnm al-Nar Period objects analyzed by PIXE 4.1 1 Selenium concentrations in A1 Sufouh, Unarl , Unar2 and Tell Abraq objects 4.12 Selenium concentrations in all Urnm al-Nar Period objects analyzed by PIXE 4.13 Silver concentrations in all Urnm al-Nar Period objects analyzed by PIXE 4.14 Lead concentrations in A1 Sufouh, Unarl, Unar2 and Tell Abraq objects 4.15 Lead concentrations in all Urnm al-Nar Period objects analyzed by PIXE 4.16 Tin concentrations in A1 Sufouh, Unarl, Unar2 and Tell Abraq objects

xiv

95 98 98 98 99 99

100 100 101 102 102 104

107 120

121 126

135 136 137

137

LIA data for all Urnm al-Nar Period objects from the U.A.E. analyzed in this study LIA data for all Urnm al-Nar Period objects, arranged by site LIA data for all Urnm al-Nar Period objects by alloy category 207Pb1206Pb isotopic composition of Urnm al-Nar Period copper objects from the UAE analyzed in this study 207Pb/206Pb Isotopic ranges for Urnm al-Nar Period objects analyzed in this study LIA data for Urnm al-Nar Period objects analyzed in this study, and Gulf copper ingots analyzed previously LIA data for Urnm al-Nar Period copper objects analyzed in this study, and copper-base artifacts and prills analyzed by Prange et al. (1999: Figure 7) 154 LIA data for Urnm al-Nar Period copper-low tin and tin-bronze objects analyzed in this study, and copper-base artifacts and prills analyzed by Prange et al. (1999: Figure 7) 154 LIA data for Urnm al-Nar Period objects analyzed in this study, and copper-base artifacts and prills from Saar, Bahrain 155 LIA data for Urnm al-Nar Period copper objects analyzed in this study, and copper artifacts and prills from Wadi SuqILate Bronze Age contexts at Tell Abraq (Weeks 1999) 155 LIA data for Urnm al-Nar Period tin-bearing objects analyzed in this study, and tin-bronze artifacts and prills from Wadi SuqILate Bronze Age contexts at Tell Abraq (Weeks 1999) LIA data for copper objects from the U.A.E. analyzed in this study, and Omani copper ores 7.13 LIA data for copper-low tin objects from the U.A.E. analyzed in this study, and Omani copper ores 7.14 LIA data for tin-bronze objects from the U.A.E. analyzed in this study, and Omani copper ores 7.15 LIA data for AsINi-copper objects from the U.A.E. analyzed in this study, and Omani copper ores

7.16 LIA data for Urnm al-Nar Period objects analyzed in this study, and Indian ores and slags 7.17 LIA data for Urnm al-Nar Period objects analyzed in this study, Iranian copper ores and slags 7.1 8 LIA data for Urnm al-Nar Period objects analyzed in this study, and Saudi Arabian copper and tin ores 7.19 LIA data for Urnm al-Nar Period objects analyzed in this study, in comparison to the isotopic characteristics of copper ores from Anatolia, the Aegean, Feinan and Timna 7.20 LIA data for tin (and zinc)-bearing objects from the Aegean and northwestern Anatolia, in comparison to tin-bronzes and copper-low tin objects from the U.A.E. Map showing ore deposits and archaeological and metallurgical sites mentioned in Chapter Eight SR2 target chamber schematic The relationship between PIXE sensitivity and atomic number The relationship between PIXE precision and element concentration 205 Chromium concentrations in al.l analyzed PIXE samples 206

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List of Tables

Chronological periodization of southeastern Arabian prehistory Geology and stratigraphy of the northern Oman Mountains Objects from A1 Sufouh analyzed by PIXE Objects from Unarl analyzed by PIXE Objects from Unar2 analyzed by PIXE AMS Radiocarbon dates associated with the Tell Abraq tomb Objects from the Tell Abraq tomb analyzed by PIXE PIXE compositional data for objects from A1 Sufouh PIXEcompositional data of objects fromUnar 1 PIXE compositional data for objects from Unar2 PIXE compositional data for objects from Tell Abraq Sulfur concentrations in Urnm al-Nar Period objects analyzed by PIXE Sulfur levels recorded in previous analytical studies Iron concentrations in Urnm al-Nar Period objects analyzed by PIXE Ironlevelsrecordedin previous analytical studies Cobalt concentrations in Urnm al-Nar Period objects analyzed by PIXE Cobalt levels in previously analyzed objects Nickel concentrations in Urnm al-Nar Period objects analyzed by PIXE Nickel levels recorded in previous analytical studies Zinc concentrations in Urnm al-Nar Period objects analyzed by PIXE Zinc levelsrecorded in previous analytical studies Arsenic concentrations in Urnm al-Nar Period objects analyzed by PIXE Arsenic levels recorded in previous analytical studies Selenium concentrations in Urnm al-Nar Period objects analyzed by PIXE 88 Silver concentrations in Urnm al-Nar Period objects analyzed by PIXE 90 Silver levels recorded in previous analytical studies 90

xvii

4.20 Antimony levels recorded in previous analytical studies 92 4.21 Lead concentrations in Umm al-Nar Period objects analyzed by PIXE 92 4.22 Lead levels recorded in previous analytical studies 94 4.23 Tin concentrations in Umm al-Nar Period objects analyzed by PIXE 94 4.24 Rank-correlation coefficients for all Umm al-Nar Period objects 97 7.1 Lead isotope data for objects from A1 Sufouh, Unarl, Unar2, and Tell Abraq 146

xviii

Introduction

Outline and Genesis of the Project This volume presents a study of early metal production, exchange and use in the Persian Gulf region. The issues addressed range from technological aspects of early metal extraction and alloy production, to the broader socioeconomic issues related to the production and trade of metallic resources in the Gulf and the use of tin and tin-bronze in early western Asia (Figure 1). Metallurgical studies have been of primary interest in the archaeology of the Gulf from the earliest periods of work in the region. This is chiefly a result of scholarly debate regarding the location of the lands of Dilmun and Magan, which are mentioned in Bronze Age historical texts from Greater Mesopotamia and which were intimately linked with the supply of copper to the Sumerians, Akkadians and Babylonians in the third and early-second millennia BCE (e.g. Oppenheim 1954; Leemans 1960; Muhly 1973a; Weisgerber 1983; Potts 1B o a : 133-149). Archaeological and Assyriological research in the twentieth century have paid great attention to locating the lands of Dilmun and Magan, and it is now clear that both are to be placed within the Gulf region: Dilmun in the central Gulf, incorporating eastern Saudi Arabia and particularly Bahrain from the later third millennium BCE onwards, and Magan at the southern end of the Gulf, incorporating southeastern Arabia and, perhaps, some areas of southeastern Iran (Heimpel 1987).

While these debates over historical geography date back to the nineteenth Century (Potts 1986:271-272), archaeological research in the Persian Gulf region is a comparatively recent pursuit. Fieldwork in southeastern Arabia was initiated by Danish archaeologists in the 1 9 . 5 0 ~and ~ a great deal of research since that time has allowed the development of a secure chronology for prehistoric southeastern Arabia (Table p), and a somewhat less assured understanding of the economic, technological, social and political characteristics of these early Gulf societies. The archaeological evidence indicates that, by the early third millennium BCE (the Hafit Period), relatively small, sedentary communities existed in southeastern Arabia that were founded upon agricultural subsistence and the exploitation of marine resources (Potts 199713). The evidence for small numbers of copper-base objects from collective Hafit graves (e.g. Frifelt 1975b) suggests that local copper extraction had already begun by this period. This subsistence basis for human settlement persisted into the later third millennium (the Umm al-Nar Period), when it was supplemented by a new form of subsistence adaptation based upon specialized production and exchange of various commodities (e.g. copper, ceramics, and stone vessels) within southeastern Arabia (Cleuziou and Tosi 1989, 2000). This regional exchange network represented a critical adaptation in an environment where resources were plentiful but often strongly localized geographically. The development of an integrated local economic system in southeastern Arabia was contemporary with a dramatic increase in the number of known settlements, and with material remains from settlement and funerary contexts indicating extremely far-flung trade contacts with regions such as Mesopotamia, Iran, the Indus Valley, central Asia and the central Gulf (Potts 1990a, 1993e, 2003a, 2003b). However, settlements remained relatively small, usually no larger than a few hectares, and there is no evidence for the development of large political institutions or significant social hierarchies (Crawford l998:l3 8). In the early second millennium BCE (the Wadi Suq Period) there was a dramatic reduction in the number of settlements, an occurrence that has been related to the increasing importance of nomadic pastoralism as a subsistence regime (Cleuziou 1981; Carter 1997).

Figure 1.1 Major archaeological sites of the U.A.E. referred to in the text.Objects analyzed in this volume come from AI Sufouh, Unarl, Unar2, and Tell Abraq.

2

Early Metallurgy of the Persian Gulf

It is against this background that the evidence for third millennium copper extraction in southeastern Arabia, the "copper mountain of Magan", must be considered. The large scale of this production was demonstrated from the late 1970s through archaeometallurgical research by the German Mining Museum in the Sultanate of Oman (Weisgerber 1980b, 1981; Hauptmann 1985, 1987; Yule and Weisgerber 1996; Weisgerber and Yule 1999; Prange et al. 1999). This ongoing field project established the production of copper in southeastern Arabia from as early as the Umm al-Nar Period, and the high-volume copper trade between the Gulf area and Mesopotamia supported by these studies and by cuneiform references is regarded as crucial in the socioeconomic development of the region in the Bronze Age and later (e.g. Edens 1992). The compositional and lead isotope analyses (LIA) which form the substantive core of this volume were undertaken on copper-base objects of this period, from four Umm al-Nar Period collective assemblages that can be dated between 2450-1900 BCE (see Chapter Three for details). As outlined above, the data and discussions presented in the following chapters exist within a local technological framework largely constructed by the German research in Oman. Nevertheless, the new analyses represent an important complement to the German research in two respects. Firstly, the analyses provide evidence of metal use in settlements that are not associated with primary copper production, which has until recently been the main focus of the German research (although see Prange et al. 1999). Secondly, the analyses are important for our understanding of metal use in more northerly areas of the Oman Peninsula rather than those where the German team has traditionally worked. Looking beyond the data from southeastern Arabia itself, the results of this study can be related to broader regional developments in western Asia, particularly the development of mining, metallurgy and pyrotechnology on the Iranian Plateau, the adoption of new alloys such as tinbronze in neighboring regions of western Asia, and the long-distance trade in metals that linked the Gulf with complex societies stretching from the Indus Valley to Anatolia.

Table 1.1 Chronological Periodization of Southeastern Arabian Prehistory Broad Chronological Phase

Cultural Period

BRONZE AGE

Hafit Period

(3100-1 300 BCE)

Umm al-Nar Period

Absolute Date BCE

Wadi Suq Period Late Bronze Age IRON AGE

Iron I

(1300-300 BCE)

Iron II lron Ill

Chronological periodization of southeastern Arabian prehistory. Note: Periodization after Velde (2003),Potts (1 997b), and Magee (1 996b).

The genesis of the volume lies in previous analyses of material from the site of Tell Abraq in the U.A.E., undertaken by the author in 1995 (Weeks 1997). That study analyzed the changes in copper alloy use at Tell Abraq through the entire occupational sequence of the site: a period of two millennia spanning ca. 2300-300 BCE. The study showed that tin-bronze had been used at Tell Abraq from the earliest phases of its occupation in the third millennium, alongside objects of relatively pure copper and arsenical copper. As such, the findings contrasted strongly with previous studies of early metal use in southeastern Arabia (e.g. Hauptmann 1987; Hauptmann et al. 1988; Berthoud et al. 1980, 1982). These studies had indicated that tin-bronze was extremely rare in the region in the third millennium and was not consistently used until the end of the second millennium. The analyses of the Tell Abraq objects thus raised the question of whether Tell Abraq, clearly the largest site on the Gulf coast of southeastern Arabia during the late-third and second millennia (Potts 1993a), was somehow unique in terms of its access to metallic resources. For example, it has been proposed that Tell Abraq functioned as the chief outlet for Omani copper in the last centuries of the third millennium (Frifelt 1995) and the site may therefore have had greater access to a variety of metal resources and other luxury goods than most sites in the Oman Peninsula. Alternatively, Carter (2001:196) has suggested that Tell Abraq might be best regarded as a trading post between the centrallnorthern Gulf and South Asia; an "exceptional" site not well integrated economically with southeastern Arabia beyond the northern coastal region.

Introduction

3

These early archaeometallurgical analyses from Tell Abraq suggested the possibility of differences in metal procurement patterns between northern and southern areas of the Oman Peninsula. Further basic questions posed by the Tell Abraq analyses related to the chronology of the earliest tin and tinbronze use in the region, and the mechanisms and routes by which this clearly foreign material reached the Gulf. However, due to the dearth of analytical programs on chronologically and geographically related metal objects, the Tell Abraq analyses stood somewhat in isolation. As a consequence, it was difficult to assess whether the site was representative of more widespread metallurgical practices in southeastern Arabia, o r whether it was indeed unique in its metalworking technology and access t o foreign resources. The analyses of objects from three other tomb assemblages in the northern U.A.E., from the sites of A1 Sufouh, U n a r l , and Unar2, are thus significant in providing a more secure analytical basis t o support the discussion of the issues raised by the initial Tell Abraq analyses. Additionally, excavation of the second half of the Umm al-Nar Period tomb a t Tell Abraq was completed in 1997-1998, bringing t o light many more copper-base objects from the late third millennium BCE. The analysis of a sub-set of these newly recovered objects using a fully quantitative technique was deemed desirable, in order to support the results of the semi-quantitative EDS analyses of material from the site undertaken previously. As a group, analyses of the four tomb assemblages allow for a relatively clear understanding of developments in alloying technology and raw material exchange patterns over the last half of the third millennium BCE in the northern Oman Peninsula. Such issues are indeed the focus of much of the discussion presented in this volume. However, other issues such as the organization of copper production in Bronze Age southeastern Arabia, and the local and foreign factors that influenced the scale of production, and the role of the Gulf in the third millennium tin trade are also addressed. These theoretical and substantive issues are outlined below in greater detail.

4

Early Metallurgy of the Persian Gulf

Copper Production and the Bronze Age Economy of Southeastern Arabia One of the main theoretical foci of this volume relates not to the interpretation of the analytical data generated by PIXE and LIA, but to an investigation of the organization of copper production in Bronze Age southeastern Arabia, and an examination of the integration of copper production with other local subsistence activities. As noted above, the Umm al-Nar Period witnessed what many archaeologists have characterized as an increasing level of cultural and economic integration. The exchange of copper produced in the mountainous areas of the interior no doubt played a significant role in this integration. In Chapter Two, the possible effects of feedback between greater economic integration and increasingly specialized craft production are examined in detail. The implications of these factors for our understanding of emerging social complexity in Bronze Age southeastern Arabia are also addressed. The importance of local exchange systems in generating demand for copper is emphasized partly to counteract the prominence that has previously been granted to foreign demand for copper from areas such as Mesopotamia, Dilmun, and perhaps the Indus Valley. It is clear that both local and foreign demand played a role in determining total output of copper in the third millennium, and also the ways in which that production was organized. As will be seen in Chapter Two, the archaeological evidence for particular modes of copper production in Bronze Age Oman is very scarce. Nevertheless, there is some evidence for Bronze Age copper extraction sites producing at very different scales, which might tentatively support the notion of distinct modes of production. Whether such differences can be linked to chronology, production for local or foreign markets, or other factors remains uncertain. Prehistoric copper production in Oman, beginning at around 3000 BCE, also witnesses distinct periods of growth and decline, to the point where long periods of complete abandonment of the industry have been hypothesized in the Late Bronze Age and the Late Pre-Islamic Period. This "periodicity" or "cyclicality" of production is another reflection of changes in local and foreign demand for copper, in addition to environmental factors, changing technology, and historically contingent political

and economic events in southeastern Arabia and neighboring regions of western Asia. In Chapter Two, the many factors that may have caused the periodicity of copper production in southeastern Arabia are examined in detail.

Alloying Practices in Bronze Age Southeastern Arabia Considerable information regarding early metalworking practices in southeastern Arabia is generated by the analytical data presented and discussed in Chapters Four and Five. When the compositional analyses are compared with the work of the German Mining Museum, important factors regarding the production and use of certain alloy types, changes in local ore types exploited, and in the technology of extraction can be examined. A brief note on terminology is required here to facilitate the discussion. All objects made of copper and its alloysarereferred to ascopper-baseobjects. In theanalyzed assemblages from Umm al-Nar Period southeastern Arabia, the most common alloy types are pure copper (which contains less than one percent of arsenic, nickel, zinc and lead, and less than two percent tin), tin-bronze (copper with more than two percent tin), arsenical copper (copper with more than one percent arsenic), and nickel copper (copper with more than one percent nickel). The last two alloy types are commonly grouped together under the label As/Ni-copper, which includes all copper samples with more than one percent of arsenic andlor nickel. No a priori assumptions are made regarding the intentional production of these alloys. Justifications for these definitions can be found in Chapters Four and Five. The discussion of the compositional data focuses on the production and use of tin-bronze and As/Ni-copper. Based upon mineralogical studies of ore deposits in southeastern Arabia, it is suggested that the latter alloy is probably a local product. In addition to the investigation of the particular kinds of Omani ore deposits that may have produced such an alloy, discussion focuses upon the various mechanisms by which As/Ni-copper may have been produced and the material properties that may have differentiated it from pure copper and from tin-bronze. Analyses of alloying processes for the production of tinbronze are also addressed, based upon tin concentrations in the objects and also evidence from minor and

trace element concentrations. Chronological aspects of tin-bronze use in the northern Oman Peninsula are also investigated and significant differences in the use of tinbronze and As/Ni copper for specific object categories are visible. The technological, economic, and ideological factors that may have mediated processes of alloy selection in third millennium southeastern Arabia are discussed in detail.

Investigationof the Bronze Age Tin Trade The investigation of early tin and tin-bronze use in the northern Oman Peninsula is important for understanding early metal use and trade both within the Gulf, and in wider western Asia. The tin sources used in Bronze Age western Asia remain unidentified after more than 50 years of investigation (Muhly 1973a; 1985a; 1993a; Stech and Piggot 1986) and related fieldwork, analytical programs and archaeological debates are actively in progress (e.g. Yener and Vandiver 1993a; Moorey l994:297-30 1; Alimov et al. 1998; Yener 2000). The debate is concerned as much with the trade routes and mechanisms by which tin and tin-bronze may have moved in the third millennium as it is with the absolute source of the material. The discovery of early tin-bronze use at Tell Abraq has highlighted the possible role of the Gulf trade in the distribution of this material, an avenue which had been largely under-emphasized due to the dearth of tin-bronzes reported in other compositional studies of material from Bahrain and southeastern Arabia (e.g. McKerrell 1977:167; Hauptmann et al. 1988; Prange et al. 1999). The archaeological objects from the four Umm al-Nar Period tomb assemblages analyzed in this volume add considerably to the body of evidence for early tin-bronze use in the Gulf. Furthermore, the significance of the timing and frequency of early tin-bronze use in the Gulf for general discussions of Bronze Age Gulf archaeology is addressed. In particular, the possible cultural contacts that might account for the use of tin in the central Gulf and in southeastern Arabia are assessed. Any discussions of this nature rely for their validity upon multiple strands of evidence from geology, archaeology and early textual sources (e.g. Muhly 1985a, 1993a; Penhallurick 1986; Stech and Pigott 1986), and these are presented in detail in order to reach a satisfactory conclusion regarding the likely sources of tin used in the Gulf in the Bronze Age.

Introduction

5

The possible significance of the early tin-bronze exchange in the Gulf for wider western Asia is also considered in detail. The results of the LIA of more than 40 objects from the four Umm al-Nar Period tomb assemblages provide crucial evidence for this discussion. The isotopic data provide important information on the extent of the early tin and tin-bronze trade in western Asia and beyond and the possible technological and socioeconomic implications of this trade are discussed in detail.

Analytical Techniques As noted above, the data presented in this volume involve both compositional and lead isotopic analyses. The compositional analyses were undertaken using the technique of Proton-Induced X-ray Emission (PIXE). Details of the application of the PIXE technique to the objects analyzed in this study, as well as information on accuracy, precision and sensitivity of the data, are provided in Chapter Four and Appendix One. PIXE analyses have been successfully used as the basis of a number of archaeometallurgical analysis programs in the Old World (e.g. Fleming and Swann 1985:142). Currently, the use of LIA is much debated within archaeological science and archaeology in general (e.g. Budd et al. 1995a, 1995b, 1996; Muhly 1995a; Pernicka 1995a; Tite 1996; Knapp 2000; Gale 2001). As the issues surrounding the application of LIA to archaeological provenance studies can be complex, a detailed discussion of the development of LIA in archaeology is given in Chapter Six. LIA can provide extremely useful information in the generation and assessment of novel archaeological hypotheses regarding provenance (e.g. Pernicka et al. 1990, 1993), as demonstrated by the results presented and interpreted in Chapter Seven. Useful results are dependent upon a detailed understanding of both geological and anthropogenic factors controlling lead isotope signatures of archaeological objects, and the value of integrating isotopic and compositional data is clear (e.g. Pernicka 1995a; Bridgford 2000; Begemann et al. 2001). Details of the analytical technique for LIA and information on data precision and accuracy can be found in Appendix One.

6

Early Metallurgy of the Persian Gulf

Outline of Chapters Following this introductory chapter, Chapter Two presents the background to the present study, summarizing all previous geological and archaeological work relevant to early metallurgy in the Gulf region. It incorporates an extensive discussion of the factors that affected the scale and periodicity of early metal extraction in southeastern Arabia; an examination of the organization of Umm alNar Period copper production; an assessment of the integration of various specialized production regimes (including metallurgy) in Bronze Age southeastern Arabia, and; a presentation of the evidence for copper-base object fabrication and alloying technologies. Chapter Three reviews the chronological and contextual information on the objects analyzed in this volume. Chapter Four presents and summarizes the compositional data for all analyzed samples on an element-by-element basis. It concludes with a statistical analysis of elemental correlations in the collected data, and of the chemical characteristics of the archaeological metal assemblages from each of the four funerary structures. The implications of the compositiona1 data and statistical analyses are discussed in Chapter Five, with particular focus upon the types of ores that may have been exploited in the Umm al-Nar Period and the production and use of various local and imported copper-base alloys such as As/Ni-copper and tin-bronze. Chapter Six is a summary of theoretical and practical developments in the application of LIA to archaeology, as a background to Chapter Seven, where the results of the LIA of copper-base objects from the four Umm al-Nar Period tomb assemblages are presented. Particular attention is paid to the possible local and foreign metal sources that were used to produce the analyzed copper-base objects. Chapter Eight focuses more specifically on the possible sources of tin used in the Gulf in the Bronze Age and includes a discussion of the trade routes, exchange mechanisms, and socioeconomic importance of the third millennium BCE tin and tin-bronze trade in western Asia. The overall results of the research are summarized in Chapter 9.

2

Geology and Early Exploitation of Copper Deposits in Southeastern Arabia

This chapter addresses the nature of copper deposits in southeastern Arabia and past archaeological studies of ancient copper production in the region. The first section of the chapter begins with a brief description of the geology of southeastern Arabia, and the A1 Hajjar Mountains in particular, including the basic stratigraphic units, their time of formation, and the mechanisms of their emplacement. Subsequently, a detailed description is given of the various copper deposits of southeastern Arabia, their geological setting, mineralogy, and importance for ancient metal production. In the second section of the chapter, archaeological research into ancient copper production in southeastern Arabia is discussed. Early approaches to provenance and the question of the location of Magan are dealt with first, followed by a section on early geological and archaeological surveys in the region and a discussion of the work of the German Mining Museum in Oman. The discussion of early primary copper extraction in southeastern Arabia concludes with an investigation of the apparent periodicity in copper production in the Bronze and Iron Ages, and an examination of the ways in which copper production was organized and integrated into the broader Bronze Age economy of the region. The chapter concludes with a discussion of changes in the technology of copper-base object fabrication over the course of the Bronze Age, examining both the range of items produced and the alloying practices that are evidenced.

Geology of Northern Oman and Masirah All of the copper deposits of southeastern Arabia, with the exception of those on Masirah Island, are to be found within various geological units of the northern Oman or A1 Hajjar Mountains. In the following sections, brief descriptions of the geology of the A1 Hajjar Mountains and Masirah Island are given, as they form an important basis for the understanding of ancient copper mining and production in southeastern Arabia. Geology of the Northern Oman (A1 Hajjar) Mountains The A1 Hajjar Mountains are comprised of a number of different groups of rocks, whose genesis, location and association have been explained in different ways over the course of geological research in the region, dating as far back as the 1900s (Pilgrim 1908). Although comprehensive local geological research did not begin until the 1960s, the geology of Oman and the U.A.E. is relatively well understood for a number of reasons. In particular, the search for new oil and gas reserves was a primary motivator of early geological research in the region, as was the chance to study the world's best exposed and most complete piece of former oceanic mantle and crust, the so-called "Semail Ophiolite" (Glennie 1995:6-9; Batchelor 1992:109). A number of important general studies of the mountains have been published (e.g. Greenwood and Loney 1968; Glennie et al. 1974; Robertson et al. 1990), as well as publications on specific geological units within the mountains, particularly the ophiolite (e.g. Lippard et al. 1986; Boudier and Nicolas 1988). The various geological divisions used to describe and explain the geology of the northern Oman Mountains (see Glennie 1995; Lippard et al. 1986) are given in Table 2.1 in stratigraphic order (oldest at the bottom). The table indicates the basic bipartite division of the rocks of the region into autochthonous and allochthonous sequences. The autochthonous units, include basement granites and shallow marine sediments that were deposited on the Arabian continental shelf or platform, and which remain in the position in which they formed. These units include the "Basement", "Hajar Supergroup" and "Aruma Group" discussed by Glennie (1995:23-32) and Lippard et al. (1986:9-16) and date from the Precambrian to the Late Cretaceous.

Above these autochthonous units sit two series of allochthonous rocks, so-named because they have been moved from their place of formation into their current position by various geological processes. Allochthonous units are noted in Table 2.1. The lower of these units, the "Hawasina," is composed largely of marine sediments that were deposited on the floor of an ancient ocean called the Neo-Tethys, which lay to the northeast of Arabia, between mid-Triassic and mid-Cretaceous times (ca. 270-70 million years ago [Ma]; Lippard et al. 1986:12; Glennie 1995:4). The upper allochthonous unit is the Semail Ophiolite, a section of oceanic upper mantle and crust that formed on the floor of one part of the Neo-Tethys in the Mid-Cretaceous (ca. 105-170 Ma; Glennie 1995:4-5). From about 105 Ma, active spreading ridges in the Neo-Tethys and the South Atlantic Ocean focused great horizontal compressive forces upon the oceanic crust of the Neo-Tethys, causing it to rupture and leading to the formation of an eastward-dipping subduction zone (Glennie 199553). It was in fact the presence of this subduction zone that led to the formation of the Semail oceanic crust in the associated back-arc environment of the subduction zone (Lippard et al. 1986:Figure 4.11). As described by Glennie (1995:5), at 105 Ma these three groups of rocks (the autochthonous series and the two allochthonous series) lay side-by-side, with the granites and shallow marine sediments of the Arabian shelf to the west and the newly-forming oceanic crust of the Semail to the east. The Hawasina sediments overlay older and deeper oceanic crust in between the Arabian platform and the Semail crust. The subduction zone in the Neo-Tethys and the compressive forces which initiated the formation of the Semail oceanic ridge led to the emplacement of first the Hawasina sediments and then the Semail oceanic lithosphere over the Arabian shelf in the period between about 105 and 70 Ma. The relative direction of transport was from northeast to southwest, and the distances involved were of the order of several hundred km (Shackleton and Ries 1990:721). Horizontal compressive forces ceased to operate at around 75 Ma, and the uplift of the partially subducted, buoyant continental crust onto which the Hawasina and Semail units had been emplaced led to the detachment of the Semail nappe

8

Early Metallurgy of the Persian Gulf

from its contiguous oceanic crust and the local elevation of parts of the nappe above sea level for the first time (Glennie l995:%-56). At this time, however, the rock units formed a chain of low-relief islands rather than a mountain range. It was not until approximately 30 Ma that these units were uplifted to form the Oman Mountains, as a result of the compressive forces arising from the separation of Arabia from Africa and the collision of the Indian plate with the southern edge of Eurasia (Glennie 199.55). In the intervening period between about 70 and 30 Ma (Mastrichtian-Lower Tertiary), shallow marine sediments were deposited above a number of the rock units that formed the island arc. These units remained in their relative place of formation after the uplift of the Oman mountains, and are thus referred to by Glennie (1995:Table 1)as "neo-autochthonous". The Oman Mountains, in their present form, comprise an arc more than 700 km long and up to 150 km wide, parallel to the Gulf of Oman. They extend from the Musandam Peninsula and the Straits of Hormuz in the north to Ras a1 Hadd in the southeast at an elevation of generally between 500-1,500 m, although Jebel Akhdar rises to ca. 3,000 m (Lippard et al. 1986:l-2). The rock formations that comprise the Oman Mountains are illustrated in Figure 2.1. The most extensive geological unit of the mountains is the Semail Nappe, with an area of approximately 20,000 km2 and a thickness of between five and ten kilometres, which has been broken into 12 generally intact blocks of varying sizes as a result of erosion and of faulting during and after emplacement (Glennie et al. 1974). The Hawasina outcrops mostly on the southern and western extremities of the Oman Mountains, but also occurs in the interior of the mountains, for example at the type site of the "Hawasina Window" in Wadi Hawasina, and in the Dibba Zone in the north. The upper and lower autochthonous units of the mountain range are exposed in the region of Jebel Akhdar, in the mountains south of Muscat, in the Huqf region, and at the northern end of the Oman Mountains in the Musandam Peninsula. Neo-autochthonous rocks are seen in the A1 Ain region, particularly at Jebel Hafit, and in the coastal region between Saih Hatat and Ras al-Hadd in Oman (Glennie 1995:Figure 10).

Table 2.1 Tectonostratigraphic Units of the Northern Oman Mountains

Age (Ma BP)

Formed 105-95

Stratigraphic Unit

Mostly shallow marine limestones (Maastrichtian-EarlyTertiary) of:

1) the Hadhramaut Group, and;

Oceanic crust (Mid-Late Cretaceous), consisting of:

1) a crustal sequence of extrusive basaltic pillow lavas and interbedded pelagic sediments; a sheeted dyke complex; high-level plutonic rocks; and layered peridotites and gabbros; 2) a mantle sequence of peridotites and harzburgites, and; 3) a basal metamorphic sheet of amphibolites and

Formed 270-70

Mostly calcareous sandstones (U. Permian-Turonian) deposited as turbidites, comprised of:

1) the Umar Group; 2) the AI AridhIKawr Groups, and; 3) the SumeiniIHamrat Duru Groups (including the Wahrah Formation).

"Aruma Group" (AllochthonousUnit) 1) Simsima limestones (U.Cretaceous-L.Tertiary); 2) Fiqa shales and conglomerates of the Juweiza Formation (Campanian),and; 3) conglomerates and turbidites of the Muti Formation (Santonian-Campanian). 270-90

"Upper Autochthon" (= Hajar Supergroup) Shallow marine limestones and dolomites comprised of (in the central mountains):

1) the Wasia Group (M. Cretaceous); 2) the Kahmah Group (L. Cretaceous);

3) the Sahtan Group (Jurassic),and; 41 the Akhdar Grow (U. Permian-U.Triassic).

650-270

"Lower Autochthon" A sedimentary sequence of limestones and dolomites consisting of:

1) Palaeozoic siltstones of Saih Hatat, Quartzites of J. Qamar and J. Ramaq, and;

2) Eocambrian rocks of the eastern Huqf. 850-650

"Basement" (AutochthonousUnit) Jebel Ja'alan sedimentary rocks (Precambrian)

Geology and stratigraphy of the northern Oman Mountains.

Geology and Early Exploitation of Copper

9

Figure 2.1 The geological units comprising the Oman Mountains.

Geology of Masirah Island Masirah Island is located 24 km off the southeastern coast of Oman (Figure 2.2). The island is 64 km long and up to 16 km wide, with a highest elevation of 277 m (Moseley 1969:293-294). It contains a suite of rocks that are very similar to those of the Semail Nappe, including mantle serpentinites, ultramafic to gabbroic cumulates, massive gabbros, sheeted dykes, basaltic pillow lavas and radiolarian cherts (Abbotts 1981; Moseley 1990:665). These rocks were originally thought to represent a part of the Sernail Nappe (Moseley 1969; cf. Moseley and Abbotts 1979), however, recent geological research has determined that the ophiolitic rocks of Masirah are genetically unrelated to the mainland ophiolite, being late Jurassic-Early Cretaceous in age (145-125 Ma; Gnos et al. 1997; Meyer et al. 1996; Smewing et al. 1991).

10

Early Metallurgy of the Persian Gulf

The ophiolitic rocks of Masirah Island are unusual in that they were emplaced a long time after their formation, having drifted in oceanic lithosphere for approximately 90 Ma (Meyer et al. 1996:187). There are actually two distinct ophiolite nappes on Masirah Island (Gnos and Perrin 1996:55), the upper of which was obducted onto the lower between the late Maastrichtian and the pre-Eocene (ca. 60-50 Ma; Gnos and Perrin 1996:62). It is likely that the emplacement of the lower Masirah Ophiolite onto the Arabian shelf was related to the northward movement of the Indian plate (although this is a complicated issue; for a full explanation and illustration, please see e.g., Moseley and Abbotts 1979; Shackleton and Ries 1990; Smewing et al. 1991), and took place slightly after the obduction of the upper ophiolite nappe onto the lower (Gnos and Perrin 1996:62).

Figure 2.2 The major copper deposits and metallurgical sites of southeastern Arabia (triangles) and third millennium settlements (small circles).

Geology and Early Exploitation of Copper

11

Copper Deposits in Southeastern Arabia The vast majority of copper deposits in southeastern Arabia (Figure 2.2) are hosted in rocks of the Semail Ophiolite, the formation and emplacement of which is described above. As shown in Table 2.1, the Semail Ophiolite consists of rock series with both mantle and crustal origins. The mantle series is the lowest stratigraphic unit in the Semail Nappe, and is composed mostly of variably serpentinized ultramafic rocks (mostly tectonized harzburgites and dunites) with an estimated maximum thickness of 10-12 km (Lippard et al. 1986:41). The peridotites of the mantle series are overlain by a magmatic assemblage of cumulate gabbros and peridotites up to four km thick (the "Layered Series"), and a sequence of high-level plutonic rocks (the "HighLevel Intrusives"), generally gabbros, of up to 500 m thick (Lippard et al. 1986:14, 41). The high-level intrusives are stratigraphically overlain by a sheeted diabase dyke complex of up to 1.5 km in thickness, which acted as a feeder for an overlying extrusive sequence of basaltic pillow lavas up to two km thick. The extrusive basalts are interbedded and overlain by pelagic sediments (Lippard et al. 1986:41, Figure 3.3). Massive Sulfide Deposits of the Semail Extrusive Series The largest copper deposits in southeastern Arabia are those concentrated in the Semail upper extrusive sequence. These massive sulfide deposits are stratabound within the pillow lavas of the ophiolite, although they are not exclusively associated with any particular stratigraphic interval, and are directly comparable to the large copper deposits of the Troodos Ophiolite in Cyprus (Coleman 1977:124-126; Batchelor 1992:108; Lippard et al. 1986:127). The copper, iron and zinc-rich ores are exhalative sedimentary deposits formed either in sea-floor depressions near oceanic ridges or as a result of sea-mount volcanism (Ixer et al. 1984:123; Hauptmann 1985:27). The ore metals themselves originated in the volcanic rocks, from which they were mobilized by hydrothermal seawater solutions (Jankovic, 1986:27; Hauptmann 1985:27). The massive sulfide deposits are comprised primarily of pyrite (FeS2),chalcopyrite (CuFeS2),and sphalerite (ZnS), but exhibit well-developed gossans consisting of brightly colored iron oxides, hydroxides and sulfates in

12

Early Metallurgy of the Persian Gulf

addition to secondary copper minerals such as malachite ( C U ~ C O , ( O H ) azurite ~), ( C U ~ ( C O ~ ) ~ ( and O H rare )~) native copper (Coleman 1977:125; Ixer et al. 1984; Hauptmann 1985:26; Weisgerber 1987: 170). Cementation zones or zones of secondary enrichment are not seen in the massive sulfide deposits (Hauptmann 1985:25; Hauptmann et al. 1988:35), although there are considerable quantities of secondary sulfur-containing minerals such as bornite (Cu5FeS4),chalcocite (Cu2S) and covellite (CuS) in some deposits (Ixer et al. 1984:120 and Table 2; Smewing et al. 1977536). The three largest deposits in the region occur in the hinterland of Sohar, at the sites of Bayda, Lasail and 'Arja, while other massive sulfide deposits and stockworks are known at Zuha, Raki, Hayl as-Safil and Daris in the Sultanate of Oman (Calvez and Lescuyer 1991). Detailed summaries of the formation and mineralogy of these deposits can be found in numerous publications (e.g. Ixer et al. 1984, 1986; Hauptmann 1985:25-27; Lippard et al. 1986:127-128; Lescuyer et al. 1988; Calvez and Lescuyer 1991; Batchelor 1992; A1 Azry et al. 1993). The extrusive lavas of the upper Semail ophiolite were formed as a result of two separate but nearly contemporary magmatic events (M1 and M2). The formation of the first series of pillow lavas (the V1 or Geotimes unit), which forms the footwall of all the main massive sulfide deposits in southeastern Arabia, was related to the first magmatic event. The Geotimes Unit directly overlies the sheeted dyke complex from which it was derived (Batchelor 1992:114) and was formed in late Albian to early Cenomanian times (Calvez and Lescuyer 1991). The Bayda massive sulfide deposit is thought to have been formed by hydrothermal activity at this time (Batchelor 1992: 114). The upper lava unit (V2, consisting of the Lasail and Alley Units) is related to the second magmatic event (M2), and its earliest manifestations are associated with the hydrothermal activity that formed the massive sulfide deposits at Lasail and 'Arja, as well as those at Zuha, Raki and Hayl as-Safil (Batchelor 1992:114). Thus, the majority of massive sulfide deposits in the Semail Ophiolite occur at the contact between the V1 and V2 volcanic units. The Lasail ore deposit has a hanging-wall of Lasail Unit lavas, whereas the 'Arja deposit has a

hanging-wall of Alley Unit lavas (Ixer et al. 1984:Figure 2). This volcanic and hydrothermal activity is of Cenomanian to Turonian age and represents the most important period of copper mineralization related to the Oman Mountains (Batchelor 1992: 114). Other Copper Deposits of the Semail Ophiolite Although the largest copper deposits of the Oman Mountains occur as massive sulfide deposits in the upper extrusive sequence, smaller vein-type deposits are in fact found throughout the ophiolite crustal sequence and in mantle sequence rocks (Hauptmann 1985:21-3 1).Minor sulfide concentrations are found in the sheeted dyke complex (Weisgerber 1 9 8 0 ~115; : Weisgerber l98Oa: 89; Hauptmann and Weisgerber 1980:134) and high level gab bros, often associated with northwest-southeast trending faults (Coleman 1977:124; Lippard et al. 1986:128). Copper deposits are also known from lower in the crustal sequence, at the contact between cumulate gabbro and cumulate peridotite near the petrological Moho (Coleman et al. 1978:12; Weisgerber 1980c:115; Weisgerber 1981:190), and along major fractures within the mantle harzburgites (Goettler et al. 1976:46-47; Hauptmann 1985:21-31; Lorand 1988; Batchelor l992:ll4). It is likely that a lot of this fracture mineralization is related to mineralization at higher levels within the ophiolite extrusive sequence (Batchelor 1992:114), although some deposits lie along northwest-trending faults related to younger tectonics (Coleman et al. 1978 12). Although these deposits are generally small, with lengths of less than 600 m and widths of less than 20 m (Hauptmann 1985:27; Batchelor l992:l l 4 ) , they are frequently of high grade and contain significant quantities of secondary minerals such as brochantite ( C U & ~ ~ ( O Hmalachite, )~), azurite and chrysocolla (CuSi03.2H20)in addition to primary chalcopyrite and pyrite (Goettler et al. 1976:47-50; Hauptmann 1985:26; Hauptmann et al. l 9 8 8:35). Geological researchers in southeastern Arabia have commonly noted an association between ancient slag heaps and these lower ophiolitic copper deposits (Greenwood and Loney l968:3 1; Glennie et al. 1974:284; Goettler et al. 1976; Coleman et al. 1978; Batchelor 1992:114), and have therefore suggested that these ores, rather than those of the massive

sulfide deposits, were of the greatest importance for early metallurgy in the region (Goettler et al. 1976:47; Hauptmann et al. 1988:35). There are significant differences in the mineralogy of the massive sulfide deposits and those from lower in the ophiolite sequence (Hauptmann 1985:21-31) which, when compared to compositional data from the analysis of archaeological copper-base objects, also support such a conclusion (Hauptmann et al. 1988:35). It should, however, be noted that significant amounts of low-grade oxidized copper minerals were available in the gossans (i.e. the upper weathered zones) of the massive sulfide deposits of the extrusive sequence (Weisgerber 198Oc:115-1 16), and that a number of these deposits in the vicinity of Wadi Jizzi were worked as early as the third millennium BCE (Weisgerber 1987:145). This is in contrast to the evidence suggesting that the unaltered primary copper ores of the massive sulfide deposits (i.e. chalcopyrite and bornite) were not worked on a significant scale until the local Iron Age, around the beginning of the first millennium BCE (Weisgerber 1987:145). Ophiolitic Copper Deposits on Masirah Island A common feature of ophiolites is the occurrence of massive sulfide deposits in the various rock units, particularly extrusive rocks, of which they are comprised (Coleman 1977:124). There are thus strong a priori reasons to suspect the presence of copper deposits on Masirah Island. In fact, copper mineralization was reported on Masirah Island as early as the 1840s (Carter 1848) in the form of disseminated carbonates (malachite and azurite) associated with haematite (Fe203)in quartz veins (Batchelor 1992:117). Other copper mineralizations are found in rocks of the sheeted dyke complex (Moseley 1990:Figure 5 ) and pillow lavas on the island (Moseley and Abbotts 1979:Figure l ) , and it has been suggested that the Masirah Ophiolite and small ophiolites at Ra's al-Madrakah and Ra's al-Jibsch on the nearby mainland "carry obvious potential for Cyprus-type copper mineralization" (Batchelor 1992:117). Only a small amount of archaeological work has been carried out on Masirah Island, but even the earliest geological reports mention the presence of ancient slag heaps (Batchelor 1992:117). Archaeological information

Geology and Early Exploitation of Copper

13

and radiocarbon analyses indicate that copper mining on Masirah Island can be placed at least as early as the eighteenth century BCE (Weisgerber l 9 8 8:footnote 7; Weisgerber 1991:327), and the copper of the island is therefore significant for discussions of Bronze Age production and trade in the region. Non-Ophiolitic Copper Deposits in Southeastern Arabia In addition to copper deposits within rock units of the Semail Ophiolite, small copper mineralizations can be found within stratigraphic units that underlie the Semail Nappe. Both massive sulfide and vein-type mineralization is found within Hawasina rocks in the Sultanate of Oman and the U.A.E. (e.g. Hauptmann et al. 1988:48). The largest Hawasina hosted copper deposit is that at A1 Ajal, not far from Muscat (Lescuyer et al. 1988; Calvez and Lescuyer 1991). This Late Permian (>250 Ma) deposit, roughly 100 m long and five m thick, has high levels of gold and silver but a relatively low concentration of copper in the gossan as a result of considerable leaching (Batchelor 1992:117). Further to the north, a number of geological surveys in the U.A.E. (Greenwood and Loney 1968; Hassan and Al-Sulaimi 1979) have demonstrated small veins of fracture-related copper mineralization in Hawasina rocks. The mineralization is usually of chalcopyrite with varying quantities of secondary copper carbonates (malachite), silicates (chrysocolla) and secondary sulfur-bearing species such as chalcocite (Greenwood and Loney 1968:29-3 1, 51). At present, there is no archaeological evidence for the exploitation of Hawasina-hosted deposits in southeastern Arabia.

Early Research into Ancient Copper Production in the Oman Peninsula Cuneiform Sources Referring to Dilmun, Magan and Meluhha The investigation of copper production in the region of southeastern Arabia began with the study of Mesopotamian Bronze Age cuneiform documents. Over the course of the third and early second millennia BCE the Gulf, known to the Mesopotamians as the Lower Sea, was the most critical trade route for the supply of luxury goods and some essential raw materials to the Mesopotamian alluvium (T. F. Potts 1994). A significant

14

Early Metallurgy of the Persian Gulf

body of cuneiform texts, dating from the Jemdet Nasr Period to the Old Babylonian Period, records the exchange of cloth, textiles, grain, silver, oils and other Mesopotamian manufactured goods with polities of the Lower Sea, for the procurement of various types of wood, semi-precious stones, ivory and above all, copper (Leemans 1960:lO-12; Oppenheim 1954). These cuneiform texts are our earliest historical references to copper trade in the Gulf region, and are reviewed here due to their importance for reconstructions of early copper production in southeastern Arabia. The three toponyms associated with the Gulf trade are Dilmun, Magan and Meluhha, each of which is mentioned as a supplier of copper at various periods in Mesopotamian history: Magan and Meluhha are referred to only in the Sargonic-Ur I11 periods (ca. 2350-2000 BCE), whereas the toponym Dilmun occurs from the Late UrukIJemdet Nasr Period through to the Isin-Larsa and Old Babylonian Periods, ca. 3100-1750 BCE (Heimpel 1987, 1988, 1993; Potts 1990a). There is a strong agreement between archaeological and textual evidence for locating Dilmun on the Arabian littoral of the central Gulf, incorporating Tarut Island by the middle of the third millennium BCE and concentrated primarily on the islands of Bahrain and Failaka by the beginning of the second millennium BCE (Crawford l998 :1-8 and Figure 1.2; Potts 1990a). Likewise, the archaeological evidence for extensive Bronze Age copper extraction in the Sultanate of Oman (see below) can be correlated with cuneiform references to Magan as a major supplier of copper, in order to suggest that Magan encompassed the area covered by the modern countries of the U.A.E. and Oman (Potts 1990a:133-149; Heimpel 1988). An association between the Oman Peninsula and the Sumerian copper-supplying land of Magan had already been suggested in the nineteenth century based upon geographical considerations (Potts 1986:271-272), and by the second decade of the twentieth century early historical references to copper production in Oman had been used to support the association (Potts 1990a:117). However, the details of a number of Old Akkadian military campaigns against the region (and the booty they brought back to Mesopotamia) are more equivocal, and suggest the possibility that areas on the north of the Straits of Hormuz were also included within the

Mesopotamian conception of Magan (Glassner 1989; Heimpel 1987). Although the possibility of a political entity spanning the Straits of Hormuz finds parallels in more recent Sasanian-early Islamic polities which did just that (Wilkinson 1979:889), archaeological assemblages from each side of the Gulf are so distinct as to suggest that Magan occupied only southeastern Arabia. Almost all the third millennium BCE cuneiform texts from southern Mesopotamia which mention specific toponyms as copper sources speak of copper from either Magan or Dilmun (T. F. Potts 1994:Table 4.1). Meluhha, the third polity of the Lower Sea, is mentioned only rarely as a copper supplier, and then for amounts of only a few kilograms (Leemans 1960:161). The common association of Meluhha with the supply of carnelian, lapis lazuli, gold, precious woods, and especially ivory, suggests that the toponym is to be related to the region between the Makran coast and Gujarat, encompassing sites of the Indus civilization (Heimpel 1993).

Dilmun and the Pre-Sargonic Gulf Trade Cuneiform references to Dilmun occur as early as the late fourth millennium BCE, in both lexical lists and economic documents of the "Archaic Texts" from the Eanna precinct in Uruk. In these texts, Dilmun is mentioned in association with a particular type of metal axe, and there is a partial text which refers to Dilmun copper and another which mentions a Dilmun garment (Nissen 1986; Englund 1983). From Pre-Sargonic Lagash, texts from the reigns of Lugalanda and Urukagina in the twenty-fourth century BCE indicate the receipt of Dilmun copper from the merchant Ur-Enki, in quantities on the order of 100 kg. Contemporary texts show that items such as milk, cereal products, fat, salve and possibly cedar resin, in addition to the wool and silver more commonly seen in later periods, were traded to Dilmun in return for copper and wood. Such successful trading expeditions seem to have been commemorated by the dedication of bronze models of Dilmun ships to the goddess Nanshe, at her temple in Lagash (Potts 1990a:182). There are also a number of references to Dilmun in the cuneiform documents from Ebla in Syria, dated to the mid-third millennium. Dilmun occurs as a toponym and as an element in professional titles (Potts 1986:Table l),

and it seems that the Dilmun shekel was used in economic transactions in Ebla (Potts 1986:Table 1; Pettinato 1983). Significantly, there are also references to Dilmun copper and Dilmun tin at Ebla (Pettinato 1983:77-78). As there are no known copper sources in eastern Saudi Arabia or Bahrain, these early references to Dilmun copper are usually taken to indicate Dilmun's role as a transhipment center for copper produced further afield. The later significance of Magan as a copper supplier, and the evidence of copper production in the later third millennium in southeastern Arabia, are often invoked as reasons to see the earliest Dilmun copper as originating in the Oman Peninsula (e.g. Cleuziou and Mkry 2002:282). As has been described above, there is evidence for the widespread use of copper-base objects in southeastern Arabia by the late fourth millennium BCE, but as yet local production has not been conclusively demonstrated before the Umm al-Nar Period (see below). Thus, the hypothesis that the early-third millennium cuneiform references to Dilmun copper reflect primary copper extraction in southeastern Arabia is yet to be verified.

Gulf Trade in the Old-Akkadian t o Ur 111 Periods By the Old Akkadian Period, direct connections are established between all the polities involved in the Gulf trade. This fact is most clearly indicated by the claim of Sargon that, under his rule, ships from Dilmun, Magan and Meluhha docked at the quay of his city at Agade (Heimpel 1987:no. 13). Economic texts detailing commercial traffic with Dilmun are relatively scarce at this time (Potts 1990a:183), although Dilmunites and Dilmun boats are still mentioned. A particular type of copper traded at the time, designated as urudu-a-EN-da, is known from a handful of Old Akkadian texts, and is thought to represent copper from Dilmun. In a number of texts this type of copper is explicitly recorded as having come from Dilmun, and Waetzoldt and Bachmann (1984:6) regard urudu-a-EN-da as coming from Dilmun even when the source is not specifically identified. Dilmun's role in the Gulf trade in wood and copper is further documented by inscriptions of Gudea of Lagash (Potts l99Oa:l84). Copper from Magan itself is mentioned in only very minor quantities at this time (Heimpel 1987:no. 20), and Manishtusu's reference to a

Geology and Early Exploitation of Copper

15

campaign against a region across the Lower Sea, where he traveled to the metal mines, is rather equivocal: although the crossing of the Lower Sea from Sherihum (in Iran) would suggest a location somewhere on the Arabian side of the Gulf, Magan is not mentioned by name, and the mines are said to be for KU, usually translated as "silver" or "precious metal" (Glassner 1989). Thus, it is difficult to regard the text as the first historical reference to copper production in Oman (contra Potts 1990a:138), although Glassner's (l989:186) claim that the lack of silver in southeastern Arabia suggests that Magan lay on the Iranian side of the Gulf is contradicted by medieval references to silver and gold mines in Oman (Weisgerber l987:147). By the Ur I11 Period, Magan seems to have been more important than Dilmun in the Gulf trade, and merchants from Ur traded directly with Magan. There are no references to copper traded from Dilmun at this time, even though there are scattered references to Dilmunites in Southern Mesopotamia and to a continued trade with Dilmun (Potts 1990a:186). A number of texts from the reign of Ibbi-Sin indicate that a Mesopotamian merchant by the name of Lu-Enlilla received large amounts of garments and wool (and at other times, oil and leather objects) from the storehouse of the temple of Nanna in order to buy copper in Magan (Leemans 1960:19). These economic documents are supplemented by a slightly earlier text which indicates that the temple received from LuEnlilla a tithe of goods that were obtained on a trip to Magan: not only copper (more than 150 kg), but also beads of semi-precious stones, ivory and "Magan" onions (Oppenheim 1954:13; Leemans 1960:21). Dilmun in Isin-Larsa and Old Babylonian Sources Magan is not mentioned in cuneiform sources after the Ur I11 period, and there is a corresponding increase in the frequency of references to Dilmun, which is particularly associated with the acquisition of copper (Oppenheim 1954:15). From the Larsa Period at Ur, specifically the tenth-nineteenth years of the reign of Rim-Sin (ca. 1813-1 804 BC on the Middle chronology: Van de Mieroop 1992:136-137) there exist a number of famous texts related to the activities of Ea-nasir, an alik Tilmun or Dilmun trader, who was involved in the copper trade in the Gulf. Individual maritime trading expeditions to

16

Early Metallurgy of the Persian Gulf

Dilmun, probably undertaken by Ea-nasir himself (Leemans 1960:52), were financed by large numbers of investors, who each contributed a small amount of capital to the mission in the form of silver rings, baskets, sesame oil, and textiles (Van de Mieroop 1992:196). Upon return from Dilmun, the proceeds were divided amongst the investors, who frequently complained about the quality of the copper that had been supplied to them (Oppenheim 1954:lO-11). Although the archives from the house of Ea-nasir indicate that the trade was undertaken by private merchants, the Palace was involved in proceedings as sometime investor, and through the collection of taxes upon the completion of the expedition (Van de Mieroop 1992:197; Leemans 1960:SO). Leemans (1960:54), in fact, sees the Palace as Ea-nasir's major client. Earlier in the second millennium, it seems that the Ningal temple was more involved in the trade than the Palace, insofar as tithes of goods or votive offerings procured by Dilmun traders were deposited at the temple (Leemans 1960:19-22; Van de Mieroop 1992:197). The volume of the copper trade was large: texts from the early Larsa period contain references to tithes of hundreds of kilograms of copper from trade expeditions to Dilmun (Leemans 1960:23-36), while individual texts from the from the house of Ea-nasir in Ur mention up to 18,000 kilograms of copper (Leemans 196050). Oppenheim (1954: 13) contrasts the copper trade undertaken by Ea-nasir with that of Lu-Enlilla from the Ur I11 Period. The goods traded between Mesopotamia and the Gulf in the Lu-Enlilla and Ea-nasir archives are very similar, but the economic context of financing the venture is different: in the Larsa Period, Ea-nasir acted a private merchant (even though the Palace may have closely monitored and been a major beneficiary of the trade), whereas in the Ur I11 Period, Lu-Enlilla seems to have been an agent of an institution, the Nanna temple (Oppenheim 1954:14). Sometime between the fall of Larsa and the decline of the Dynasty of Hammurabi, Dilmun ceased to supply copper to southern Mesopotamia. Although still mentioned in cuneiform sources, it was known only for its local agricultural products and sweet water, not as a supplier of copper (Oppenheim 1954:15-1 6). Crawford (1996, 1998:154-155) has suggested that this was probably the result of the disruption caused by the establishment of a

unified Babylon under Hammurabi, and his conquest of Mari and the middle-Euphrates region. Hammurabi's actions simultaneously decimated Mesopotamia's major point of access to the Gulf trade, led to a widespread depopulation of southern Mesopotamia, and opened up routes to alternative copper sources in Anatolia and the Mediterranean. It is perhaps no coincidence that a text from the fifth year of the reign of Hammurabi's successor, Samsu-Iluna, bearing the first cuneiform reference to copper from Cyprus (Alashiya), also contains the last reference to Dilmun copper (Potts 1990a:226; Crawford 1998:155). As for the earlier periods of the Gulf trade, the copper of the Dilmun trade in the Isin-Larsa and Old Babylonian Periods is most commonly regarded as having originated in southeastern Arabia. As outlined below, however, the evidence for copper production at this period in the Oman Peninsula is extremely limited, a situation which is surprising given the fact that the Gulf copper trade seems to have reached its greatest extent at this time. Any hypotheses suggesting the exclusive origin of early second millennium Dilmun copper in Oman are impossible to evaluate at this stage, and will require extensive archaeometallurgical research to verify.

Arab and European Historical Sources There is an enormous chronological gap before the next historical references to copper production in southeastern Arabia in the tenth century CE. These sources consist of Arab historical and legal documents from the medieval period and later (Weisgerber 1987:l47-148), which are supplemented by the accounts of early European explorers in the Gulf region (Potts l99Oa: 114-1 17). They possess the distinct advantage of referring directly to copper production in Oman, rather than to the trade through the Gulf of copper which may or may not have originated in southeastern Arabia. Amongst the earliest of these sources is the Arab historian and geographer Abul Hasan Ali Al-Mas'udi, who visited Sohar in the early tenth century CE and noted that copper was produced in the region. A later Persian manuscript from the fourteenth century CE by AlMustaufi indicates the production of gold, silver and iron in southeastern Arabia (Weisgerber 1987:147), but does not mention copper. These accounts were substantiated

by those of eighteenth and nineteenth Century European explorers in the region such as Carsten Niebuhr, J. R. Wellsted, H. J. Carter, A. Germain and S. B. Miles (Potts 1990a:114-116; Carter 1848). These observers refer consistently to local copper mines in Oman and on Masirah Island, although the operational status of these mines appears uncertain. There are also Arabic historical texts dealing with mining regulations in Oman. The earliest reference is alJami by Ibn Ja'far which dates to ca. 900 CE, while mines in the vicinity of Izki and in Wadi al-Jizzi are mentioned in the twelfth century CE without specific reference to the materials extracted from them (Weisgerber 1987:147; Potts l99Oa:ll4). The records indicate that mines could be sub-let from their owners, probably merchants in Sohar, for 10 percent of the net profit of the mine (J. C. Wilkinson 1979:892). Rules existed to cover the leasing of mines when the lessee had terminated work or when rent was not being paid. Mining licenses could be unlimited, but could also be granted for limited time periods of up to 100 years, and included details of the topographical limits of the claim (Weisgerber 1987:148). Additionally, partnerships existed between owners and miners, in which profits and risks were shared (Weisgerber 1987:148). These early legal documents and historical sources, in addition to the reports of the first European explorers in the region, provide important information which cannot necessarily be supplied by archaeological evidence alone. For example, information on the administration and legal control of mining in the tenth century CE adds considerably to our understanding of the organization of production at this time, while the limited evidence for local production recounted by later European explorers can also corroborate archaeological evidence of declining production in the second millennium CE. Unfortunately, the accuracy of some of the European material is questionable (Potts 1990a:115), while the Arabic sources focus primarily upon the laws of mine ownership and the division of profits (Potts 1990a:114-115; Weisgerber 1987:147-148), without mentioning important operations such as ore concentration, smelting, and refining. Archaeometallurgical evidence will always be critical in supplying evidence for copper production in periods where historical data are lacking, and for providing a material framework to aid in the interpretation of historical records when they exist.

Geology and Early Exploitation of Copper

17

Early Scientific Analyses The earliest scientific investigation of copper production in the region was undertaken in the 1920s, as one component of research into the sources of copper used by the Sumerians (Peake 1928). In this analytical program, a number of early copper objects from Mesopotamian sites such as Ur, Kish and Tell alUbeid, were analyzed for their composition. It was hoped that such analyses, when linked with analyses of ores and slags from western Asian mining regions, could have provided evidence of which sources were most likely to have provided the copper used by the Sumerians. The conclusions of the study were founded upon the idea that relatively high percentages of nickel characterized both the ore sample from Oman and early copper objects from Mesopotamia. It followed that, during the third millennium, at least some copper used in Mesopotamia was obtained from Oman (Peake 1928). While recent research has indeed indicated that this conclusion is true, the metallurgical bases of the arguments used in the Antiquity article are in fact erroneous. Modern geological and archaeological research indicates that nickel occurs in many copper deposits of western Asia (Cheng and Schwitter 1957:351; Muhly 1973a:229), and therefore high nickel levels in archaeological objects cannot be used to suggest that early Mesopotamian copper came from the relatively nickel-rich deposits of Oman. Additionally, nickel does not occur with the same frequency in all the copper deposits of Oman and the U.A.E., meaning that copper produced in southeastern Arabia could have very low levels of nickel (Hastings et al. 1975:lS; Goettler et al. 1976:46-47; Batchelor 1992). In general, the reliability of using compositional data to source archaeological objects of copper has been increasingly questioned since the 1970s (e.g. Craddock 1976; Craddock and Giumlia-Mair l 9 8 8; Pollard and Herron 1996:302 ff.; Budd et al. 1996; Pernicka 1999). Another problem with this early study was the extremely small database employed to support hypotheses of provenance. A total of only 20 archaeological objects were analyzed, along with one copper slag and one ore sample from Oman.

18

Early Metallurgy of the Persian Gulf

Geological and Archaeological Surveys in the Early 1970s The next phase of research into early metallurgy in southeastern Arabia did not occur until the 1970s, and involved the first significant archaeological and scientific study of the material remains of ancient smelting operations within Oman. During this period, the importance of southeastern Arabia to studies of the Gulf copper trade was first clearly demonstrated, through the discovery of evidence for copper production from the third millennium BCE onwards. This archaeological evidence came to light primarily through research programs conducted by the geological survey company Prospections Limited Oman (Goettler et al. 1976), by Harvard University (Hastings et al. 1975), and by the Institute for Human Palaeontology in Rome (Tosi 1975). Geological research in the region was undertaken by Prospections Limited Oman from 1973. Interestingly, geological survey for copper deposits in Oman was to a large degree inspired by Geoffrey Bibby's then recently published book, Looking for Dilmun (Bibby 1970; Goettler et al. 1976:43). One of the major approaches utilized in Prospection Limited's survey for copper deposits was the questioning of local inhabitants with regard to their knowledge of old smelting places in the mountains (Weisgerber 1991b:79). As a result, the investigations of Prospection Limited resulted in some important archaeological discoveries, including the remains of at least 44 ancient production sites. These sites were recognized primarily by the presence of slag produced by ancient smelting operations, estimated visually to range from "a few tons to, in one instance, more than 100,000 tons" (Goettler et al. 1976:43-44). Examples of slag heaps associated with early copper smelting in the region are illustrated in Figures 2.3-2.4. Nineteen deposits were estimated to have at least 1,000 tonnes of slag. The variations in the size of slag deposits at different smelting sites were thought t o reflect the fact that smelting operations at a newly discovered ore body were part of the prospecting process (Goettler et al. 1976:44). In this model, small slag heaps represented "test runs" in which the viability of an ore body had been assessed and found to be non-economic.

Figure 2.3. Slag heaps at Samdah, Oman (from Weisgerber 1978: PI. 12b).

Evidence for the extraction of copper ores was also recorded. Surface mining was recorded in the form of small pits and trenches, as well as larger "open" pits of up to 100 m wide, while shafts and adits of considerable depth were found at a number of sites. The overall impression gained by the geologists of Prospection Limited was that "a major effort involving extremely hard, highly organized work was mounted" in order to extract and process the copper ores (Goettler et al. 1976:45). Consideration was also given to the technology employed in the copper smelting and the types of

ores exploited. It was suggested that secondary copper minerals such as malachite, azurite and turquoise ( C U A ~ ~ ( P O ~ ) ~ ( O Hwould ) ~ - S have H ~ ~been ) the primary ores utilized. This supposition was supported by the fact that 23 of the 44 production sites were adjacent to workings in shear zones in basic intrusions, in which only secondary minerals were present (Goettler et al. 1976:46-47). It was thought that secondary ores would have provided a high-grade feed to the smelters, and would have been easily seen and separated by early miners due to their bright colors. Additionally, the major sulfidic ore found in Omani

Geology and Early Exploitation of Copper

19

Figure 2.4. Slag fields at Tawi 'Arja, Oman (after Weisgerber 1978: PI. 18a).

deposits, chalcopyrite, was generally found to be highly intermixed with other minerals in the ore body, and hence difficult to extract by hand sorting (Goettler et al. 1976:47). Native copper was regarded as occurring so rarely as to have been insignificant for early copper use in the region (Goettler et al. 1976:47). Establishing the periods of use of the mines and smelters located in the geological survey was considered of basic interest, but conclusions were difficult to draw and required the introduction of archaeological evidence. Goettler et al. (1976:45) suggested three main periods of exploitation: a pre-Islamic phase, a phase dating to the nineth to tenth centuries CE, and finally a phase dating to the fifteenth to sixteenth centuries CE. Workings of the pre-Islamic phase were considered, partly on archaeological evidence collected by the Harvard Archaeological Survey, to have been worked as early as 2500 BCE, possibly continuing into the second millennium BCE (Goettler et al. 1976:45-46). The later phases of extraction were determined through the analysis of pot-sherds from various smelting sites, and also through the radiocarbon dating of charcoal inclusions in slag samples (Goettler et al. 1976:46).

20

Early Metallurgy of the Persian Gulf

Evidence of third millennium BCE mining activities was also recorded by the Italian expedition to Oman (Tosi 1975) and by the Harvard Archaeological Survey (Hastings et al. 1975). The Harvard survey was not aimed solely at the discovery of sites related to copper production, nevertheless third millennium BCE sites with evidence of copper smelting were recorded at Wadi Samad 5, Batin 1, and Zahir 2-3 (Hastings et al. 1975:12 and Figure 2). Fieldwork by the Italian mission also generated discussion on ancient mining in the region, and Tosi and Piperno suggested that "surface mining in the deposits or the gathering of metal-bearing pebbles from the wadi beds probably prevailed over actual mining operations" (Tosi 1975:198). The evidence for third millennium copper smelting in the region was regarded by the Italian mission as very similar to midthird millennium material with which the authors were already familiar, from the site of Shahr-i Sokhta in Iranian Seistan (Tosi 1975:202). However, the reconstructions of smelting technology suggested by both the Italian mission and the Harvard team (Hastings et al. 1975:12) were speculative efforts unsupported by scientific analyses of the extant smelting remains.

Brief mention is made, in both archaeological and geological reports from the early 1970s, of the importance of these discoveries for the location of the land of Magan. A number of compositional analyses of ore was presented by Prospection Limited (Goettler et al. 1976:49-SO), in which the presence of nickel was demonstrated (particularly for deposits in shear zones in ultrabasic rocks), in support of the conclusions of Peake (1928) discussed above. In contrast, Hastings et al. (1975:l.S) noted that, although there was good evidence for the production of copper in the region in the third millennium BCE, at the time of their article there was no clear evidence for the export Omani copper in the Bronze Age. Indeed, the area was regarded by these researchers as "a scene of quiet well being untouched by the maelstrom of Mesopotamia or Iran" (Hastings et al. 1975:15). Sensibly, however, they allowed that excavation might change the reconstructions suggested by their survey data. Thus, the archaeological and geological work carried out in Oman between 1973 and 1975 was able to demonstrate significant evidence for ancient copper production in the region. Theories were proposed regarding the technologies and processes of copper smelting at various periods in the region's past, although archaeometallurgical and related analyses were extremely limited. Estimation of the periods of copper production also proved problematic, while calculations of the volume of copper production in the various periods of extraction were not possible due to this chronological uncertainty, in addition to the incomplete nature of survey and the lack of detailed archaeometallurgical analyses.

Analyses by the Centre National de la Recherche Scientifique (CNRS), France In the late 1970s and early 1980s, a number of archaeometallurgical studies were published by scholars from the Centre National de la Recherche Scientifique (CNRS), the Commissariat i1'Energie Atomique, and the Laboratoire de Recherche des Musies de France that included analyses of material from southeastern Arabia (Berthoud 1979; Berthoud et al. 1980, 1982; Berthoud and Cleuziou 1983). The articles represented an effort to characterize the evolution of alloying techniques in early western Asia (Berthoud et al. 1982), and

to scientifically determine the provenance of copper used in various regions bordering the Gulf in the fourth and third millennia BCE (Berthoud et al. 1980; Berthoud and Cleuziou 1983). Surprisingly, these were the first published analyses of copper-base objects from the Gulf since the work of Peake for the Sumerian Copper Committee in the 1920s. The provenance program was based on two series of compositional data: one on copper ores from various ancient mining regions in western and central Asia, the second on copper objects from Iran, Mesopotamia and southeastern Arabia (Berthoud and Cleuziou 1983:242). Berthoud et al. (1980:88; Berthoud and Cleuziou 1983:242-243) noted a great similarity in the composition of copper used in the mid-third millennium from the "Vase i la Cachette", late third millennium BCE copper objects from Ur, and Umm al-Nar Period objects from southeastern Arabia (Hili and Umm al-Nar Island), as well as distinct differences in the composition of copper produced in Iran and Oman. They concluded, amongst other things, that southern Mesopotamia and Khuzistan obtained their copper from southeastern Arabian sources at least by the Early Dynastic I11 period, and perhaps as early as the EDII period (Berthoud and Cleuziou 1983:243). The analytical approach of Berthoud (1979) has been questioned (Seeliger et al. 1985:642-643, note 74) on the grounds that the analyses were of an accuracy and precision insufficient to allow the stated conclusions of the work, and on the limited number of analyses used to characterize copper produced in different areas (Hauptmann 1987:209; Hauptmann et al. 1988:34). The claimed ability of the analyses to satisfactorily delineate between southeastern Arabian and Iranian ore sources has been particularly disputed. The limited nature of the ore database is particularly clear in some instances, for example in southeastern Arabia where analyzed ores contained arsenic levels of up to only 690 ppm, whereas objects from the region contained up to seven percent arsenic (Berthoud et al. 1982:45). Nevertheless, the French analytical program was important for providing the first characterization of the chemical composition of significant numbers of copper-base objects from

Geology and Early Exploitation of Copper

21

southeastern Arabia, and for focusing on material from the northern part of the Oman Peninsula, in the modern U.A.E. The subsequent work by the German Mining Museum, to which we will now turn, has dealt almost exclusively with material from more southerly regions, in the modern day Sultanate of Oman.

German Mining Museum Project in Oman The work in Oman of the German Mining Museum began in January 1977, as a collaboration with the Oman Department of Antiquities and scholars from the University of Naples (Costa 1978:9). It was agreed at that time that a German expedition to the region was to be entrusted with all studies concerning archaeometallurgy (Costa 1978:13), and important field seasons were conducted by this expedition in the late 1970s and early 1980s (Weisgerber 1978a, 1978b, 1980b, 1980c, 1981, 1987, l 9 8 8; Hauptmann and Weisgerber 1980; Hauptmann 1985, 1987; Hauptmann et al. 1988). German research in the Sultanate of Oman with a strong, though far from exclusive, emphasis upon copper production continues to this day (e.g. Yule 1996; Yule and Weisgerber 1996; Prange et al. 1999). The early survey work of the German team was able to build upon the results of the geological survey undertaken by Prospection Limited in the early 1970s (Weisgerber 1978a:20), and was particularly focused upon the importance of Oman and southeastern Arabia in general as a potential location of Magan (e.g. Weisgerber 1983, 1984, 1991b). This research focus was inspired by Geoffrey Bibby's Looking for Dilmun (Weisgerber 1991:76), and remains a hallmark of more recent archaeometallurgical work on Omani material by the German team (Prange et al. 1999). Their initial research centered upon mining sites in the hinterland of Sohar, at Lasail, Bayda, 'Arja and Samdah, and on the third millennium BCE site of Maysar 1 in the Wadi Samad that had been discovered by the Harvard Archaeological Survey (Figure 2.2; Hastings et al. 1975; Weisgerber 1978a; see also Lamberg-Karlovsky 2001:xxxiv-vi). It was soon realized that the vast majority of the more than 150 mining and smelting sites that they recorded were worked in the Islamic period (Weisgerber 1980b:68; l98Oc: 115),

22

Early Metallurgy of the Persian Gulf

although it was recognized that evidence for earlier periods of production at these sites could occasionally be found (e.g. Weisgerber 1980b:lOl; 198l:l87-190). The situation encountered by the German team in Oman is paralleled by that in Cyprus, where evidence for significant Bronze Age production is often obscured or destroyed by later Phoenician and Roman workings (Weisgerber 1982:28). Over the course of four field seasons in the Sultanate of Oman, the German Mining Museum expedition was able to provide an outline of the periods of copper production in the region (e.g. Weisgerber l 9 8 1:Abb. 4), characterize the development of copper mining and extraction technology (e.g. Hauptmann 1985), estimate the volume of copper produced in some historic and prehistoric periods (Hauptmann 1985:108-1 O9), and begin to address the social and economic implications of this industry for southeastern Arabia (e.g. Weisgerber l98Oc: 117-1 18). Additionally, as the archaeology of southeastern Arabia was so poorly known in the 1970s, the fieldwork of the German mission was crucial in the development of a basic chronological framework for discussion of the archaeology of the region (Weisgerber 1982:29). As such, the results of these investigations rank as amongst the most important contributions to the archaeology of southeastern Arabia by a single research group. The archaeometallurgical results of this research are summarized below. Periods of Production It is estimated that there are approximately 50 major copper deposits and more than 100 minor deposits in the mountains of northern Oman (Weisgerber 1983:270). The majority of these ore-bodies show signs of exploitation in the Islamic period, however multi-period exploitation has been found to be commonplace (Weisgerber 1983:274) and the earliest period of copper exploitation in the region can be traced back to the third millennium BCE. The German mission in Oman has provided a reasonably secure chronological basis for the discussion of various periods of copper production in southeastern Arabia based upon typological analyses of excavated material (e.g. Weisgerber 1987:Figure 76; Hauptmann 1985:38-40) and programs of scientific dating, notably radiocarbon and thermoluminescence (e.g.

3

1OOm

50 I

1

I

l

l

'

,

,

'

)

Figure 2.5.The settlement at Maysar 1, the mining area M2,and the cemetery M3, in Oman (from Weisgerber 1983: Figure 2).

Geology and Early Exploitationof Copper

Weisgerber 1981:250-251 and Abb. 95; Yule and Weisgerber 1996:141). Nevertheless, some limitations in the chronological attribution of smelting sites do exist, and their effect on archaeological theories are discussed in the relevant sections below. As outlined below, evidence for local copper production in the Hafit Period is entirely circumstantial, and includes the presence of copper objects in Hafit graves and in the upper levels of fifth-third millennium BCE shell-middens at Wadi Shab GAS1, Ra's al-Hamra and Ra's al-Hadd. Copper production sites of this period are not reported by the German researchers, however an early but undated "trial and error" phase of copper production from Maysar 1 is thought to represent copper extraction prior to the Bliitezeit of production at the site in the late third millennium BCE (Hauptmann l985:ll3). Copper "droplet-slags" from this period at Maysar 1 are extremely high in copper, suggesting an inefficient extraction of metal which may have been carried out in open crucibles (Hauptmann 1985:92). A second smelting site recorded at al-Batin has been dated by thermoluminescence to ca. 2500 BCE, i.e. a few centuries before production at Maysar 1 (Yule 1996; Yule and Weisgerber 1996:141). The slag from al-Batin is typologically distinct from that produced later in the Urnm al-Nar Period (Yule and Weisgerber 1996:l 4 l ) , but little more can be said about the technology of copper extraction in southeastern Arabia in the early-mid third millennium BC. Archaeological evidence suggests an expansion of production from the later third millennium BCE. Sites of this period are generally referred to in German reports as "Bronze Age (third to second millennium)", but are clearly regarded as dating to the Urnm al-Nar Period rather than the Wadi Suq Period (Hauptmann 1985:113-115). At least twenty sites with evidence for copper extraction are listed by Hauptmann (1985:116-117), some of the most important being Maysar 1, Assayab, Bilad al-Maaidin, Wadi Salh 1 and Tawi-Ubaylah (Weisgerber l 9 8 1:l87-190; Hauptmann et al. 1988:35). Up to 4,000 tonnes of slag are recorded at individual Bronze Age smelting sites, although the reconstructions of smelting technology depend mostly upon material excavated from the late Urnm al-Nar Period settlement at Maysar 1 (Figure 2.5), which pro-

24

Early Metallurgy of the Persian Gulf

duced only about 100 tonnes of slag (Weisgerber 1980b; 1981; Hauptmann 1985:92-95). Although only around 20 sites with Bronze Age slag were recorded by the German team, they envisage that contemporary copper extraction would have taken place at many, perhaps most, of the known copper deposits in the region (Weisgerber 1984:198; Hauptmann l985:95). The evidence from many sites may have been completely covered or destroyed by later mining activities, particularly during the early Islamic period. The association of Urnm al-Nar Period burial cairns with numerous extraction sites showing no signs of Bronze Age exploitation is regarded as suggestive of the widespread distribution of early mining and smelting activities in the region (Weisgerber 1978a: 19-20). However, this hypothesis is unproven. The combined results of archaeological survey, excavation and archaeometallurgical analysis have allowed a reconstruction of the volume of copper produced in southeastern Arabia in the second half of the third millennium BCE. Based on the amount of Bronze Age slag recorded at smelting sites in Oman (ca. 10,000 tonnes) and an experimentally calculated slag to copper ratio of between 5:l and 10:1, Hauptmann (1985:108) was able to arrive at a minimum figure for Urnm al-Nar Period copper production of between 1,000 and 2,000 tonnes. Given the likelihood that many Urnm al-Nar Period smelting sites were destroyed by later mining activities, a conservative estimate of total production of between 2,000 and 4,000 tonnes was suggested (Hauptmann 1985:108). Extensive evidence for copper use in the Wadi Suq Period exists in the form of copper-base grave goods (Velde 2003:109-112; Weisgerber 1991a; Potts 1990a:252-253), and primary copper production is thought by some scholars to have continued in this period, perhaps at levels similar to that in the preceding Urnm al-Nar Period (e.g. Velde 2003: 109; Weisgerber 1988:285). However, it must be stressed that the use of copper objects is at best circumstantial evidence for contemporary primary copper extraction (contra Velde 2003:109), given the fact that much of the copper used in the Wadi Suq Period could have been obtained from robbing the richly-furnished Urnm al-Nar Period graves that covered the peninsula, or through trade (e.g.

Weisgerber l 9 8 1:2l9). In contrast to the third millennium or the Iron Age, very few Wadi Suq Period settlements are known (Velde 2003:Table 1; Carter 1997), and none show evidence for primary copper smelting such as that seen in the Wadi Fizh or at Maysar 1. The only clear evidence for contemporary primary production is the presence of copper mines on Masirah Island, which have been radiocarbon dated to approximately 1800 BCE (Weisgerber 1988:note 7; unfortunately details of calibration are not given). In addition, copper smelting in this period has been hypothesized based upon the presence of Wadi Suq type tombs in Wadi Salh and Wadi Samad in areas adjacent to copper smelting refuse, although the contemporaneity of the tombs and the smelting practices is far from certain (Weisgerber 1988:285 and note 7). No published reports exist regarding the volume of slag of Wadi Suq date from these sites, and the technological basis of production remains unknown (Yule and Weisgerber 1996: 144). If it is maintained that significant copper production continued into the second millennium BCE in Oman, the continued non-appearance of Wadi Suq extraction and smelting sites must be explained through either: 1) incomplete survey; 2) near-complete destruction or obscurement by later production, or; 3) problems in the recognition or dating of this material on archaeological sites (cf. Hauptmann 1985:95). With fieldwork by the German mission continuing into the 1990s, the likelihood of incomplete survey as an explanation for the dearth of Wadi Suq-related smelting sites is quickly diminishing (cf. Weisgerber 1988:285). Likewise, the discovery of Bronze Age and Iron Age smelting remains amongst extensive early Islamic operations at numerous sites suggests that the second factor is unlikely to have completely compromised the search for second millennium smelting remains. With regard to the third possibility, Velde (2003:109) has suggested that the "scanty knowledge" of second millennium material culture at the time the German surveys were undertaken may have affected the recognition of Wadi Suq Period smelting sites. However, even the early publications of the German team (e.g. Weisgerber 1981:219) show awareness of the second millennium funerary material recovered by Frifelt (1975a) in the Wadi Suq and by the French excavations at the Hili-8 settlement (Cleuziou

1980, 1981). The non-recognition of this material by the German researchers, therefore, seems unlikely. Furthermore, the continuation of the German fieldwork into the late 1990s, when 2nd millennium material culture sequences were much more clearly known, suggests that the continued scarcity of Wadi Suq Period smelting sites is unlikely to be explained by non-recognition of diagnostic material remains. It is the chronological range of putative "Bronze Age" smelting sites which may require closer scrutiny. The ceramic material from Bronze Age smelting sites located within settlements (e.g. Maysar 1, Wadi Fizh 1) shows that they date exclusively to the later Umm al-Nar Period (e.g. Weisgerber 1981:Abb. 17). However, most "Bronze Age" smelting sites are not associated with settlement remains and, consequently, lack ceramics. These sites are thus dated by comparison to Maysar 1 slag typologies rather than to ceramic typologies, and could feasibly cover a greater time period than Maysar 1 itself. Specifically, such sites may have resulted from primary copper production well into the Wadi Suq Period. Clearly, detailed archaeometallurgical investigations are required at such extraction sites, and in areas such as Masirah Island where some evidence for Wadi Suq Period copper production does exist. Until such work has been undertaken, reconstructions of the volume and periodicity of local copper production in the second millennium BCE, such as presented by Weisgerber (1981:Abb. 4) and Hauptmann (1985:Abb. l),remain conjectural (see below). An increase in copper production has been hypothesized for the Iron Age in southeastern Arabia, as a result of the first exploitation of the massive sulfide deposits of the upper extrusive sequence of the Semail Ophiolite (Weisgerber l 9 8 8:286). At least twenty archaeological sites related to Iron Age copper extraction are recorded (Hauptmann 1985:116-1 17), including large-scale mines (Weisgerber 1987:150), slag fields, and settlements for which copper processing was an important economic activity (e.g. Costa and Wilkinson 1987:99-103). Some of the more important sites include Lasail (Weisgerber 1987:150), Raki (Weisgerber 1988:286; Yule and Weisgerber 1996:142-144; Weisgerber and Yule 1999:109-116 and Figure 12) and 'Arja site 132 (Weisgerber 1987:l48), although analysis of archaeomet-

Geology and Early Exploitation of Copper

25

allurgical finds is minimal and technological details of Iron Age smelting processes remain largely unknown (Yule and Weisgerber 1996: 142). Evidence for technological change within the Iron Age is provided by stratified slag deposits from Raki, which show two different slag types, and which are at least partially datable to ca. 1100-800 BCE by radiocarbon determinations (Weisgerber and Yule 1999:115). Iron Age sites face, in general, the same problems of preservation as Bronze Age sites. They are very prone to destruction by early Islamic activities, particularly as they concentrated upon the exploitation of the same ore bodies (massive sulfide deposits) as mined in the Islamic period, and their original number was undoubtedly greater than that observed through modern survey and excavation. As for the Bronze Age, Iron Age copper extraction at a number of sites has been postulated on the basis of nearby Iron Age burial cairns (e.g. Yule and Weisgerber 1996:142) Although no published estimates exist for the amount of copper produced in the Iron Age, a considerable increase from preceding Bronze Age output is clear, judging from the volume of surviving extraction waste. Single smelting sites with as much as 45,000 tonnes of Iron Age slag have been recorded (Hauptmann 1985:107, 116-117; cf. Yule and Weisgerber 1996:142-144), and a minimum production of 7,000-20,000 tonnes can be confidently suggested, based on Hauptmann's (1985:108-109) calculations for the massive sulfide extraction of the early Islamic period and the presence of more than 80,000 tonnes of Iron Age copper slag at the sites of Raki 2 and Tawi Raki 2 alone (Hauptmann 1985:ll6-117). The great quantity of copper-base objects from Iron Age tombs in southeastern Arabia, for example Qidfa (Im-Obersteg 1987; Corboud et al. 1988) and IbriISelme (Weisgerber l 9 8 1:232-233; Yule and Weisgerber 2001), provides additional circumstantial support for the large-scale local production of copper in the Iron Age. A significant gap seems to exist in the evidence for copper production in southeastern Arabia between the mid first millennium BCE and the mid first millennium CE. Very few radiocarbon dates exist for smelting operations from the first millennium BCE (see Weisgerber 1981:Abb. 95), as sites were dated by the presence of

26

Early Metallurgy of the Persian Gulf

diagnostic Iron Age or "Lizq Period" ceramic sherds. Pottery of the later first millennium BCE and early centuries CE in Oman (the so-called "Samad Period") has not been recovered from any smelting sites, and the next evidence for production is provided by some slag samples from 'Arja which yielded late pre-Islamic radiocarbon age ranges of the fifth to seventh centuries CE (Weisgerber 1980b:Table 2; Weisgerber 1987:148-149 and Table 14). At present, copper processing of this period is recorded only at two sites in the vicinity of the Bayda gossan, and at Raki (Yule 1996:176), although it is thought that late Sasanian exploitation of other copper mines in the region is likely (Weisgerber 1987:149). Copper production in southeastern Arabia reached its greatest extent in the early Islamic period, and the enormous quantities of waste material generated by these activities have obliterated most traces of earlier activity. Almost all the known copper deposits of the Oman Mountains were worked at this time (Weisgerber 1980:115; Weisgerber 1980:68; Weisgerber 1983:270). Production was found to have peaked in the ninth and tenth centuries CE, based upon ceramic finds and numerous radiocarbon analyses (Weisgerber 1991b:80-81), with quantities of slag of up to 100,000 tonnes reported from Lasail. Most important sites in this period were located in the hinterland of Sohar, which provided the trading outlet for the enormous surplus of production (Whitehouse 1979:874-875; J.C. Wilkinson 1979:892), and included Samdah (ca. 40,000 tonnes of slag), 'Arja and Bayda (Hauptmann 1985:116-117). Inland sites such as Raki and Wadi Salh were also important copper sources (Hauptmann 1985:116-117). Because of the large quantities of available archaeological evidence, a great deal is known about the technological aspects of copper production in this period and, to a lesser extent, the organization of production at the mining sites and the economic regulation of the trade in this material through Sohar (J. C. Wilkinson 1979:892; Weisgerber 1987:144). Around 600,000 tonnes of early Islamic slag have been recorded in Oman and calculations of production during this period, based upon a slag to copper ratio of between 12.5:l and 10:1, suggest a total output of between 48,000 and 60,000 tonnes of copper (Hauptmann 1985:108-109).

Figure 2.6. Evidence for Umm al-Nar Period mining at Maysar 2, Oman (from Weisgerber l98Ob: Abb.48).

There appears to be a hiatus between the largescale copper production of the early Islamic period in southeastern Arabia and subsequent production, the first evidence for which dates to the twelfth century CE (Weisgerber l98Oc: 118-1 19; Weisgerber l 9 8 1:Table 2). Copper extraction from the twelfth century onwards is represented by much less archaeological evidence, reflecting drastically reduced levels of production and lower levels of technological understanding in comparison to earlier smelting operations (Hauptmann 1985:103-107). Approximately forty extraction sites dating from the twelfth to nineteenth centuries CE are known from German surveys and excavation in Oman, some of the most important being Abu Zainah and Tawi 'Arja (Hauptmann 1985:107, 116-117). Copper production (whether continuous or not) over these seven centuries produced a total of approximately 25,000 tonnes of slag which, at a ratio of slag to copper of between 6.7:l and 8.3:1, represents a total production of 3,000-3,700 tonnes of copper (Hauptmann 1985:109).

Mining In the Umm al-Nar Period, evidence of techniques used in the mining of copper ores comes primarily from sites in the vicinity of the settlement of Maysar 1 (Weisgerber 1983:271). The nearest mining site, Maysar 2 (Figure 2.6), is less than 100 m from Maysar 1 and contains evidence in the form of deep "surface scratches" for the extraction of approximately 10,000 m3 of ore and gangue through open cast mining (Weisgerber 1980a:77; Weisgerber 1980b:89 and Abb. 28). Other mine sites of this period, Maysar 16 and Maysar 49, exhibit evidence for similar extraction techniques, although at Maysar 16 deeper mining is suggested by the presence of two infilled shafts (Hauptmann 1985:91). In the vicinity of Maysar, the most frequently mined copper deposits of the third millennium BCE were the small, fault-controlled stock-work ores located in basic and ultrabasic rocks of the ophiolitic upper mantle sequence or the lower cumulate sequence of the ophiolite crust (Weisgerber 198010389; Hauptmann 1985:Abb. 6). These ores, although of a sulfide basis like all copper

Geology and Early Exploitation of Copper

27

ores in southeastern Arabia (Weisgerber 1983:270), had intense areas of secondary mineralization, including such species as malachite, chrysocolla, brochantite and antlerite ( C U ~ S O ~ ( O HThe ) ~ )ores . selected had low proportions of iron sulfide (pyrite) and copper-iron sulfide (chalcopyrite), and high copper contents of five to 56 percent (Hauptmann 1985:91), both of which are important considerations for early smelting technology. Significantly, copper ores from such deposits are likely to have different mineralogical characteristics to massive sulfide ores from the extrusive sequence. In particular, nickel (Ni),arsenic (As)and cobalt (CO)levels are likely to be higher in the types of deposit exploited at Maysar, as mineral species containing these elements are often intergrown with the local copper ores (Hauptmann et al. 1988:35). As noted above, very little is known about copper mining in the following Wadi Suq Period. Mines dated to ca. 1800 BCE by radiocarbon analysis have been recorded on Masirah Island (Weisgerber 1988:285), but no further details of mining techniques or the ores extracted are available. Similarly, although smelting remains of Iron Age date are known from about 20 sites in Oman, little has been written on mining techniques of this period. The Iron Age is said to represent the first period in which the ophiolitic massive sulfide deposits were exploited for their copper content (Weisgerber l 9 8 8:286), and Iron Age mining activities are likely to have been significantly destroyed by early Islamic operations in the region (e.g. Weisgerber 1987:148). Evidence from the site of Lasail suggests that an enormous open cast mining area in the deposit gossan, up to 30 m deep, may date to the first millennium BCE (Weisgerber 1987:150). The most extensive evidence for mining activities in southeastern Arabia comes, unsurprisingly, from the early Islamic period. As noted by Weisgerber (1980c:115), mining techniques in Oman were shaped by the geological nature of copper deposits in the ophiolite. The most intensely mined deposits in Oman were those in which significant amounts of copper remained in the gosSan. In some cases, the gossan itself was nearly completely removed in a procedure whereby the "weathered and concentrated ore-body was dug in front, the ore was taken out at the spot, and the waste deposited behind" (Weisgerber l98Oc:ll6). Sites such as Assayab, Mullaq

28

Early Metallurgy of the Persian Gulf

and Samdah show evidence for the removal through mining of large amounts of the original gossan (Weisgerber 1980c:116). For other deposits, underground mining using galleries, shafts and pits is evidenced. Rectangular shafts of ca. 80 X 60 cm (Weisgerber 198013366-67 and Abb. 6) are typical of mining operations of this period at sites such as Bayda, Tawi Ubaylah, Lasail and al-Sayab, and inclined shafts and galleries have been found at depths of up to 87.5 m (Weisgerber 1987:150 and Figure 67). Archaeological evidence indicates that these galleries had roof supports of acacia wood and roofs of date palm matting, lighting was provided by terracotta oil lamps, and ore and gangue were removed through the use of lifting devices such as windlasses as well as by hand (Weisgerber 1987: 150-15 1, Figure 68). For all periods of mining activity in southeastern Arabia, the discovery of metallic extraction tools is unlikely because of the sulfidic nature of the ores, which generated an acidic environment within the mine deposits that would have destroyed any remaining metal artifacts. As for the Iron Age, the most important ores sought by the early Islamic miners were mixed iron and iron-copper sulfides (Hauptmann 1985:95), as well as the extensive low-percentage copper mineralization in the gossans of the massive sulfide deposits (Hauptmann 1985:107-108, Abb. 85). Analyses of slags produced in this period indicate that relatively little gangue material was included in the furnace charge, suggesting that either the massive form of the ore made sorting easy or that ore concentration processes prior to smelting were more thorough in the early Islamic period (Hauptmann 1985:95). The copper content of the concentrated sulfidic ores used for smelting was in the range of 15-20 percent (Hauptmann 1985:95). The mining of copper ore is not thought to have taken place to any significant extent in the later Islamic period in Oman (Hauptmann 1985:103). Copper production in the twelfth to nineteenth centuries CE is thought to have relied on the reworking of earlier Islamic and perhaps pre-Islamic slag, as evidenced by the pits dug into many slag heaps of these periods at sites where later Islamic workings are known (Weisgerber 1978a:19; Weisgerber 1980b:73; Weisgerber 1987:160-161; Hauptmann 1985:103).

Figure 2.7. Hammer and anvil stones from Maysar l , Oman (from Weisgerber 1978: PI. 1 1c).

Ore Concentration In all periods of copper production in southeastern Arabia, ore crushing and concentration was carried out using hand held hammerstones and large stone anvils. Numerous examples of such objects are known from third millennium BCE levels at Maysar 1 (e.g. Weisgerber 1978a:Pl. l l c ) as well as at sites of the Islamic period such as Samdah and Tawi 'Arja (e.g. Weisgerber 1978a:Figure 9, P1 15b, 21d; Weisgerber 1987:152-153). Anvil stones are usually identified by the presence of multiple concavities caused by repeated hammering (e.g. Weisgerber 1978a:Pl. 21c), and smaller cubic hammerstones often show evidence for use of all six faces during ore crushing and concentration activities (e.g. Weisgerber 1978a:Figure 10). There is little or no variation through time in the typology of the hammer and anvil stones used in southeastern Arabia, and such items are thus chronologically non-diagnostic when seen at smelting sites in the region. Maysar 1 examples are illustrated in Figure 2.7.

Smelting The evidence for copper smelting in southeastern Arabia in the third millennium BCE comes primarily from the Maysar 1 settlement site excavated by the German team. The archaeological remains from this site have been well documented in a number of publications (e.g. Hastings et al. 1975; Weisgerber 1978a; 1980b; 1981), and are significant for the presence of large amounts of material such as ore, slag, furnace fragments and bun-shaped copper ingots which indicate the primary extraction of copper at the site. This range of material, in addition to the evidence from the nearby extraction site of Maysar 2, has allowed a detailed reconstruction of the smelting technology used at Maysar 1 in the third millennium BCE (Hauptmann 1985; Hauptmann et al. 1988). The earliest copper production at Maysar 1 occurred in the first half of the third millennium BCE, although the archaeometallurgical evidence of these operations is extremely limited. Very small smelting furnaces or crucibles were used, although no evidence of their actual form remains, and secondary oxides and sulphur-bearing

Geology and Early Exploitation of Copper

29

Figure 2.8 Fragments of the base of a smelting furnace from Maysar 1, Oman (from Weisgerber 1983: PI. 9).

copper minerals were processed (Hauptmann 1985:92). Only moderate smelting temperatures were reached, the reduction of copper ores to metal was incomplete and the separation of copper from slag was poor, leading to slags with very high copper contents of up to 30 percent (Hauptmann 1985: 113). The nature of the analyzed slags of this period from Maysar 1 strongly suggests that these operations represent a "trial and error" phase of copper production at the site Later Umm al-Nar Period smelting at Maysar 1 utilized a mixture of the secondary ores mined at sites such as Maysar 2, Maysar 16 and Maysar 49, including malachite and chrysocolla as well as sulfur-containing ores such as brochantite (Hauptmann et al. 1988:36,71-72). No roasting of the ores was undertaken prior to smelting operations (Hauptmann et al. 1988:36, 71-72). These ores were mixed with charcoal produced from local tree and shrub species (e.g. acacia, prosopis and zizyphus), and iron ores such as haematite (Fe203)and limonite were used as fluxes (Hauptmann et al. 1988:37). The iron-rich fluxes were necessary as the copper ores used were intensively intergrown with siliceous country rock,

30

Early Metallurgy of the Persian Gulf

not all of which could be removed during ore concentration processes. The surviving furnace fragments from Maysar 1 (see Figure 2.8) indicate that the smelting furnaces in use at the site were made of leaned clay, and had a diameter of 40-50 cm, a height of approximately 40 cm and a volume of between 10 and 15 liters (Weisgerber 1983:274; Hauptmann 1985:92). Exact details of the forced air supply to the furnaces are not known, although fragments of tuygres have been recorded at the site and the use of bellows is regarded as likely (Hauptmann 1985:92). The large number of furnace fragments at Maysar 1 in comparison to the quantity of slag has suggested to the German team that smelting furnaces of the third millennium BCE at Maysar 1 had a short lifespan, and were frequently rebuilt (Hauptmann 1985 :92). During the one-step smelting process, both copper and relatively pure matte (mostly Cu2S, with low levels of iron) were produced. Copper was precipitated within the furnace by reduction of the ore in the presence of charcoal and also by the principle of the "roast reaction", in which matte is oxidized to cuprite (Cu20),which then reacts

with the remaining matte to produce metallic copper, as follows (Hauptmann 1985:94): I. 2Cu2S + 3 0 2 2Cu20 + 2S02+ 2. Cu2S + 2Cu2O 3 6Cu + SO2+ The oxide-sulfide mineral interaction central to Hauptmann's roast reaction is thus akin to the concept of "CO-smelting"investigated by a number of archaeometallurgists (e.g. Lechtman and Klein 1999; Rostoker and Dvorak 1991; Rostoker et al. 1989), which will be discussed later in this volume with regard to the production of arsenical copper alloys. Studies of the slag and furnace fragments from Maysar indicate that temperatures in the range 1,150-1,200 degrees C were achieved in the furnaces (Hauptmann et al. 1988:3640). However, the viscosity of the resulting slag/matte/copper mix within the furnace was relatively poor, meaning that separation of these elements was sometimes less than ideal (Hauptmann et al. 1988:40). Slag was tapped from the smelting furnace in a viscous state, and thus frequently contained high levels of residual copper (see Hauptmann 1985:119-120). Examples of the different types of slag found at Maysar 1 are illustrated in Figure 2.9. At the end of the smelting process, the newly-won copper and matte were separated by mechanical means (Hauptmann 1985:1l4), although high levels of sulfur and iron in analyzed copper samples from the region indicate that significant amounts of matte can remain in copper produced by this process (Hauptmann et al. 1988:37; see also Rostoker et al. 1989:Figures 6-7). Following mechanical separation, the small copper lumps produced by the primary smelting operation were remelted together in ceramic crucibles and finally cast into planoconvex ingots in appropriately-shaped cavities dug into the sandy floor of the copper workshops at Maysar 1 (Weisgerber and Yule 2003:4849) without being further refined (Hauptmann 1985:93-94). There is no clear evidence from Maysar 1 to indicate that the matte produced during primary smelting was further processed into metallic copper, although this is envisaged (Hauptmann 1985:Abb. 74; Hauptmann et al. 1988:37). The total production of copper in the settlement at Maysar 1 is thought to have been relatively small, and probably for domestic use (Hauptmann 1985:114). In comparison, much larger contemporary extraction and smelting sites such as Wadi Salh 1and Tawi Ubaylah have been recorded in Oman, suggesting that production on a larger

o

Gasblasen

W Kupferstein Kupfer

Figure 2.9. A slag typology for Umm al-Nar Period copper production at Maysar l , showing (A) large tapslags, (B) plate-like tapslags with negative impressions of mixed copper-matte concentrations on the base, (C) thin tapslags or "plate-slagsyand (D) droplet-slags (from Hauptmann 1985: Abb. 16).

scale may also have occurred in southeastern Arabia in the Umm al-Nar Period (Hauptmann 1985:34,95,114). This issue is further investigated below. Regardless of the scale of production activities, copper extraction at all known sites seems to reflect a similar technological basis to that seen in the settlement metallurgy of Maysar 1 (Weisgerber 1981:210). In contrast to the Umm al-Nar Period, very little is known regarding Wadi Suq or Iron Age smelting technology in southeastern Arabia. Slag or other extraction debris of Wadi Suq date has not been recorded by the German mission. Although more than twenty sites with evidence for Iron Age smelting have been recorded (see Figure 2.1 O), the "blocky black slag with fragments of brick-red lining on the outside" and the "silvery gray" tapslags (see Figure 2.11) which are characteristic of Iron Age smelting operations remain largely unanalyzed (Weisgerber 1987:148; Yule and Weisgerber 1996:144; cf. Hauptmann 1985:123). Iron Age smelting furnaces seem to have been excavated in areas of soft ground, and used over more than one smelting operation, however very few other technical details have been given (Weisgerber 1987:148). During the HellenisticISamad period in southeastern Arabia, the possibility of small-scale copper smelting in crucibles within settlements is suggested by excavated material from Mleiha, in the U.A.E. (Ploquin and Orzechowski 1994:30-32).

Geology and Early Exploitation of Copper

31

Figure 2.10. lron Age smelting remains from Oman, including hammer stones and slag (from Costa and Wilkinson 1987: PI. 51).

Figure 2.1 1 lron Age copper slag fromlArja in Oman (after Weisgerber 1978: PI. 16a).

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Early Metallurgy of the Persian Gulf

The next major smelting operations in the region are those undertaken in the early Islamic period, in the 9th and tenth centuries CE. These operations have left vast quantities of archaeometallurgical remains at extraction sites in southeastern Arabia, and as a result are very well studied and characterized (Hauptmann 1985). As noted above, predominantly massive sulfide ores were exploited at this time, and a complicated and relatively advanced extraction technology was developed to deal with the primary, unweathered ores of pyrite, chalcopyrite and bornite (e.g. Hauptmann 1985:107-108, Abb. 79). The extraction process in the early Islamic period is best conceived of as a complicated process involving repeated stages of alternating roasting and smelting operations (Weisgerber 1987:153; see also Rostoker et al. 1989:70-72 and Figure 1). Poor quality ores would require more roasting stages than better quality ones, and historical evidence from sixteenth century CE Europe suggests that the total roasting time for the ores could have approached one month (Hauptmann 1985:96).

The ores were roasted in a series of stone- and mortar-lined pits, usually about l m in diameter, which were dug into hill slopes at the production sites (Weisgerber 1980b:Abb. 7). Subsequently, they were smelted in shaft furnaces dug into rocky hill slopes, often behind and above roasting installations, in the vicinity of the mines themselves (Weisgerber 1987:154). Early Islamic roasting ovens and smelting furnaces have been excavated at a number of sites in Oman and the U.A.E., such as Lasail, Bayda and 'Arja and Wadi Madhab, and show a great degree of structural similarity across the region. Each smelting operation produced 20-50 kg of tapslag (e.g. Weisgerber 1978a:Figure 2) and 5-6 kg of copper matte containing 50-60 percent copper, which would have separated by density in the tapslag pit at the front of the furnace (Hauptmann 1985:114; see also Franklin et al. 1976). Following initial smelting, the refined copper matte, separated mechanically from the iron-rich slag, would have been roasted and re-smelted a number of times before finally being reduced to metallic copper (Hauptmann 1985:Abb. 79). The smelting furnaces used in southeastern Arabia in the early Islamic period were relatively robust, as they were used for significant periods of time and occasionally rebuilt (Weisgerber l987:156). The location of the furnaces seems to have been changed when too much slag built up in the direct vicinity, and so individual slag heaps from this period tend not to exceed 6,000 tonnes (Weisgerber 1987:156). Following the century or so of early Islamic smelting in southeastern Arabia, there is a gap in archaeological evidence for copper extraction (see above) followed by the introduction of completely new and technologically inferior smelting techniques in the twelfth to nineteenth centuries CE. Indeed, slags of this period from such sites as Tawi 'Arja and Abu Zainah were initially thought to represent the remains of prehistoric smelting operations due to their low technological standard (Weisgerber 1978b:29-30). Radiocarbon analyses of charcoal inclusions on the slags soon indicated their relatively recent age (Weisgerber l 9 8 1:Table 2). As noted above, there seems to have been little mining of copper ores at this time, and the basic smelter feed consisted of recycled early Islamic slag with high

matte content and some iron oxides and secondary copper minerals from early Islamic refuse piles (Hauptmann 1985: 103-1 04). The smelting furnaces used were bowlshaped and were partly dug into the ground (Hauptmann 1985:Abb. 82). A small clay superstructure, without a chimney shaft, extended above ground (Hauptmann 1985:104). Slag and matte were not tapped from these furnaces, but rather were allowed to solidify after smelting. This resulted in a large slag cake with a copper matte "ingot" at its base which was extracted by destroying the furnace superstructure and digging the remains from the ground (Weisgerber 1987: 159). Each smelting operation therefore required the construction of a completely new furnace, usually in the vicinity of previous examples, leading to the characteristic thin and dispersed nature of the bowl-slag fields of this period (Weisgerber 1987: 159). The slag and matte would have been separated by mechanical means. No evidence regarding the further treatment of the copper matte produced in twelfth to nineteenth century CE smelting operations has been recorded at any archaeological sites in Oman, so the final stages in the production of metallic copper at this time remain unknown (Hauptmann 1985:107).

Periodicity in Copper Production in Prehistoric Southeastern Arabia As described above, archaeometallurgical research regarding the chronology of copper production in Oman indicates that mining and extraction processes went through a number of periods of low or negligible output. An expression of this variability is given in Weisgerber's (1981:Abb. 4 ) summary of early German work in the region, which suggests a significant reduction in copper production in the second millennium BCE, and a complete lack of production between ca. 500 BCE and 800 CE, and ca. 1200-1800 CE. Although these exact ranges are modified in more recent publications (cf. Weisgerber l 9 8 8:285 on Wadi Suq mining; Weisgerber 1987: 148-149 on Sasanian workings; Hauptmann 1985:109 for twelfth to nineteenth century workings), copper production in Oman still appears to exhibit a distinct periodicity. The factors contributing to such variations in copper production in the Bronze and Iron Ages are discussed in this section.

Geology and Early Exploitation of Copper

33

Figure 2.1 2 Periods of copper production in southeastern Arabia. Part a) after Hauptmann (1985: Abb. 1). Part b) showing average copper production (tonneslyear)for the regions based upon the calculations of Hauptmann (1985: 115) and data in Batchelor (1992:Table 1). Data: Umm al-Nar Period production = 4,000 tonnes, duration = 400(min.)700(max.) years. Iron Age production = 10,000 tonnes, duration = 500(min.)-1,00O(max.) years. Early Islamic production = 60,000 tonnes, duration = 100 years.Twelfth-nineteenth century CE production = 3700 tonnes, duration = 700 years. Modern production = 107,200 tonnes from 1983-1990.

The summary of periods of production given by Hauptmann (1985:Abb. 1)is presented in Figure 2.12(a). The diagram is admittedly schematic, but nevertheless unintentionally suggests that copper production occurred at similar levels in the Umm al-Nar Period, the Iron Age, the early Islamic Period, and the modern period of the Oman Mining Company. More problematically, the diagram intentionally suggests that these levels of production were much higher than those of the second millennium BCE and the twelfth-nineteenth centuries CE. A rough guide to the levels of copper production in the region is provided by averaging estimations for total production in each period over the duration of the period, as is presented in Figure 2.12(b). This is a graph of the average copper production (tonneslyear) in each period, based on the production volumes determined by Hauptmann (1985:115) and data in Batchelor

34

Early Metallurgy of the Persian Gulf

(1992:Table 1).In contrast to Hauptmann's depiction, Figure 2.12(b) suggests that copper production in the Umm al-Nar and early Islamic periods, and the latetwentieth century were different by orders of magnitude, and that Umm al-Nar Period copper production was probably of a scale much more comparable to the twelfth-nineteenth century CE workings in the region than to the industrial production of the early Islamic and modern periods. This realization is critical in considering the organization of copper production in prehistoric southeastern Arabia, as discussed below. Likewise, the continuation of copper production throughout the second millennium BCE suggested by Hauptmann's diagram is not currently supported by any more archaeological evidence than is available for the Late Pre-Islamic Period (see above), which is presented as a period of zero copper production.

In attempting to explain these variations in production, the first question that arises is whether the pattern is the result of incomplete or unrepresentative archaeological research. The position taken in the following discussion is that, given the extent and duration of archaeometallurgical fieldwork in Oman, it is likely that the observed variations in copper production are a relatively accurate reflection of real phenomena, and require archaeological explanation. The major caveat that must be considered when evaluating this assumption is the lack of detailed archaeological research on Masirah Island. Given the lone radiocarbon date of ca. 1800 BCE that has come from a copper mine on the island (see above), this locality might contain evidence critical for our understanding of Wadi Suq Period and Late Bronze Age metallurgy. As noted above, there is also an element of uncertainty regarding the absolute date of the "Bronze Age" smelting remains recorded by the German Mining Museum, and a continuation of copper production into the Wadi Suq Period is possible. To begin, there are a number of factors that likely affected production levels at all periods in the history of copper extraction in southeastern Arabia. The first of these is the environmental cost of large-scale copper smelting, especially in terms of the amount of wood and wood-charcoal required for generating the high temperatures and reducing atmospheres necessary for smelting. A calculation of the wood requirements for the roasting and smelting of 600,000 tonnes of slag in the early Islamic Period, for example, suggests that perhaps 25 million acacia trees were harvested over a period of approximately 100 years to produce the required amounts of charcoal (cf. Weisgerber 1980a:75-76; l98Oc:ll9; Hauptman 198S:ll4). It is thought that such activities may have exhausted wood supplies, at least within the region of the mines themselves, and led to severe deforestation and desertification (Weisgerber 1991b:86). These figures, when applied to the 10-20,000 tonnes of slag produced in the Umm al-Nar Period (see above), suggest that perhaps a million trees were harvested for copper smelting in the second half of the third millennium BCE. Likewise, the minimum 80,000 tonnes of recorded Iron Age slag might have required the harvesting of several million trees. Although the amount of fuel required in the prehistoric

period is much lower than for the complex Islamic roasting and smelting operations, the reduced output of the Wadi Suq Period also correlates with increasing aridity in the region (e.g. Brunswig 1989; Carter 1997), which may have exacerbated the effects of large-scale fuel gathering. Thus, the enormous fuel requirements of Bronze Age and Iron Age smelting operations may have ultimately limited output, and may partially explain the observed periodicity in Omani copper production. The second factor to be considered for all prehistoric periods in southeastern Arabia is the prevalence of copper procurement through grave robbing. For example, although the evidence for primary copper production diminishes in the early second millennium BCE, a great number of copper-base objects are known from Wadi Suq and Late Bronze age funerary contexts, and secondary copper refining and casting are known from Tell Abraq (Weeks 1997) and the Shimal settlement (Vogt and Franke-Vogt 1987). Likewise, there is a significant number of copper-base objects, and copperworking areas, known from settlements and graves of the later first millennium BCE and early centuries CE (e.g. Ploquin and Orzechowski 1994; Haerinck 1994), yet this is a period for which no evidence of primary production has been recorded. It is likely that in these periods, the recycling of copper objects through tomb robbing was an important practice. Objects deposited in graves represented a source of metal that required simpler technology and fewer resources to exploit, and whose distribution was significantly wider than that of the copper ores themselves. Indeed, recycling must be regarded as an economically-viable alternative to primary copper smelting for any period of Oman's metalusing past, particularly from the late third millennium BCE onwards. It is likely, however, that tomb-robbing could have supplied only local needs, not foreign demand, especially given the practice of depositing copper-base objects in burials which continued into the early first millennium CE. In contrast to these factors which may have operated at all periods of local copper production, it is also apparent that some of the variations in output broadly coincide with economic and social changes in wider western Asia: Umm al-Nar Period production with the florescence of the Gulf trade (e.g. Edens 1992); Wadi

Geology and Early Exploitation of Copper

35

Suq recession with its collapse (e.g. Crawford 1998); early Islamic Period "industrial" production with the boom period of the Indian Ocean trade (e.g. Whitehouse 1979). That is, it seems clear that copper production in southeastern Arabia also responded to historically contingent events and processes. In the following discussion, the socio-economic and technological factors which interacted to affect copper production in southeastern Arabia are discussed.

Origins and Growth of Production in the Third Millennium BCE As described later in this chapter, the first copper-base objects appear in southeastern Arabia in the late fourth to early third millennium BCE, in both settlement and funerary contexts. Given the long history of metal use in the neighboring regions of Baluchistan, Iran and Mesopotamia prior to the third millennium, the origins of metallurgy in southeastern Arabia have usually been seen as external rather than indigenous. The origin of the southeastern Arabian copper extraction technology in southeastern Iran or Baluchistan is regarded by some scholars as particularly likely, even "obvious" (Cleuziou and M i r y 2002:304). These areas have a long history of primary metal extraction, and demonstrable technological parallels with the Oman Peninsula in other crafts, such as ceramic production. In fact, the stylistic and technological aspects of early pottery production in southeastern Arabia bear such close resemblance to contemporary industries across the Straits of Hormuz that a movement of people between the regions has been hypothesized (Miry 1996: 168-1 69). However, while the evidence for the origin of early Omani pottery technology in Iran/Baluchistan is compelling, the lack of information on the earliest copper production in southeastern Arabia means that hypotheses regarding the origins of smelting technology remain conjectural. The little evidence that does exist in Oman suggests a low level of technological understanding characterizable as a "trial and error" phase of production (Hauptmann 1985:92), which is inconsistent with the direct adoption of a developed extraction technology. Difficulties in assessing such hypotheses are further exacerbated by our limited understanding of earlier and contemporary metal

36

Early Metallurgy of the Persian Gulf

smelting in the putative "origin" zone, at sites such as Tepe Ghabristan, Tal-i Iblis and Shahdad on the Iranian Plateau (Pigott 1999a). Well-studied extraction procedures, such as those known from Bronze Age site of Tepe Hissar, for example (Pigott et al. 1982; Pigott 1989), cannot be paralleled in Oman. The evidence might therefore best be considered as an example of "stimulus diffusion": the idea of metal use may have originated elsewhere, for example with the people who brought pottery technology to southeastern Arabia, but the smelting technology itself did not, and was developed locally. A Mesopotamian connection to early Omani copper extraction was hypothesized in a number of early archaeological studies, based upon the discovery of Jemdet Nasr pottery vessels and beads in local Hafit graves alongside the earliest copper-base objects (e.g. During Caspers 1971:43; Frifelt 1980:278). However, Mesopotamia was a center of metalworking and the production of finished objects rather than of mining and smelting, and the presence of Mesopotamian prospectors in Oman (e.g. Orchard 1995:155; Frifelt 1980) seems a priori to be unlikely. Mesopotamian influence on early copper production in southeastern Arabia is much more likely to have been in the economic sphere rather than the technological. For example, the expansion in scale and geographic scope of the Gulf trade from the third millennium has been related to an increasing Mesopotamian demand for metals, woods, and luxury goods that, with the collapse of the Uruk expansion, could no longer be obtained from lands to the north of Mesopotamia (e.g. Crawford 1998:34; Cleuziou and Tosi 1989:30; Potts 1990a:92). Some scholars regard the scale of Omani copper production as reflecting this Mesopotamian demand quite directly. C. Edens (1992:130-132), for example, hypothesizes a dramatic increase in the demand for copper in the Old Akkadian Period, as copper moved from a luxury good to a necessity in Mesopotamian society. Copper production in southeastern Arabia is thought to have escalated in response to this changing demand, partly as a result of the fact that participation in the Gulf trade had become "deeply embedded" in local southeastern Arabian communities (Edens 1992:118).

The theorized increase in Mesopotamian demand and Omani copper production is contemporary with a significant expansion in the number and size of southeastern Arabian settlements, and the three developments have therefore been regarded as causally linked (e.g. Berthoud and Cleuziou l983:243-245; Cleuziou 2002: 199-200). Costa and Wilkinson (1987:232), for example, suggest that copper production was "the prime stimulus" behind the expansion of settlement in the Umm al-Nar Period, and it is not hard to find parallels with models relating external demand to intensification of settlement in other copper-producing regions of Bronze Age western Asia (e.g. Knapp 1986:12). Omani participation in the longdistance exchange network linking Mesopotamia and Meluhha, grounded upon copper production, also introduced a great variety of foreign goods of prestige nature into the region. As discussed fully in Chapter Eight, the exchange of these goods probably played a significant role in the economic integration of southeastern Arabia. The significance of this newly-emerged integration for copper production is discussed below. General studies of the cuneiform sources discussed above also suggest that Magan's role in the Gulf trade peaked in the later third millennium BCE, contemporary with the increased Mesopotamian demand for copper hypothesized by Edens. Unfortunately, although Umm alNar Period copper production refuse can be clearly differentiated from that of the Iron Age or the early Islamic Period, there have been no systematic studies of variation in the scale and technology of copper extraction within the more than half a millennium span of the Umm al-Nar Period itself. While the evidence from the site of Maysar 1 suggests a date in the last few centuries of the third millennium BCE, the date of other "Bronze Age" smelting sites is far from certain. Thus, it is impossible from archaeological evidence to support or deny hypotheses like increased Omani copper production in the Akkadian Period, much less causally link this increased production to category shifts in Mesopotamian demand for raw materials and the expansion of Omani settlement. Regardless of the limitations of the available archaeological evidence, there can be little doubt that external factors such as those outlined above played a role in the development and scale of Umm al-Nar Period copper production in southeastern Arabia.

Having considered southeastern Iran and Baluchistan in terms of the origins of Omani metallurgy, and Mesopotamia in terms of increasing foreign demand for the raw material, one could also consider the role of other trading partners of Magan, notably Dilmun and Meluhha, as important consumers of southeastern Arabian copper. The evidence for copper use in both these areas is significant, although reliable analytical links to the use of Omani copper are scarce. The case for the use of Omani copper in Dilmun seems simplest, as Dilmun's role as middleman in the Bronze Age copper trade through the Gulf is well established). Nevertheless, the limited evidence that exists comes only from the terminal third and early second millennia BCE (Prange et al. 1999; Weeks forthcoming a), and while strongly indicative of the use of Omani copper, may also support the use of metal from other sources. The case for the use of Omani copper in the Indus region is less certain: the presence of planoconvex ingots at Lothal has been regarded as evidence for the use of southeastern Arabian copper, as has the trace element composition of objects from the site and elsewhere in the southern Harappan orbit (Rao 1979:233; 1985524-527). Needless to say, these arguments are of limited strength, as planoconvex ingots occur widely across western Asia and are unlikely to have been an exclusive product of southeastern Arabia (Chakrabarti l998:3 11; Weisgerber and Yule 2003:48), and trace elements can only rarely provide a conclusive guide to metal provenance. Nevertheless, hypotheses suggesting the use of Omani copper in the Indus are plausible, given the archaeological evidence for exchange between the two regions (Weisgerber 1984; Potts 1993c; Edens 1993), and the likelihood that a region as large as the Indus must have been utilizing copper from multiple sources (Kenoyer and Miller 1999: 117-1 18). Certainly, such theories deserve to be assessed on their archaeological merit, rather than dismissed as reflecting supposed political biases or the desire to explain South Asian civilization as non-indigenous (cf. Chakrabarti and Lahiri 1996:199). Having discussed the external factors affecting copper production in Bronze Age southeastern Arabia, it is clear that the internal factors, including the demand for copper from a growing Omani population increasingly

Geology and Early Exploitation of Copper

37

reliant on metals, must also have influenced production. The scale of local consumption is reflected in the large number of copper-base objects deposited in the Umm al-Nar Period collective graves found across the peninsula (e.g. Benton 1996; Potts 2000). These funerary practices must have been supported by levels of copper production much higher than seen in the early third millennium, where comparatively few copper-base objects are known from funerary contexts (see below). A corresponding increase in metal use in Umm al-Nar Period settlements is also seen, with sites such as Umm an-Nar Island (Frifelt 1995), Tell Abraq (Weeks 1997), Bat (Frifelt 1979:584), Ra's alJinz RJ-2 (Cleuziou and Tosi 200057-59), and Ghanadha 1 (A1 Tikriti 1985:15) containing relatively large numbers of copper-base objects. In examining the internal socio-economic factors affecting copper production in southeastern Arabia, the nature of local subsistence and exchange patterns is of particular significance. The third millennium is usually characterized as a period of increasing cultural integration in the Oman Peninsula, directly related to the expansion and consolidation of intra-regional trade networks linking the complementary subsistence regimes of coastal and inland settlements (Cleuziou and Tosi 2000:26; Cleuziou and Tosi 1989:17; Crawford 1998:120; Mkry 1997: 188; Charpentier 1996). There seems little doubt that copper produced in the mountainous interior would have been a significant component of this internal exchange system, along with agricultural and marine products, as attested by the distribution of metal at Bronze Age sites across the peninsula. For example, the abundance of copper objects in debris contexts from Ra's al-Jinz RJ-2 suggests that copper was far from a rare resource in this coastal area distant from inland primary production centers (Cleuziou and Tosi 2000:57-59), and this finding is supported by discoveries at other third millennium coastal sites listed in the preceding paragraph. The increasing economic integration of the region may thus have played a role in the expansion of local copper production. Although the power of long-distance exchange to act as an agent of economic growth has been emphasized by a number of scholars,

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Early Metallurgy of the Persian Gulf

Figure 2.1 3 A slag-filled planoconvex copper ingot from AI-Aqir in Oman (Hauptmann 1987: Abb. 2).

Cleuziou and Tosi (2000:71 n. 21) are no doubt correct in stating that local exchange networks were of much greater importance than foreign exchange to the economic welfare of the Bronze Age inhabitants of the Oman Peninsula. Parallels can be drawn with a thought-provoking analysis of Bronze Age metal extraction in Europe by S. Shennan (1999), that examined the production of copper in the eastern Alps in cost-benefit terms, based around Ricardo's "Law of Comparative Advantage" and the notion that early copper producers were rational economizers (1999:353). Shennan's study was itself based upon

earlier ethnographic studies of pre-modern production and inter-regional exchange systems in the Grassfields region of Cameroon, undertaken by M. Rowlands and J. Warnier (Shennan 1999:353). The model could be reduced to the idea that "it is not worth producing commodity X yourself if you're better off producing commodity y and obtaining commodity X in exchange for it, in other words, by specializing" (Shennan 1999:353). According to Ricardo's Law, specialization is ultimately rooted not only in the localized distribution of necessary raw materials, but in regional variability in the costs of production caused by ecological, technological and social determinants (Shennan 1999:354; see also Costin 2001:308). Ricardo's Law represents an explicitly formalist understanding of production and exchange systems, which some scholars may regard as unjustified. Nevertheless, the economic nature of the Gulf trade is made eminently clear by the surviving cuneiform evidence from Mesopotamia (see above). Although often funded by large Mesopotamian institutions, the copper trade was undertaken as a venture in which the economic success or otherwise of the individual merchant was calculable. Moreover, specific details of the trade, especially the attempts to distribute raw materials of questionable quality for which Ea-Nasir was so strongly criticized by his partners, clearly resemble aspects of modern entrepreneurial behavior. The presence of a number of planoconvex copper ingots from Bahla with deliberately-produced cores of slag (see Figure 2.13) tallies well with the cuneiform evidence for complaints about low quality copper traded by Ea-Nasir. It has been suggested that these ingots represented a votive deposit for a dam at AlAqir, and that their slag cores reflect the production of "cheaper" offerings to an unknown deity or deities (Weisgerber and Yule 2003:SO-51). However, such an interpretation is far from certain, and the ingots might also indicate that the Omani producers of the copper sought economic gain from their activities, to the point of deception. Overall, the "spirit of the gift" seems not to have influenced exchange relationships to a significant extent, and a formalist approach to Gulf copper production and trade seems justified.

Similarities are immediately apparent between the pre-modern Grasslands and Alpine Bronze Age economic systems described by Shennan, and the southeastern Arabian Bronze Age production and exchange network. For example, there is evidence for only a limited number of production centers for Omani black-on-red funerary pottery in the region in the third millennium, whose wares were distributed on a regional and sub-regional scale (M6ry 1996, 2000). Similarly, there is evidence for localization of shell ring production in the Ra's al-Jinz and Ra's al-Hadd regions (Charpentier 1994; Cleuziou and Tosi 2000:35), soft-stone vessel manufacture at Maysar 1 and elsewhere (Weisgerber 1981; David 1996). In each of these cases (pottery, shell rings, soft-stone vessels), the geographical distribution of raw materials would have allowed for production to take place at a great many more locations than it actually was. The fact the production loci are limited in number suggests that some form of regional specialization existed in third millennium southeastern Arabia, that might be understood as reflecting the operation of Ricardo's Law. The variability and complementarity of specialized subsistence and production activities within southeastern Arabia, and the regional exchange systems that developed in the Umm al-Nar Period, have been commented upon by numerous scholars. Most importantly for our study, Shennan (1999:362) noted that "one of the consequences of large scale regional exchange systems that operate on Ricardian principles ...is that they led to economic growth. That is to say, total regional production is higher than it would have been if individual communities had remained self-sufficient". Ricardo's Law is significant in providing an economic underpinning for the interdependence of specialization, exchange, and economic growth in so-called "commercial" models of the development of social complexity (e.g. Brumfiel and Earle 1987:l). Such growth in the Bronze Age exchange system of southeastern Arabia has been commented upon specifically by Cleuziou and Miry (2002:307, 310), who emphasize that exchange is "the main concept which rules any successful adaptation to an ecological milieu in Arabia".

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Thus, the significance of intra-peninsular exchange networks in the development of southeastern Arabian copper production should not be underestimated. When examining the apparent increase in social complexity in the region in the later third millennium, it is also useful to consider the nature of the exchange systems which develop under Ricardian principles: although all benefit from increased specialization and economic integration, not all benefit to the same degree (Shennan 1999:354). The inequalities inherent in the developing regional exchange system, and the competition between local and kinship groups that this fostered, may have played a significant role in the development of social complexity in southeastern Arabia in the Umm al-Nar Period, as discussed more fully below.

Possible Reduction in Copper Production in the Second Millennium BCE There is a dramatic reduction in the amount of evidence for copper production in southeastern Arabia in the early second millennium BCE. As discussed above, it is difficult to know if this lack of evidence reflects an actual reduction in production in the Wadi Suq Period, or if it is merely a product of a biased archaeological record or uncertainty in the interpretation of the evidence. A number of scholars have argued, based upon circumstantial evidence, that copper production in the Wadi Suq period continued at levels similar to those seen in the third millennium. However, there is little in the way of conclusive evidence to support either position, and it is worth considering some of the factors that may have contributed to a decline in Wadi Suq Period copper production, as hypothesized by Weisgerber (1981) and Hauptmann (1985). In particular, the apparent reduction in copper extraction is contemporary with a decline in the number, size, and complexity of settlements in southeastern Arabia (Cleuziou 1981; Carter 1997; Magee 1999:51). This change was initially regarded as a transition to an archaeological "dark age", resulting from the domestication of the camel and a consequent move to full-time camel nomadism (Cleuziou l 9 8 1).However, recent evidence for the continued presence of sedentary communities throughout the second millennium has made it clear

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that this period represents an evolution in the prehistory of southeastern Arabia society (Potts 1997b:52), rather than a revolution as initially characterized. Nevertheless, while a transition to full-time nomadism is no longer supported by the evidence (e.g. Carter 1997; Potts 1997b:52), an explanation of the development of the Wadi Suq Period that incorporates at least some movement away from sedentary life remains plausible (contra Carter 1997:96). The transition from a third millennium cultural milieu in which nomadic elements and seasonal sites played a significant role (e.g. Cleuziou and Tosi 1989, 2000; Crawford 1998:140), to one in which nomadism played a greater or dominant role is not difficult to imagine. This view is compatible with the archaeological evidence, which indicates that very few large sites are occupied in the second millennium BCE, that these few sites are all located in the northern coastal region (Carter 1997:Figure 2), and that they witness a strong (though not complete) re-orientation of their economy away from agricultural production to the exploitation of marine resources (Carter 1997:94; Potts 1997b352). Significantly, an hypothesized move towards nomadism cannot be used a priori t o explain a reduction in the amount of copper produced in southeastern Arabia. The ability of nomadic groups to mine and smelt large quantities of copper has been demonstrated in other Bronze Age archaeological contexts, most notably on the Eurasian Steppe a t the site of Kargaly (Chernykh 2002). Such evidence counters Carter's (2001:196) claims that there was a lack of permanent sedentary settlement in the copper-producing regions of inland Oman "such as would underpin an export trade in copper of the scale indicated by the Mesopotamian texts". A better explanation of the situation perhaps lies in the decay of the integrated system of exploitation of agricultural, marine and mineral resources that characterized the third millennium BCE. As discussed earlier in this chapter, the economic integration and regional specialization of production within southeastern Arabia at that time no doubt led to a growth in the scale of the local economy. In contrast, there is evidence to suggest that the Wadi Suq Period witnessed an economic disintegration characterized by significantly reduced regional interaction

(e.g. Magee 1999:51). In particular, the limited importance of agricultural settlements in the interior oases (Carter 1997) was almost certainly of great significance, representing the disappearance of one of the major nodal categories of the Bronze Age regional exchange system. The consequent reduction in economic integration is indicated archaeologically by the proliferation of raw-material sources exploited for pottery and stone vessel manufacture in the second millennium, and the lower quality of the vessels produced, which suggests the existence of non-specialized production at multiple locations (David l996:3 8-39; MCry 2000), in addition to "new patterns of distribution and consumption" (Cleuziou and M i r y 2002:302). Reduced intra-regional integration, if operating within the economic model discussed by Shennan (1999), may have led to lower levels of copper production. Of course, it is also possible to relate the reduced Wadi Suq Period copper production to broadly contemporary external economic factors. These include, in particular, the reduction in the foreign demand for Omani copper caused by political upheavals in Mesopotamia, the availability of Anatolian and Cypriot copper in Babylonia by ca. 1750 BCE, and the end of the Mature Harappan Period in the Indus region at ca. 1900 BCE. The general importance of the Gulf trade for the Mesopotamian political economy is indicated by a number of Mesopotamian cuneiform inscriptions in which the rise to power of a leader is accompanied by claims alluding to his newly-restored control of trade through the Gulf. Examples include Ur-Nanshe's claims of wood brought from Dilmun (Potts 1990a:88), Sargon's boast of boats from Dilmun, Magan and Meluhha docking at the quay of Agade, and the "restoration" of the Magan trade into Nanna's hands achieved by Ur-Nammu (Potts 1990a:144). It is interesting that these declarations generally come from the formative periods of new political entities in southern Mesopotamia, indicating that political instability in southern Mesopotamia could have seriously deleterious effects on the Gulf trade (e.g. Crawford 1996). Thus, the political and economic changes in southern Mesopotamia in the Old Babylonian Period (Crawford 1996) almost certainly had a serious effect on the demand for southeastern Arabian copper.

Looking to the east, the status of the Indus region as a consumer of Omani copper is still disputed (e.g. Weisgerber 1984; Rao l985:.S24; Cleuziou and Tosi 1989:42; Chakrabarti and Lahiri 1996:199). As has been discussed above, the use of Omani copper in the Indus region remains a very plausible hypothesis due to the geographical proximity of the two regions, the archaeologica evidence for close exchange contacts between them, and the likelihood that an area as large and densely occupied as the Indus was utilizing copper from a multiplicity of sources. Any reliable proof of this hypothesis, however, will depend upon further programs of archaeometallurgical research. Even if copper was not exchanged between the two regions, the demise of the Harappan civilization may nevertheless have been important for copper production in southeastern Arabia, as a factor in the general decline in scale and geographic scope of the Gulf trade in the early second millennium BCE. Significantly, however, the cultural and economic developments in the various regions discussed above are not perfectly synchronized. The Wadi Suq Period in southeastern Arabia, and the dramatic changes in settlement size, frequency, location, and subsistence that characterize it, is generally regarded as beginning between 2000-1900 BCE. This is broadly CO-incidentwith the disappearance of Magan from Mesopotamian cuneiform sources, and the end of the Indus civilization. However, cuneiform evidence indicates that the first quarter of the second millennium BCE witnessed a flourishing copper trade between Dilmun and Mesopotamia. Thus, if the meager evidence for primary copper production in the Wadi Suq Period is regarded as an accurate reflection of the situation, it is possible that "Dilmun" copper was coming from a region other than southeastern Arabia by this time, a possibility already suggested by R. Carter (2001:196). As discussed in Chapter Seven, there is evidence from archaeological lead isotope analyses which may tentatively support the idea that some metal from non-Omani sources was reaching Dilmun (Weeks, forthcoming a). However, one other factor to consider, as noted above, is the imprecise chronology for copper extraction in the Oman Peninsula. "Bronze Age" smelting sites recorded by the German Mining Museum Project, usually dated to the Umm al-Nar Period, could feasibly represent the remains of copper production into

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the Wadi Suq Period. Regardless, it is clear that explanations for the changes in copper production in southeastern Arabia in the early second millennium BCE must allow for complex interactions between local and regional economic systems, environmental considerations, and the ways in which copper production was articulated with broader subsistence practices. Expansion and Contraction of Iron Age Copper Production Copper production in southeastern Arabia again attains significant levels in the local Iron Age. The increase in the quantity of smelting debris dating to the late second or early first millennia BCE can be correlated with the dramatic expansion of settlement in piedmont areas of southeastern Arabia, probably related to the introduction of falai irrigation technology in the local Iron I1 period (Magee 1999). Internal factors seem to have played a major role in the development of copper production at this time, most notably the increase in demand generated by a greatly expanded population. This hypothesis is supported by numerous examples of large-scale local consumption of copper-base objects (Weisgerber l 9 8 8). These include unrobbed Iron Age tombs such as the collective horseshoe-shaped grave from Qidfa in Fujairah which contained hundreds of leaf-shaped arrowheads, dozens of vessels, large braceletslbangles, axes, and more than 10 hilted copper daggers (Corboud et al. 1988), the purported tomb robber's hoard from IbriISelme with more than 300 copper-base objects including vessels, braceletslbangles, and hilted daggers (Yule and Weisgerber 2001), and the graves and settlement occupation at A1 Qusais in Dubai which produced more than 800 copper-base arrowheads (Potts 199Oa:359-361). Interestingly, the increase in copper production in the Iron Age is contemporary with an increase in regional economic integration, very similar in nature to that seen in the Umm al-Nar Period. Although the absolute scale of settlement and population in Oman in the Iron Age was greater than in the third millennium, a similar polycentric distribution of power is hypothesized (Magee 199954-55), based upon the control of regionally diverse and complementary resources. Magee and Carter (1999:176) have proposed a model in which coastal, desert, and inland settlements formed a

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"regionally-specialized economy" that, following the model discussed above, is likely to have generated an increase in local copper production. P. Magee (personal communication) sees greater local demand for copper as related particularly to increasing conflict between Iron Age polities (and the consequent need for weaponry), and the role of copper implements in status display by newly-emergent elites. There is some evidence that Iron Age copperworking was practiced by "attached specialists", if the concentration of copperworking activities within the unusual columned building at Muweilah is any guide (Davis 1998). The role of attached specialists in the generation and maintenance of social hierarchies has been widely discussed (e.g. Earle 1994:426 ff.), and indeed a similar situation in the Umm al-Nar Period might be indicated by the location of copperworking facilities directly adjacent to the main tower at Hili-8 (Cleuziou 1989). The dearth of archaeometallurgical research on Iron Age copper smelting means that is virtually impossible to address the technological developments which may have underlain this increase in copper production in southeastern Arabia. It seems that the Iron Age saw the first large-scale exploitation of the massive sulfide copper deposits (Weisgerber 198 8 :286 ) , incorporating the smelting of both oxide ores from the gossan and unaltered sulfide ores. The massive sulfide deposits at sites like Lasail, Bayda and 'Arja are the largest copper ore-bodies in southeastern Arabia, and the ability to exploit them would no doubt have allowed a significant increase in copper production in the region. However, certain technological advances would have been required to effectively utilize the sulfidic ores, and intensive mining would have been necessary to exploit the low-grade oxide mineralization of the gossans. The lack of detailed archaeological evidence for these mining and smelting technologies precludes the formation of a sound hypothesis regarding their effect on Iron Age copper extraction. Assessing the impact of foreign demand for Omani copper in the Iron Age is also difficult. There is a complete lack of textual evidence regarding southeastern Arabia in the early first millennium BCE, and it is not until the reign of Assurbanipal in 640 BCE that Neo-Assyrian cuneiform sources mention a ruler of the

region, Pade king of Qade, who brought unspecified (but rich) tribute to Assyria (Potts 1990a:393). Later documents related to the Achaemenid administration of southeastern Arabia (Potts 1990a:394-400) do not mention the export of goods at all. It has been suggested that Neo-Assyrian and Neo-Babylonian references to obtaining bronze from Dilmun, sometimes in quantities of hundreds of kilograms, reflects the use of metal originally from southeastern Arabia (Potts l99Oa:NO). This hypothesis remains uncertain, but is certainly supported by the evidence for Iron Age copper extraction in Oman. One need only examine the meager historical evidence for copper export from Oman in the early Islamic Period to understand that large-scale copper production and trade can be seriously under-represented in historical sources. Thus, external markets for the copper produced in Iron Age southeastern Arabia may have been important. In this context, it is interesting to note the suggestion of Magee and Carter (1999:175) that developments in the early Iron Age in southeastern Arabia might be related to a "revitalized exchange relationship with Iran". This contact with the north is indicated by a wide range of material goods recovered in southeastern Arabian contexts, particularly ceramics (e.g. Magee 2002:Figure 2). Likewise, there is abundant archaeological evidence attesting to contact between southeastern Arabia and the central Gulf in the Iron Age (e.g. Potts 1990a:325-326), and Dilmun may have been an important foreign consumer of Omani copper. The factors underlying the apparent reduction in copper smelting in the later stages of the Omani Iron Age remain obscure. This is chiefly because there has been so little analytical work on Iron Age smelting sites in Oman, and the chronology and development of copper extraction within the Iron Age are consequently unknown. The only secure dates for Iron Age smelting relate to the very large-scale extraction in the Raki area, which is radiocarbon dated to ca. 1100-800 BCE (see above) and thus must be placed early in the local Iron Age sequence. Evidence from other elements of the archaeological record indicates a significant contraction of Omani settlement beginning in the Iron I11 Period, i.e. after about 600 BCE. Explanations proposed for the reduction in settlement

largely revolve around access to water, and have included the lowering of local water tables and the silting up of the falaj irrigation systems that were critical for agricultural production in the preceding Iron I1 Period (Magee 1999). As the florescence of Iron Age copper production seems to be related predominantly to an increase in the internal demand from a rapidly expanding Iron I1 population, lowered production from the mid-first millennium BCE might likewise be due to the reduction in local settlement and population. The possible continued importance of Bahrain as a consumer of Omani copper in the sixth to fourth centuries BCE is indicated by the extent of metalworking operations at Qala'at al-Bahrain City IVc-d (Harjlund and Andersen 1997:165-1 74). The continued use of copper for tools and weapons in the central Gulf in the first millennium BCE is stressed by Harjlund and Andersen (1997:210). Thus, external demand for copper does not seem to have disappeared, but internal variations in demand for copper remain the most likely cause of falling production.

Organization of Early Copper Production As outlined above, archaeological evidence and Mesopotamian historical sources indicate that copper production was a major productive activity in Bronze Age southeastern Arabia, and that copper from Magan was the most prominent material exchanged in the Gulf and Indian Ocean trade network. It is of interest to know both how Bronze Age metal mining and smelting were organized to meet the large internal and external demand for copper, and how the production of this copper affected other areas of southeastern Arabian economy and society. Natural limitations on the distribution of raw materials and the complexity of extraction technology have suggested to scholars that early metallurgy required inherent specialization (e.g. Childe 1937:9; Kristiansen 1987:33; White and Pigott 1996:151; Ottaway 2001:95). Moreover, examination of the archaeological record from Bronze Age southeastern Arabia indicates that primary copper extraction was undertaken at a limited number of sites, and thus must have been a specialized activity. Archaeological discussions of the economic and

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socio-political consequences of specialized metal production on ancient societies can be traced back to the writings of V. Gordon Childe and his contemporaries. However, as noted by Clark (1995) and Wailes (1996b:5), much early archaeological research on specialized production proceeded without an explicit understanding of what was in fact meant by the term "specialization". One result of this lack of definitional clarity was that anachronistic analogies based upon modern craft specialists and specialization were commonly employed (e.g. Clark 1995; Budd and Taylor 1994), with mining, smelting and smithing in particular regarded by Childe (1937:40, 134-136) as demanding full-time specialization. Such biases limited the ability of scholars such as Childe to accurately characterize and comprehend the great variability of early specialized production systems, and to assess their interaction with other social, political, and economic factors. These oversights have been remedied in the modern literature on the topic, where explicit (if sometimes competing) definitions of specialization can be found (esp. Costin 2001, 1991; Clark 1995; Clark and Parry 1990). Specialization can be defined in the simplest terms as the degree to which there are fewer producers than consumers of a particular object or material (Costin 2001:276), with the caveat that consumers are nondependents of the producer. Correspondingly, as distribution is a necessary complement to specialization, it is clear that specialized production was as widespread in prehistory as exchange, and must have existed in one form or another in most societies (Clark 1995:279). Archaeological studies of specialization are abundant, and have focused predominantly on identifying different types of specialized production in past societies, and determining the relationship between craft specialization and social complexity (e.g. Costin 1991; Clark and Parry 1990; Stein and Blackman 1993; Cross 1993; Wailes 1996a; Brumfiel and Earle 1987; Peacock 1982; Van Der Leeuw 1977). The material correlates of particular specialized production regimes have received particular attention. This is because definitions of specialization in non-Capitalist contexts have most commonly been extracted from historical sources or ethnographic studies, in which the type or degree of specialization is recognized by such

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characteristics as the amount of time spent in a particular activity, the proportion of subsistence needs obtained from the activity, payments in goods or money received for production, and the existence of a name for the specialist activity (Costin 1991:3). These characteristics have few or no readily identifiable material correlates, and the reconstruction of production systems in non-literate ancient societies would be an impossible undertaking if such variables were all that was available for investigation. However, it is obvious that ancient production processes do leave behind material remains, and Costin (1991:l) has suggested that production should be more readily reconstructable from archaeological evidence than a number of other economic processes (such as exchange) that have received a great deal of archaeological attention. The material remains of production processes (e.g. tools, raw materials, waste products, finished objects), and their differential spatial distributions, have significant potential to act as indices of both the type and extent of specialization. They can provide a window into specific craft production systems. From the preceding paragraph, it can be seen that accurate reconstructions of ancient production systems are dependent upon two main factors. These relate to our ability to: 1. Identify the material remains of specific production technologies (i.e. tools, raw materials, waste, finished products). 2. Recognize the material correlates of specialized production, which might include variations in the spatial distribution of production loci, as well as evidence for the standardization, skill and efficiency of manufacturing techniques. Understanding of the first component derives largely from detailed technical studies of archaeological materials, informed by laboratory analyses, modern experimental reconstructions of ancient technologies, and by ethnographic and historical accounts of non-industrial production technologies. The second component is perhaps more complex and frequently less certain in its outcomes, requiring the development of ethnographically, historically, or otherwise empirically-informed theories (i.e. middle-range theories) relating artifact attributes and the differential spatial distribution of production indices to specific forms of specialized production.

One of the most frequently cited methodologies for investigating specialization and production in the archaeological record is that developed by Costin (1991). As noted by Clark (1995:288), this is partly because Costin's discussion of the issue, like the important work of Evans (1978) before it, focuses very closely upon the identification of the archaeological correlates of production behavior. To use Costin's (1991:43) own words, her definition of specialization "is relatively straightforward to operationalize archaeologically", and focuses upon the four production variables of context, concentration, scale, and intensity (Costin 1991:8-18, Figure 1.4). Context reflects the degree of elite sponsorship of production, varying from attached to independent production. Concentration represents the spatial distribution of production loci, varying from dispersed to nucleated. Scale is a measure of the size and constitution of individual production units or groups, varying from small and usually kin-based units to larger groups of unrelated individuals. Intensity represents the amount of time spent doing the specialized task in comparison to other activities, varying from part-time to full-time. Based on the most common associations of these four variables, Costin constructs a typology incorporating eight production types, e.g. "community specialization" and "nucleated workshops", which can be compared to those found in earlier typologies of craft production, including Peacock (1982) and Van Der Leeuw (1977). The clearest conclusion to be drawn from the archaeological literature on craft production is that "specialized" copper production in southeastern Arabia could have taken a number of different forms: from small scale, independent, part-time or seasonal production by semi-specialists to full-time production with very high output by specialists attached to large political institutions. Given the emphasis that has been placed upon certain types of craft specialization in the development of political complexity (e.g. Wailes 1996a; Clark and Parrty 1990; Brumfiel and Earle 1987), the implications of these different production types for our understanding of Bronze Age southeastern Arabia are clear. Utilizing the categories discussed by Costin (1991) allows us to move beyond the a priori and un-enlightening understanding of metallurgy as a specialized

discipline, to examine in detail the economic, technological and socio-political factors that contoured copper production in Bronze Age southeastern Arabia. The evidence for the mode(s) of copper production prevalent in Bronze Age southeastern Arabia is addressed below. Primary Copper Production in Bronze Age Southeastern Arabia The manufacture of any copper object incorporates a number of discrete stages of production, from mining, ore preparation, smelting, and refining, to object fabrication processes such as casting and hammering. Significantly, there is clear potential for a geographical separation of these productive activities: it is not only theoretically possible for these processes to have taken place in widely separated locations, it is clear from the archaeological record of Bronze Age southeastern Arabia that primary extraction was generally undertaken near to copper ore sources, while newly-won (and probably recycled) copper was utilized for object fabrication at habitation sites distant from the loci of primary copper extraction. Such a wide geographical focus (Omani copper was used as far away as Mesopotamia and perhaps the Indus Valley) introduces many difficulties in the interpretation of production. In the following discussion, therefore, the focus is upon the organization of primary copper extraction only, i.e. mining, smelting, and the production of ingots. Copper in ingot form is a widelyexchanged category of material that moved both within and beyond the boundaries of Bronze Age southeastern Arabian society. Newly-won raw copper and semiprocessed copper ingots form a class of goods whose production and trade can be studied, in many respects, separately from the productive processes associated with object fabrication in southeastern Arabian settlement sites and across western Asia. Even a study of production limited to primary copper extraction is not without complications. Each of the main activities of mining, ore processing, and smelting has unique requirements in terms of technological and ritual knowledge, tools, raw materials, physical strength, etc., and each may have had distinctly constructed ideologies delineating the status of the activity, rights of participation, access to requisite knowledge (Ottaway 2001). Thus, there is no reason to assume that mining,

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ore processing, and smelting were organized along similar lines, or that production groups for each of these activities were constituted in the same way (i.e. of the same or similarly related individuals). In the case of southeastern Arabia, evidence for early copper extraction of the standard required to adequately reconstruct production systems is meager. For example, the archaeological evidence available for Bronze Age mining is almost non-existent. Where estimations of the scale of orelgangue extraction are available, as at Maysar 2 (10,000 cubic meters of rock mined using open-cast methods), no data regarding the duration of exploitation, or the scale of production (i.e. size of production units) is available. Archaeological evidence of ore processing activities is available from many sites, but again the lack of chronological and spatial control at most Bronze Age sites severely limits attempts at explanation. Furthermore, the archaeological evidence for houses, storage areas, and other habitation remains at copper extraction sites, which is crucial for assessing the possible scale and intensity of production, is extremely limited. Such information is available only from sites where primary extraction was undertaken in sedentary habitation contexts, as at Maysar 1 and Wadi Fizh 1, and only Maysar 1 has been the subject of archaeological excavation (Weisgerber 1980b, l 9 8 1; Hauptmann 1985). As a result, reconstructions of copper production in the region have utilized estimates of total output as a proxy for the organization of extractive industries. Hauptmann's estimates of total copper production in Bronze Age southeastern Arabia are of the order of a few thousand tonnes (see above), a value that indeed seems very large when considered in terms of the number of individual smelting operations that it might represent. For example, if one smelting furnace produced approximately five kg of copper per operation (see above), then Bronze Age production in southeastern Arabia represents hundreds of thousands of smelting operations. These raw numbers suggest the possibility of highly specialized, large-scale, intensive and closely controlled copper production in the region. Based upon such considerations, Hauptmann (1985: 114) regards copper production at some sites in Bronze Age Oman as having taken place "on an industrial scale".

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However, the absolute level of output is not used by Costin (1991) in her analyses of specialized production, and she has outlined the weakness of such an approach (Costin 2001:291): "The use of 'output' as an indicator of the organization of production warrants greater caution, particularly in the absence of detailed knowledge of technology, intensity, and an approximation of the number of sources or work groups and the time over which an assemblage was produced and used ...There is, at best, only a weak correlation between the quantity of an artifact recovered, the output (or scale of production) of the individual production units making those objects, and the way production was organized." Archaeological and ethnographic research has repeatedly demonstrated that very high levels of output can be achieved by groups operating under relatively simple production regimes (White and Pigott 1996:169; Shennan 1998:200-201). Thus, when the limitations of the archaeological evidence from southeastern Arabia regarding chronology, scale, and intensity are considered, industrial organization becomes only one possible explanation for high total output, and is certainly no more plausible than less intense production undertaken over many generations or centuries. Given the chronological limitations of the evidence from Oman, largescale extraction (as seen in the open-cast mining operations at Maysar 2) cannot be linked with intensive exploitation of the resource. Furthermore, the copper deposits most frequently exploited in Bronze Age Oman are relatively small, numerous, and found across a large area, a factor that limited the ability to intensify mining activities at individual large ore deposits. On a smaller scale, estimates of total output at Maysar 1 (Weisgerber 1980b, 1981; Hauptmann 1985) in the Wadi Samad, Oman, have also been used as a proxy for the way in which production was organized. The relatively small amount of primary smelting slag found at Maysar 1 (approximately 100 tonnes) is regarded as evidence that copper production was a "part-time activity, one that for most residents was secondary to agricultural and pastoral pursuits" (Edens and Kohl 1993:26). It is doubtful whether it is correct (or even useful) to classify copper production at Maysar 1 as "secondary" to agricultural production based upon

total output: a term such as complementary is perhaps more appropriate. Nevertheless, the location of metal extraction facilities within an agricultural village does indeed suggest that metal production was integrated with subsistence production, with resultant implication for the intensity of production. It seems likely that production in such a context was seasonal, if not in terms of the total cessation of production, at least in terms of changes in productive intensity. This is not a surprising conclusion, for as noted by Costin (2001:280), the evidence from ethnographic studies overwhelmingly indicates that "for most nonindustrial artisans production intensity varies throughout the year". Seasonal production of copper in southeastern Arabia is also thought to have been indicated by other evidence, notably the location of sites in relation to natural resources: "It is interesting that the third millennium copper smelting sites found in 1975 were all located near water and arable land ...These settlements are not situated on top of the ore deposits as became true later on. The difference between the third millennium smelting village in its fertile surroundings compared with later Islamic smelting villages in places where cultivation would be very difficult, suggests that in early times copper production was an integrated part of community life while later on it became a specialized industry, possibly for export at the behest of foreign authorities" (Hastings et al. 1975:12). It is clear that characteristics other than "overall output" must be studied in order to adequately understand the organization of copper production, and the investigation of the evidence from individual sites is an obvious starting point. Examination of the distribution of metal production refuse at Maysar 1 and other sites in the Wadi Samad facilitates an investigation of the context, concentration, scale and intensity of productive activities. At Maysar 1, pyrotechnological processes were distributed across a number of architectural units. House 1 has been described as a coppersmith's workplace for purifying smelted copper and perhaps further reworking it (Weisgerber 1981:192). It contained the base of a smelting furnace, near which was an irregular pit partly covered by an ashy layer, that contained small slag

Figure 2.14The hoard of planoconvex copper ingots found at Maysar 1 in House 4 (from Hauptmann 1985:Abb.61).

droplets, lots of charcoal, and small fragments of furnace, in addition to another pit filled with charcoal (Weisgerber 198Ob:82). House 4 contained a fireplace, a possible kiln (Weisgerber 198013:8 8), and a hoard of plano-convex copper ingots weighing about six kg (see Figure 2.14; Weisgerber l 9 8 1:192). Evidence for metallurgical activities also came from one area of House 6, separated from the rest of the house by a small wall. The main installation was a large oval fireplace with broken furnace fragments and copper slag and a great deal of ash (Weisgerber 1981:193). Copper ingot fragments were also recorded on the surface of House 31, which displayed two phases of use. In the earliest phase, a large storage vessel was dug into the ground, filled in its upper levels with charcoal. Other small pits were found nearby, one of which contained a large flat copper axe (Wesigerber 1980b:Abb. 78.5). The fact that these installations were related to copper smelting is only demonstrated indirectly, by material incorporated into the walls of the second phase of the house. These walls contained furnace, slag, crucible and mould fragments (Weisgerber 198013:8 8-89). Based upon the above evidence, Hauptmann (1985:114) has described copper production at Maysar 1 (see Figure 2.5) as being organized along "small workshop" lines, probably for domestic use. Some con-

Geology and Early Exploitation of Copper

47

Figure 2.1 5 The third millennium BCE copper-smelting settlement of Zahra l , in the Wadi Bani 'Umar al-Gharbi,Oman. Crosses indicate concentrations of furnace fragments (after Costa and Wilkinson 1987: Figure 35).

fusion is introduced by the fact that, amongst archaeologists who have discussed the organization of production, the term "workshop" has a number of incompatible definitions. Clearly, the Maysar 1 "workshops" discussed by Hauptmann agree with the use of the term as defined by Peacock (1982:9), but are better referred to as simply "production loci" using Costin's (2001:296) terminology. Regardless, surveys of third millennium BCE sites in the Wadi Fizh and Wadi Bani 'Umar alGharbi west of Sohar (see Figure 2.15) provide similar

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examples of smelting installations within the bounds of small sedentary agricultural villages (Costa and Wilkinson 1987:223), although such sites unfortunately remain unexcavated. However, reconstructions of the organization of copper production at Maysar 1 must account not only for the existence of specialized production loci (e.g. House l ) , but also for the agglomeration of a number of such production loci within the one settlement (i.e. Houses 1, 4, 6 and 31). Weisgerber, for example, has

contrasted the findings from Maysar 1 with those from a small test trench at the site of Maysar 6, about one km to the southwest. There, remains of smelting operations or pyrotechnology were absent from surface collections and excavated deposits, and animal bone was much more abundant. Weisgerber (1981:205) thus regarded Maysar 6 as a "Wohnsiedlung", in contrast to Maysar 1, which he characterized as a "Wirtschaftsiedlung". He regarded the apparent concentration of production in one site as a clear indication of the "social differentiation" of the Bronze Age population of the Maysar area (Weisgerber l 9 8 1:197). Although such conclusions remain to be thoroughly evaluated (excavations at Maysar 6 were very limited), the archaeological data indicate a concentration of individual production loci in the settlement at Maysar 1, which is suggestive of specialization at a level above the individual household or workshop. It is possible to summarize the situation, using the variables proposed by Costin. Firstly, the context of copper production at Maysar 1 seems to have been independent of any elite control. There is no evidence at the site for the existence of elites who could have controlled the output of a group of attached specialists. Of course, such elites could have lived in a different location, but, as discussed more fully below, the evidence for elites with coercive political, economic, or military powers in third millennium southeastern Arabia is very limited. Examining the concentration of production, it can be seen that copper smelting refuse was concentrated within a number of architectural units in both the northern and southern areas of Maysar 1. Hauptmann has suggested that each unit represented a "workshop", and it is clear that a number of distinct production loci existed at Maysar 1, each specifically oriented towards the extraction of copper. Looking at a larger scale, Weisgerber has contrasted the rich evidence for craft production at Maysar 1 with the apparent absence of such activities at the nearby contemporary site of Maysar 6, as a demonstration that production was nucleated in certain settlements. Regarding the scale of production, it seems that the size of individual production units was not particularly large, probably representing production by autonomous household units. It is, therefore, highly unlikely that workgroups were com-

posed of unrelated individuals. Finally, the apparent integration of copper extraction with subsistence activities at Maysar 1, although not conclusively demonstrated, does suggest that the intensity of production changed on a seasonal basis, indicating that copper extraction can have been only a part-time specialization for the inhabitants of the site. Using the typology developed by Costin ( l 9 91:Table 1.1),we would describe copper extraction at Maysar 1 as representing "community-based production". This category of specialized production is defined simply as "autonomous individual or household-based production units, aggregated within a single community, producing for unrestricted regional consumption" (Costin 1991:8). Such a reconstruction faces the problem that the intended market (local, regional, international) for the copper ingots produced at Maysar 1 is unknown, but the general division of production into a number of individual household units at Maysar 1 seems quite clear. Production systems similar to that which characterized primary copper extraction Maysar 1 have been described in other archaeological production typologies: for example, Van Der Leeuw's (1977:Table 1)category of "village industry". However, an adequate understanding of copper production in Bronze Age southeastern Arabia is unlikely to be achieved by examining only the evidence from Maysar 1. Indeed, both ethnography and archaeology have highlighted instances in which the production of a particular good was organized in very different ways within the one society. In the particular case of southeastern Arabia, field research has indicated that there were a few Umm al-Nar Period copper extraction sites much larger than Maysar 1 or sites in the Wadi Fizh. These larger extraction sites have thousands of tonnes of slag and, unlike Maysar 1 and Zahra 1, are not found within or directly associated with sedentary agricultural settlements. In fact, around 80 percent of the total 10,000 tonnes of Bronze Age slag recorded during German fieldwork came from only two sites: Tawi Ubaylah and Wadi Salh 1, each with approximately 4,000 tonnes of slag (Hauptmann 1985:95). The question that immediately arises is whether such differences in the amount of debris at extraction sites are indicative of differences in the organization of production. For

Geology and Early Exploitation of Copper

49

example, Hauptmann (1985:95) regards such sites as representing Bronze Age copper production at an "industrial" scale, in contrast to production on a smaller scale as typified by Maysar 1 and Zahra 1. Of course, Hauptmann's claims are only for output at an industrial scale, not for truly industrial production. In a strict sense, industrial production requires "industrialization" of the manufacturing process as occurred in eighteenth century Britain: the development of factories which produced full-time utilizing full-time specialists, and relied upon power other than that provided by humans or animals, such as water mills and steam engines (Peacock 1982:10). The requirement for nonhuman or animal sources of power indicates clearly that industrial copper production was not undertaken in Bronze Age Oman, and even the requirement for fulltime production is far from demonstrated in the Omani case, as has been shown above for Maysar 1. Costin's (2001:280) discussion of the ethnographic data on premodern production systems must once again be borne in mind, particularly her conclusion that "it is well to more seriously consider seasonality-and the ability to work year-round-in studies that assert high intensitylfull-time production." In assessing the evidence from Bronze Age Oman, the realization that production without "industrial" organization can nevertheless lead to very high levels of output (e.g. Burton 1984) is an important one. The location of two very large extraction sites, ca. 250 km apart towards the northern and southern ends of the copper-bearing Semail Ophiolite, is perhaps significant. Tawi Ubaylah in the north represents the closest copper source to the third millennium settlement agglomeration in the A1 AinIBuraimi oasis (Cleuziou 2003). One obvious reconstruction of non-industrial production at Tawi Ubaylah might see the site as representative of seasonal (or more sporadic) operations over several centuries, undertaken by household, kin or community groups from the nearby oasis during lulls in the agricultural cycle. Parallels for such a mode of production can be drawn with the long-term, intensive, seasonal exploitation of other localized resources in the Oman Peninsula, such as the processing of marine resources at the Bronze Age site of Ra's al-Jinz 2 (Cleuziou and Tosi 2000). Looking further afield, V. Pigott's (1998)analysis of Bronze Age copper production in Thailand has utilized

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ethnographic studies of stone quarrying (Burton 1984) to suggest that production at a very large scale could result from repetitive exploitation (every few years) by cooperative kin or residence-based groups within tribal societies. Moreover, Muller's (1984)study of salt production in preColonial North America indicates that a large quantity of production refuse can accumulate at a production site that was probably exploited by non-specialist producers on a seasonal basis, but over a very long period of time. Muller's study demonstrates the crucial distinction between site specialization and producer specialization that must be made when investigating prehistoric production systems. Therefore, the much greater scale of production at Tawi Ubaylah in comparison to a site like Maysar 1 could represent one or a combination of numerous factors. It may reflect a different mode of production, a more intensive and larger-scale production made possible by the greater size of the workforce from the A1 AinIBuraimi oasis available for mining and smelting. It has been ethnographically observed that increasing community size not only provides the potential for greater output, but also allows for more diversity in the types of specialized production practiced by the polity as a whole (Costin 2001:274). However, a similar agglomeration of Bronze Age population cannot currently be documented for the Wadi Salh 1 region. Alternatively, as basic questions regarding the duration of smelting operations at Bronze Age sites remain unanswered, the greater scale of smelting debris at Tawi Ubaylah and Wadi Salh 1 might simply reflect production over a longer period. These sites could represent examples of "site specialization" as defined by Muller. Certainly, given the lack of published evidence for habitation remains in the vicinity of Tawi Ubaylah, its status as a specialized production site, or "limited activity" area is clear. This is interesting, as sites such as Maysar 1 and Wadi Fizh 1 have been regarded as full-activity sites, where metal extraction was integrated with daily and seasonal subsistence activities (see above). In general, the fact that some extraction sites are associated with permanent settlements and others are not suggests that there was more than one mode of specialized copper production in Bronze Age southeastern Arabia.

In discussing this issue, an accurate understanding of the socio-political organization of the region in the third millennium BCE is critical, as indigenous social and political formations no doubt influenced the nature of primary extraction (e.g. O'Brien 1998; Pigott 1998).Of course, the relationship between social organization and production is not determinative, but "with increasing social complexity the potential for complex procurement systems is enhanced" (Pigott l998:215). More generally, Costin (1991:2)has observed that a true understanding of the organization of a production system requires an understanding of both the natural and social contexts in which it operates. It is well established that the third millennium in southeastern Arabia witnessed an increase in the level of economic articulation and integration between local farming, fishing, and herding communities (e.g. Cleuziou and Tosi 1989).Such integration is usually regarded as having been strongly affected by prevailing environmental conditions, particularly the intense localization of productive natural resources in the Arabian peninsula that necessitated the development of connections between groups of specialized producers and the emergence of "trade as a subsistence activity" (Afanas'ev et al. 1996; see also Cleuziou and Tosi 1989; Cleuziou and Mkry 2002; Piesinger 1983:709). Regardless of its underlying causes, it is clear from the distribution and small size of known Umm al-Nar Period settlements (contra Orchard 1995; Orchard and Stanger 1994),and the limited adoption of administrative tools such as stamp seals (Cleuziou and Tosi 2000:59-63), that economic integration was not accompanied by the development of a state-like political structure (Crawford l998:138; Cleuziou 2002:225). In fact, the socio-political organization of southeastern Arabia in the third millennium has most commonly been compared to that of the ethnographically-documented, kin-based, tribal groups of that inhabited the region into modern times (e.g. Cleuziou and Tosi 1989:17; Cleuziou 2003:140; Cleuziou l996:162; Crawford 1998:140). Following such a reconstruction, the Umm al-Nar Period villages built around one or a small number of stone and mudbrick towers are best seen as the manifestation of a polycentric distribution of power between numerous, competing petty sheikhs or rulers (cf. Edens and Kohl 1993:25-26; Edens 1992:128).

Support for such a reconstruction is provided by the analysis of funerary evidence from southeastern Arabia and by Mesopotamian historical texts. In the cuneiform sources, sporadic references to "kings" of Magan in the third millennium (Potts 1990a:137, 144) suggest a higher degree of social hierarchy in the southern Gulf region than indicated by the material record. However, these texts are probably best seen as resulting from either the "inflationary" tendencies of Mesopotamian royal inscriptions (distorting the standing of their eastern counterparts in order to increase the prestige of military victories and trade relationships, cf. Heimpel 1987:44; Kohl 2001: 228-229), or as reflections of short-lived military coalitions formed in response to Mesopotamian aggression (Cleuziou 1996:161). Regarding the funerary evidence, while the rich burial goods found in Umm al-Nar Period graves such as at Tell Abraq (Potts 2000) are suggestive of differences in wealth or status amongst members of the community, the collective nature of burial may reflect strong ideological sanctions operating against the formation of entrenched political hierarchies. However, as stated by (Cleuziou 2003:141): This strong manifestation of 'equality' inside the community should not be taken as testimony of a strictly egalitarian society, but rather as an ideological affirmation beyond diversity and power amongst the living. Tosi, Crawford (1998) and Cleuziou (2002,2003) clearly regard Umm al-Nar Period burial practices as emphasizing a social system based around membership of kinship groups, or "corporate lineage groups of common descent" (Tosi 1989:155). Leadership is conceived of as proceeding by negotiation and the manipulation of "an intricate web of matrimonial, economic and social relations" (Cleuziou 2003:145) rather than the possession of significant coercive power. The increasing complexity in Bronze Age southeastern Arabia can thus be seen as having developed more strongly along heterarchical rather than hierarchical lines. Significantly, a number of scholars have stressed the importance of interregional exchange and economic specialization in the horizontal integration of such competing polities (e.g. White and Pigott 1996: 170). Production and exchange of commodities in the region did indeed intensi-

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51

fy in the Umm al-Nar Period (e.g. Afanas'ev et al. 1996; Cleuziou and Tosi 2000:26), and there is evidence for increasingly specialized production: pottery manufacture in the Hili oasis and wider Oman (Miry 1996, 2000); soft-stone vessel manufacture at Maysar 1 and elsewhere (Weisgerber 1981; David 1996), and shell rings in the Ra's al-Jinz and Ra's al-Hadd regions (Charpentier 1994; Cleuziou and Tosi 2000:35). This aspect of regional specialization and inter-regional exchange has been addressed above, where the discussion focused upon Ricardo's Law of Comparative Advantage as the economic force underlying the development of specialized production at the community and sub-regional levels. Funerary pottery, soft-stone vessels and shell rings seem to have been manufactured under household or community-based modes of production. The evidence for copper production at Maysar 1 fits comfortably within this model of geographically-localized production for distribution within southeastern Arabia, but the large sites of Tawi Ubaylah and Wadi Salh 1 raise other possibilities.

Finally, in comparing Bronze Age copper extraction with the production of items such as pottery, shell rings, and soft-stone vessels, we must remain cognizant of the major differences between the scale of demand for Omani copper and these other commodities. Although some Omani pottery vessels and soft-stone vessels were traded overseas, particularly to the central Gulf region (Miry 2000; David 1996), pottery, soft-stone and shell rings were produced predominantly for consumers within southeastern Arabia. Copper, on the other hand, although utilized locally in undoubtedly large quantities, may at certain times or locations have been produced predominantly for foreign markets. The great differences in scale of Omani smelting sites might therefore be a reflection of production for different consumers, with different scales of demand. A parallel for this situation can be drawn with archaeometallurgical reconstructions of Iron Age copper exploitation on Cyprus, where very large copper extraction sites are also found to be contemporary with extraction on a much smaller,

Figure 2.16 An Iron Age slag heap at Raki 2, Oman (after Wesigerber and Yule 1999: PI.4).

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Early Metallurgy of the Persian Gulf

"workshop" scale. It has been hypothesized that the large-scale extraction on Cyprus might be for export, while workshop production is focused towards local consumption (Kassianidou l998:23 8). As can be seen from the above discussion, the archaeological evidence for the organization of copper extraction in Bronze Age Oman is so minimal as to make hypothesizing over modes of production a rather difficult undertaking. The evidence for copper production at sites such as Maysar 1, Zahra 1, and Wadi Fizh 1 suggests household or workshop production loci agglomerated at an extra-household level: a village or community-based craft. The evidence from Tawi Ubaylah and Wadi Salh 1 is equivocal, especially given the complete lack of evidence regarding the duration of operations at either site, and the number of production units that may have simultaneously operated at each. Nevertheless, the scale of production at Tawi Ubaylah and Wadi Salh 1 suggests the possibility of copper extraction at the extra-community level. There is no evidence from the Umm al-Nar Period for any long-lived political hierarchy that may have emerged to control such a production system, although at least one ethnographic study of stone quarrying (Burton 1984) has demonstrated that such leadership is not essential to coordinate production within a large, kin-based, tribal groups. Clearly, more fieldwork will be required to elaborate our understanding of the organization of copper production in third millennium southeastern Arabia. Organization of Production in Later Periods The same issues can be raised again in regard to copper production in Iron Age southeastern Arabia, although unfortunately at this time there is even less evidence from archaeometallurgical studies to support the archaeological data. In contrast to what appears to have been the predominant integration of third millennium copper production within villages concerned with agricultural and pastoral subsistence activities, surveys in Wadi Fizh suggest that a different relationship may have existed in the Iron Age (Costa and Wilkinson 1987:225, 232). Iron Age settlements in the region show much less evidence for primary copper extraction, whist the enormous size of Iron Age slag heaps at sites such as Raki 2 (ca. 45,000 tonnes; see Figure 2.16) and Tawi Raki 2 (ca.

40,000 tonnes) indicates that production levels are perhaps many times higher than in the Umm al-Nar Period (see above). Furthermore, Iron Age mining and smelting for the first time dealt with ores from the massive sulfide deposits: both the low grade secondary mineralization of the gossans and the sulfidic ores of the unweathered ore body (Weisgerber 1987, 1988; Hauptmann 1985:Abb. 85). These deposits are much larger than those exploited in the third millennium BCE, and fewer in number. Thus, we have a situation whereby higher levels of production were undertaken at a limited number of larger copper ore bodies, and intensive, even full-time production seems much more probable. The apparent functional distinction of Iron Age settlements into agricultural and smelting sites, which more closely parallels the situation of the early Islamic period, may reflect such a mode of production, although further field research will be required to adequately address this issue. Production is certainly on a large scale, but whether it is organized at a community or extra-community level is almost impossible to determine given our limited information on the scale of smelting operations at any one time, their chronological duration within the Iron Age, and the possibility of seasonality in production. Interestingly, although levels of copper production are significantly higher in the Iron Age than in the third millennium, the political organization of the region seems similar: there is no evidence for development of a clear settlement hierarchy, large public buildings, or a state-like level of complexity. Despite rare references to "kings" of the region in cuneiform sources, the distribution of power is still generally characterized as polycentric (e.g. Magee 1999). Clearly, the high output of copper in Iron Age southeastern Arabia reflected the economic complexity of the region rather than its political stratification. As for most other categories of information related to copper extraction in southeastern Arabia, the best evidence for the organization of production comes from the early Islamic Period. Reconstructions of output at this time indicate clearly that copper was produced on an industrial scale, although not classifiable as "industrial" following the strict definitional requirements of the term outlined above. Individual mining and extraction sites such as Lasail have up to 100,000 tonnes of slag; the total amount of early Islamic slag reported from Oman

Geology and Early Exploitation of Copper

53

is more than half a million tonnes; and the estimated total copper production is 60,000 tonnes over a period of only a century (see above). Our understanding of the organization of this industrial-level production is informed by a small number of historical sources, which provide fragmentary evidence for trading, contractual arrangements, taxes and administration Archaeological survey and excavation have delineated the settlement structures associated with mining and smelting sites, and indicated the physical mechanisms by which copper production was organized and controlled at the extraction sites themselves. Basic settlement structures with storage areas for crucial elements of production and subsistence, such as water and charcoal, are known from 'Arja, Lasail, Samdah, Mullaq, Wadi asSafafir and other sites (Weisgerber l98O:ll8; Ibrahim and El Mahi 1998). Most houses seem to have been concentrated into residential areas or villages in the vicinity of the mines themselves, however different arrangements were also seen. For example, at 'Arja production seems to have been organized into units, in which one house seems to be related to one mine, smelting furnace and slag heap, and there is no evidence for the existence of an accumulation of dwellings in one area to form a "village" (Weisgerber 1987:158). Utilizing the evidence from early historical sources, these mining units are interpreted as the remains of a production system in which each miner (and perhaps additional kin) exploited his own mine, essentially independently (Weisgerber 1987: 158). Unfortunately, no historical texts survive which discuss the organization of smelting, as opposed to mining. Other aspects of settlement in the early Islamic mining regions, such as mosques, graveyards and extensive architectural features related to agricultural water management, have also been recovered archaeologically (Weisgerber 1980:118; Ibrahim and ElMahi 1998:132). Additionally, the presence of large, fortified buildings in prominent and defensible locations (such as on hills, high terraces, or at the entrance to the mining wadis) at many early Islamic sites has been used to suggest the presence of people who had some role in the control or protection of the mining district (Weisgerber 1980:117). The function of Sohar as the outlet for the majority of copper produced in the Wadi al-Jizzi area is also supported by historical documentation (Whitehouse

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Early Metallurgy of the Persian Gulf

1979:874; J. C. Wilkinson 1979:892), and by archaeological evidence from Sohar itself (Williamson 1973:16 and Figure 3a). A contextualization of the evidence for early Islamic copper production with other archaeological and historical evidence is far from complete, although efforts at defining the inter-relationship of settlement and copper exploitation in the hinterland of Sohar have been undertaken (Costa and Wilkinson 1987; Ibrahim and El Mahi 1998). It is clear that copper production and agriculture were specialized activities carried out in separate areas, leading to inter-dependence between Sohar and its mining hinterland (Costa and Wilkinson 1987:232).

Copper-Base Objects in Bronze Age Southeastern Arabia Having examined the evidence for primary copper extraction, we turn now to the evidence of how such metal was utilized locally in the production of finished objects. This section will focus predominantly on the types of finished objects that were produced, rather than on the technology of their production, as evidence for secondary refining and fabrication at Umm al-Nar Period sites is slim and understudied. As summarized in Weeks (1997:17-20), the most extensive evidence comes from Umm an-Nar Island, where crucible and mould fragments and numerous metallic refining and casting residues attest to the melting and refining of raw copper produced further inland. Metalworking areas have also been recorded at Hili 8, in Periods IIe and IIf (ca. 2500-2000 BCE), and small quantities of refining and casting debris are found as early as Phase Ib (ca. 2900 BCE) at the site (Cleuziou 1980, 1989). At Tell Abraq, there is abundant evidence for metalworking in the second and first millennia BCE, but Umm al-Nar Period metalworking debris is limited to a single amorphous metal lump dated to the terminal third millennium (Weeks 1997:28). The evidence from sites such as Bat (Frifelt l979:584) and Ghanadha (A1 Tikriti 1985:16), where surface finds of copper-base scrap are said to be numerous, remains unstudied. The earliest copper-base objects in southeastern Arabia appear in the late fourth and early third millennia BCE, at middens and settlements such as Wadi Shab GAS1, Ra's al-Hadd and Ra's a1 Hamra (Durante and

Tosi 1977; Uerpmann 1992:97; Cleuziou 1996:160; Tosi and Usai 2003:20), at Hili-8 Period Ib, where copper working debris is also recorded (Cleuziou 1989:Pl. 33), and in contemporary beehive and Hafit-type burial cairns (Frifelt 1971, 1975b; Benton and Potts, 1994). Interestingly, the earliest use of copper-base objects at Wadi Shab GAS1 and Ra's al-Hamra, although significantly later than seen in the neighboring regions of Mesopotamia, Iran, or Baluchistan, occurs in local material assemblages which are still pre-ceramic. The objects produced at this period are simple tools, such as small blades, fish hooks and pinslawls, that occur in small numbers on coastal sites with a strong orientation towards seasonal exploitation of marine resources (Cleuziou and Tosi 2000:26-27). The metal objects from Hafit tombs include a number of copper-base items such as blades, rivets, tweezers and long awls or "eye-pencils" (Frifelt 1975b:61-67, Figures 3, 5; Frifelt 1971:Figure 12; Cleuziou and Tosi 2000:26) commonly associated with bi-conical pottery of the Mesopotamian Jemdet Nasr tradition. The technology of this copper use remains uninvestigated, and it has not been demonstrated whether these earliest metal objects were made from local or imported copper. The considerable evidence for later Urnm al-Nar Period copper production in the region makes it likely that they represent the products of the earliest copper extraction in southeastern Arabia. This theory is supported by Frifelt (1975b:69), who suggests that by the early third millennium, "the grave builders of BatIIbri and Buraimi were all engaged in the copper trade from inner Oman with Buraimi as a market place at the crossroads and Urnm an-Nar as one of their shipping places". Occupation on Urnm an-Nar Island is thought to have begun at around 2700 BCE, and continued to as late as 2200 BCE (Frifelt 1995:237-239). The inventory of copper-base objects from the collective tombs on the island is limited to simple tanged or riveted knives and daggers, pinslawls and fish hooks (Frifelt 1991:98-103). All the excavated pinslawls come from Grave V, regarded as earlier in date than material from Graves I, I1 and V1 (Frifelt 1991:125), although virtually identical objects are recorded in later Urnm al-Nar Period tombs at A1 Sufouh (Benton 1996:Figure 192) and Hili North Tomb A (Cleuziou and Vogt 1985:Pl. 28). Settlement contexts

on Urnm an-Nar Island produced a similar array of objects to that found in the graves, including fish hooks, knivesldaggers, pinslawls, chisels, "borers" (hollow cone-shaped points), and a blade axe. In addition, there is evidence for metalworking in the form of copper ingot fragments, clay moulds, processing resides and crucible fragments (Frifelt 1995:70, 188-191, Figures 108-118, 263-280). A very similar array of copper-base objects has been recovered from the seasonal Urnm al-Nar Period settlement of Ra's al-Jinz (RJ-2) in the Ja'alan, which also has evidence for the secondary working of copper (Cleuziou and Tosi 200054-57, Figures 12-14). Copper fish hooks, in particular, seem to be ubiquitous at coastal sites from the third millennium BCE onwards; they are recorded in their hundreds at RJ-2 (Cleuziou and Tosi 200054) and known from sites as distant as Urnm an-Nar Island and SWY-3, located near Suwayh on the Arabian Sea (Mery and Marquis 1998:220-223 and Figure 10). Overall, fish hooks, pinslawls, and blades typify the copper-base objects found in third millennium settlement sites of southeastern Arabia, and indicate a basic metalworking technology aimed at the production of simple and functional tools necessary for everyday subsistence activities. The practice of metalworking within settlements at this time is attested by pieces of copper scrap and working debris found at sites such as Hili-8, RJ-2, Bat and Tell Abraq (Cleuziou 1989; Cleuziou and Tosi 2000:54-59; Frifelt 1979584; Weeks 1997). As noted above, these metalworking operations are largely unstudied, but they likely included melting, casting, and secondary refining to remove impurities from raw copper, but not primary smelting. A more diverse array of copper-base objects, in terms of typology, size, and perhaps metalworking technology, is found in graves of the later Urnm al-Nar Period. Finger, toe, and earrings become a particularly common find category, for example at Hili North Tomb A (Cleuziou and Vogt 1985:Pl. 28), Hili Tomb N (AlTikriti and Mery 2000:213 and Figure 10), A1 Sufouh (Benton 1996:Figures 194-195), Moweihat (Haerinck 1991) and Tell Abraq (Potts 2000:77). A number of examples of flat "razors" are also known from Hili Tomb N and Hili North Tomb A (Al-Tikriti and Mery 2000:Figure 10; Cleuziou and Vogt 1985:Pl. 28.1), Tell Abraq (Potts 2000:76), and Ra's al-Jinz (Cleuziou and

Geology and Early Exploitation of Copper

55

Tosi 2000:Figure 15). The very end of the third millennium witnesses the introduction of the socketed spearhead, as found in the Asimah grave alignment (Vogt 1995) and in large numbers in the Tell Abraq tomb (Potts 2000:68-69). This type continues in use into the Wadi Suq Period, as seen by its occurrence in graves at Shimal (Vogt and Franke-Vogt 1987:Figure 21), AlWasit (Al-Shanfari and Weisgerber 19895'1. 5), Ghalilah (Donaldson 1985:Figure 28), Bidyah (A1 Tikriti 198913: PI. 73) and Ghanadha Island (Al-Tikriti 1985:Pl. 16). While some continuity is thus seen between the metal assemblages of the third and second millennia BCE in southeastern Arabia, the Wadi Suq Period and Late Bronze Age also witness the introduction of new forms of weaponry. Examples include the long copperbase swords found in collective burials at Al-Wasit, Qattarah and Qarn Bint Saud (Cleuziou 1981:Figure 12; Al-Shanfari and Weisgerber 1989:Pl. 5; Potts 1990a:252 and Figure 29), and tanged arrowheads, often with incised decoration, which appear at sites across the peninsula from the mid-second millennium onwards (Magee 1998a). Additionally, copper- base vessels, which are extremely rare in third millennium contexts in southeastern Arabia (e.g. Vogt 1995:Figure 55), appear more frequently in tomb assemblages of the second millennium BCE (e.g. A1 Tikriti 1989:Pl. 70-72). A limited amount of compositional analysis of third millennium BCE metalwork has been undertaken, including fully-quantitative and semi-quantitative analyses of objects from Umm an-Nar Island (Berthoud 1979; Frifelt 1975, 1990; Craddock l 9 8 1; Hauptmann 1995; Prange et al. 1999), sites in A1 Ain (Berthoud 1979) and the Wadi Samad (Hauptmann et al. 1988), and Tell Abraq (Weeks 1997; Pedersen and Buchwald 1991). The great majority of analyses have indicated that tin-bronze was very rarely used at Umm al-Nar Period sites in southeastern Arabia. Objects were predominantly of copper, with the elements arsenic and nickel occurring in quantities of up to four percent or higher, a pattern of impurities generally consistent with contemporary ingot and raw copper fragments from Maysar 1, Wadi Bahla, Umm an-Nar Island and Ra's al-Hamra (Hauptmann 1987, 1995; Hauptmann et al. 1988; Craddock 1981). As has been noted previously, the Tell Abraq analyses contrast strongly with this pattern; tin-bronze was used

56

Early Metallurgy of the Persian Gulf

for more than half of the 31 analyzed objects from Umm al-Nar Period settlement and funerary contexts at this site (Weeks 1997). The only other tin-bronzes reported from this period are isolated examples from a tomb at Hili (Berthoud 1979:Table 5), two objects from unspecified sites in the region (Prange et al. 1999:Figure 6), and beads from Ra's al-Hadd (personal communication J.E. Reade). Evidence for the local working of tin-bronze is also provided by the analyses of a piece of metalworking debris from Hili-8 Period IIf, which contained ca. 0.5 percent tin (Cleuziou 1989:74). Nevertheless, the first significant appearance of tinbronze in southeastern Arabia is still sometimes claimed to occur only in the second millennium BCE (e.g. Prange et al. 1999), before it becomes the dominant alloy in the local Iron Age, as represented by the analyses of objects from the IbriISelme hoard (Prange and Hauptmann 2001). However, compositional variability between individual assemblages seems to be a feature of southeastern Arabian metallurgy, making chronological distinctions in alloy use hard to support. For example, the analyses presented in this volume clearly support the findings of the Tell Abraq study regarding the use of tin-bronze in the third millennium BCE in the northern part of the Oman Peninsula. Such results cannot be used to push back the "introduction" or "origin" of tin-bronze in the region, however, as later assemblages such as that from the early second millennium Qattarah tomb contain no tin-bronze objects (Cleuziou l 9 8 l:288). Likewise, the total dominance of the tin-bronze alloy in the southeastern Arabian Iron Age suggested by analyses of the IbriISelme hoard is not evident at the Iron Age settlements of Tell Abraq and Muweilah, where only one-quarter of finished objects are of tin-bronze (Weeks, forthcoming b:Tables 3 and 4; 1997:Table 7). The adoption of tin-bronze technology in southeastern Arabia is a complex issue which will be discussed at length in the following chapters. Alloys other than tin-bronze and AsINi-copper are extremely rare in southeastern Arabia before the end of the Iron Age. The exception concerns a group of ten objects from collective graves on Umm an-Nar Island, analyzed by both X-ray diffraction and atomic absorption spectrometry (Frifelt 1991:lOO). Eight of the objects contained significant amounts of zinc, in the two to 10 percent range, sometimes occurring in addition to other

elements such as nickel and arsenic (one to two percent), and lead (up to 25 percent). The two remaining objects also contained high lead concentrations, in the three to 11 percent range. While these objects are compositional rarities in third millennium southeastern Arabia, and generally in wider western Asia, they are paralleled in compositional terms by a number of contemporary shaft-hole axes from the Royal Cemetery at Ur, dated to the ED 111-Early Akkadian Period (Miiller-Karpe 1989:Table 1 and Abb. 6). Additionally, broadly contemporary copper-base objects with significant zinc and lead concentrations are reported from the Aegean site of Thermi, on the island of Lesbos (Begemann et al. 1992, 1995; Stos-Gale 1992), and from the site of Ikiztepe on the Black Sea coast of Turkey (Bilgi 1984). The use of other metals is first documented in the later Umm al-Nar Period, by the appearance of numerous silver beads of various shapes from Tell Abraq, Hili North Tomb A (Cleuziou and Vogt 1985:33), and Moweihat (A1 Tikriti 1989a:95, PI. 56c), as well as gold beads, a ring, and two gold animal pendants (one in the form of a ram and the other depicting a pair of longhorned caprids) from Tell Abraq (Potts 2000:54). There is also a small gold object from Cairn X on Umm anNar Island (Berthoud and Cleuziou 1983:243). The tradition of animal-shaped pendants in precious metals continues into the Wadi Suq Period, where similar examples in gold, electrum and silver are known from tombs at Qattarah (Cleuziou 1981:Figure 13), Bidya (Al-Tikriti 1989b:Pl. 74a) and Dhayah (Kastner 1991). Iron objects have not been found in the region before the middle of the local Iron Age, and even then occur only rarely (Magee 1998b; 2002:Figure 2; Magee et al. 2002:Figure 30).

Summary Archaeometallurgical work in southeastern Arabia has been inspired predominantly by Mesopotamian historical accounts of trade and traders in the Persian Gulf. One cannot but be impressed by the scale of the Dilmun copper trade in the early second millennium BCE recorded in cuneiform documents, or by references to the "copper mountain" of Magan where the majority of this metal seems to have been produced. Since the 1970s, geological and archaeological surveys in southeastern Arabia have recorded more than 150 copper

deposits mountainous regions of the interior, and have demonstrated the importance of the region as a copper producer in the ancient world. Omani copper deposits are found principally in rocks of the Semail Ophiolite complex, a piece of ancient oceanic crust that was obducted onto the mainland Arabian Plate between 90-70 million years ago. The largest copper deposits in the region are found in the upper extrusive sequence of the Semail Ophiolite, at sites such as Bayda, Lasail, 'and Raki, and consist of massive sulfide deposits with brightly colored gossans containing low-grades of secondary copper mineralization (oxides, carbonates and sulfurbearing species). The copper minerals found in the gossans of these deposits could have been exploited in the Bronze Age, although some evidence indicates that the systematic exploitation of the gossan ores began at the same time as the first large-scale exploitation of the unaltered primary massive sulfides, i.e. in the Iron Age. Many copper deposits with intensive areas of secondary mineralization exist in the lower units of the Semail Ophiolite, and these ores are regarded as being of paramount importance for Bronze Age smelting operations in southeastern Arabia. Significantly, Bronze Age copper mining is also known to have taken place in the Masirah ophiolites, which are a geologically similar but unrelated formation located on Masirah Island off the south coast of the Sultanate of Oman. A number of small copper deposits have also been recorded in rock units of the mainland that are older than the Semail ophiolite. Following from the results of geological survey in southeastern Arabia, work by the German Mining Museum in the Sultanate of Oman since 1977 has clearly demonstrated that metallic copper was produced in large quantities as early as the Umm al-Nar Period. The German analyses strongly support the hypothesis suggested on archaeometallurgical grounds as early as the 1920s by the Sumerian Copper Committee, and later supported by the provenance analyses of the French CNRS: the mountains of the northern Sultanate of Oman and the U.A.E. are the source of the copper of Magan. Production seems to have peaked in the later third millennium, when a few thousand tonnes of copper were produced for local use and foreign exchange. Specialization in copper production is clearly observed at this time, with a number of settlements providing evi-

Geology and Early Exploitation of Copper

57

dence for production units organized along household or "workshop" lines, nucleated within individual agricultural villages. Two larger smelting sites suggest the possibility of more intensive copper extraction, but critical archaeological evidence regarding the duration and intensity of production is absent, making conclusions regarding multiple modes of Bronze Age primary copper production impossible to verify. Bronze Age copper production in southeastern Arabia witnessed distinct periods of growth and decline, which can be correlated with a number of technological, environmental, and socio-economic factors. While there is little evidence for the direct adoption of a developed smelting technology from Iran or Baluchistan, the possibility that the idea of copper extraction arrived via stimulus diffusion from the north is plausible. Local extraction appears to have begun in the late fourth or early third millennium BCE and there was a significant increase in output over the course of the third millennium. Increased Umm al-Nar Period production is correlated with a growth of local population and settlement, greater economic integration within southeastern Arabia, and increasing intensity in maritime exchanges with polities in Mesopotamia, Iran, the central Gulf and the Indus region. In a similar manner, the apparent decline in copper production in the early second millennium BCE is correlated with a decline in the internal economic integration of southeastern Arabia, the collapse of the Gulf trade, and perhaps environmental degradation exacerbated by excessive wood harvesting for smelting. While most studies of copper production in the region have stressed the importance of foreign markets in determining copper production levels in southeastern Arabia, it is clear that the scale and integration of the local southeastern Arabian economy was also critical in determining levels of copper extraction and exchange in the Bronze Age. In contrast to the large-scale primary extraction that characterized the Umm al-Nar Period, the object analyses and descriptions presented earlier in this chapter demonstrate little in the way of elaborate metalworking techniques. Local metalworking industries were characterized by a relatively limited array of simple tools related to everyday subsistence activities, such as fish hooks, pinslawls, and basic blades. Assemblages of metalwork

58

Early Metallurgy of t h e Persian Gulf

from contemporary funerary contexts demonstrate a wider repertoire, including non-utilitarian objects such as rings and beads, in addition to weapons such as spearheads. Compositional analyses have indicated that, in addition to local copper and copper alloys, foreign metal was utilized in significant quantities at least one site (Tell Abraq) in the northern Oman Peninsula and perhaps in more limited quantities at other Umm al-Nar Period sites. The potential importance of this foreign metal for the local Omani metalworking industry, its likely sources, and its use in southeastern Arabia outside the settlement of Tell Abraq, will be discussed at greater depth in the later chapters of this volume.

3

Analyzed Artifacts: Contexts and Chronology

This chapter presents background stratigraphic, chronological and contextual information on the metal samples that are analyzed in this volume. A total of 83 copper-base objects of Urnm al-Nar date were analyzed using PIXE, in addition to the analysis of one tin ring by EDS. All objects of Urnm al-Nar Period date analyzed compositionally come from funerary contexts. Material was obtained from four sites, including Urnm al-Nar-type tombs at A1 Sufouh (Dubai Emirate) and Tell Abraq (Sharjah Emirate), and two Urnm al-Nar tombs known as Unarl and Unar2 near the village of Shimal (Ras al-Khaimah Emirate). Approximately 20 copper-base objects have been analyzed from each of the tombs, and efforts have been made to analyze objects of varied typology from each assemblage. The chronological ranges of the sites are shown in Figure 3.1, and are discussed more fully below.

Excavation of one occupation area (Area B) to the north of the Urnm al-Nar tomb revealed the edge of an extensive area of cooking hearths. Material from excavated deposits consisted primarily of burnt marine shell and fish bones, in addition to a number of ceramic sherds datable typologically to the Urnm alNar Period. The Urnm al-Nar ceramics suggest that occupation in Area B was at least partly contemporary with the construction and use of the tomb at A1 Sufouh, although two sherds of Barbar pottery discovered during excavation indicate continued occupation or re-occupation in the early second millennium BCE (Weeks 1996). It has been suggested that the site represents a seasonal camping ground that must have been utilized over a significant period of time. As such, the site is comparable to other ephemeral third millennium coastal settlements on the southern Gulf shores, such as Ras Ghanadha (al-Tikriti 1985). All the analyzed copper-base samples from A1 Sufouh come from the main Urnm al-Nar tomb at the site (Tomb I), shown in Figure 3.2. The tomb is a typical example of Urnm al-Nar Period funerary architecture: it is circular, with a diameter of 6.5 m, and divided into six internal chambers. Both the ringwall and the internal walls are made of unworked stone blocks, although the ring-wall is faced with a single layer of well-masoned ashlars (Benton 1996:Figures 21 and 23). A significant amount of human skeletal material was excavated from within the tomb itself and from three pits that were dug in the vicinity of the tomb (Tombs 11-IV). The estimated

-

AI Sufouh The archaeological site of A1 Sufouh is located about one km from the modern shore of the Gulf, on the southern outskirts of the city of Dubai. The site, discovered in 1988, consists of a number of distinct, low mounds with evidence for human occupation in the form of ash, shell, bone, pottery and other artifacts (Benton 1996:20). Significant areas of the site were destroyed during recent construction activities, however a number of occupation areas and a round, stone-built, Urnm al-Nar-type tomb survived and were the subject of rescue excavations in mid-l 994 (Dubai Museum) and a thorough excavation in early 1995 (University of Sydney, see Benton 1996).

Tell Abraq Unar2

-Illlllllllllllll

Unarl AI Sufouh I

I

1

I

I

I

I

I

2700 2600 2500 2400 2300 2200 2100 2000 1900 1800

Years BCE

Figure 3.1 Chronology of the tombs from which the copper-base objects analyzed in this volume were excavated.

number of individuals interred at the site is 121, with a MNI of 1 3 people calculated for Tomb I (Benton 1996:49). Over 60 ceramic vessels have been recovered from all burial contexts at A1 Sufouh, including at least 20 examples of black-on-red Umm al-Nar style pottery and three Iranian black-on-gray vessels from Tomb I (Benton 1996:Figure 129). Further examples of Iranian gray-wares were found in Tomb 11. Nearly 14,000 beads were recovered from burial contexts at the site, over 90 percent of which were of serpentinite or talcose steatite (Benton 1996:Figures 133-1 35, Table 10). However, other materials such as soft-stone, shell, rock crystal and agate were also found, in addition to approximately 300 carnelian beads (nine of which were etched) and two lapis lazuli beads. Three lapis lazuli pendants were also recovered (Benton 1996:Figure 198). Copper-base objects such as blades, rings and pins or awls were also recovered (Benton 1996:Figures 183-195). The excavated material from A1 Sufouh suggests that the tomb was built and used in the middle of the Umm al-Nar Period. In particular, the lack of se'rie re'cente soft-stone vessels in the tomb assemblage suggests that the tomb deposits pre-date the manufacture of such objects in southeastern Arabia, which Benton (1996:Table 17) places at ca. 2300-2000 BCE. The black-on-red and grayware ceramics from the tomb suggest deposition sometime shortly after the middle

of the third millennium BCE, and Benton (1996:Figure 204) has proposed a chronological range for the use of the tomb of ca. 2450-2300 BCE. The copper-base objects from A1 Sufouh analyzed in this volume are listed in Table 3.1 and some are illustrated in Figure 3.3. As can be seen, only samples from Tomb I were analyzed, all of which were found in the western half of the tomb. Only material that was already fragmentary was sampled, meaning that daggers and blade fragments were analyzed but no rings or pinslawls. The group of analyzed samples is thus a biased one in terms of object types. Additionally, there is the possibility that the 22 analyzed fragments may have come from less than 22 objects. A total of 35 copper-base finished objects were recovered from the A1 Sufouh burials, including 22 from Tomb I, as well as numerous unidentifiable metal fragments (Benton 1996: 145). Fourteen dagger blades are recorded from all burial contexts at the site, and it must be remembered that material found in Tombs 11-IV could once have been interred in Tomb I and have left fragmentary remains there (although this view is contradictory to the chronological associations proposed by Benton (1996), see Kennet (1998) for an alternative view). Comparisons of PIXE data (see Chapter 3) for the fragments indicate groups of samples with very similar composition, but these are as likely to reflect a common metal source (whether ingot or mine) as a common object.

Figure 3.2 AI Sufouh Tomb I after excavation, seen from the west (photo courtesy of Daniel Potts).

60

Early Metallurgy of the Persian Gulf

Unarl The archaeological sites of Shimal lie about eight km northeast of the modern city of Ras al-Khaimah, at the foot of the limestone mountains which comprise the Musandam Peninsula near the modern village of Shimal (Vogt and Franke-Vogt 1987:Figure 2). The Umm al-Nar Period tomb designated Unarl was excavated by the German Mission to Ras al-Khaimah in 1988 (Kastner et al. 1988), and remains largely unpublished. A preliminary report on the discovery and excavation of the tomb (Sahm 1988) provides basic information on the cultural and skeletal material found, and on architectural, taphonomic and chronological issues. The tomb is a relatively large example of typical Umm al-Nar type: circular (with a diameter of 11.5 m), stone-built on a low plinth wall, and divided internally into eight chambers by a north-south running dividing wall and three east-west cross walls (Sahm 1988:2). It is illustrated in Figure 3.4. The tomb is badly disturbed, with architectural features and archaeological material preserved more fully on its eastern side. The tomb was robbed in antiquity, and evidence exists to suggest that the robbery took place only a short time after the construction and use of the tomb (Sahm 1988:2), i.e. by the early second millennium BCE. The tomb is highly disturbed and only minor areas of articulation are visible in the excavated skeletal material, which is also largely burnt (Blau and Beech, 1999:34). Physical anthropological examination indicates that a minimum of 438 individuals were buried in the tomb (Blau 2001:Table 1). Pottery vessels and metal objects were found in small numbers inside the tomb, in addition to numerous beads made of "steatite paste" and an etched carnelian bead. A few examples of se'rie re'cente soft-stone were recovered from immediately outside the tomb, and it has been suggested that some of them may post-date the third millennium BCE (Sahm 1988:3). The excavated ceramic vessels were mostly fine wares and predominantly local black-on-red examples but there were also three black-on-gray Iranian vessels and one sherd of incised gray ware from Iran (Sahm 1988:Figure 10). Metal finds include one gold bead

and two silver beads, as well as a number of small fragments of copper-base objects such as rings and pins or awls. Additionally, a broken socketed spearhead was excavated from the tomb deposit (Sahm 1988:Figure 11.3). The majority of the excavated material from Unarl suggests a date in the middle Umm al-Nar Period, ca. 2400-2200 BCE (Blau 2001:Table l ) , however the possibility of re-use in the late third or early second millennium cannot be excluded because of the presence of the socketed copper-base spearhead. The analyzed copper-base objects from Unarl are shown in Table 3.2 and examples are illustrated in Figure 3.5. In addition to the rings and pinslawls mentioned by Sahm, there are a number of thin, flat metal fragments from the tomb that may once have belonged to vessels or blades, and some curved fragments that Table 3.1 Objects from AI Sufouh analyzed by PlXE Context

Object

ALSUFOOH

Reg. No.

Tomb I: chambers 4,6

blade fragment

ALSUFOU

Tomb I: chambers 4,6

blade fragment

ASI-l

Tomb I: chambers 4,6

flat fragment

ASI-2

Tomb I: chambers 4,6

thick flat fragment

ASI-3

Tomb I: chambers 4,6

thin flat fragment

ASI-4

Tomb I: chambers 4,6

blade edge fragment

ASI-5

Tomb I: chambers 4,6

blade edge fragment

ASTOMBI a

Tomb I: chambers 4,6

blade fragment

ASTOMBI b

Tomb I: chambers 4,6

blade edge fragment

ASTOMBI c

Tomb 1:chambers 4,6

blade edge fragment

ASTOMB1d

Tomb I: chambers 4,6

thin flat fragment

ASTOMBI e

Tomb I: chambers 4,6

thin flat fragment

ASTOMBI f

Tomb I: chambers 4,6

thin flat fragment

ASTOMBI g

Tomb I: chambers 4,6

thick flat fragment

ASTOMBI h

Tomb I: chambers 4,6

thin flat fragment

M10-15

Tomb I: chambers 4,6

blade edge fragment

M10-31

Tomb I: chambers 4,6

rivet

M 10-34

Tomb I: chambers 4,6

dagger-riveted-long

M10-36

Tomb I: chambers 4,6

dagger-riveted-tang

M10-30

Tomb I: chambers 4,6

blade edge fragment

M10-41

Tomb I: chambers 4,6

dagger-tanged

M 10-43

Tomb 1:chambers 4,6

thin flat fragment

Copper-base artifacts from the Umm al-Nar Period tomb at AI Sufouh that are compositionally analyzed in this study.

Analyzed Artifacts: Contexts and Chronology

61

gQm

-p-

pJm.*

...-. '

. ..

. :v

Figure 3.3 A selection of fragments of copper-base objects from AI Sufouh analyzed in this study.Top row, left to right: ASI-5, ASI-4, M10-30, ASTOMB1 b, ASTOMB1c, ASTOMB1a. Middle row, left to right: ASTOMBlf, ASI-3, ASTOMB1d, ASTOMB1h, ASI-2, M10-42 (not analyzed).Bottom row, left to right: ASI-1, M10-43, ASTOMBl g, M10-31.

Figure 3.4The Unarl Umm al-Nar Period tomb (photo courtesy and copyright C.Velde).

62

Early Metallurgy of the Persian Gulf

may have been tubes or spouts. Although the copperbase objects remaining at Unarl are obviously only a small fraction of those which may once have been interred there, enough typological diversity exists to suggest that the compositional variability of the original deposit may also be reasonably well represented.

Unar2 The Umm al-Nar tomb Unar2 (see Figure 3.6) is located in the Shihu village of Shimal North, in the Emirate of Ras al-Khaimah, about 200 m south of the Unarl tomb described in the previous section (Blau and Beech 1999:34). The site was excavated over two seasons in 1997 and 1998, revealing a round, stone-built tomb with a diameter of approximately 14.5 m, making Unar2 the largest Umm al-Nar funerary structure yet discovered in southeastern Arabia. The interior of the tomb was divided into 1 2 chambers forming three separate units, possibly related to familylkinship groups (Velde 1999; see Blau 2001:Figure 3; Blau and Beech 1999:Figure 2), although the original architectural features of the tomb have been disturbed by tomb-robbing. Evidence exists to suggest that the tomb may originally have stood to a height of about three meters and included an upper story (Velde 1999). The tomb remains partially unpublished, although notes on the ceramic assemblage (Carter 2002) and skeletal remains (Blau 2001; Blau and Beech 1999) have appeared, and a brief site summary (Velde 1999) and physical anthropology report (Blau 1999) have been posted on the National Museum of Ras al-Khaimah website. Anthropological studies by S. Blau (2001,1999) indicate that at least 43 1individuals were interred in the Unar2 tomb. Articulated skeletons were rare, being found only in chambers D and G, and more than 90 percent of the disarticulated bone was burnt. As for most Umm al-Nar tomb skeletal assemblages, the bones were predominantly of adults, although fetal, infant, child and adolescent bones were found in each chamber (Blau 1999).It is suggested by Velde (1999)that bodies may first have been interred on the chamber floors until no space remained in the tomb, at which point the bones were removed for cremation and later deposited in the upper story of the tomb (see also Carter 20025). The period of use of the tomb is regarded as lasting more than 100 years (Velde 1999).

Table 3.2 Objects from Unarl analyzed by PlXE Reg. No.

Context

L11D-PIN

Unarl Tomb

pinlawl fragment

L14N-PIN

Unarl Tomb

pinlawl fragment

LlSRlNG

Unarl Tomb

ring fragment

M10-7

Unarl Tomb

flat fragment

M10-12

Unarl Tomb

thin flat fragment

M10-13V

Unarl Tomb

thin flat fragment

Object

M10-1

Unarl Tomb

tubelspout fragment

M10-17

Unarl Tomb

ring fragment

M10-18

Unarl Tomb

ring fragment

M10-19

Unarl Tomb

ring fragment

M10-20V

Unarl Tomb

thin flat fragment

M10-21V

Unarl Tomb

tubelvessel fragment

M10-22R

Unarl Tomb

ring fragment

M10-35

Unarl Tomb

thin flat fragment

M10-38

Unarl Tomb

tubelspout fragment

M10-39

Unarl Tomb

thin flat fragment

M10-44

Unarl Tomb

pinlawl fragment

M10-46

Unarl Tomb

ring fragment

Copper-base artifacts from the Unarl Umm al-Nar Period tomb at Shimal that are compositionally analyzed in this study.

Figure 3.5 A selection of fragments of copper-base objects from Unarl analyzed in this study.Top row, left to right: LISRING, M10-22R, M10-46, M10-18. Bottom row, left to right: M10-44, L14N-PIN, L1 1DPIN, M10-16, M10-12.

Analyzed Artifacts: Contexts and Chronology

63

Figure 3.6 The Unar2 tomb after excavation, showing chamber designations, viewed from the north (photo courtesty of D. Kennet).

Pottery and stone vessels, metal objects and jewelry remained in the tomb even after robbing, with the pottery indicating contacts with Mesopotamia, Bahrain, Iran and the Indus Valley (Carter 2002; Velde 1999). Typical black-on-red indigenous funerary vessels comprise more than 80 percent of the ceramic assemblage, while imported Iranian black-on-gray and incised graywares represent just over 10 percent of the excavated pottery (Carter 2002:7-10). A small number of sherds of socalled "Kaftari ware" from Fars province in Iran has been recovered, and Barbar, Mesopotamian and Indus wares are similarly rare (Carter 2002:9-10). Assessment of the material from the site was initially used to suggest a date of ca. 2300-2100 BCE (Blau and Beech 1999:34). However, ceramic parallels cited by Carter (2002:12-13) suggest a foundation date perhaps 50-100 years later than this, and abandonment some time in the last century of the third millennium BCE, i.e. a construction and use spanning ca. 2200-2000 BCE. Thus, although earlier reports had described the Unar2 tomb deposits as late Umm an-Nar but not in the terminal phase, the new ceramic studies and particularly the presence of a number of anomalous ceramic forms led Carter (2002:13) to suggest that use of Unar2 may have continued into the terminal Umm al-Nar Period. Carter (2002:6) also observes that approximately six percent of the analyzed ceramic assemblage from Unar2 consists of later intrusive material from the second millennium, Iron Age and more recent periods. The possi-

64

Early Metallurgy of the Persian Gulf

bility that any analyzed metal objects from Unar2 are intrusive is small, but should not be forgotten. The analyzed copper-base objects from Unar2 are listed in Table 3.3 and illustrated in Figure 3.7, and consist primarily of rings, pins or awls and thin flat fragments. These are, in general, the largest metal objects that remained in the tomb after it was plundered in antiquity. It is likely that a much larger and more typologically diverse group of copper-base objects was once buried within the tomb.

Tell Abraq The archaeological site of Tell Abraq is situated on the border of the Emirates of Sharjah and Umm al-Qaiwain, several kilometers south of the present shore of the Gulf. The site has been systematically excavated for five seasons, from 1989-1993 and in the winter of 1997-1998, following test excavations at the site by an Iraqi team in the 1970s (Potts 1990b). Material from the first four seasons of excavation has been published and discussed in a number of places (Potts 1990b, 1991, 1993a), and some material from the most recent excavation season is also published (Potts 1998, 2000, 2003b). Tell Abraq is one of the largest sites on the southern shores of the Gulf, and shows evidence for continuous occupation from ca. 2300-300 BCE (i.e. Umm alNar Period to Iron Age), with a later re-occupation in the Ed Dur period (Potts 1993a). The chronology of

occupation at Tell Abraq, particularly in the third millennium BCE, is well established by both stratigraphic and typological considerations and by radiocarbon determinations (Potts 1997a:Table 3; Potts and Weeks 1999). The earliest occupation at the site is represented by the construction of a large stone and mud brick tower, approximately 40 m in diameter, which stood approximately eight m above the surrounding ground surface (Potts 1993a:118). Such towers are typical of third millennium BCE settlements in southeastern Arabia (Potts 1997b:47), although the Tell Abraq tower is the largest known example of its type. Occupation of the tower continued in the second millennium BCE, and a settlement also spread out around the fortified structure in the form of palm-frond houses, known locally as barasti or 'arish (Potts 1991:36-42; King 1997:87). By the end of the second millennium, most of the large architectural structures at the site seem to have been covered by earth and archaeological deposits, forming a mound around which barasti occupation spread in the first millennium BCE (Potts 1993a:119). For most of the period of its occupation, Tell Abraq is likely to have been the largest settlement on the southern shores of the Gulf. The material remains recovered during excavation (Potts 1990b; 1991; 1993a), and the reconstructions of past subsistence practices (Willcox and Tengberg 1995), indicate that in most respects Tell Abraq fits comfortably within the spectrum of local Bronze and Iron Age societies. Towards the end of the third millennium BCE, an Umm al-Nar type tomb was constructed just 10 m to the west of the fortification tower at Tell Abraq (Potts 1993a). The circular tomb (see Figure 3.8) is built of rough stones with an external facing of finely fitted ashlar masonry. The tomb diameter is approximately six m, it has one internal wall that divides the tomb into eastern and western chambers, and survives to a height of 1.5 m in places. The tomb is unusual in southeastern Arabian archaeology as it has remained untouched by looters and largely undisturbed since its construction and use (although the northwest corner of the tomb was destroyed in antiquity by later construction activities). This is perhaps due to the fact that the tomb was covered already by settlement deposits as early as the first half of the second millennium BCE (Potts 1993a:119).

Table 3.3 Objects from Unar2 analyzed by PlXE Reg. No. Context

Object

1005.40

NW quadrant

lump

1007.41

outside tomb

thin flat fragment

1007.42

outside tomb, west side

ring fragment

1012.52

SE quadrant

ring fragment

1014.1 58

SW quad, chamber JIK

ring fragment

1014.76

SW quad, chamber JIK

ring fragment

1015.1 44

chamber H

thin flat fragment

1015.95

NW quad, chamber H

thin flat fragment

1018-3.93

NE quad, chamber A

pinlawl fragment

1018-3.99

NE quad, chamber A

thin flat fragment

1019-3.1 04

NE quad, chamber A

pinlawl fragment

1019-3.105

NE quad, chamber C

thin flat fragment

1019-3.1 24

NE quad, chamber C

thin flat fragment

1019-3.59

NE quad, chamber C

thin flat fragment

1019-3.60

NE quad, chamber C

chisel (7)

1019-4.1 08

NE quad, chamber C

pinlawl fragment

1019-4.1 13

NE quad, chamber C

pinlawl (7)

1019-5.71

NE quad, chamber C

ring fragment

1022-2.1 60

NW quad, chamber H

pinlawl fragment

1023-2.1 10

no data

lump

1023-4.10

NE quad, chamber C

ring fragment

surf. 56

surface

pinlawl fragment

Copper-base artifacts from the Unar2 Umm al-Nar Period tomb at Shimal that are compositionally analyzed in this study.

The western chamber of the tomb was excavated in 1993, revealing the disarticulated remains of at least 119 individuals, including all age groups from fetal to very old (>S0 years old) adults (Blau 1996:151; cf. Potts 1993a:120-121, who suggests a MNI of 155). In addition to skeletal material, typical Umm al-Nar ceramic and soft-stone vessels were recovered from the western chamber, as well as copper and bronze objects (see Figure 3.9), carnelian and agate beads, linen (Reade and Potts 1993) and other items including an ivory comb likely to be of Bactrian origin (Potts 1993d). Preliminary typological comparisons suggested that the tomb deposits could be dated to the very end of the third millennium BCE, the local pottery in particular showing form and technical detail more common in Wadi Suq ceramics (Potts 1993a:120). Additionally, two radiocarbon dates

Analyzed Artifacts: Contexts and Chronology

65

Figure 3.7 A selection of fragments of copper-base objects from Unar2 analyzed in this study.Top row, left to right: 10194.108,1018-3.93,1019-3.104,1019-4.113,surf.56.Second row, left to right: 1014.76,1014.158,1012.52,1023-4.10,1019-5.71. Third row, left to right: 1019-3.60,1022-2.160,1015.95,1007.42,1005.40. Bottom row, left to right: 1023-2.110,101 9-3.59, lOO7.41,lOl 5.1 44,101 9-3.1 24.

66

Early Metallurgy of the Persian Gulf

from a charcoal deposit running directly beneath the tomb building surface show calibrated ranges in the last third of the third millennium BCE (samples K-5574 and K-5575, see Table 3.4 and Potts 1993a:Table l),providing a useful terminus post quem for the construction of the tomb. Due to a border dispute at the site, the eastern chamber of the Umm al-Nar tomb was not excavated until 1997-1998, and remains largely unpublished. As for the western chamber, large amounts of disarticulated and partially articulated skeletal material were recovered, and the MNI for the entire tomb is about 330 individuals (D. T. Potts, personal communication). The cultural material from the eastern chamber represents the kind of extremely rich assemblage that may have characterized many Umm al-Nar tombs prior to robbery. In addition to numerous examples of local Umm al-Nar ceramic and soft-stone vessels, pottery from Mesopotamia, Bahrain, southwest and southeast Iran was present in the tomb (Potts 1998:10, 28-29; Potts 2000:l l 6 ff.; Potts 2003a). Additional finds included: numerous copper-base objects; more than ten ivory combs with Indus and central Asian parallels (Potts 1998:28-29); at least four alabaster vessels (Potts 2000:125); gold, lapis lazuli and carnelian beads with parallels in the Indus Valley region; and gold and silver animal pendants (Potts 2000:24, 54; see also Potts 2003 b). A series of five radiocarbon dates were run on wood charcoal from various levels of the bone deposit in the eastern chamber, the results of which are published in Potts and Weeks (1999), listed in Table 3.4. They confirm the dating of the tomb to the final stages of the third millennium BCE, but show no stratigraphic dependence. In fact, the five dates from the eastern chamber are statistically identical at a 95 percent confidence level, and provide an average 2 0 calibrated range of 2200-2040 BCE (Potts and Weeks 1999). The analyzed metal objects from Tell Abraq are listed in Tables 3.4 and 3.5 and illustrated in Figures 3.10-3.16. A total of 21 copper-base samples were analyzed, representing 10 percent of the 202 copperbase objects recovered from the eastern tomb chamber. The analyzed samples show significant typological diversity, including rings, daggers, spearheads and thin

Figure 3.8 The Tell Abraq tomb after excavation, looking from the north (photo D. Potts).

Figure 3.9 Two copper-base rings from the Tell Abraq tomb, as excavated in position on disarticulated human phalanges (photo D. Potts).

flat fragments. The total assemblage of copper-base objects from the eastern chamber of the tomb includes 2 1 socketed spearheads similar to Wadi Suq types, 10 dagger blades of varying typology, and more than 120 finger rings, toe rings and earrings.

Analyzed Artifacts: Contexts and Chronology

67

Table 3.4

Table 3.5

AMS radiocarbon dates associated with the Tell Abraq Tomb Calibrated I4cAge BP Age BCE Sample Code Context (Raw) (2 o range)

Objects from the Tell Abraq Tomb analyzed by PlXE Reg. No.

Context

Object

east chamber: layer 1

fragment

burnt layer

east chamber: layer 2

dagger (tanged)

underlying tomb

east chamber: layer 2

ring

east chamber: layer 3

lump

burnt layer

east chamber: layer 1

dagger (rounded)

underlying tomb

east chamber: layer 4

blade fragment (riveted)

east chamber: layer 3

spearhead (tanged)

east chamber

east chamber: layer 5

dagger (tanged)

level 3(7.4-7.5 m)

east chamber: layer 4

dagger (tanged)

east chamber: layer 3

dagger (tanged)

east chamber: layer 3

ring (flat band)

east chamber level 4 (7.6-7.7 m)

east chamber: layer 4

ring (broad flat band)

east chamber: layer 6

dagger (tanged)

level 6 (7.8-7.9 m)

east chamber: layer 5

ring

east chamber: layer 5

ring fragment

east chamber

east chamber: layer 5

ring

level 6 (7.8-7.9 m)

east chamber: layer 5

ring

east chamber: layer 6

thin flat fragment

east chamber: layer 6

thin flat fragment

east chamber: layer 6

spearhead (socketed)

east chamber: layer 6

ring

east chamber

east chamber level 6 (7.87 m) AMS radiocarbon dates from the eastern chamber of the Umm alNar Period tomb at Tell Abraq. All dates are calibrated with CALlB 4.1.2 (Stuiver and Reimer 1993), using dataset 1 (decadal dataset t o 23,999 cal BP) and calculation method B (probabilities). Calibrated ranges have been rounded t o nearest 10 years.

68

Early Metallurgy of the Persian Gulf

Copper-base artifacts from the Umm al-Nar Period tomb at Tell Abraq that are compositionally analyzed in this study.

Figure 3.10 A selection of fragments of copper-base objects from Tell Abraq analyzed in this study. Top row, left t o rig ht:TA2094,TA2679,TA281 6,TA233g1TA2677. Middle row, left t o right:TA2440 (tip), TA291 8,TA243S1TA2678. Bottom row, left t o right:TA2733,TA2732,TAI 785,TA2135.

Analyzed Artifacts: Contexts and Chronology

69

Figure 3.1 1 Spearhead TA2183 from the Tell Abraq Urnm al-Nar Period tomb. Length ca. 26.7 cm.

Figure 3.12 Daggerlknife blade TA2268 from the Tell Abraq Urnm al-Nar Period tomb. Length ca. 27.2 cm.

Figure 3.1 3 Dagger/knife bladeTA2270 from the Tell Abraq Urnm al-Nar Period tomb.

Figure 3.1 4 Daggerlknife blade TA2315 from the Tell Abraq Urnm al-Nar Period tomb. Length = 23.2.cm.

Figure 3.1 5 Daggerlknife blade TA2440 from the Tell Abraq Urnm al-Nar Period tomb. Length ca. 19.5 cm.

Figure 3.1 6 Socketed spearhead TA2757 from the Tell Abraq Urnm al-Nar Period tomb. Length = 33.8 cm.

70

Early Metallurgy of the Persian Gulf

4

Results of Compositional Analyses

Introduction In this chapter, the results of the chemical analysis of 83 archaeological objects from A1 Sufouh, Unarl, Unar2, and Tell Abraq are presented and discussed. The data are the results of Proton-Induced X-ray Emission (PIXE) analyses conducted at the Australian Nuclear Science and Technology Organisation (ANSTO), Lucas Heights, New South Wales. The PIXE compositional data for all objects are presented in Tables 4.1-4.4, on a site-by-site basis. Details of the analytical techniques used in this volume, including sample preparation, instrumental settings, accuracy, precision and sensitivity can be found below or in Appendix One. A brief introduction to the analyses and a general description of data treatment and presentation is given below, following which the PIXE data are presented and discussed in a univariate manner element by element. Subsequently, relationships between elements and archaeological assemblages are investigated through bivariate and multivariate statistical techniques. Sensitivity, Precision, and Accuracy of the MXE Data PIXE data were collected and quantified for the elements silicon (Si),phosphorus (P),sulfur (S),chlorine (Cl),potassium (K), calcium (Ca),titanium (Ti),vanadium (V),manganese (Mn), chromium (Cr),iron (Fe), cobalt (CO),nickel (Ni),copper (Cu),zinc (Zn),arsenic (As),selenium (Se), bromine (Br), rubidium (Rb), strontium (Sr), silver (Ag),

tin (Sn), antimony (Sb), lead (Pb), gold (Au) and bismuth (Bi). All measured phosphorus, rubidium, gold and bismuth concentrations were below levels required for acceptable analytical precision, and are not discussed further in this section. All chromium determinations have been disregarded due to the possibility of spurious Cr peaks in some samples due to occasional problems with beam alignment (see Appendix One (Section 1.1.4). All data have been normalized following procedure outlined in Appendix One (Section 1.2.1). PIXE data are presented as either percentage or parts per million (ppm) values, depending upon their concentration in the object. The sensitivity of the PIXE technique is represented by a quantity known as the minimum detectable level (MDL). The MDL is the theoretical minimum amount of an element that can be discerned by the PIXE analytical technique. Factors governing the MDL are discussed in Appendix One. MDLs are important in understanding the precision of the compositional data generated by PIXE; the higher the concentration of a particular element above the MDL, the better the precision that can be associated with the measurement. Values below the MDL, although frequently produced by the quantification software, are highly unreliable and must be regarded as at best a rough guide to element concentration (personal communication, Dr. G. Bailey, ANSTO, 1997). Further, it can generally be taken that the calculated concentration of an individual element is relatively imprecise (220-40 percent) at levels of one to three times the MDL. At concentrations of more than five times the MDL, precision is better than f10 percent for most elements. In the statistical summaries presented below, data tables for individual elements include a footnote containing numerical values for the MDL for each sample. The MDL value presented for each element is the average of the large amount of raw MDL data collected during PIXE analyses. The overall accuracy of the PIXE system at ANSTO is approximately 210 percent (Dr. R. Siegele, ANSTO, personal communication). However, the corroded nature of the majority of analyzed samples renders the quest for absolute accuracy of measurement somewhat futile. It must be accepted that the composition of the archaeological samples may have changed significantly from that of the objects during their original period of use (Scott 1991).

Table 4.1 Compositionaldata for AI Sufouh objects Lab Code

Object

ASI-l

flat fragment

ASI-2

thick flat fragment

ASI-3

thin flat fragment

ASI-4

blade edge

ASI-5

blade edge

M10-15

blade edge

M10-31

rivet

M10-34

dagger-riveted-long

M10-36

dagger-riveted-tang

M10-30

blade edge

M10-41

dagger-tanged

M10-43

thin flat fragment

ALSUFOOH

blade

ALSUFOU

blade

ASTOMBI a

blade fragment

ASTOMBI b

blade edge

ASTOMBI c

blade edge

ASTOMBI d

thin flat fragment

ASTOMBI e

thin flat fragment

ASTOMBI f

thin flat fragment

ASTOMBl g

thick flat fragment

ASTOMBl h

thin flat fraqment AVERAGE MDL

S

Fe

CO

Ni

Cu

Zn

As

(%)

(%)

(%)

(%)

(%)

(%)

(%)

0.10

0.007

0.01

0.04

0.007

0.012

0.008

Se

Ag

( P P ~ ) (pp4

50

240

Sb

Sn

(PP~)

(96)

(pprn)

0.13

135

700

Pb

PIXE compositional data for copper-baseobjects from AI Sufouh. Note: blank cells indicate concentrations below the MDL; nm = not measured.

Presentation of the PIXE Data As noted above, the normalized PIXE data is presented in Tables 4.1-4.4. However, the discussion presented below employs a number of statistical summaries of the PIXE concentration data. When the data for individual elements are discussed, they are summarized statistically (Table 4.5) by giving the median and the tenth-ninetieth percentile range. Furthermore, the statistical summaries for each site are presented in three broad categories: a summary for all objects from the site, a summary for the subset of tin-bronzes (i.e. samples containing more than two percent tin), and a summary for the samples with less than two percent tin (designated "copper"). Details regarding the selection and application of these statistical analyses are given in Appendix One (Section 1.2.2).

72

Early Metallurgy of the Persian Gulf

In addition, summaries of previous analyses are presented for most elements (e.g.Table 4.6). These summaries allow the composition of the Umm al-Nar Period material analyzed in this study to be compared with the contemporary and later objects from southeastern Arabia analyzed as a part of othek analytical programs. Summaries of previous analyses are provided for the following categories: Umm al-Nar Period objects (2700-2000 BCE); Umm al-Nar Period ingot and raw copper fragments (2700-2000 BCE); Wadi SuqILate Bronze Age objects (2000-1300 BCE); mixed Wadi SuqIIron Age tomb groups (2000-300 BCE); and Iron Age objects (1300-3 00 BCE). Geographic and bibliographic details of the previously collected data summarized in these tables is given in Appendix One (Section 1.2.3). Important information on arsenic, nickel and tin

Table 4.2 Compositional data for Unarl objects Lab Code

Object

M10-7

flat fragment

M10-12

thin flat fragment

M10-13V

thin flat fragment

M10-16

tube/spout

M10-1

ring

M10-18

ring

M10-19

ring

M10-2OV

thin flat fragment

M10-21V

tube/vessel

M10-22R

ring

M10-35

thin flat fragment

M10-38

tubelspout

M10-39

thin flat fragment

M10-44

pinlawl

M10-4

ring

L11D-PIN

pinlawl

L14N-PIN

pin/awl

LlSRlNG

S

Fe

CO

Ni

(%)

(%)

(%)

(%l

0.007

0.01

0.012

rinq AVERAGE MDL

0.10

0.008

0.007

50

240

700

0.13

135

PIXE compositional data for copper-base objects from Unarl. Note: blank cells indicate concentrations below the MDL.

concentrations in Bronze Age and Iron Age objects has also been presented in graphical form by Prange et al. (1999), and semi-quantitative compositional data exist for copper-base objects from the sites of Tell Abraq (Weeks 1997) and Umm an-Nar Island (Craddock 1981). Results of these studies are referred to in the text where relevant, but are not presented with the statistical summaries of previous analytical programs. In most cases, statistically summarized data distributions are accompanied by graphical presentation of the data to aid interpretation (e.g. Figure 4.1). Data are summarized graphically in the form of frequency histograms. The histograms are presented in either percentage terms or ppm on a logarithmic scale, with each order of magnitude divided into four geometric intervals. On the histograms, the bar delineated by crosshatching represents the number of objects in which the elemental concentration was below the MDL. Further details of the construction of these histograms are provided in Appendix One (Section 1.2.4).

Elemental Concentrations Sulfur (S) A summary of the PIXE sulfur measurements from this study is given in Table 4.5 and Figures 4.1-4.2. Ranges reported are tenth to ninetieth percentile values. As shown, sulfur concentrations are less than one percent in most of the samples. Seven of the 83 analyzed samples contain S concentrations of greater than one percent, with levels reaching as high as 5.5 percent in a spearhead from Tell Abraq (TA2183) and 3.7 percent in a riveted dagger from A1 Sufouh (M10-34). Relatively high sulfur concentrations appear in a thin flat fragment (TA2732,2.4 percent S) and an unidentified fragment (TA1785, 1.5 percent S) from Tell Abraq. Both Table 4.5 and Figure 4.2 indicate a significant difference in the sulfur content of copper objects and tin-bronzes, the latter containing lower median sulfur concentrations and a significantly smaller tenth to ninetieth percentile range. Further illustrating this point, only one analyzed tin-bronze, from Unar2, contains in excess of one percent sulfur (1015.144, 1.5 percent S).

Results of CompositionalAnalyses

73

Table 4.3 Compositional data for Unar2 objects S Lab Code

Object lump

(%)

Fe

CO

Ni

Cu

Zn

As

Se

(%)

(%)

(%)

(%l

(W

('W

(wm)

Ag

Sb

Sn

(pprn)

(PP~)

(%l

Pb (PP~)

0.25

thin flat fragment 0.22 ring ring ring

0.45

thin flat fragment ring thin flat fragment 1.49 pinlawl thin flat fragment 0.24 thin flat fragment chisel? ring

0.22

ring

0.53

pinlawl

0.20

thin flat fragment thin flat fragment pinlawl

0.09

pinlawl pinlawl

0.37

lump pinlawl

0.23

AVERAGE MDL

0.10

PIXE compositional data for copper-base objects from Unar2. Note: blank cells indicate concentrations below the MDL.

No consistent chronological variation in sulfur concentrations can be seen, although variation by site is clear. Figure 4.1 documents objects from Unar2 that have lower median S concentrations and ranges than material from the other Umm al-Nar Period tomb assemblages. In particular, half of the analyzed objects from Unar2 contain S concentrations of less than the minimum detectable level (ca. 0.10 percent) of the PIXE technique. Furthermore, only one object from Unar2, the previously mentioned tin-bronze (1015.144) contains more than approximately 0.5 percent S. Only a small number of previous analyses of S concentrations in archaeological copper-base objects are published, and these are summarized in Table 4.6. Fully published analyses from the Umm and-Nar and Wadi Suq Periods are all of copper objects, and have a much lower median S concentration but a similar range of up to

74

Early Metallurgy of the Persian Gulf

ca. 0.8 percent. Contemporary samples analyzed in a previous study of the metallurgy at Tell Abraq (Weeks 1997: Table 14) have median S concentrations of ca. 0.1-0.2 percent, close to the detection limit of the EDS analytical technique used, and a maximum value of ca. one percent S. Analyses of Bronze Age copper ingots and raw copper fragments by Hauptmann (1985:Table 21) show high S concentrations of up to approximately five percent, with median concentrations of approximately one percent S. Analyses of the same samples are given in Hauptmann et al. (1988), but do not show S determinations. Similarly, high sulfur concentrations of up to six percent were found in the copper ingots from the slightly later Saar settlement on Bahrain (Weeks, forthcoming a). The high sulfur concentrations in these semi-processed objects suggest a relationship between S content and the degree of metal refining which will be addressed in the following chapter.

Table 4.4 Compositionaldata for Tell Abraq objects Lab Code

Object

S

Fe

CO

Ni

Cu

Zn

As

(%)

(%)

(%)

(%l

('W

(W

(W

0.007

0.01

0.04

0.007

fragment

1.46

dagger-tanged

0.1 2

ring

0.3 1

lump

0.91

dagger-rounded

0.23

Se (ppm)

Ag (PP~)

Sn

(%l

Pb (PP~)

blade fragment (rivets) 0.31 spearhead-tanged dagger-tanged dagger-tanged dagger-tanged ring-flat ring-broad flat dagger-tanged ring ring fragment ring ring thin flat fragment thin flat fragment spear-socketed ring

0.02

AVERAGE MDL

0.10

58.7 0.012

0.008

0.40

PIXE compositional data for copper-base objects from Tell Abraq. Note: blank cells indicate concentrations below the MDL. Table 4.5 Sulfur in Umm al-Nar Period objects analyzed in this study Median

Median

Sulfur (%)

(all)

(copper)

Median

AI Sufouh

0.35

0.36

Unarl

0.30

0.30

0.29

0.15-0.61

0.1 6-0.58

0.1 2-0.72

Unar2

<0.10

0.1 0

0.1 5

<0.10-0.44

<0.10-0.28

<0.10-0.51

Tell Abraq

0.29

0.45

0.23

<0.10-1.46

<0.10-2.67

<0.10-0.37

All Objects

0.24

0.3 1

0.22

<0.10-0.89

<0.10-1.0

<0.10-0.52

(tin-bronze)

Range

Range

Range

(all)

(copper)

(tin-bronze)

<0.10-0.98

<0.10-1 .O

Sulfur concentrations in Umm al-Nar Period copper-base objects from AI Sufouh, Unarl. Unar2. and Tell Abraa analvzed bv PIXE. Averaae MDL = 0.1 0 Percent S.

Results of Compositional Analyses

75

Table 4.6 Sulfur levels recorded in previous analytical studies Archaeological Material

No. of Analyses

Median Concentration %

Range

(%l

Objects

(2700-2000BCE)

20

0.04

0.01-0.81

9

0.99

0.58-4.38

10

0.23

0.09-1.l 7

26

0.20

0.09-0.79

51

0.1 7

0.04-0.71

IngotdRaw Copper

(2700-2000BCE) Objects

(2000-1300 BCE) Objects

(2000-300BCE) Objects

(I300-300 BCE)

Sulfur concentrations in copper-base objects from southeastern Arabia analyzed in previous studies. Note: details of previous analyses may be found in Appendix One, Section 1.2.3.

The analyses of material from Wadi Suq, Late Bronze Age and Iron Age assemblages indicates sulfur concentrations similar to those seen in the Umm al-Nar Period objects analyzed in this volume, although a slight reduction through time is indicated by the figures. Most samples have less than approximately 0.8 percent S, but a number of objects with sulfur concentrations in excess of one percent are recorded at the Late Bronze Age settlement of Shimal Area SX (Weeks 2000a), in a mixed Wadi Suq-Iron Age tomb assemblage at Sharm (Weeks 2000b), and in Iron Age tomb and settlement contexts at Qidfa and Muweilah respectively (Weeks 2000a; Weeks forthcoming b). In the central Gulf, half of the analyzed objects from the Saar settlement contained from 1.0-2.2 percent S, and further support for a relationship between sulfur levels in finished objects and degree of metal refining was provided by the analyses of metallurgical waste samples from the site, which showed median sulfur concentrations of 1.3 percent, ranging up to 12 percent S (Weeks, forthcoming a). The possibility that sulfur could be present in the samples as a result of corrosion, in the form of sulfate minerals such as brochantite ( C U ~ S O ~ ( O Hhas ) ~ )been , suggested by R. G. Thomas (personal communication). He states that "the chloride figures do not account for

76

Early Metallurgy of the Persian Gulf

all of the copper and so there must be another anion and sulfate is the likely candidate". Sulfur, like chlorine, could potentially have been derived from the groundwater (see e.g. Ullah 1931a:486; Caley 1971: 106). The sulfur concentrations recorded in this study are, however, similar to the analyses that have been carried out previously on un-corroded samples using different analytical techniques, as described above. Furthermore, the metallographic analyses from the Gulf sites of Tell Abraq (Weeks 1997), Saar (Weeks, forthcoming a), IbriJSelme (Prange and Hauptmann 2001) and Muweilah (Weeks, forthcoming b) demonstrate the presence of numerous copper-sulfide inclusions in copper-base objects of Bronze Age and Iron Age date. These inclusions no doubt reflect the presence of copper-sulfide inclusions in the Bronze Age copper ingots used in the Gulf region (Weeks, forthcoming b), which indicates the use of copper-sulfide ores in the production of these objects. This evidence suggests that the high sulfur concentrations of the early Gulf material analyzed in this volume reflect the sulfur content of the objects at their time of production, rather than contributions from the process of contamination. Iron (Fe) Iron levels in the objects analyzed by PIXE can be relatively high, reaching concentrations of greater than three percent in some objects. The collected data are summarized in Table 4.7 and Figures 4.3-4.4, where clear differences by site and alloy type can be seen. The highest iron concentrations are reported in two amorphous "lumps" from the tombs at Unar2 (1005.40, 6.6 percent Fe) and Tell Abraq (TA2135, 32 percent Fe). These objects are typologically similar to pieces of metalworking debris from settlement contexts at Tell Abraq, Saar, and Muweilah (Weeks 1997; Weeks, forthcoming a, b), and share the high iron concentrations common to such material. The presence of metalworking debris in a tomb deposit seems unusual, but it may reflect the occupation of one of the people interred within. A number of finished copper objects, such as a blade (ALSUFOUH, 2.5 percent Fe) and rivet (M10-31, 2.6 percent Fe) from A1 Sufouh contain in excess of two percent iron, as does one thin flat fragment of tin-bronze from Unarl (M10-39, 2.5 percent Fe).

Figure 4.2 Sulfur concentrations in all Umm al-Nar Period objects analyzed by PIXE, showing copper objects (top) and tin-bronzes (middle).

Figure 4.1 Sulfur concentrations in AI Sufouh, Unarl, Unar2 and Tell Abraq objects.

Results of Cornpositional Analyses

77

Table 4.7 lron in Umm al-Nar Period objects analyzed in this study Median Median Median Range Iron (%) (all) (copper) (tin-bronze) (all)

Range (copper)

Range (tin-bronze)

AI Sufouh

0.72

0.72

Unarl

1.04

1.OO

1.07

Tell Abraq

0.52

0.32

0.72

0.20-1.24

0.02-5.74

0.34-1.24

All Objects

0.70

0.68

0.72

0.1 7-1.57

0.09-1.73

0.27-1.21

0.1 7-1.62

0.1 7-1.65

0.63-1.60

0.55-1.59

0.75-1.75

lron concentrations in Umm al-Nar Period copper-base objects from AI Sufouh, Unarl, Unar2, and Tell Abraq analyzed by PIXE. Average. MDL = 0.007 percent Fe.

Figure 4.3 demonstrates that iron concentrations are highest in the material from Unarl, with the most common Fe concentrations in the 1.0-1.8 percent range, and no objects with less than 0.4 percent Fe. The assemblages from A1 Sufouh and Unar2 have modes in the 0.56-1.0 percent Fe range, but exhibit numerous objects with concentrations of 0.1-0.5 percent Fe or less. The lowest mode for the analyzed assemblages is for material from Tell Abraq, where most objects contain approximately 0.32-0.56 percent Fe, and two have concentrations of approximately 0.03 percent Fe or less. The differences between copper samples and tinbronzes are clearly illustrated in Figure 4.4 and summarized in Table 4.7. While both alloy groups show distinct modes in the 0.56-1.0 percent Fe range, the range of iron concentrations in the copper samples is much higher than in the tin-bronzes. Samples with less than 0.1 percent Fe are not recorded in the analyzed tin-bronzes, whereas six copper objects contain such low Fe concentrations. At the higher end of the concentration range, only one tinbronze contains more than 1.5 percent Fe, whereas eight copper objects contain from approximately 1.6-32 percent Fe. The data generated for iron concentrations in this analytical program are significantly higher on average than Fe levels measured in previous analytical studies, which are summarized in Table 4.8. Most Umm al-Nar Period objects analyzed in earlier studies contained less than 0.5 percent Fe, although one object from Hili analyzed by Berthoud (1979:Table 5 ) contained four percent Fe. The earlier analysis of Umm al-Nar Period material from Tell Abraq using EDS (Weeks 1997:Table 14) revealed median Fe concentrations of approximately 0.32

78

Early Metallurgy of the Persian Gulf

percent, with maximum concentrations in the one to two percent range; very similar to the values for Tell Abraq material found in this study using PIXE. Similarly high iron values are reported in studies of late third millennium BCE copper ingots and raw copper, commonly ranging up to one percent Fe (Hauptmann 1987; Hauptmann et al. 1988). Analyzed planoconvex copper ingots from the Saar settlement contain approximately four to ten percent Fe (Weeks, forthcoming a), amongst the highest iron content of all the analyzed Gulf objects, and the compositional data suggest a relationship between iron content and degree of refining. For material from later periods, iron concentrations in excess of one percent have been recorded in Wadi SuqILate Bronze Age material from Masirah site 38 (Hauptmann et al. 1988), Shimal settlement Area SX and Shimal tomb SH102 (Weeks 2000a). High iron levels were also recorded in an object from the mixed Wadi Suq-Iron Age tomb deposits at Shimal tomb 2 (Craddock 1985), and in a number of samples from the Sharm tomb (Weeks 2000b). Previously analyzed Iron Age objects have the lowest median iron concentrations, as can be seen in Table 4.8, but a small number of objects with more than one percent Fe are recorded from the Bithnah and Qidfa tombs (Corboud et al. 1996; Weeks 2000a), from the IbriISelme hoard (Hauptmann et al. 1988; Prange and Hauptmann 2001), and from the Muweilah settlement (Weeks, forthcoming b). It is likely that higher Fe concentrations in the PIXE analyses in this study result, in part, from the introduction of iron with contaminating soil and rock particles incorporated during corrosion. A correlation exists between silicon and calcium contamination levels in

Figure 4.4 lron concentrations in all Umm al-Nar Period objects analyzed by PIXE, showing copper objects (top) and tin-bronzes (middle).

Figure 4.3 lron concentrations in AI Sufouh, Unarl, Unar2 and Tell Abraq objects.

Results of Compositional Analyses

79

analyzed samples and iron levels. The median Fe concentration in low-contamination samples (i.e., those with less than three percent Si+Ca) is approximately 0.34 percent, whereas high-contamination samples have a median concentration of 0.66 percent Fe. It should be noted, however, that the median Fe concentrations and tenth to ninetieth percentile ranges are still higher in PIXE samples with low contamination levels than in the Umm al-Nar objects analyzed in previous studies. Thus, contamination is not the sole factor leading to the discrepancy noted above.

Table 4.8 Iron concentrations recorded in previous analytical studies Archaeological Material

No. of

Median

Analyses

Range

('W

Concentration %

Objects (2700-2000 BCE)

31

0.1 8

0,01-0.44

27

0.24

0.01-1 .o

18

0.39

0.20-1.37

58

0.26

0.10-1.31

154

0.17

0.05-0.69

IngotsIRaw Copper (2700-2000 BCE) Objects (2000-1 300 BCE) Objects (2000-300 BCE) Objects (1300-300 BCE)

lron concentrations in copper-base objects from southeastern Arabia analyzed in previous studies. Note: details of previous analyses may be found in Appendix One, Section 1.2.3.

Cobalt (CO) The cobalt concentrations of the analyzed objects are summarized in Table 4.9 and Figures 4.5 and 4.6, where a clear and consistent chronological variation can be observed. Median cobalt concentrations and absolute ranges are significantly higher in the earlier Umm al-Nar tomb assemblages from A1 Sufouh and Unarl than in the later objects from Unar2 and Tell Abraq. The objects from A1 Sufouh show a mode in the 0.06-0.1 percent CO range, although 13 further objects from the site contain 0.1-0.5 percent CO, and one thin flat fragment (ASI-3) contains 1.2 percent Co. Material from Unarl shows a much stronger mode in the 0.06-0.1 percent CO range, with only three samples containing 0.1-0.3 percent Co. The Unar2 material has a clear mode in the range 0.03-0.06 percent CO, lower than any samples from A1 Sufouh and Unarl, while the mode for the Tell Abraq assemblage is even lower, at 0.02-0.03 percent. Both Unar2 and Tell Abraq show rare objects with approximately 0.1-0.2 percent CO, and one amorphous lump from Tell Abraq (TA2135) which has very high iron levels also contains 1.3 percent Co. Figure 4.6 shows a difference between the cobalt concentrations of copper and tin-bronze objects, with a mode for copper objects in the 0.06-0.1 percent CO range compared to a mode for tin-bronzes in the 0.03-0.06 percent range. Additionally, many more copper objects than tin-bronzes contain in excess of 0.1 percent Co. These patterns, however, may reflect more the chronological variation in CO levels in the analyzed samples rather than differences in alloy groups: within individual site assemblages, copper objects and tin-bronzes appear to have similar CO concentrations summarized in Table 4.9.

Table 4.9 Cobalt in Umm al-Nar Period objects analyzed in this study Median

Median

Cobalt (%)

(all)

(copper)

AI Sufouh

0.14

0.1 4

Unarl

0.07

0.07

Median (tin-bronze)

Range

Range

(all)

(copper)

Range (tin-bronze)

0.08-0.41

0.08-0.41

0.07

0.07-0.1 4

0.07-0.1 1

0.07-0.1 4

Unar2

0.05

0.05

0.05

0.04-0.1 2

0.03-0.1 2

0.04-0.09

Tell Abraq

0.03

0.04

0.02

0.02-0.08

0.03-0.29

0.02-0.03

All Objects

0.07

0.09

0.05

0.03-0.22

0.03-0.35

0.02-0.10

Cobalt concentrations in Umm al-Nar Period copper-base objects from AI Sufouh, Unarl, Unar2, and Tell Abraq analyzed by PIXE.Average MDL = 0.01 percent Co.

80

Early Metallurgy of the Persian Gulf

AI Sufouh

Copper Objects Only

Unarl Tin-Bronze Objects Only

All Objects

CO ("h) Tell Abraq

Figure 4.6 Cobalt concentrations in all Umm al-Nar Period objects analyzed by PIXE, showing copper objects (top) and tin-bronzes (middle).

Figure 4.5 Cobalt concentrations in AI Sufouh, Unarl, Unar2 and Tell Abraq objects.

Results of Compositional Analyses

81

The summary of previously analyzed material presented in Table 4.10 indicates that, while previously analyzed samples have lower median cobalt concentrations, samples with significant COconcentrations are found. In particular, analysis of Umm al-Nar material from Umm an-Nar Island, Hili and Jebel Hafit by Berthoud (1979:Table 5) indicates three objects with greater than 2,000 pprn CO, with a highest concentrations of more than 5,000 pprn Co. Likewise, a number of samples with greater than 2,000 pprn COare recorded in Wadi Suq and Late Bronze age contexts at Masirah site 38 (Hauptmann et al. 1988) and Shimal settlement Area SX (Weeks 2000a), and in mixed Wadi Suq-Iron Age tomb assemblages at Shimal tomb 2 (Craddock 1985) and Sharm (Weeks 2000b). In contrast, Table 4.1 0 Cobalt concentrations recorded in previous analytical studies Archaeological Material

No. of Analyses

Median

Range

Concentration (ppm)

(ppm)

Objects (2700-2000 BCE)

18

190

10-2,960

27

360

80-1,600

18

680

240- 1,800

45

860

170-2,340

153

170

30-700

IngotsIRaw Copper (2700-2000 BCE) Objects (2000-1 300 BCE) Objects (2000-300 BCE) Objects (1300-300 BCE)

Cobalt concentrations in copper-base objects from southeastern Arabia analyzed in previous studies. Note: details of previous analyses may be found in Appendix One, Section 1.2.3.

of more than 150 analyses of Iron Age material, only one tanged blade from the Qidfa grave contains more than 2,000 ppm, and only two objects contain more than 1,000 pprn CO (Prange and Hauptmann 2001; Weeks forthcoming b, Weeks 2000a). In a number of cases, high cobalt concentrations are associated with high iron levels, although this correlation is not exclusive. Examples include two copper ingots from Saar (Weeks, forthcoming a), and a number of high-iron pieces of metallurgical debris from Saar and Muweilah (Weeks, forthcoming a, b).

Nickel (Ni) The results of the PIXE compositional analyses for nickel are summarized in Table 4.11 and Figures 4.7-4.8. As can be seen, there are significant differences by site, and differences by alloy category. Median nickel concentrations and absolute ranges are highest in the objects from A1 Sufouh and, to a lesser extent, Unar2. Seven copper objects from A1 Sufouh and three from Unar2 contain in excess of one percent Ni, with the highest levels recorded in three thin flat fragments from A1 Sufouh (ASI-3, 2.8 percent Ni; ASTomble, 3.2 percent Ni; ASTomblf, 3.4 percent Ni), and a pinlaw1 from Unar2 (10119-4.1 13, 2.1 percent Ni). The differences between copper objects and tinbronzes are illustrated by the fact that, while around one quarter of copper objects contain more than one percent Ni, only one tin-bronze object does: a low tinbronze thin flat fragment from A1 Sufouh (ASTombld, 2.3 percent Ni). While Figure 4.7 indicates that most sites show a mode in the 0.1-1.0 percent nickel range, it Can be seen that objects Unarl and Abraq show a mode in the 0.03-0.06 percent Ni range.

Table 4.1 1 Nickel in Umm al-Nar Period objects analyzed in this study Median

Median

Nickel ( %)

(all)

(copper)

AI Sufouh

0.57

0.48

Median (tin-bronze)

Range

Range

(all)

(copper)

0.32-2.74

Range (tin-bronze)

0.31 -2.79

Unarl

0.1 9

0.21

0.06

0.04-0.84

0.04-1.30

0.03-0.59

Unar2

0.25

0.50

0.25

0.02-1 .l 8

<0.012-1.74

0.05-0.86

Tell Abraq

0.1 0

0.07

0.1 1

<0.012-0.49

<0.012-0.54

0.03-0.28

All Objects

0.25

0.38

0.22

0.03-1.54

0.02-1.84

0.03-0.78

Nickel concentrations in Umm al-Nar Period copper-base objects from AI Sufouh, Unarl, Unar2, and Tell Abraq analyzed by PIXE. Average MDL = 0.01 2 percent Ni.

82

Early Metallurgy of the Persian Gulf

Figure 4.8 Nickel concentrations in all Umm al-Nar Period objects analyzed by PIXE, showing copper objects (top) and tin-bronzes (middle).

Figure 4.7 Nickel concentrations in AI Sufouh, Unarl, Unar2 and Tell Abraq objects.

Results of Compositional Analyses

83

In particular, four rings from Unarl with tin-concentrations in the 0.7-2.7 percent range (M10-17, M10-19, M10-46, LISRING) fall into this range of Ni concentrations. In the later assemblages from Unar2 and Tell Abraq, six objects with Ni concentrations of less than the MDL of approximately 100 ppm are also recorded, including three tanged-daggers from Tell Abraq (TA2268, TA2270, TA2315). A summary of the data obtained for Ni concentrations in previous analytical studies is shown in Table 4.12, and indicates the presence of objects with high nickel concentrations at contemporary and later sites in the region. Analyses by Berthoud (1979:Table S), Frifelt (1975; 1991) and Hauptmann (1995) have indicated that objects with two to four percent Ni are common on Umm an-Nar Island in the third millennium BCE, and one further object from the site with the extremely high concentration of 21 percent Ni was recorded by Berthoud (1979:Table 5). This object finds a parallel in an Umm al-Nar Period object, from an unspecified site, which contained 12 percent Ni (Prange at al. 1999:189). Previous EDS analyses of Umm al-Nar material from Tell Abraq (Weeks 1997:Table 14) indicate a median nickel concentration of 0.3 percent, with a maximum concentration of approximately three percent and a number of Table 4.1 2 Nickel levels recorded i n previous analytical studies Archaeological Material

No. of Analyses

Median Concentration %

Range

(%l

Objects (2700-2000 BCE) IngotsIRaw Copper (2700-2000 BCE) Objects (2000-1 300 BCE) Objects (2000-300 BCE) Objects (1300-300 BCE) Nickel concentrations i n copper-base objects from southeastern Arabia analyzed i n previous studies. Note: details o f previous analyses may be found i n Appendix One, Section 1.2.3.

84

Early Metallurgy of the Persian Gulf

samples in the one to two percent Ni range. These values are significantly higher than those recorded at Tell Abraq using PIXE, but compare well with the PIXE analyses from A1 Sufouh, Unarl and Unar2 presented in this study. In contrast, the remaining Umm al-Nar Period analyses presented in graphical form by Prange et al. (1999:Figures 4-5) suggest the most common Ni concentration is in the 0.2-0.5 percent range, with only one sample containing in excess of one percent Ni. Prange et al. (1999:Figure 5 ) trace an increase in nickel concentrations in objects from Oman and Bahrain dated to the second millennium BCE, which may be partially reflected in the analyses of material from the Sharm tomb, where nickel concentrations of three to five percent are found in two rivets and a vessel rim fragment (Weeks 2000b). Objects with two to six percent Ni were also found in the Late Bronze Age settlement at Shimal Area SX and in the contemporary Shimal tomb SH102 (Weeks 2000a). Likewise, analyses of mixed Wadi SuqIIron Age tomb assemblages from Shimal by Craddock (1985) indicate a number of objects containing three to five percent Ni. The pattern of increased Ni concentration in the second millennium BC is not seen at the Saar settlement, where PIXE and EDS analyses revealed concentrations of one to two percent Ni in only one finished object and two pieces of metallurgical debris (Weeks, forthcoming a). Only one finished object analyzed thus far from an exclusively Iron Age context contains in excess of one percent Ni (Prange et al. 1999:Figure 5; Weeks 2000a; Prange and Hauptmann 2001; Hauptmann et al. 1988), although two pieces of metallurgical debris from Muweilah contain nickel in the one to two percent range (Weeks, forthcoming b). The differences in nickel content by alloy category are clear: all finished objects with greater than one percent Ni are of copper, with the exception of one fragment from A1 Sufouh which is a low-tin bronze (ASTombld, approximately two percent Sn). A spearhead from Suweiq analyzed by Hauptmann et al. (1988) contains 1.2 percent Sn in addition to 3.8 percent Ni. As can be seen in Table 4.12, there is also a clear difference between Ni levels in finished Umm al-Nar Period objects and those in contemporaneous copper ingots and raw copper pieces. The ingots and raw copper pieces analyzed in previous studies (Hauptmann 1987; Hauptmann et al. 1988) are datable to the late third millennium or

Table 4.1 3 Zinc in Umm al-Nar Period objects analyzed in this study

Median

Median

Zinc (%)

(all)

(copper)

Median

AI Sufouh

0.1 1

0.1 1

Unarl

nm

nm

nm

nm

nm

nm

Unar2

0.1 0

0.1 0

0.1 0

0.09-0.1 2

0.09-0.1 1

0.09-0.1 2

Tell Abraq

0.1 0

0.1 0

0.1 1

0.09-0.1 3

0.09-0.1 4

0.09-0.1 2

All Objects

0.10

0.1 0

0.1 0

0.09-0.1 2

0.09-0.1 2

0.09-0.1 2

(tin-bronze)

Range

Range

Range

(all)

(copper)

(tin-bronze)

0.09-0.1 1

0.09-0.1 1

Zinc concentrations in Umm al-Nar Period copper-base objects from AI Sufouh, Unarl, Unar2, and Tell Abraq analyzed by PIXE. Average MDL = 0.04 percent Zn. Note: nm = not measured.

early second millennium, and yet almost all contain less than 0.5 percent Ni at a time when finished objects with one to four percent Ni are commonplace. This discrepancy has been mentioned in a number of places (e.g. Prange et al. 1999:190; Hauptmann et al. 1988), and will be discussed further below.

Table 4.14 Zinc levels recorded in previous analytical studies

Archaeological Material

No. of Analyses

Median

Range

Concentration (ppm)

(ppm)

Objects (2700-2000 BCE)

28

105

20-44,200

28

230

60-600

8

190

70-300

23

350

100- 1,960

134

40

20-970

Ingots/Raw Copper

Zinc (Zn) Zinc concentrations measured by PIXE are summarized in Table 4.13. Zinc levels were not recorded for all PIXE samples, given the problems created in X-raybased analyses of copper alloys by the proximity of the copper and zinc a and P emission lines. The large amount of copper in most samples tends to obscure the small amounts of zinc that are present, leading to a low sensitivity for Zn. Given the virtually invariant values reported for the material analyzed in this study, and the problems of spectral overlap mentioned above, it seems likely that Zn concentrations below approximately 1,500 ppm are artifacts of sample matrix effects rather than measures of concentration, and are thus unreliable. Previous analytical studies have used a wide variety of analytical techniques, some of which are more sensitive to low zinc levels than PIXE. These studies (see Table 4.14) suggest that median Zn values of 300-500 ppm characterize pre-Iron Age finished copper objects from the region, with tenth to ninetieth percentile ranges commonly extending from ~100-2,000ppm. Zinc levels recorded for late third or early second millennium BCE copper ingots and raw copper pieces from southeastern Arabia show similarly low median values, and tenth t o ninetieth percentile ranges of approximately 60-600

(2700-2000 BCE)

Objects (2000-1 300 BCE)

Objects (2000-300 BCE)

Objects (1300-300 BCE)

Zinc concentrations in copper-base objects from southeastern Arabia analyzed in previous studies. Note: details of previous analyses may be found in Appendix One, Section 1.U.

ppm. However, analyses of daggers and fragments from mid-third millennium BCE burials on Umm an-Nar Island have revealed eight samples with Zn levels of 2.3-10.0 percent (Frifelt 1975, 1990). The composition of these objects is completely un-paralleled in southeastern Arabia before the Ed Dur period (Weeks 2000a), and will be discussed further below. Arsenic (As) The compositional data for arsenic is summarized below in Table 4.15 and Figures 4.9 and 4.10, where significant variation between assemblages is observable. The majority of objects from A1 Sufouh contain in excess

Results of Compositional Analyses

85

Table 4.15 Arsenic i n Umm al-Nar Period objects analyzed i n this study Arsenic (%)

Median

Median

Median

(all)

(copper)

(tin-bronze)

AI S U ~ O Uh

1.82

1.80

Unarl

0.1 3

0.1 1

0.14

Range (all)

Range (copper)

0.24-3.64

0.20-3.65

0.03-1.78

0.05-2.30

Range (tin-bronze)

0.03-0.42

Unar2

0.91

0.72

0.91

0.03-2.20

0.01 -2.64

0.20-2.1 1

Tell Abraq

0.37

0.24

0.70

0.02-1.57

0.01 -2.75

0.34-0.94

All Objects

0.70

1.OO

0.44

0.03-2.97

0.03-3.46

0.1 1-1.83

Arsenic concentrations in Umm al-Nar Period copper-base objects from AI Sufouh, Unarl, Unar2, and Tell Abraq analyzed by PIXE. Average MDL = 0.007 percent As.

of one percent As, and seven objects contain more than three percent As. The highest levels occur in a thin flat fragment (ASI-3, 6.2 percent As) and a blade edge fragment (ASTomblc, 4.2 percent As). Arsenic levels are generally lower in material from the other tomb assemblages, although half of the objects from the Unar2 tomb contain more than one percent As, with the highest levels recorded in a pinlawl fragment (surf.56, 3.9 percent As) and two tin-bronze rings (1007.42, 2.4 percent As; 1019-5.71, 2.2 percent As). All tomb assemblages contain objects with more than two percent As, even when, as at Unarl, many objects have relatively low arsenic concentrations of less than 0.1 percent. As illustrated in Figure 4.10, distinct differences in arsenic content can be seen by alloy type, with a greater range of arsenic compositions in copper samples than in tin-bronzes. Half of the analyzed copper samples contain in excess of one percent As, whereas only about one-quarter of the tin-bronzes contain this much arsenic. At the lower end of the arsenic concentration ranges, it can be seen that around one-quarter of copper samples contain very low levels of arsenic, less than 0.1 percent. In contrast, only 10 percent of tin-bronzes contain such low arsenic concentrations. The tin-bronzes are, as a group, more homogeneous than the copper samples in terms of their arsenic concentrations. Other than for the ends of the arsenic concentration ranges, however, tin-bronzes show similar median As levels to copper objects in most of the assemblages. Previous analyses of copper-base objects from southeastern Arabia are summarized in Table 4.16.

86

Early Metallurgy of the Persian Gulf

The overall ranges of As concentrations reported in previous studies are very similar to those measured in this study using PIXE, excepting that fewer low arsenic (less than 0.1 percent As) samples were found in the earlier studies. Chronological variation is clear in the results of previous analyses, in that there is a distinct reduction in median arsenic concentrations and ranges in the Iron Age. Previous analyses of Umm al-Nar Period samples have revealed the regular presence of objects with greater than one percent As. From Umm an-Nar Island, seven objects are recorded with more than two percent As, with concentrations reaching approximately seven percent in two objects analyzed by Berthoud (1979:Table 5). The objects thus appear very similar in composition to the contemporary material from A1 Sufouh. Such compositions were becoming less frequent in analyses of Wadi Suq and Wadi SuqIIron Age material, although nine objects with 1.0-2.0 percent As were recorded in contexts from Oman and the U.A.E (Hauptmann et al. 1988; Craddock 1985; Weeks 2000a) and two objects with greater than two percent As were recorded from the tomb at Sharm (Weeks 2000b). Similar results are presented in graphical form by Prange et al. (1999:Figure 5), although the proportion of Wadi Suq Period and Late Bronze Age objects with one to two percent As is slightly higher than found in the other studies discussed here. In contrast, of the 154 Iron Age objects for which As concentrations have been previously recorded, the highest arsenic concentrations of 1.O-1.5 percent were noted in only two objects from the Qidfa tomb (Weeks 2000a) and one from the settlement at Muweilah (Weeks, forthcoming b).

Figure 4.10 Arsenic concentrations in all Umm al-Nar Period objects analyzed by PIXE, showing copper objects (top) and tin-bronzes (middle).

Figure 4.9 Arsenic concentrations in AI Sufouh, Unarl, Unar2 and Tell Abraq objects.

Results of Compositional Analyses

87

Additionally, as noted above for nickel, there is a discrepancy between the As concentrations recorded in previous analyses of copper ingots and raw copper pieces and those found in finished objects. Only one ingot fragment from Umm al-Nar Island and one raw copper piece from Maysar contain more than one percent As, while levels recorded in finished objects could reach in excess of five percent As. Selenium (Se) Selenium levels recorded in this study are summarized below in Table 4.17 and Figures 4.11-4.12. A significant percentage of objects from the analyzed assemblages contain less than the minimum detectable level of selenium for the PIXE system, of about 50 ppm. Table 4.1 6 Arsenic levels recorded in previous analytical studies Archaeological Material

No. of Analyses

Median

Range

Concentration %

(%)

Objects (2700-2000 BCE)

20

1.43

0.1 9-5.42

28

0.41

0.08-0.87

18

0.29

0.09-0.9 1

58

0.28

0.04-1.04

154

0.1 4

0.02-0.38

IngotsIRaw Copper (2700-2000 BCE)

Objects (2000-1 300 BCE)

Objects (2000-300 BCE)

Objects (1300-300 BCE)

Arsenic concentrations in copper-base objects from southeastern Arabia analyzed in previous studies. Note: details of previous analyses may be found in Appendix One, Section 1.2.3.

Selenium concentrations in the 50-300 pprn range are most frequently found in the remaining objects, although samples with 500 pprn Se or more are occasionally found. Examples include two tin-bronze rings from the Tell Abraq tomb (TA2677, approximately 800 pprn Se; TA2816, approximately 1,100 pprn Se), a copper "lump" from Tell Abraq (TA2135, approximately 550 pprn Se), and a tin-bronze ring (1023-4.10, 500 pprn Se) and pinlaw1 fragment (surf.56, 500 pprn Se) from Unar2. Variation by site is clear, with objects from Unarl having generally lower levels of Se than material from the other tomb assemblages, especially Unar2 and A1 Sufouh. The statistical summary presented in Table 4.17 indicates very few differences in Se concentration between alloy categories, and the general similarity of copper and tin-bronze samples is also illustrated in Figure 4.12. It can be seen that, although the highest Se levels are recorded in tin-bronzes, the majority of copper and tin-bronze samples have very similar Se concentrations. The selenium concentrations recorded in previous studies of Umm al-Nar Period material by Berthoud (1979:Table 5 ) are very similar to those recorded in this study, with a median concentration of 150 pprn Se, and a maximum concentration of 600 pprn Se in 11 analyzed samples. Slightly higher median values of approximately 350 pprn Se are recorded in the finished objects from the Saar settlement on Bahrain, although maximum values are still 600 ppm. Analyses of Wadi Suq, late Bronze Age and Iron Age material from the U.A.E. indicates a slight reduction in selenium levels over time, with median values for objects from these periods not exceeding 100 pprn Se, and maximum values not greater than approximately 400 pprn Se.

Table 4.1 7 Selenium in Umm al-Nar Period objects analyzed in this study Selenium

Median

Median

(PP~) AI Sufouh

(all)

(copper)

125

100

Unarl

<50

<50

Median (tin-bronze)

Range

Range

Range

(all)

(copper)

40-250

<50-250

(tin-bronze)

<50

<50-100

<50-100

<50-100 <50-375

Unar2

175

275

150

<50-445

<50-430

Tell Abraq

<50

280

<50

<50-550

<50-280

<50-800

All Objects

100

100

100

<50-400

<50-355

<50-450

Selenium concentrations in Umm al-Nar Period copper-base objects from AI Sufouh, Unarl, Unar2, and Tell Abraq analyzed by PIXE. Average MDL = 50 pprn Se.

88

Early Metallurgy of the Persian Gulf

Figure 4.1 2 Selenium concentrations in all Umm al-Nar Period objects analyzed by PIXE, showing copper objects (top) and tin-bronzes (middle).

Figure 4.1 1 Selenium concentrations in AI Sufouh, Unarl, Unar2 and Tell Abraq objects.

Results of Compositional Analyses

89

Table 4.1 8 Silver i n Urnm al-Nar period objects analyzed i n this study Silver

Median

Median

Median

Range

Range

Range

(PP~)

(all)

(copper)

(tin-bronze)

(all)

(copper)

(tin-bronze)

AI Sufouh

<240

<240

Unarl

<240

<240

<240

<240

<240

<240-420

Unar2

<240

c240

320

<240-960

<240-280

<240-1210

Tell Abraq

<240

<240

<240

<240-1050

<240-280

<240-1500

All Objects

<240

<240

<240

<240-690

<240-260

d40-1250

<240-300

<240-300

Silver concentrations i n Urnm al-Nar Period copper-base objects from AI Sufouh, Unarl, Unar2, and Tell Abraq analyzed by PIXE. Average MDL = 240 pprn Ag. Table 4.1 9 Silver levels recorded i n previous analytical studies Archaeological Material

No. of Analyses

Median Concentration (ppm)

Range (ppm)

Objects (2700-2000 BCE)

20

90

40-3,680

4

60

10-21 0

18

40

0-1 10

58

90

0-240

146

30

0-1 20

IngotsIRaw Copper (2700-2000 BCE) Objects (2000-1 300 BCE) Objects (2000-300 BCE) Objects (1300-300 BCE)

Silver concentrations in copper-base objects from southeastern Arabia analyzed previously.Note:details of previous analyses in Appendix One (1.2.3).

Silver (Ag) Silver levels in the objects analyzed in this study are summarized in Table 4.1 8 and Figure 4.13. As can be seen, median silver concentrations for each chronological period and compositional group are less than the MDL for silver of approximately 240 ppm. Similarly, the tenth to ninetieth percentile silver ranges are often below the three MDL concentration levels required for acceptable analytical precision. However, some significant patterns can be reliably extracted from this otherwise imprecise data. Approximately 25 percent of analyzed objects contained silver in concentrations of greater than

90

Early Metallurgy of the Persian Gulf

300 ppm. Three objects contained in excess of 2,000 pprn Ag, including a tanged copper dagger from A1 Sufouh (M10-41, approximately 2,100 pprn Ag), a tinbronze ring from Tell Abraq (TA2677, 5,250 pprn Ag), and a tin-bronze ring from the Unar2 tomb at Shimal (1007.42, approximately 2.3 percent Ag). The statistical summary in Table 4.18 and Figure 4.13 indicate that significant differences exist between the silver contents of copper objects and tin-bronzes. Only three of 62 analyzed copper objects from Urnm al-NarISaar contexts contain 400 pprn Ag or more, whereas 1 3 of 33 tin-bronzes contain 400 pprn Ag or more. Previous analyses of copper-base objects from southeastern Arabia have recorded silver concentrations that are generally similar to those obtained in this study. The results of previous studies are summarized in Table 4.19, and indicate median silver concentrations of less than 100 pprn for all chronological and compositional groups. However, relatively high silver concentrations of 1,000-5,000 pprn have been recorded in six copper objects from Urnm al-Nar Period contexts, mostly from Urnm an-Nar Island itself (Hauptmann 1995; Berthoud 1979:Table S), so the association between silver concentrations and tin-bronzes might not be as strong as the PIXE data alone would indicate. Of the six raw copper and ingot fragments from Urnm an-Nar Island and Saar whose silver concentrations have been measured, none contain more than 250 pprn Ag (Hauptmann 1995; Craddock 1981; Weeks, forthcoming a). The great majority of copper objects from Oman, in all chronological periods, contain less than 200 pprn silver.

Antimony (Sb) Median antimony concentrations for the assemblages analyzed by PIXE fall well below the MDL of 700 ppm. Likewise, tenth t o ninetieth percentile ranges rarely exceed the MDL for antimony, let alone the 3MDL values necessary for acceptable analytical precision. However, a number of samples contain high levels of antimony which can be reliably measured by PIXE, and some sites show larger ranges of antimony concentrations which can also been reliably characterized by this technique. Nine of 2 2 samples from A1 Sufouh contain more than 700 pprn Sb, with maximum values of approximately 1,900 pprn Sb in two thin flat copper fragments (ASTomble and ASTomblf). N o other site has more than three objects with greater than 700 pprn Sb. Other high-Sb samples from Umm al-Nar contexts include a thin flat copper fragment from the Unarl tomb (M10-20V, 5,250 pprn Sb) and a tin-bronze ring (1007.42, 1,850 pprn Sb) and a thin flat tin-bronze fragment (1018-3.99, 2,300 pprn Sb) from the Unar2 tomb. N o objects with more than the minimum detectable level of antimony were recorded from Tell Abraq. A summary of previous analyses using more sensitive techniques is given in Table 4.20. These studies concur with the PIXE analyses, in that very few samples with greater than 1,000 pprn antimony were recorded. A copper chisel and a copper axe from Maysar 1 contained 1,050 and 2,200 pprn Sb respectively (Hauptmann et al. 1988), and analyses by Berthoud (1979:Table 5) revealed one sample from Umm an-Nar Island with 1,200 pprn Sb. Copper ingots and fragments of raw copper generally contained levels of less than 200 pprn Sb, with the exception of a raw copper fragment from Maysar 1 that contained approximately 3,300 pprn Sb (Hauptmann 1987). A copper arrowhead from the Wadi SuqIIron Age deposit of Shimal tomb 2 contained approximately 1,700 pprn Sb, while a copper rivet and a tin-bronze vessel fragment from the mixed Wadi SuqIIron Age tomb deposit at Sharm were also found to contain relatively high concentrations of more than 1,500 pprn Sb (Weeks 2000b). Samples with more than 1,000 pprn antimony are not recorded

Figure 4.1 3 Silver concentrations in all Umm al-Nar Period objects analyzed by PIXE, showing copper objects (top) and tin-bronzes (middle).

Results of Compositional Analyses

91

fragment from Unarl (M10-20V, 1.45 percent Pb), a copper pinlaw1 fragment from Unar2 (surf.56, 5,250 pprn Pb), and a tin-bronze ring from Tell Abraq (TA2679, 1.3 percent Pb). Samples with lead concentrations of less than the minimum detectable level of approximately 135 pprn Pb comprise approximately 15 percent of the analyzed objects, and occur with similar frequency in each of the four tomb assemblages. There does not appear to be a distinct difference in lead concentration ranges between alloy groups, as illustrated in Figure 4.15. High lead levels (greater than 1,000 pprn Pb) occur with greater frequency in tin-bronzes than in copper samples (30 percent of tin-bronzes contain more than 1,000 pprn Pb, while only 18 percent of copper samples do) but when the analyses are examined on a siteby-site basis (see Table 4.21) it can be seen that in one case (Tell Abraq) tin-bronzes have a greater range of lead concentrations than copper samples, in another case (Unar2)the ranges are the same, and in the third case (Unarl)copper objects have a greater range of Pb concen-trations than tin-bronzes. Figure 4.15 does indicate a different distribution pattern for lead concentrations in copper objects and tin-bronzes. While both groups exhibit a strong fall off at the 1,000 ppm Pb level, tin-bronzes show a distinct bi-modal pattern in the 0.01-0.1 percent Pb range, with the

in the previously analyzed Iron Age objects from the region (Prange and Hauptmann 2001; Weeks, forthcoming b; Weeks 2000a). Lead (Pb) The lead concentrations recorded in objects analyzed for this study are summarized in Table 4.21 and Figures 4.14 and 4.15. Median lead concentrations are around 500 ppm, and the majority of samples contain less than 1,000 pprn Pb, although individual sites show variation in Pb concentrations. For example, more than 33 percent of analyzed objects from Unar2 contains in excess of 1,000 pprn Pb. Four samples contain greater than 3,000 pprn Pb, including a copper blade edge fragment from A1 Sufouh (ASI-5, 6,600 pprn Pb), a thin flat copper Table 4.20 Antimony levels recorded i n previous analytical studies Archaeological Material

No. of Analyses

Median Concentration (ppm)

Range

(ppm)

Objects (2700-2000 BCE)

16

550

40-1 ,l20

26

50

20-200

15

5

0-340

53

150

0-660

149

70

0-31 0

Ingots/Raw Copper (2700-2000 BCE) Objects (2000-1 300 BCE)

strongest mode in the 560-1,000 ppm bracket, whereas the distribution pattern for copper objects is invariant in the 0.01-0.1 percent range. Lead levels recorded in previous analytical studies of material from southeastern Arabia are summarized in Table 4.22. The results are, in general, similar to those obtained by PIXE. For all periods, the majority of samples contain less than approximately 500 ppm

Objects (2000-300 BCE) Objects (1300-300 BCE)

Antimony concentrations in copper-base objects from southeastern Arabia analyzed previously. Note: details of previous analyses i n Appendix One (1.2.3). Table 4.21

Lead i n Umm al-Nar Period objects analyzed i n this study Lead

Median

Median

Median

Range

(PPm) AI Sufouh

(all) 380

(copper) 350

(tin-bronze)

(all) <135-1180

Unarl

550

600

250

< l 35-2830

Range (copper) <135-950

Range (tin-bronze)

200-2900

< l 35-1,600

150-2280

< l 35-2,290

Unar2

780

550

780

< l 35-2330

Tell Abraq

450

140

500

< l 35-1 700

< l 35-790

250-1,700

All Objects

500

400

700

<135-2130

<135-1560

<135-2,310

Lead concentrations i n Umm al-Nar Period copper-base objects from AI Sufouh, Unarl, Unar2, and Tell Abraq analyzed by PIXE. Average MDL = 135 ppm.

92

Early Metallurgy of the Persian Gulf

Figure4.15 Lead concentrations in all Umm al-Nar Period objects analyzed by PIXE, showing copper objects (top) and tin-bronzes (middle).

Figure 4.14 Lead concentrations in AI Sufouh, Unarl, Unar2 and Tell Abraq objects.

Results of Compositional Analyses

93

Pb, although objects with 1,000-5,000 ppm Pb are sometimes found at Bronze Age sites like Umm anNar Island (Berthoud 1979:Table 5), Maysar 1, and Masirah Site 38 (Hauptmann et al. 1988), in mixed Bronze and Iron Age tomb assemblages, for example at Sharm (Weeks 2000b), and in Iron Age objects from the IbriISelme hoard (Prange and Hauptmann 2001) and the Qidfa tomb (Weeks 2000a). A small number of objects with more than one percent lead were also recorded in previous studies, including leaded tin-bronze arrowheads from Wadi Suq-Iron Age burials at Shimal Tomb 1 (3.5 percent Pb; Craddock 1985) and Sharm (1.2 percent Pb; Weeks 2000b), three leaded tin-bronze bracelets from the Table 4.22 Lead levels recorded i n previous analytical studies Archaeological

No. of

Material

Median

Analyses

Range

Concentration (ppm)

(ppm)

Objects (2700-2000 BCE)

29

140

IngotsIRaw Copper (2700-2000 BCE)

10-260

28

Objects (2000-1 300 BCE)

18

250

40-740

41

150

30-500

152

100

0-1,820

Objects (2000-300 BCE) Objects (1300-300 BCE)

Lead concentrations i n copper-base objects from southeastern Arabia previously analyzed. Note: details of previous analyses may be found i n Appendix One, Section 1.2.3.

IbriISelme hoard (with up to 6.35 percent Pb; Prange and Hauptmann 2001) and a late pre-Islamic, leaded brass ring from the tomb at Bithnah (5.6 percent Pb; Corboud et al. 1996). Very high lead concentrations, and unusual alloy types, were also found in three objects from Umm anNar Island datable to the mid-third millennium BCE (Frifelt 1975a, 1990). Two daggers and one unidentified fragment were found to contain from 3.7-25.0 percent Pb. One of the daggers, in addition to 25 percent Pb, contained approximately 2.3 percent zinc. Such lead concentrations are uncommon in southeastern Arabia and western Asia generally in this period, although they are known (see e.g. Malfoy and Menu 1987; Philip 1991). Tin (Sn) Tin concentrations measured for the Urnm al-Nar Period tomb assemblages are summarized in Table 4.23 and illustrated in Figures 4.16 and 4.17. It is clear that copper with significant levels of tin, much higher than would have been naturally present in locally-produced Omani copper, was present already in the region in the mid-third millennium BCE, as indicated by the analyzed material from A1 Sufouh. Although only one object from this site contained more than two percent tin (the definition of a tin-bronze for the purposes of this study), six remaining objects from the site contained between 0.5 and two percent Sn (see Figure 4.16). Such low-tin objects might indicate the practice of recycling imported tin-bronze objects in this period, involving the mixing of imported tin or tin-bronze with local copper, but this issue will be discussed in more detail in the following chapters. In total, 33 of the 83 Urnm al-Nar Period

Table 4.23 Tin i n Urnm al-Nar Period objects analyzed i n this study Median

Median

Median

Range

Range

Range

Tin (%)

(all)

(copper)

(tin-bronze)

(all)

(copper)

(tin-bronze)

AI Sufouh

0.1 6

Unarl

1.03

0.1 6 0.20

<0.13-1 .56

<0.13-1.27

7.7

<0.13-10.3

<0.13-1.04

2.2-1 3.9

Unar2

8.81

<0.13

21.4

<0.13-23.9

<0.13-0.47

5.1 -24.3

Tell Abraq

3.99

<0.13

27.8

<0.13-38.8

<0.13-1.30

5.0-46.2

All Objects

1.04

<0.13

19.8

<0.13-24.6

<0.13-1.25

2.4-36.0

Tin concentrations i n Urnm al-Nar Period copper-base objects from AI Sufouh, Unarl, Unar2, and Tell Abraq analyzed by PIXE. Average MDL = 0.1 3 percent Sn.

94

Early Metallurgy of the Persian Gulf

Figure 4.17 Tin concentrations in all Umm al-Nar Period objects analyzed by PIXE.

Figure 4.16 Tin concentrations in AI Sufouh, Unarl, Unar2 and Tell Abraq objects.

objects analyzed in this study contain more than two percent Sn, and are thus classified as tin-bronzes. This represents about 40 percent of the assemblage, although distinct differences by site can be seen in that only one tin-bronze is found at A1 Sufouh, roughly one-third of the Unarl objects are of tin-bronze, while 50-60 percent of objects from Unar2 and Tell Abraq are of tin-bronze. Furthermore, the amount of tin in the tin-bronzes increases from the earliest material at A1 Sufouh to the latest material from Unar2 and Tell Abraq. As noted above, numerous objects from A1 Sufouh contain approximately 0.5-2.0 percent Sn. This pattern is repeated at Unarl, although tin-bronzes with tin concentrations or more than five percent begin to be seen at this time (see Figure 4.16). Examination of the Unar2 and Tell Abraq material reveals a few low-tin bronzes with tin concentrations of less than three percent, but a dramatic increase in the number of tin-bronzes with more than 10 percent Sn, with a distinct mode in the 18-32 percent range. The overall distribution pattern for tin, shown in Figure 4.17, is tri-modal; most samples contain less than the MDL for tin on the PIXE system of approximately 0.13 percent, however there is a strong mode in the one and two percent Sn range, and an even clearer peak in the 18-32 percent Sn range. The various alloying practices and exchange mechanisms that may have led to this pattern will be discussed in the following chapter. Tin levels in the tin-bronzes are diverse, reaching levels of greater than 40 percent Sn in two objects from Tell Abraq (TA2435, approximately 52 percent Sn; TA2677, approximately 46 percent Sn). The very high tin concentrations reported are almost certainly a reflection

Results of Compositional Analyses

95

of sample corrosion, which commonly involves the leaching of copper (but not tin) from the object matrix, leading to an increase in the proportion of tin remaining in the corroded object (Scott 1991). The effect of corrosion on the analyzed PIXE samples is suggested by the fact that measured tin levels in objects which were uncorroded or contained significant remaining metal were in all cases less than 20 percent Sn (although uncorroded objects with approximately 15-20 percent Sn were relatively common). Analyses returning concentrations of greater than 20 percent tin were exclusively of corroded material. The analyses of the objects from the Umm al-Nar tomb assemblages presented here contrast strongly with the results of previous studies of contemporary material. Only three tin-bronzes were recorded in the analyses of more than 80 Umm al-Nar Period objects published in full or in part from Umm an-Nar Island and the Hili Oasis in the U.A.E and other locations in Oman (Frifelt 1975a, 1991; Craddock 1981; Berthoud 1979; Hauptmann et al. 1988; Hauptmann 1995; Prange et al. 1999:Figure 6). These three objects include a dagger with six percent Sn from a tomb on Umm an-Nar Island (Berthoud 1979:Table 5) and two objects with more than approximately five percent Sn from unspecified locations in southeastern Arabia (Prange et al. 1999:Figure 6). The new data from PIXE analyses are, however, in accord with the semi-quantitative EDS analyses of material from settlement and burial contexts at Tell Abraq (Weeks 1997), which indicated significant tin-bronze use at the site already by the third millennium BCE. Tin-bronze continues to comprise around onethird of analyzed copper-base objects from second millennium BCE contexts and mixed Wadi Suq-Iron Age tomb assemblages (Craddock 1985; Hauptmann et al. 1988; Prange et al. 1999:Figure 6; Weeks 2000a, 2000b), before becoming the dominant alloy used in the region in the Iron Age. Analyses of more than 150 Iron Age objects presented by Prange and Hauptmann (2001), Pedersen and Buchwald (1991), Im-Obersteg (1987) and Weeks (Forthcoming b, 2000a) indicate that tin-bronzes account for approximately 80 percent of analyzed copper-base objects from this period, although there is strong variation by site.

96

Early Metallurgy of t h e Persian Gulf

Elemental Relationships: Rank-CorrelationAnalyses In the previous sections of this chapter, variation in the composition of objects has been summarized using a univariate, element-by-element approach. A first step towards the examination of correlations between elements was provided by the separation of objects into "copper" and "tin-bronze" compositional groups, and these beginnings are taken further in the final part of this chapter. The investigation of elemental relationships is important in understanding aspects of the ore sources used to produce the objects and the processes of alloy production and selection that affected their manufacture. Introduction and Description of Statistical Techniques In this section, bivariate relationships between elements are investigated, in an attempt t o outline latent structure in what is a large and complex data set. This section begins with an examination of the bivariate correlations between elements for analyzed samples from different sites. Such relationships have been investigated in a number of previous analytical studies from southeastern Arabia. For example, high levels of arsenic are frequently associated with high levels of nickel in copper objects from third and second millennium BCE sites (Hauptmann et al. 1988; Hauptmann 19951; Prange et al. 1999). Elemental associations have been investigated in the PIXE data using the statistical measure of association known as the correlation coefficient (denoted here as "r"; Freedman et al. 1991:118). Values for the correlation coefficient range from -1 to +l,with -1 indicating perfect negative correlation and + l indicating perfect positive correlation. Values at or around zero indicate very little or no correlation between the two variables. However, r is a measure of linear association, and can be a poor descriptor for non-linear relationships between variables, and in situations where outliers occur (Freedman et al. 1991: 139-40). To overcome these problems, the PIXE compositional data in percentageslppm have been converted to rank order, and the correlation coefficient calculated on the ranked values. This is similar to the Spearman's rank-correlation coefficient

described in Freund et al. (1988:499), and provides a "simple and theoretically sound cure" to the problems of statistically describing non-linear elemental relationships (Wright 1992:38). Using the rank-correlation coefficient, matrices of elemental correlations have been constructed on a siteby-site basis. The strongest positive correlations are between arsenic, nickel, and cobalt, and perhaps antimony. Lead is correlated with arsenic and nickel in some assemblages, but also with silver and tin. Negative correlations are seen at most sites, particularly between copper and a series of alloying elements, including tin, arsenic, and nickel, as well as iron. There is also a negative correlation observable between tin and cobalt in some assemblages, and particularly in the analyses of the assemblage as a whole. The correlation matrix for all Urnm al-Nar Period objects as a group is presented in Table 4.24.

Negative Correlations A number of the negative correlations found in the PIXE data can be explained as a result of the replacement of one alloy constituent by another, given the restrictions placed on concentration by the constant sum of the normalized compositional data. For example, copper and tin show large and statistically significant negative r values (-0.73 on Table 4.24) for finished objects from all sites. This strong negative correlation

can be simply explained by the fact that tin is the major alloying component for copper-base objects in the Bronze Age, and tin-bronzes will obviously have lower copper levels than un-alloyed objects. Similar reasoning can be used to explain the negative correlations between copper and arsenic at A1 Sufouh and Tell Abraq, and in the group of Urnm alNar objects as a whole: arsenic also replaces copper in alloys, whether these are intentionally produced or not. In general, As concentrations are lower than Sn concentrations in tin-bronzes, so the negative correlation is not as strong as for copper and tin. The negative correlation between tin and cobalt suggested by the rank-correlation analyses of the entire Urnm al-Nar assemblage and the material from Tell Abraq is illustrated in Figure 4.18. It can be seen that only three tin bronzes contain in excess of 1,100 ppm CO (ASTombld, 1023-4.10, M10-22R), whereas more than 40 percent of copper objects contain more than 1,100 ppm Co. The result of the relationship between Sn and CO is that a high positive correlation between copper and cobalt is also reported by a rank-correlation analysis of the tin-bronzes.

Arsenic, Nickel, Cobalt and Antimony Correlations significant at the 99 percent confidence level were found between arsenic and nickel for all Urnm al-Nar sites. In the correlation analysis of all

Table 4.24 Elemental relationshipsin Urnm al-Nar Period copper-base objects

S Fe CO Ni CU AS Se

Ag

Sb SnL PbL

S

Fe

1.OO

Ag

Sb

Sn

-0.08

-0.1 1

-0.1 1

-0.19

-0.02

0.02

-0.02

0.14

0.07

-0.05

0.47

0.24

-0.09

0.44

-0.46

0.06

0.82

0.47

0.1 7

0.57

-0.18

0.38

-0.46

-0.37

-0.36

-0.09

-0.73

-0.32

1.OO

0.51

0.29

0.59

-0.04

0.46

1.OO

0.42

0.22

-0.01

0.27

1.00

0.08

0.26

0.41

1.00

-0.16

0.22

1.00

0.19

Cu

As

Se

-0.07

0.05

-0.06

0.19

-0.30

0.08

0.61

0.10

1.OO

-0.30

1.00

CO

Ni

0.20

0.1 6

1.00

0.33

1.00

Pb

1.oo

Rank-correlation coefficients for all Urnm al-Nar Period objects analyzed in this study. Statistically significant values are shown in bold.

Results of Compositional Analyses

97

Tin vs. Cobalt

Urnm al-Nar samples as a group, the positive As:Ni correlation was clearly the strongest elemental relationship (Table 4.24). The correlation between As and Ni is illustrated in Figure 4.19. It can also be seen that arsenic and nickel are correlated in tin-bronzes as well as in copper objects, although absolute As and Ni concentrations are lower in the tin-bronzes (Figure 4.19). The correlations between nickel and cobalt and arsenic and cobalt are illustrated in Figures 4.20 and 4.21 respectively. In both cases, the correlations are much stronger in copper objects than in tin-bronzes. It is likely that these correlations reflect the mineralogy of the copper deposits that were the source for the analyzed objects, and this issue will be discussed in detail in the following chapter. Antimony and arsenic are correlated in material from A1 Sufouh and Unar2. However, the strength of the correlation is significantly less than that between As and Ni seen in all Urnm al-Nar Period material, and investigation of the relationship is hampered by the low sensitivity of the PIXE technique in the determination of Sb concentration. A correlation between As and Sb might be expected on a mineralogical basis, given their common occurrence in sulfidic copper ore bodies as species of the tennantite (Cu12As4S13)-tetrahedrite (CuI2Sb4Sl3)series. Nickel and antimony are also correlated in the Urnm al-Nar objects as a group (see Table 4.24). As for the correlation between As and Sb, however, assessing the relationship between Ni and Sb is complicated by the low sensitivity of the PIXE Sb measurements.

0

l0

Figure 4.18 The negative correlation between tin and cobalt in the Urnm al-Nar objects analyzed by PIXE. Arsenic vs. Nickel

Figure 4.19 Arsenic and nickel in Urnm al-Nar Period objects analyzed by PIXE. Nickel vs. Cobalt

-

1 o tin-bronze I 1

W

H

Figure 4.20 Nickel and cobalt in the Urnm al-Nar Period objects analyzed by PIXE.

98

Early Metallurgy of the Persian Gulf

Tin and Silver As noted above, silver concentrations seem to be higher in tin-bronzes than in copper objects from Urnm al-Nar Period contexts. However, tin and silver show significant rank-correlation coefficients (at the 99 percent level) only in material from Tell Abraq. At the 95 percent confidence level, correlations are also seen at Unar2 and in the assemblage as a whole. The relationship between Sn and Ag concentrations in late third millennium BCE material is illustrated in Figure 4.22. It is clear that Ag concentrations in excess of approximately 400 ppm occur much more frequently in tinbronzes than in contemporary copper objects.

Principal Components Analyses (PCA) This section presents the results of principal components analyses (PCA)of the collected PIXE data, which were conducted in order to further investigate elemental correlations, and to characterize the compositional variability within and between metal objects from individual tomb assemblages. PCA is a widely used multivariate tool useful in reducing large, multi-dimensional data sets to limited numbers of components (usually six or less), which describe significant amounts of the latent structure in the data and can be easily conceived of and represented graphically (Wright 1992:34-63; Magee et al. 1998:239). The technique is conceptually simple because, as noted by Wright (1992:60), "it is nothing more than the extension, into hyperspace, of the simple concept of lines of best fit through a system of points". Thus, PCA is a linear technique, and works best when the relationships between variables and between the components and the variables are linear also. In order to avoid the possibility of overlooking non-linear correlations within the collected PIXE data, the concentrations in percentage and ppm form have been converted to rank-order, as suggested by Wright (1992:38). This transformation provides the equivalent of a PCA of the rank-correlation coefficient (Wright l992:3 8). The PCAs presented in this section were carried out using the program MV-Nutshell (R.V.S. Wright 1994). A standard correlation PCA was used, as it is widely considered to be the most appropriate multivariate descriptive technique for quantitative compositional data (e.g. Magee et al. 1998:239). Correlations Between Elements Correlations between different element concentrations in analyzed metal samples can be investigated using PCA, as above using the rank-correlation coefficient. The results of the PCA of the ranked compositional data are best illustrated graphically in one, or a series of, bivariate scattergrams. In the following scattergrams, the proximity of elements reflects the correlation between them. Elements that plot very closely together on a PCA scattergram are positively correlated, whereas elements that plot widely apart are negatively correlated. The results are discussed below, and their implications are addressed in Chapter Five.

Arsenic vs. Cobalt 10

I

W

copper

0

tin-bronze

Figure 4.21 Arsenic and cobalt in the Umm al-Nar Period objects analyzed by PIXE. Tin vs. Silver

10000

0.1

10

1

100

Sn (%) Figure4.22Tin and silver in the Umm al-Nar Period objects analyzed by PIXE. One high-silver outlier i s not shown.

As illustrated in Figure 4.23, the elemental correlations found by the PCA of the compositional data and the ranked data show similar patterns to those presented in the previous section. The relative proximity of arsenic, nickel, cobalt and antimony on both scattergrams in Figure 4.23 indicates a strong correlation between these elements. This correlation is likely to reflect mineralogical issues related to the ores used to produce the copper in the objects, an issue that will be discussed in detail in the following chapter. The strong negative correlations between copper, tin, and nickellarsenic are indicated by the large distances between these elements on the PCA scattergrams in Figure 4.23. These elements form the points of a triangle on the PCA plots, representing the three most common alloy types found within the assemblage;

Results of Compositional Analyses

99

Element Loadings (concentrations)

-0.2

0

0.2

0.4

0.6

0.8

1

PC1 Element Loadings

(ranked data)

0.8

1

I

Figure4.23 Element Correlations as found in a PCA of the unmodified PlXE compositional data (top) and of the PlXE data converted t o rank-order (bottom). 0.7

0.6 0.5 0.4

A TA2677 A TA28 16

ATell Abraq

TA2435A

Figure 4.24 PCA scattergram of untransformed PlXE data for objects from Tell Abraq and AI Sufouh.The distribution of tinbronzes and AsINi-copper objects corresponds to the element loadings illustrated in Figure 4.23 (top).

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Early Metallurgy of the Persian Gulf

pure copper, copper with significant amounts of arsenic andlor nickel (AsINi-copper), and copper with significant amounts of tin (tin-bronze). The object distributions on the PCA scattergrams reflect these element relationships, as shown in Figure 4.24; A1 Sufouh objects are distributed along the horizontal axis (PC1) from relatively pure copper samples to high arsenic and nickel alloys (ASI-3), while objects from Tell Abraq are largely arrayed along the vertical axis (PC2) from relatively pure copper objects to tin-bronzes with high tin contents (TA2435, TA2816, TA2677). This pattern is replicated in the PCA of ranked data from A1 Sufouh and Tell Abraq (see below, Figure 4.25B). Relationships Between Archaeological Assemblages In addition to the investigation of relationships between elements in a compositional dataset, PCA can also be used to investigate the similarities and differences in the compositional properties of assemblages of metal objects. For each of the PCAs conducted in the previous section, a specific location in multivariate space was calculated for every analyzed object, as it was for every element. Plotting individual objects in terms of pairs of principal components can provide a "map" of the multivariate distribution of groups. Direct comparison can be made between group locations and compositional characteristics, if element scores are plotted on the same chart or an immediately adjacent one (e.g. Benton 1996:Figures 111, 113). This allows similarity or divergence in the multivariate distribution of assemblages to be assessed in terms of the presence or absence of specific elements. The multivariate distribution of the analyzed Umm al-Nar Period objects is illustrated in Figure 4.25. The elemental distribution is presented in Figure 4.25A7 with the location of each object in this multi-dimensional space indicated by a gray circle. In Figure 4.25 (B and C), the objects from each site are presented (note the different scale of these plots). The scattergrams indicate that the metal objects from Tell Abraq and A1 Sufouh are relatively distinct in terms of their overall composition. By comparison with Figure 4.25A, these differences in composition revolve largely around the concentrations of CO, Sb, Ni, and As, which are found in higher concentrations in the A1 Sufouh material, and tin and silver, and found in much higher concentrations in the

Tell Abraq objects (see above, Tables 4.5-4.23). An exception to this difference is TA2135, a high As/Ni/Fe "lump" which plots with the A1 Sufouh objects in Figure 4.25B. It is possible that the chronological separation of the two assemblages may explain their compositional divergence: A1 Sufouh is the earliest tomb assemblage analyzed, while Tell Abraq is the latest. While the objects from A1 Sufouh and Tell Abraq appear to have quite different compositions, the material from the Unarl and Unar2 tomb assemblages is much more difficult to separate compositionally, and also shares compositional similarities with Tell Abraq and A1 Sufouh objects (see Figure 4.25C). It is notable, however, that a high proportion of objects from Unar2 fall into the bottom right quadrant of the PCA plots in Figure 4.25, along with five objects from Tell Abraq and only one each from Unarl and A1 Sufouh. These objects are generally tinbronzes, characterized by relatively high lead and arsenic concentrations, and occasionally high silver levels. As the PCA plots suggest, this kind of bronze is found with particular frequency at Unar2. Separate PCAs performed on the subsets of copper objects and tin-bronze objects were also undertaken. As can be seen in Figure 4.26, very few consistent compositional differences can be seen between copper objects from each of the four tomb assemblages, although as noted above, Tell Abraq and A1 Sufouh objects show relatively distinct minor and trace element patterns. In contrast, it appears that tin-bronzes from Unarl, Unar2, and Tell Abraq are made from compositionally distinct material. As illustrated in Figure 4.27, Unarl tin-bronzes are quite distinct from those of Tell Abraq, and examination of the element loadings for this PCA would suggest that sulfur, iron and cobalt are present in higher concentrations in the Unarl tin-bronzes, whereas tin and silver are found in higher quantities in the Tell Abraq tin-bronzes. These conclusions are verified by the compositional summaries presented in Tables 4.5-4.23 above. While some of the tin-bronzes from Unar2 have compositions similar to those from Tell Abraq or Unarl, most have a different distribution in multi-dimensional space which correlates with relatively high levels of nickel, arsenic and lead in these tin-bronzes. Again, these conclusions are supported by the previously presented compositional data summaries (Tables 4.5-4.23).

Figure 4.25 PCA scattergrams of ranked PlXE data for all Umm al-Nar Period objects, showing element and object loadings (A), and objects loadings by site (B, C). Note the different scales of plots A, B and C.

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Summary

Figure 4.26 PCA scattergrams of Umm al-Nar Period copper objects only, showing element and object loadings (top) and object loadings by site (bottom).Note the different scales of the upper and lower plots.

Figure 4.27 PCA scattergrams of Umm al-Nar Period tin-bronzes only, showing element and object loadings (top) and object loadings by site (bottom).

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An overview of the analyses of the A1 Sufouh, Unarl, Unar2 and Tell Abraq assemblages highlights a number of chronological andlor site-specific variations in metallurgical technology and alloy use. As illustrated in Figure 4.28, objects of unalloyed copper, occasionally containing significant amounts of iron and sulfur as impurities, are used throughout the archaeological sequence covered, approximately 2450-2000 BCE. The dominant alloys utilized include copper with one to six percent arsenic andlor one to 3.5 percent nickel (AsINi-copper), and copper with more than two percent tin (tin-bronze). AsINi-copper is particularly prominent in the earlier Umm al-Nar objects from A1 Sufouh, but appears in all four tomb assemblages studied. Of the 26 AsINi-copper objects recorded during analysis ( 3 1 percent of the total assemblage), 11 contained both arsenic and nickel in quantities of greater than one percent, 15 contained copper with only arsenic in excess of one percent, and one object contained only nickel in excess of one percent. Statistical analyses of bivariate and multivariate elemental associations indicate that arsenic and nickel are highly correlated in the analyzed objects, suggesting a mineralogical association which will be discussed further in the following chapter. Additionally, mineralogical factors probably underlie the relationships between arseniclnickel and the trace elements cobalt and antimony, which were clearly observed in the statistical analyses. Tin-bronze objects were also found in all tomb assemblages, although in contrast to AsINi-copper, tinbronze appears gradually over the course of the later third millennium BCE (see Figure 4.28). A few tinbronzes with low tin concentrations are recorded at A1 Sufouh and Unarl, whereas very high frequencies of tinbronze use (50-60 percent of objects) are observed in the latest Umm al-Nar assemblages from Unar2 and Tell Abraq. The increase in the frequency of tin-bronze use in the tomb assemblages was accompanied by an increase in the concentration of tin in the bronzes themselves. The tin-bronzes are also characterized by higher levels of silver than contemporary copper and AsINicopper samples, and by higher lead concentrations in the case of Unar2 tin-bronzes.

A number of objects, particularly from the Unar2 tomb, are ternary alloys with significant concentrations of both tin and arsenic. Interestingly, given the high correlation between arsenic and nickel in the analyzed objects, a nickel concentration of more than one percent was reported in only one tin-bronze object, from the A1 Sufouh tomb. Other complex alloys are rare, but include two objects with one to two percent lead (a thin arsenical copper fragment and a tin-bronze ring) and a tinbronze ring from Unar2 with 2.4 percent arsenic and 2.3 percent silver. Principal components analyses of the collected PIXE compositional data indicate that the strongest compositional differences between individual tomb assemblages are between material from A1 Sufouh (very few tinbronzes and relatively high concentrations of arsenic, nickel, cobalt and antimony) and Tell Abraq (numerous tin-bronzes, relatively high silver concentrations, and low concentrations of As, Ni, CO and Sb). Given that these are, respectively, the earliest and latest Umm alNar tomb assemblages analyzed, a chronological factor might explain the observed compositional diversity. Material from the chronologically intermediate tomb assemblages of Unarl and Unar2 has characteristics similar to material from both A1 Sufouh and Tell Abraq, although compositional idiosyncrasies in the objects from each site are also observable. PCA of the copper objects and tin-bronzes as separate groups indicates that the copper objects from each of the tomb assemblages were relatively similar in terms of their minor and trace element compositions. In contrast, the tin-bronzes from Unarl, Unar2 and Tell Abraq were relatively distinct in terms of their overall composition, with Unarl tin-bronzes higher in sulfur and iron, Unar2 tin-bronzes higher in arsenic and lead, and Tell Abraq tin-bronzes distinguished by higher levels of silver and low cobalt concentrations. In the following chapter, the various metallurgical practices and exchange patterns that have shaped the compositional data presented here are discussed. Attention is paid particularly to the mining, smelting and alloying processes which may have facilitated the production of the AsINi-copper so prominent in the early Umm al-Nar Period objects from A1 Sufouh, and to the exchange systems which brought tin and tin-bronze

to southeastern Arabia, an area totally devoid of tin deposits. In addition, alloy use in different object categories is investigated, as a guide to the metallic properties which were most crucial to the adoption of new alloys, especially tin-bronze, in later third millennium BCE southeastern Arabia.

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A1 Sufouh

Unar2

Unar l

Tell Abraq

Figure 4.28 Alloy use in the four Umm al-Nar Period tomb assemblages.

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5

Discussion of Compositional Results

Introduction This chapter addresses the PIXE compositional data summarized in Chapter Four. Mineralogical and technological perspectives are examined to determine the nature of the ore sources that may have been exploited, and to review processes of alloy selection and manufacture. Discussion of alloying practices in the metal assemblages is relevant to elements such as tin, arsenic, and nickel that are present in amounts greater than one to two percent, although these same elements are commonly present in quantities of less than one percent and the boundary between "alloying element" and "impurity" is in some cases unclear (cf. Wertirne 1973:882). A detailed discussion of different approaches to the question of "intentionality" in alloy production is presented. Furthermore, compositional analyses of copper-base artifacts have frequently been used as the basis for discussions of provenance and reconstructions of trade patterns (e.g. Berthoud et al. 1980; Malfoy and Menu 1987). The feasibility of using "diagnostic" trace element concentrations alone to outline ore sources has been seriously questioned over the last twenty years and more (e.g. Craddock 1976:94; Gale and Stos-Gale 1982: 11; Budd et al. 1992:678; Craddock and Giumlia-Mair 1988), although elements which are more likely to be representative of provenanceasopposed to extraction o r alloying processes have been delineated by Pernicka (1999). However, as has been noted by Moorey (1982:82), "once industries had developed to the point.. .when a variety of

ores were being used under different conditions, with or without fluxes, alloys were commonplace, and the recycling of copperwork was normal practice, provenience studies depending on elemental analysis are as likely to confuse as they are to clarify the relationships of source areas and distant production centres". When the multiple factors potentially contributing to the final composition of a metal object are considered, the difficulties involved in determining provenance based purely upon compositional analysis are clear. However, compositional studies can play an important role in discussions of trade, if interpreted within a framework that allows for the complexity involved in metal extraction and object fabrication and the compositional heterogeneity of many ore sources (e.g. Budd et al. 1996). For example, basic geological considerations limit the areas in which tin deposits are likely to occur (McGeehan-Liritzis and Taylor 1987): the geology of southeastern Arabia precludes the formation of such deposits, and the use of tin in copper-base objects from this region is therefore important information for delineating the movement of tin or tin-bronze into this area. In the sections below, a number of different aspects of the PIXE data are discussed. Firstly, the significance of the iron and sulfur levels found in the samples is addressed. Subsequently, the compositional data for the two major alloy categories (arseniclnickel-copper and tinbronze) are investigated, with particular emphasis on possible techniques of production, aspects of alloy selection, and the trade in metals.

Iron and Sulfur Iron and sulfur are addressed here together because they frequently appear combined in non-metallic inclusions in copper objects as a result of the exploitation of Cu-Fe sulfides (Hauptmann et al. 1988:37; Weeks, forthcoming a), and are both impurities that are generally removed during the refining process to improve the quality of the finished object. As outlined in Chapter Four, iron concentrations in the Umm al-Nar Period objects were commonly on the order of 0.2-2.0 percent, with a mode in the 0.56-1.0 percent Fe range. Objects generally contained less than one percent sulfur, with one mode in the 0.18-0.32 percent S range and another for samples with S concentrations less than the MDL of approximately 0.1 percent S.

The iron and sulfur concentrations recorded in the PIXE samples are sometimes as high as elements like arsenic, nickel, and tin, which are treated as alloying components. However, the presence of sulfur and iron in the Umm al-Nar Period objects analyzed in this volume are likely to reflect processes other than intentional alloying. For example, Fe and S have been regarded as indicative of the ores selected (e.g. Friedman et al. 1966; Rapp 1988), the smelting technology used (Tylecote et al. 1977; CraddockandMeeks 1987; Craddockl995: 137-140) or the refining practices employed (Tylecote and Boydell 1978), and the possibility of their presence through contamination must also be considered (Craddock 1976:96). To discuss the final possibility first, it has already been clearly shown in the Chapter Four that part of the iron content in the analyzed PIXE samples probably reflects contamination after deposition. However, the amount of iron possibly contributed by contamination is unlikely to have dramatically altered the basic pattern of the iron concentrations of the analyzed samples. Both high- and low-contamination samples show iron concentrations frequently approaching one percent, with occasional objects containing significantly higher amounts. It is also unlikely that the sulfur concentrations recorded by PIXE are the result of contamination, as discussed in Chapter Four. Sulfur concentrations recorded in this study compare closely with previous studies of uncorroded metal objects from the Gulf region and can be related to the presence of numerous copper sulfide (matte) inclusions in finished objects and ingots from Bronze Age and Iron Age contexts in the Gulf (Weeks 1997; Weeks, forthcoming a, b; Prange and Hauptmann 2001; Pedersen and Buchwald 1991). Thus, although the possibility of the inclusion of contaminant iron and sulfur in the PIXE samples exists, most indicators would suggest that contamination levels were relatively low in comparison to the original Fe and S concentrations of the objects. However, such considerations create uncertainty over the reliability of the PIXE data for iron and sulfur, and the following discussion should be read with such a caveat in mind. The data for iron and sulfur are important in reconstructing a number of aspects of ancient metal use in the region, but the problems associated with their measurement in corroded samples have permitted me only a conservative interpretation.

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Iron As noted by Craddock and Meeks (1987:189), "of all the minor and trace elements regularly found in early copper, iron is the most dependent on the smelting process". Iron is frequently included in furnace charges, either as a component of the ore being smelted (e.g. chalcopyrite, bornite, or arsenopyrite) or as a flux used to aid the separation of copper from siliceous gangue (e.g. hematite). The transfer of significant amounts of this iron to the raw copper produced at the end of the smelt is controlled in part by the extraction process that is used (Craddock and Meeks 1987; Lechtman and Klein l999:5 17). Copper smelted using a slagging process (often incorporating iron-bearing fluxes), is likely to contain significant amounts of iron (experimental reconstructions have produced raw copper with from 10-50 percent Fe; see Merkel 1983, 1986). This is because iron is soluble in copper, and dissolves readily into the newlyformed copper droplets as they drain to the bottom of the furnace through the iron-rich slag (Craddock and Gale 1988:179; Craddock 1995:Figure 4.6). In contrast, "primitive" smelting procedures such as reconstructed for the Early Bronze Age of western Europe and the British Isles (Budd et al. 1992), which involved only the smelting of high-grade copper ores at lower temperatures and in a less reducing atmosphere, are likely to result in the production of copper with much lower levels of iron (Craddock and Meeks 1987:Table 1; see also Cowell 1987:99). Average iron concentrations of around 0.05 percent are characteristic of copper produced using such non-slagging extraction techniques, whereas a slagging process commonly produces iron concentrations an order of magnitude higher (Craddock 1995:139). Experiments undertaken by Lechtman and Klein (l999:5 15-5 16) also demonstrated the strong uptake of iron in smelting operations with mixed oxide, carbonate and sulfidic ores (known as "CO-smelting"),with concentrations approaching 8 percent Fe in some cases. It is an interesting feature of early metal use and trade that raw copper in ingot form frequently contained significant amounts of impurities such as iron and sulfur. The purity or otherwise of a shipment of copper was obviously of concern to those involved in the movement of this material in Bronze Age western Asia, as a number of textual references testify (Leemans 1960:36-54).

However, the refining and purification of raw copper seems generally to have been the responsibility of the metalworker who received the material at its destination, rather than the producer of the metal at its source (Moorey 1994:243, 249; Moorey et al. 1988:47; Craddock and Giumlia-Mair l988:318). Although the tendency to trade copper of highly variable quality was no doubt a problem for merchants in the late third and early second millennia in southern Mesopotamia (Oppenheim 1954; Leemans 1960:19-54), and may even have led to an occasional attempt at deception (Hauptmann 1987:Abb. 2; Weisgerber and Yule 2003), it was probably undertaken to avoid the further use of fuel in source areas with limited wood supplies, and facilitated by the ease of purification of the metal at its destination. Iron concentrations could easily be reduced to approximately 0.5 percent by the refining of the raw copper in a crucible (Craddock and Meeks 1987:192). With the addition of sand or crushed quartz to the molten metal, an iron-rich crucible slag would form and float to the surface of the metal, where it could be removed by skimming (Tylecote and Boydell 1978). Iron concentrations in copper ingots and raw copper pieces analyzed in previous studies of Gulf metallurgy are occasionally very high; in the one to four percent Fe range in Umm al-Nar Period ingots from Oman (Hauptmann 1987) and up to 10 percent Fe in ingots from the early second millennium BCE settlement of Saar on Bahrain (Weeks, forthcoming a). Such high iron levels match those of raw copper produced by extraction processes involving slag production at other sites in western Asia such as Timna (see Craddock and Giumlia-Mair l 9 8 8:Figure 182), and would have had a strongly deleterious effect on the working properties of the metal. In southeastern Arabia, a number of forms of evidence suggest that such raw copper was regularly refined prior to object fabrication. Firstly, the widespread presence of metallurgical refining debris on settlements in southeastern Arabia and on Bahrain suggests that copper refining away from areas of primary production was commonplace. For example, at the Bronze Age sites of Ra's alJinz (Cleuziou and Tosi 2000:57), Tell Abraq (Weeks 1997), Qala'at al-Bahrain (e.g. Harjlund and Andersen

1994:378) and Saar (Weeks, forthcoming a), and the Iron Age settlement of Muweilah (Weeks, forthcoming b), many hundreds of fragments of metallurgical refining waste have been recovered. The compositional data for metallurgical waste samples from these sites (Weeks 1997; Weeks, forthcoming a, b) indicate that refining was carried out primarily to remove impurities of iron and sulfur from the raw copper (see Figure 5.1). Secondly, the relatively low iron concentrations of most finished objects analyzed in this volume in comparison to data for raw copper ingots are suggestive of a refining stage between smelting and object fabrication. However, the presence of relatively high iron concentrations (in excess of approximately one percent Fe) in more than one-quarter of the analyzed objects indicates that refining may not have been rigorously practiced in the production of objects at settlements in southeastern Arabia. The experimental smelting studies of Tylecote et al. (1977) indicated that iron levels in raw copper produced from roasted sulfidic ores are much lower than in copper objects produced by direct reduction from oxide ores. The commonly posited beginning of the exploitation of massive sulfide deposits in southeastern Arabia in the Iron Age (Weisgerber 1987:145; Weisgerber 198 8:286), which probably required the introduction of the roasting techniques necessary to exclusively exploit such ores, may be reflected in the lower Fe concentrations in Iron Age samples analyzed in previous studies.

Figure 5.1 Iron and sulfur levels in finished objects from AI Sufouh, Unarl, Unar2, and Tell Abraq, in comparison to secondary refining waste from the later settlements of Saar (Bahrain) and Muweilah (U.A.E.).

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Sulfur As for iron, sulfur can be introduced to the furnace charge as a component of the copper ore, or through the slagging and fluxing components (Rapp 1989: 107; cf. Tylecote 1977:Table 5). A study by Rapp (1989) has suggested that the sulfur concentrations of finished objects may be a good discriminator of smelted copper as opposed to native copper, as well as potentially indicate the type of ore that was used. Rapp's research indicates that S concentrations in native copper are generally very low (on average <400 ppm), with slightly higher values recorded in oxidized copper ores like malachite and azurite (on average <1,000 ppm S), while copper smelted from sulfur-bearing ores is likely to have significantly higher S concentrations. However, other studies have suggested that the discrimination of ore type based on sulfur and other trace elements is not possible (Ericson et al. 1982). For example, Tylecote's (1977:Table 5) study of the sulfur concentrations of oxide and roasted sulfide ores show no significant differences between the two ore types, and a study of the compositional groupings observable in Early Bronze Age metal objects in the British Isles ignores sulfur and iron concentrations as "not significant for classification purposes" (Northover l977:69). In other instances, the use of sulfidic ores is thought to have been demonstrated by the presence of copper sulfide (matte) inclusions in copper objects, although the reliability of such a conclusion has been brought into question by the observation of matte inclusions in copper objects produced from relatively pure oxidized copper ores (Gale et al. 1985: 91-92; Charles 1980:164). Thus, the issue of determining ore types utilized in antiquity by examining the sulfur composition of contemporary finished objects is a complex one. In addition to the requirement for distinct differences in the sulfur concentrations of oxide and sulfide ores, correct attributions to ore types must also account for the effects of the: 1. Possible roasting of sulfidic ores prior to smelting to remove sulfur. 2. Sulfur content of the fluxes used during smelting. 3. Refining processes undertaken after the initial smelting. 4. Contribution of sulfur by alloying and recycling additions. 5. Possible presence of sulfur as a contaminant.

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Obviously, roasting processes which are designed either to concentrate copper-sulfides and oxidize ironsulfides (partial roasting), or to convert copper-sulfides to oxides (dead-roasting) will affect the amount of sulfur in the final metal. Significant contributions of sulfur by fluxing agents have been noted in the smelting and trace element partitioning studies undertaken by Tylecote (1977:Table 5; Tylecote et al. 1977), while almost all newly-smelted copper produced from a slagging process is likely to have required refining to reduce its iron content (see above). These refining operations will also have significantly reduced the sulfur concentration of the finished metal object (Tylecote et al. 1977:330). When added to the further unknown sulfur contribution of alloying components (e.g. Charles 1980:164) and the possible inclusion of recycled material of uncertain composition, attempts to determine ore type based on sulfur levels can be seen to face the same problems which have confounded metal provenance studies based only on compositional data. In a southeastern Arabian context, determining whether the sulfur concentrations in the analyzed PIXE samples represent the use of oxide or sulfide ores is an issue of little concern. The high sulfur levels (from approximately 0.2-1.2 percent) in copper ingots from Maysar 1 result from the presence of matte inclusions (consisting of nearly pure Cu2S) in the objects, which are demonstrated to have resulted from the use of sulfurbearing ores as well as oxide ores in the smelting charge (i.e. CO-smelting)already by the third millennium BCE (Hauptmann et al. 1988:36-37). The composition of the matte in the Maysar 1 ingots probably indicates that sulfur-bearing ores with a low iron concentration (chiefly brochantite) were selected for use (however, see Lechtman and Klein 1999, for smelting experiments with high-Fe charges that produced copper with no iron-bearing matte inclusions). Very large matte inclusions of relatively pure copper sulfide have also been observed in copper ingots from the Early Dilmun settlement of Saar (Weeks, forthcoming a:Figure 3). The occasional occurrence of copper ingots with high levels of iron and sulfur is thought to reflect instances where ores with higher iron contents have been smelted, with both the iron and sulfur present in the metal as matte inclusions (Hauptmann et al. 1988:36-37).

Matte inclusions have been observed in finished objects from the region, particularly at Tell Abraq (Pedersen and Buchwald 1991:7; Weeks 1997:Figures 34-36), and are likely to account for the majority of the sulfur and at least part of the iron present in the finished objects analyzed by PIXE. The high sulfur content of the Umm al-Nar Period objects thus results from the smelting of mixed oxide and sulfur-bearing copper ores, and the incomplete separation of metallic copper from the matte which was also produced during the one-step smelting process employed in southeastern Arabia in the Bronze Age (Hauptmann 1985). A comparison of Fe and S concentrations in finished objects and secondary refining waste is illustrated in Figure 5.1, and suggests raw copper produced in southeastern Arabia was refined prior to object fabrication principally to remove such iron and sulfur impurities. The high levels of iron seen in many of the analyzed samples cannot be accounted for purely by the presence of iron-rich matte inclusions (as proposed by Hauptmann et al. 1988:37). As described above, iron-bearing fluxes can contribute a significant amount of metallic iron to the raw copper produced during a smelt.

Arsenic, Nickel and Cobalt As noted in the previous chapter, nickel and arsenic occur frequently in the copper-base objects analyzed in this volume at concentrations of approximately one to five percent, and occasionally higher. Cobalt levels in finished objects are commonly in the range of 0-0.3 percent, with a few objects containing more than 0.5 percent Co. The results of the PIXE analyses concur with previous analyses of material from southeastern Arabia, and more generally with analyses of early metal objects from both the Old and New Worlds. Enormous numbers of analyses of copper-base objects have clearly indicated that in many areas of Europe, Asia and the Americas copper objects with significant levels of arsenic and other elements such as antimony and nickel were a feature of early metallurgy (as even a cursory glance at the literature will reveal, e.g. Cheng and Schwitter 1957; Charles 1967, 1980; Junghans et al. 1968; Branigan 1974:71-76; Eaton and McKerrell 1976:Figure 9; Eaton 1977; Heskel and Lamberg-Karlovsky 1980; Moorey 1982:87, 1994:250-251; Agrawal 1984; Cowell 1987;

Malfoy and Menu 1987; Hosler 1988, 1995; Lechtman 1988, 1996; Lechtman and Klein 1999; Chernykh 1992; Riederer 1994; Lahiri 1995:Figure 2; Tadmor et al. 1995; Hauptmann 1995; Montero Fenoll6s 1997:13-15). In the following sections, the data for As, Ni and CO concentrations in the objects analyzed in this volume are discussed in relation to data from southeastern Arabia and elsewhere. The possible mineralogical and technological reasons for the production and use of high-AsINi objects are investigated, in addition to explanations for the chronological variation in As, Ni and CO concentrations. Mineralogy: Associations of Arsenic, Nickel, Cobalt and Copper in Ore Deposits "In both the Old World.. .and the Americas, copperarsenic alloys were produced over a vast area, from Russia to Great Britain and from Chile to Mexico. This production was made possible by the relatively large number of metallic mineral species that contain arsenic, by their geological CO-occurrencewith ores of copper, and by the widespread association of these ores in the earth's crust" (Lechtman 1996:477). As the passage above suggests, the widespread production and use of copper with As concentrations of greater than approximately one percent is at least partly related to the mineralogy of the copper deposits which were exploited in antiquity. A similar explanation is likely to be an important factor in the appearance of high levels of elements such as antimony, nickel and cobalt in some early copper-base objects. Ores containing arsenic, antimony, nickel and cobalt can be found associated with copper in the oxidized, enriched and primary ore zones of many weathered ore deposits (Charles 1985:25; Pigott 1999a, 1999b). For example, arsenopyrite (FeAsS) is virtually ubiquitous in the primary unweathered zone of many copper deposits (Rutley 1988:250), including those in Peru used by the early metal producers of the Andean culture area (Lechtman 1988:356; 1996:478). Antimony and arsenic are often concentrated in the secondary enriched zone of copper deposits as copper sulfarsenides, where they form a mineralogical series from tennantite (Cul2As4SI3)to tetrahedrite (Cu12Sb4S13) (Dana 1958:454; Tadmor et al. 1995; Shalev et al. 1992; Lechtman 1988, 1996), as found in a number of copper

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Rapp, these last two minerals could account for the occamines in eastern Turkey and Iran (e.g. Zwicker sional high Ni or CO concentrations of arsenical copper. 1977:106; 1989). Such ores are likely to weather to Moreover, Budd et al. (1992:680; also Budd 1993:36) malachite and azurite and other complex oxides of copnote the visual similarity of copper arsenates (including per, arsenic and antimony that are present in the upper nickel-bearing species) and more common copper mineroxidized zone of many copper deposits (Lechtman als such as malachite, and suggest that such minerals are 1996:477; Rapp 1988:25; Budd et al. 1992:680; Charles likely to have been inadvertently incorporated into the 1985:25). smelting charge (see also Charles 1980:168-1 69). To give a relevant example of the mineralogical Thus, an understanding of the mineralogy of the association of copper with elements such as As, Sb, Ni copper deposits of southeastern Arabia is of crucial and CO, the Talmessi mine in the Anarak region of Iran importance in determining the metal products that might has been described as follows: be extracted from them. Predictably, most modern geoAn extraordinary assemblage of primary and logical research has focused upon the geochemistry and secondary minerals has been identified at the mineralogy of the massive sulfide copper deposits in the Talmessi mine, including primary copper, Sultanate of Oman. In contrast, archaeometallurgical nickel and cobalt arsenides (algonodite, research has highlighted the importance of copper domeykite, nickeline, rammelsbergite, safdeposits from lower in the ophiolitic sequence and the flonite, skutterudite), native copper, chalmineralogical differences between these ores and the cocite, and concretionary pitchblende. In massive sulfide deposits. more or less intimate association are the less Although there is significant mineralogical variation abundant sulfides (pyrite, galena, sphalerite, between each of the major massive sulfide copper bornite, covellite, chalcopyrite) and cuprite" deposits in southeastern Arabia (i.e. Lasail, Bayda, 'Arja (Bariand et al. 1993:464). and Raki), the levels of As, Sb and Ni in these deposits In addition to this collection of minerals, native copper, are generally very low. The 'Arja deposit has higher relanickel and cobalt have been recorded at Talmessi, and tive As concentrations than either Lasail or Bayda (Ixer the nearby Meskani mine has similar mineralization et al. 1984:B122), and contains minor concentrations of (Bariand et al. 1993:464; see also Heskel and Lambergtennantite with compositions very close to the tennantite Karlovsky 1980; Pigott 1999a, 1999b). end-member of the tennantite-tetrahedrite series (Ixer et Studies of early metallurgy have attempted to outal. 1986:42). While Ni and As levels are lower at Lasail line which kinds of ores were the most likely to have and Bayda (c250 ppm), these deposits have higher CO been exploited to produce copper with significant quanconcentrations of up to approximately 550 ppm (Ixer et tities of As, Sb, Ni or other elements. For objects from al. 1984:B118; cf. Goettler et al. 1976:49 for similar patthe Chalcolithic Nahal Mishmar hoard, for example, terns; Batchelor 1992:B116). At Lasail, CO, Ni and As high As and Sb concentrations, correlations between As, occur within the minor quantities of carrolite that are Sb, Ag and Bi concentrations, and the presence of Cufound in the chalcopyrite and within zoned pyrite (Ixer Sb-As-sulfide inclusions in the objects are clear evidence et al. l984:Bll8). Arsenopyrite and enargite (Cu3AsS4) for the use of sulfidic ores of the fahlerz type in their are present in trace quantities at Raki, but not at Lasail, production (Tadmor et al. 1995:131-132; Shalev et al. Bayda and 'Arja (Lescuyer et al. 1988:499 and Table 1). 1992:69). Other scholars have stressed the technological The use of rich fahlerz ores for copper production in complexity of extracting copper from sulfidic ores, and southeastern Arabia is extremely unlikely, as zones of proposed that arsenates from the oxidized zone of ore secondary enrichment are not reported from any of the deposits are more likely to have been the basis of early major massive sulfide deposits (Hauptmann 1985:25). arsenical coppers. Rapp (1988:25) l'ists numerous arsenates Nickel is present in minor amounts in all iron- and copwhich occur with copper in Europe, Russia, western Asia phases in all the massive sulfide deposits and elsewhere, including erythrite ( C O ~ ( A S O ~ ) ~ . ~ H ~ Oper-bearing ) (Ixer et al. 1986:43). and annabergite (Ni3(As04)2.8H20).According to

110

Early Metallurgy of the Persian Gulf

In contrast, the oxidized copper deposits of the lower crustal and mantle sequences of the Semail ophiolite, which are exceptionally abundant in comparison to other ophiolites (Lorand l 9 8 8:68), show much higher concentrations of Ni, As and Co. As noted by Hauptmann et al. ( l 9 88:35), nickel "is clearly concentrated with cobalt and arsenic in veins situated in peridotitic rocks (Ni up to 0.6 percent, CO up to 0.12 percent, As up to 0.2 percent)". The much higher nickel concentration of copper deposits in mantle-level rocks is indicated by the studies of Goettler et al. (197650) and Hauptmann (1985:32 and Table 2), who notes that in mantle-hosted deposits, chalcopyrite is intergrown with small amounts of cobaltite (CoAsS), loellingite (FeAs2), and other Fe-CO-Ni-As minerals and nickel silicates (Hauptmann et al. 1988:35; Hauptmann 1985:32; Prange et al. 1999:188). Hauptmann (1995:246-248) further notes that nickeline (or kupfernickel NiAs) is one of the most frequent nickel ores associated with copper ores in basic and ultrabasic plutonic rocks such as those found in southeastern Arabia, and suggests that metal produced from such deposits is likely to contain As and Ni as natural impurities (Hauptmann 1995:246-248). Furthermore, Hauptmann and Weisgerber (1980:135-1 37) note the presence of one piece of arsenic speiss at the Bronze Age site of Maysar, the composition of which suggested the exploitation of arsenic minerals such as domeykite (Cu3As), as yet undiscovered, which are nevertheless likely to have occurred in the region. This position is supported by the CO-smeltingstudies of Rostoker and Dvorak (1991), which indicate that the direct dissolution in molten copper of soluble minerals such as nickeline and dome~kiteis a feasible process for the production of nickel and arsenic alloys (cf. Heskel and LambergKarlovsky 1980). This archaeometallurgical research is supported by general geological studies, and by specific geological/mineralogical studies of ophiolite-hosted ores in southeastern Arabia and Cyprus. General studies indicate the occurrence of Ni-CO-Cu sulfides in ophiolitic serpentinites (Jankovic 1986:26) and, as noted by R. G. Thomas (personal communication 1999) "associations of As, CO, Cu and Ni are exactly what one would expect from ultramafic deposits.. .There are numerous Co-As-

sulfides and Ni-As-sulfides that oxidize to a solid solution series from erythrite to annabergite". Geological research in the Sultanate of Oman has recorded the presence of Fe-Ni-Cu sulfides in upper mantle tectonite peridotites in the Semail Ophiolite, while both primary and secondary Cu-Fe-Ni-S mineral assemblages have been found in Semail upper mantle rocks affected by serpentinization (Lorand l 9 8 8:62). These secondary Cu-Fe-Ni minerals occur only within intergranular sulfides in contact with serpentine veinlets, and include awaruite (Ni3Fe),native copper, native iron and traces of millerite (NiS) and heazlewoodite (Ni3S) (Lorand l988:62). The Ni and As-rich peridotite-hosted deposits of the Semail Ophiolite are very similar to those recorded in the Limassol Forest Plutonic Complex of the Troodos Ophiolite on Cyprus, which were probably exploited as early as the Classical or Roman periods. The Cu-Ni-CoFe sulfide mineralization of the Limassol Forest is in the form of lenses, veins and disseminations of sulfides and minor (nickel) arsenides in highly deformed and serpentinized peridotites or dunites (Panayiotou 1980: 102). Overall, it is clear that the significant quantities of As, Ni, and CO in the objects from Umm al-Nar Period tomb assemblages, and in particular the correlations between these elements, are compatible with the geological milieu of copper deposits in southeastern Arabia. However, as noted above, the potential of the PIXE analyses to confidently suggest a local provenance for the objects is limited by both archaeological and geological factors. Processes of refining, alloying, recycling, and corrosion have no doubt affected the composition of the copper-base objects since the initial extraction of their metal. Moreover, copper ores with significant As, Ni and CO concentrations are also to be found in geological contexts outside southeastern Arabia, most significantly in some of the copper deposits of the Iranian Plateau. The discussion of provenance will be resumed in Chapter Seven, where the evidence from lead isotope analyses will be introduced alongside the compositional data. Metallurgy: Properties of Copper Alloys with Arsenic and Nickel The discussion above serves to indicate that copper with relatively high levels of As, Ni and CO could have been produced (inadvertently or otherwise) from copper ores

Discussion of Compositional Results

1 11

available locally in southeastern Arabia, or from more distant sources. In discussing the alloying practices of the region, it is important to understand the properties that such copper alloys would have possessed. A significant amount of information on the properties of arsenical copper has appeared in archaeometallurgical literature over the last twenty years, and the understanding of the mechanical properties of this alloy is well advanced. The effects of other alloying elements occasionally present in quantities of approximately one to 10 percent, such as antimony and nickel, have been less thoroughly investigated. As has been noted by Lechtman (1998:84), the lack of modern industrial uses for the copperarsenic-nickel alloy has meant that metallurgists have not characterized the physical properties of this ternary alloy. The discussion of the properties of AsINi-copper is, as a result of this lacuna in research, somewhat speculative in nature. The addition of arsenic to copper in quantities of up to seven or eight weight percent allows for large improvements in ductility, and produces and alloy which can be both hot and cold worked to a significant degree without breakage (Charles 1967:24, 1985; Coghlan 1972; Northover 1989: 112). Furthermore, Charles (1967:24) notes that the improvements in workability offered by arsenical copper are most apparent in samples with high oxygen levels, similar to those which might be produced by primitive casting processes. Arsenic in concentrations of greater than one percent is also likely to improve the casting properties of the metal, by lowering the melting point of the alloy and acting as a deoxidant (Craddock 1995:291). The majority of studies examining the mechanical properties of arsenical copper have been interested in assessing the performance of the alloy against that of tin-bronze. Charles (1967:24) has stated that alloys with up to 8 percent As "can give strength and hardness equivalent to tin bronze", a conclusion supported by a number of subsequent studies (Ravich and Ryndina 1995:6; Lechtman 1996506). Within this range, Northover (1989:113) argues that arsenic concentrations of approximately two percent or less offer very little improvement over pure copper, and only alloys containing approximately four percent As or more have the significantly improved strength, toughness and casting

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Early Metallurgy of the Persian Gulf

properties typical of medium tin-bronzes. It is generally acknowledged that while tin-bronze can be work hardened to a greater extent that arsenical copper (Lechtman 1996:506), arsenical copper has greater ductility and can be worked hot or cold, whereas tin-bronze is hot-short. However, determining the exact properties of an arsenical copper alloy based upon compositional analysis is potentially complicated by a number of factors. Bulk chemical analysis cannot always be directly related to mechanical properties because the amount of arsenic in solid solution (and thus able to affect the properties of the metal) is indeterminate: up to 25 percent of the As in an object might be isolated as arsenious oxide (As2O3) (Northover 1989: 111-1 12). Additionally, mechanical and other properties of the metal, such as its physical appearance, can also be difficult determine due to the process of inverse segregation which is seen in many copper-arsenic alloys. As described by Eaton (1977: 164): "A high arsenic content imports to copper a bright silver colour, a 'silver' which indeed tarnished less readily than silver per se. On casting even a relatively low arsenic content in the copper exhibits the phenomenon of inverse segregation. In this phenomenon, a small quantity of high arsenic content copper (approximately 15-20 percent As) is forced to the surface to form a complete outer 'skin' of silvery metal". For example, analyses of surface and core samples of arsenical copper objects from the Bronze Age Levant revealed arsenic concentrations of approximately 28 percent at the surface of objects with core levels of only 4.56 percent As (Shalev 1988:Table 2). Due to the non-equilibrium conditions in which most pre-Industrial metalworking operations were undertaken, segregation begins to be a feature of cast alloys with as little as two percent As, with the resulting silver surface tarnishing to a golden colour (Northover l 9 8 9 : l l S ) . Numerous Old World examples of silvered surfaces produced by manipulating the arsenic content of objects and its tendency to segregate have been listed by Eaton and McKerrell (1976:175-177; see also Smith 1973; Craddock 1995:290-292), and comparable examples from the New World are not difficult to come by (e.g. Hosler 1995:lOO-101). In a number of cases, archaeometallurgists regard the use of silver-colored arsenical coppers as evidence for traditions in which

maximum mechanical efficiency is not the only aim of alloy production (e.g. Philip 1991:lOl). The primary archaeological examples of the effects of arsenic (and antimony) on the appearance of copper alloys are the objects from the Chalcolithic Nahal Mishmar hoard (Tadmor et al. 1995) and a number of figurines from Bronze Age Anatolian sites such as Horoztepe (Smith 1973). The effect of significant arsenic concentrations on the colour of copper is also demonstrated by a piece of metallurgical debris, perhaps a casting spill, from the Saar settlement on Bahrain, which contained approximately 20 percent As and had a very bright silver-white appearance (Weeks, forthcoming a). Nickel is likely to produce some effects in copper alloys similar to those produced by quantities of As in the one to five percent range (cf. Lechtman 1998:84), and the common association of elevated nickel levels with elevated As concentrations is highlighted by Riederer (1994:89). Cheng and Schwitter (1957:351) state that the effect of nickel as an alloying element becomes noticeable at concentrations in excess of one percent, and suggest that a copper-nickel alloy would have "proved more effective for implements and weapons than ordinary copper or bronze". From such a statement, it can be concluded that Ni could improve the strength and hardness of copper. Additionally, the common designation of Chinese and western nickelcopper alloys with approximately five to 1 5 percent Ni as "white copper" or "white metal" (Cheng and Schwitter 1957:354-358) suggests that nickel could change the appearance of copper metal, to the light or silvery colour described above for some arsenical copper samples. Modern metallographic studies of copper nickel alloys containing from two to 30 percent Ni report segregation between the alloying elements, and complete homogenization is not achievable even through repeated mechanical and thermal treatments (Copper Development Association 2003). One Umm alNar Period object from southeastern Arabia analyzed by Prange et al. (1999:189) contained 1 2 percent nickel, and was said to possess a distinctive "pale golden colour", and Lechtman (1998:84) reports that "depending upon the relative amounts of arsenic and nickel present, the alloy colour can range from pale yellow to silver".

Thus, copper-base objects from the U.A.E and the Sultanate of Oman which contain in excess of approximately one to two percent of arsenic andlor nickel are likely to have had physical properties distinctly different to those of pure copper. These properties are hard to quantify, but it is clear that As-Ni-copper would have provided a significantly better material for casting than pure copper, particularly as concentrations reached two percent A s N i or higher. Numerous studies have attested to the great ductility and workability of arsenical copper, and increases in alloy hardness are likely to be significant in the three to seven percent A s N i range. A final factor that must be considered is the appearance of these alloys. In a number of ancient production centers, alloys of copper with arsenic and nickel are known to have been used because of the changes in surface appearance that they display. The property of inverse segregation possessed by arsenical copper alloys means that objects with bulk compositions of as low as two to three percent As can have arsenic-enriched surfaces with a bright, silvery appearance. The similar manipulation of alloy colour through the addition of nickel has also been documented, although concentrations are generally in the five to 15 percent Ni range. It is likely that copper-base objects from southeastern Arabia with arsenic and nickel concentrations in excess of three to four percent were of significantly different appearance to other copper objects. Fifteen of the 50 copper objects from Umm alNar tomb contexts analyzed in this study contain more than 3 percent of combined As and Ni, with nine of these from A1 Sufouh. The special and advantageous physical properties of these objects are likely to have distinguished them from contemporary copper-base objects. Technology: Production of As-Ni-copper Alloys Two basic mechanisms for producing arsenical copper can be envisaged: the addition of arsenic or arsenic-bearing minerals to molten copper at a relatively late stage in the production process, or the smelting of a mixed furnace charge bearing both copper and arsenic minerals (or combined copper-arsenic ores such as enargite and tennantite). The first practice would suggest the intentional production of a copper-arsenic alloy, whereas smelting of mixed copper and arsenic minerals could feasibly have resulted from either the accidental or inten-

Discussionof Compositional Results

1 13

tional mixture of such ores (see Rostoker and Dvorak 1991:S, for a discussion of potential processes). Lechtman (1996:481) has stated that the production of arsenical copper in South America "was inescapable, once arsenic-bearing ores were included in the furnace or crucible charge, as they often were". However, the types of ores exploited to produce such alloys in many prehistoric metallurgical systems remain a matter of debate (Budd et al. 1992:679-680). As noted above, arsenic ores are associated with copper in both the oxidized and primary unweathered zones of many base metal deposits, and secondary enriched ores of the fahlerz type include mineral species such as enargite and tennantite which contain both copper and arsenic. The most basic reconstruction is given by Budd et al. (1992), who propose the utilization of oxidized arsenic-bearing copper ores (copper arsenates) as the basis of the production of arsenical copper in Early Bronze Age Britain, in which objects never contained more than approximately five percent As. They argue that smelting operations must have been conducted at relatively low temperatures (approximately 900 degrees C) in order to avoid the occasional production of highAs alloys. At low temperatures, As uptake is controlled by kinetic considerations rather than Cu:As ratios in the furnace charge, meaning that alloys with approximately one to five percent As will be produced (Budd et al. 1992:680). They state that "suites of arsenic and antimony-bearing oxide zone copper (11) minerals can be simply smelted, with or without common secondary copper ores such as azurite and malachite and at temperatures obtainable in the most basic furnace structures (or with no structures at all), to form copper alloys of the compositions reported for Copper and early Bronze Age metalwork from the British Isles" (Budd et al. 1992:683). A similar process is thought to explain the incorporation of Ni into copper, although the temperatures required are slightly higher (approximately 1000 degrees C) (Budd 1993:36-37). The studies by Budd et al. (1992, 1993b; see also Budd 1993:34) challenge evolutionary models of the development of metal technology and alloying practices (e.g. Wertime 1973), by explicitly claiming that early copper alloys such as arsenical copper and nickel-copper were the product of smelting methods too primitive to produce pure copper.

1 14

Early Metallurgy of the Persian Gulf

Of course, scholars working on the Early Bronze Age metallurgy of the British Isles have a particular archaeological problem to address in their reconstructions: until recently archaeological research had failed to recover any copper smelting furnaces or slag dating to this period (Craddock and Meeks 1987; Budd et al. l993b:l.S5; Craddock 1995:141-142; Northover 1999:211; O'Brien 1999a). This situation necessitated reconstructions of early metal production based on the use of very pure oxide ores of copper, which would have produced little waste material during copper extraction (Craddock and Meeks 1987: 193; Craddock l989:202). However, the recent discovery of third millennium BCE mining and extraction operations at Ross Island, southwestern Ireland, suggest that the earliest arsenical copper in Britain may have resulted from the use of exclusively sulfidic ores, although the technology of ore extraction and the possible production of slag and matte has not been investigated (O'Brien 1999a, 1999b). In contrast to Bronze Age Britain, even the earliest copper production in the third millennium BCE in southeastern Arabia produced slag (Hauptmann 1985: 113). The well documented slagging technology used at this time, and the mixtures of oxide, sulfur-containing and partly sulfidic ores that are known to have been exploited (Hauptmann 1985:ll3-114; Hauptmann et a1 1988:36), allow alternative explanations for the generation of arsenical-nickel copper alloys to be proposed. The exploitation of copper and arsenic-bearing sulfide ores (copper sulfarsenides) is generally thought to have required either: 1. The roasting of the ores, in order to convert the majority of sulfides to oxides, followed by reduction smelting, or 2. The direct smelting of the sulfide ores to matte, followed by further roasting, before a final reduction smelting. Both of these approaches would have led to a significant reduction in the amount of volatile elements (such as arsenic) which remained in the final metal product (Tylecote 19775-7; Tylecote et al. l977:33O). Thus, many scholars argue that arsenical copper is unlikely to have been produced by any smelting operation based upon sulfidic ores, as the processes of matte production and roasting would have removed most of the arsenic in

the ore prior to smelting (Tylecote et al. 1977; Budd et a1 1993b:155). Other archaeometallurgists have pointed out that slow, careful roasting of copper sulfide ores can leave up to half of the original arsenic content (Eaton 1977:164), and Lechtman and Klein (1999:498-499) report the production of an arsenical copper alloy with seven percent As through the smelting of a rich enargite ore which had been dead roasted. A further consideration with the direct smelting of sulfidic ores to matte is that almost all nickel present is lost to components which are slagged, producing a raw metal product with very low nickel concentrations (Tylecote et al. 1977). However, a number of archaeometallurgists (e.g. Lechtman and Klein 1999:499) regard the roastinglmatting process as a relatively modern technique for copper extraction that is unlikely to have been used in prehistoric contexts (cf. Tylecote 19775-7; Craddock and Gale 1988:181). They state that "there is no archaeological evidence to support the suggestion that early metalworkers produced arsenic bronze by roasting sulpharsenide ores, then direct smelting the oxide products of the roast" (1999:499). Certainly, there was no roasting of the mixed oxide and sulfur-bearing ores utilized for Bronze Age copper extraction in southeastern Arabia (see Chapter 2). As an alternative, Lechtman and Klein (1999) have investigated the possibility of producing copper-arsenic alloys by CO-smelting,i.e. smelting mixtures of copper "oxide" ores (including also the carbonate, sulfate and chloride ores of copper) and arsenic-bearing sulfide ores (sulfarsenides) of iron (e.g. arsenopyrite) and copper (e.g. enargite) (cf. Rostoker and Dvorak 1991; Rostoker et al. 1989). A mixture of oxide and sulfide ores allows sulfur, rather than carbon monoxide, to act as the reducing agent. Additionally, eliminating the roasting step dramatically reduces the opportunity for the loss of arsenic as As2O3 (Lechtman and Klein 1999:499). Their experiments produced metallic arsenical-copper ingots over a wide range of oxide-sulfarsenide ratios without the use of added fluxes or the prior roasting of the sulfide ores. Lechtman and Klein (1999:497) conclude that "the copper-arsenic alloys found in ancient artifacts could have been made easily, deliberately or accidentally, by CO-smeltingprocedures".

Lechtman and Klein stress that the required mixture of oxide and sulfide ores need not have been deliberate. As miners approach the primary ore body, "they frequently encounter ore that is partly weathered, containing mixtures of primary sulfides and oxide alteration products. Such ore constitutes a natural CO-smelting charge and would yield metallic copper or a copperarsenic alloy upon smelting" (Lechtman and Klein 1999:499-500). Indeed, unless miners deliberately discarded the darker-colored sulfides, such a mixture would have been natural (Lechtman and Klein 1999522; see also Charles 1980; Taylor 1999:25). This factor is also emphasized by Rostoker et al. (1989:85), who regard cosmelting as a critical step in the transition from the exploitation of oxide ores to sulfide ores. However, Lechtman and Klein do not only state that CO-smeltingis possible; they also suggest that the length of time over which arsenical copper was produced in the Old World indicates that CO-smeltingnaturally mixed charges must have accounted for a significant amount of total production (1999522). Furthermore, they regard their reconstruction of metallurgical practice as more feasible, archaeologically, than the use of the roasting andlor matting approach. Their study is said to demonstrate "that CO-smeltingis a straightforward and simple technology, relying on a set of procedures that departs only slightly, if at all, from those metalworkers had developed for the direct reduction smelting of oxide ores" (1999522). As these conclusions deal almost exclusively with the production of arsenical copper (and to a lesser extent antimony-copper), the observations of Cheng and Schwitter (1957:361) regarding high-nickel copper must be added: in the second millennium CE, Chinese metalworkers apparently "experienced no great difficulty in smelting a nickel-copper sulfide ore to obtain a reasonably refined, malleable, natural alloy" of nickel and copper. The process was envisioned as one of roasting followed by reduction-smelting, but there is no specific evidence to support such an assumption. Rostoker and Dvorak (1991:6) note a historical example of the successful smelting of mixed copper and nickel oxides and they suggest, based on theoretical considerations, that cosmelting of nickel-bearing oxide and sulfide ores to produce a natural Cu-Ni alloy is also feasible.

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However, the possibility must also be considered that arsenic, nickel or AsINi-bearing minerals or alloys were added to copper at a late stage of the production process intentionally to produce As-Ni-copper alloys. Native arsenic and nickel are very rare, and objects of metallic nickel or arsenic are not known from any prehistoric archaeological context (Muhly 1993a:119-120). Furthermore, there are no words for arsenic or nickel in Bronze Age written sources from western Asia, suggesting that it was unknown to the metalworkers of this period (Muhly 1993:119-120; cf. Montero Fenoll6s 1997:14 who suggests that the Sumerian term SU.GAN might refer to arsenic). Thus, the addition of metallic arsenic or nickel to molten copper, in the manner of the production of tin-bronze from metallic copper and tin, is extremely unlikely (Rapp l 9 8 8:X). Charles (1985:25) states that arsenical copper could have been produced by the addition of arsenic minerals to molten copper under charcoal, in a manner similar to the production of tin-bronze by the addition of cassiterite or stannite to molten copper (see also Charles 1978), and a similar approach using nickel minerals is feasible. Arsenic- and antimony-bearing minerals have occasionally been found on archaeological sites in the Old World, for example loellingite (FeAs2)has been recorded at an Indus Valley site (Ullah 1931b; this mineral often contains significant amounts of nickel and cobalt) and As/Sb-rich copper ores have been recorded at Norsun Tepe in eastern Anatolia (Zwicker 1977). Intentional production of arsenical copper from metallic copper and arsenic-rich minerals is hypothesized for the third millennium BCE sites of Ikiztepe on the Anatolian Black Sea coast (Gedik et al. 2002) and Poros on Crete (Doonan et al. 2002), amongst others. In Iran, the earliest arsenical copper objects have been linked with the use of two copper arsenides, algonodite ( C U ~ - ~ A and S ) domeykite (Cu3As), which occur in copper-bearing gossans in the Talmessi and Meskani mines in the Anarak district (Pigott l999a:ll2). Heskel and Lamberg-Karlovsky (1980:258-259) have argued that simple melting together of native copper and these copper arsenides in a crucible would have led to the production of arsenical copper, and they suggest that this is indeed the process that was used to produce the arsenical copper objects

1 16

Early Metallurgy of the Persian Gulf

used throughout the occupation sequence at Tepe Yahya, and perhaps at Neolithic and Chalcolithic sites across the Iranian Plateau generally (see also Pigott l999a: 112-1 13). Alternatively, it has been suggested that a form of CO-smelting,as described above, may have been important for the production of arsenical copper at Bronze Age Iranian sites such as Shahdad, Shahr-i Sokhta and Tepe Hissar, where significant amounts of slag are recorded (Pigott 1999a:114-116; 199913384-86; Hauptmann et al. 1988:46). A different mechanism is proposed by Eaton and McKerrell (1976:178; cf. Eaton 1977:164), who suggest that it would have been tiresome and unnecessary to produce a batch of arsenical copper whenever required. Rather, they posit the alloying (melting together) of copper and high-arsenic metal (up to 15 percent As) under charcoal. In support of this theory, they note the appearance high As/Sb beads and ingots from the Caucasus and Europe which could have been used for this purpose, and enter a debate on the translation of three terms from ancient texts: the Sumerian AN.NA (Akkadian: annakum, generally translated as "tin metal"); the Egyptian "d(mm(thought to denote a precious metal, perhaps electrum); and the Greek term oreichalkos (which undoubtedly means brass in Roman contexts) (Eaton and McKerrell 1976: 179-18 8). In each of these cases, Eaton and McKerrell regard the term as signifying, instead, a high-arsenic copper alloy of silvery appearance. These interpretations have been criticized on a number of points (e.g. Craddock 1978; Muhly 1978:47; 1985:279-280; Waetzoldt l 9 8 l:378; Van Lerberghe and Maes 1984). Chiefly, however, the theory fails due to the lack of archaeological evidence for the postulated high-As "master alloys" suggested by Eaton and McKerrell. They are able to list fewer examples of high As/Sb objects than even the known Bronze Age occurrences of metallic tin, and the example of the material from the Nahal Mishmar hoard which can now be added fails to support their case. The high As/Sb material found at this site was clearly worked and used separately from objects of pure local copper (Tadmor et al. 1995). Furthermore, different cuneiform terms have been suggested to refer to non-tin-bronze copper alloys (Zaccagnini 198 8).

Clearly, copper rich in arsenic andlor nickel could have been produced using a wide variety of As- and Ni-bearing ores under a range of smelting conditions. Once arsenic or nickel were included in a furnace charge, it seems likely that AsINi-copper would have been produced at some stage. One point which must be remembered is that the technology involved in producing such alloys was often unknown to the very metalworkers who were utilizing the material in contemporary metalworking centers away from areas of primary production (e.g. Healy 1978). Furthermore, the production process at the primary smelting site may also have been poorly understood (at least from a modern mineralogical perspective) and regulated by its practitioners. Intentionality? As-Ni-Copper in Southeastern Arabia Earlier in this chapter, it was shown that ores of copper, arsenic, nickel (and cobalt) are associated in mineral deposits from many parts of the world. In southeastern Arabia, ores containing arsenic and nickel seem to be particularly concentrated in the high-grade copper deposits associated with ultrabasic rocks in the mantle sequence of the Semail Ophiolite, whereas the larger massive sulfide copper deposits situated in the upper extrusive sequence of the ophiolite contain much lower concentrations of these elements. Furthermore, it was established that arsenic and nickel in concentrations of greater than approximately two percent in copper alloys would have caused significant improvements in the casting and working characteristics of copper, and that the colour of the metal would have changed from the reddish appearance of copper to a paler, silvery or golden colour as combined As and Ni concentrations reached three to four percent or higher. Various studies of early copper extraction procedures from both the Old and New Worlds have also demonstrated that arsenical copper, and very probably nickel and antimony-rich copper, could have been produced by smelting oxide ores, by smelting carefully roasted sulfidic ores, or by CO-smeltingmixtures of oxide and sulfide ores. It remains now to determine the importance of each of these factors for the development of metallurgy and alloying practices in southeastern Arabia.

From the beginning of archaeological investigation of early copper metallurgy, the question has been raised as to whether the alloys uncovered, such as arsenical copper or tin-bronze, were intentionally produced. As phrased by Northover (1989:111): There are several routes by which such compositions might have been reached, some deliberate, some more or less accidental and a consequence of the ores being used. The questions we should be asking are: were the producers and users of these coppers sufficiently aware of the properties of their metals to select particular compositions for particular tasks? Furthermore, did their metallurgical capabilities extend to the deliberate manufacture or control of those compositions? Archaeologists and scholars of ancient metallurgy have gradually discovered that alloy composition could have been determined at a number of stages in the production of an object, as outlined above. Determining the intentional production of an alloy has become a complicated issue in which the definition of "intentional" is as crucial to the answer as any properties of the objects being studied. The mixing of two metallic components to form an alloy is an example of an unambiguously intentional alloying process analogous to modern practice, providing a technique against which other proposed procedures can be assessed. Mixing molten metal with other ores under charcoal also seems a clear example of intentional alloying, but how should the mixing of ores in a smelting furnace (e.g. Lechtman 1996:506) be regarded? What about the mining and collection of specific ores (e.g. Rapp 1988), or the manipulation of smelting conditions (e.g. Budd et al. 1992:680)? Additionally, metal of particular composition could have been selected after its production by examining its appearance or comparing its working properties with other alloys (Northover 1989: 115). Approaches which seek to understand prehistoric alloying processes must, therefore, account for the geological milieu from which the metals were formed, the mechanical treatment which was given to objects of particular composition, and the functional uses to which metal of that composition was put (Craddock 1995:287) in order to arrive at a sensible conclusion on the "intentionality" issue.

Discussion of Compositional Results

1 17

As an example, the occasional appearance of highnickel and high-arsenic objects in the Bronze Age Aegean has been convincingly linked by Gale et al. (1985:89-92) to the ores that were being exploited at the time. Evidence from the analysis of copper inclusions in slag samples pointed to the accidental smelting of objects with up to five percent of Ni and As. Although probably an unintentional result of ore selection processes, Gale et al. (1985:90) allowed that the properties of this accidentally-produced metal "no doubt resulted in their being selected as an especially good sort of copper for casting and cold-working to produce a tougher metal". Analyses of Bronze Age daggers from Palestine indicate the intentional manipulation of the properties of inverse segregation exhibited by arsenical copper alloys, in order to produce objects with distinctive appearances (Philip 1991).Similarly, the Nahal Mishmar hoard showed the use of unusual higharseniclantimony alloys for the production of particular object categories alongside the use of more common pure copper for other object types (Tadmor et al. 1995). In these cases, however, it remains unclear as to whether alloy selection was based upon intentional control of ores and smelting techniques, or upon the appearance and working characteristics of the metal once it had been produced. The summary of the mineralogy of southeastern Arabian copper deposits presented above suggests the possibility of arsenical-nickel copper objects being a natural product of the smelting of local ores. The PIXE analyses of objects from the U.A.E, when compared to the geological data on southeastern Arabia, suggest an extraction of the AslNi-copper from Bronze Age contexts from copper deposits in mantle-level or lowercrustal rocks of the Semail Ophiolite rather than from the large copper deposits located at the top of the ophiolitic sequence. Furthermore, the common association of As, Ni and CO ores in mantle-hosted copper deposits is mirrored in the correlations between these elements seen in the analyzed finished objects described in Chapter Four. This conclusion is completely in accord with the suggestions of Hauptmann et al. (1988:35), although it must be noted that some of the early data from Oman showed significantly higher As and Ni concentrations in

1 18

Early Metallurgy of the Persian Gulf

finished objects than in copper ingots, suggesting some form of intentional alloying (e.g. Hauptmann 1995: Abb. 1).These differences have been largely explained as resulting from either an enrichment of arsenic during later stages of object production, the lack of a database of ore and object analyses large enough to reflect the true variability of the ancient metal products of the region (Hauptmann et al. 1988: 42-46), or preferential separation of high-AsINi copper from the slag during smelting (Prange et al. 1999:190). Other possible explanations for the appearance of high As levels in southeastern Arabian copper objects, such as the use of fahlerz ores of the tennantite-tetrahedrite series, can be ruled out by the lack of such ores in southeastern Arabia, and by the very low Sb, Ag and Bi levels in the majority of samples (even those with high As levels). Of course, there are a large number of objects from the Bronze Age, in addition to the great majority of Iron Age objects (Weeks 2000a; Prange and Hauptmann 2001), which contain less than one percent of both As and Ni. The question must be asked as to whether these were produced from copper ores located in massive sulfide deposits (either primary sulfidic ores or oxidized ores from the gossan) or from copper deposits of the lower-crustal or mantle sequence which did not have high concentrations of nickel and arsenic. It seems likely that, in Bronze Age smelting operations, the use of ores with variable quantities of arsenic, nickel and cobalt could explain the appearance of copper objects containing any concentration between approximately 0.1-5.0 percent As or Ni. The As and Ni concentrations in the Umm al-Nar Period objects analyzed in this study seem to show a relatively consistent distribution across the one percent boundary (see Chapter 4, Figures 4.8 and 4.10). In contrast, it is tempting to correlate the low Fe, S, As, Ni and CO concentrations seen in the Iron Age with the first exploitation of the primary ores from the massive sulfide deposits. This chronology for the exploitation of the copper deposits of the region has already been suggested by the work of the German Mining Museum in the Sultanate of Oman (Weisgerber 1987:145; Weisgerber 1988:286), and is strongly supported by the surviving evidence for Iron Age extraction sites which are frequently found in the vicinity of massive sulfide deposits (see also

Hauptmann 1985: 116-1 17). However, new techniques of metal extraction which included one or more roasting stages could also have led to significant reduction in the arsenic content of finished objects (Tylecote et al. 1977; Budd et al. 1993b) without the utilization of new ore sources. This picture of prehistoric mining in southeastern Arabia has also been challenged by new analyses of finished objects from the region undertaken by Prange et al. (1999). These analyses indicate that arsenic and nickel concentrations were actually higher in Wadi Suq Period objects than in Umm al-Nar Period objects, and it is suggested that mining may have concentrated on massive sulfide ores in the third millennium BCE and then moved to smaller stock-work mineralizations lower in the Ophiolitic series in the first half of the second millennium BCE (Prange et al. 1999:190). However, the significant number of third millennium As/Ni-copper objects recorded in previous analytical studies from southeastern Arabia (see Chapter 4 ) indicate that such a reconstruction is not accurate. In considering this issue, it may be useful to examine the C O N ratios of the copper-base objects as determined by PIXE. Hauptmann (1985:30) has noted that CoINi ratios vary widely between the different types of copper deposits in southeastern Arabia while remaining relatively constant in both the primary and secondary minerals of a single deposit (see also Wagner et al. 1989:303). It is clear that C O N ratios are much higher in massive sulfide deposits such as Lasail and 'Arja (generally greater than 100) than in mineralized fracture zones in banded gabbros and peridotites (generally less than 1) (Hauptmann 1985:Table2). Examination of the CoINi ratios of finished copper objects can, theoretically, allow us to determine the types of local ore-bodies from which they may have been produced. The Co/Ni ratio has been used by a number of investigators to examine compositional groups, as CO and Ni are siderophile elements that are similarly partitioned in copper extraction (Seeliger et al. 1986; Hauptmann et al. 1988; Wagner et al. 1989; Pernicka 1999). However, direct comparison between artifact and ore may not be possible, as C O N ratios appear to change during the processes of alloying and corrosion (Hauptmann et al. 1988; Tylecote et al. 1977), although not necessarily during smelting.

Taking these factors into consideration, an examination of the C O I N ratios of the analyzed copper objects still produces some interesting patterns. The data are presented graphically in Weeks (2003:Figure 6), and indicate that Bronze Age copper objects exhibit a fall-off curve, with very few objects showing Co/Ni ratios of greater than one. In contrast, most copper objects from the Iron Age show much higher Co/Ni ratios, with modes in the three to five percent range and very few samples with ratios of less than two. The PIXE data certainly suggest compositional differences between copper objects from Bronze Age and Iron Age contexts, which might reflect a change in the ore bodies which were exploited in the region in the Iron Age. Previous analyses of Umm al-Nar Period material (Berthoud 1979; Hauptmann et al. 1988; Hauptmann 1995) indicate a similar concentration of copper objects with C O N ratios of less than one, which supports the hypothesis. However, it must also be noted that copper objects from Iron Age contexts, such as those from the T-shaped tomb at Bithnah (Corboud et al. 1996), have Co/Ni ratios of less than one. Thus, the conclusions to be drawn from a study of Co/Ni ratios in finished objects from southeastern Arabia are somewhat equivocal with regard to the types of ore sources that were being exploited in the Bronze and Iron Ages. It is also clear from the detailed analyses of metal extraction at Maysar 1 that copper from different types of deposits could have been collected and smelted together. For example, oxide ores, sulfur-bearing ores and sulfidic ores were available from mantle-level deposits near Maysar, in addition to copper from stockwork zones in rocks of the upper gabbroic sequence of the ophiolite which would have been mineralogically quite distinct (Hauptmann 1985:Abb. 6). In other areas with evidence for Bronze Age copper extraction, such as at Raki (Hauptmann 1985: 116), oxidized copper ores were available from the gossans of massive sulfide deposits. Hauptmann and other scholars have stated their belief that, during the Bronze Age, most of the 150 copper deposits in southeastern Arabia were being exploited (Hauptmann 1985:95; Weisgerber 1984: 198). This means that copper with widely varying compositions (and C O N ratios) should have been produced. If such is the case, the few Bronze Age copper objects with

Discussionof Compositional Results

1 19

high C O N ratios found during the PIXE analyses may represent objects manufactured using copper from the upper zones of massive sulfide deposits. However, such arguments cannot be taken too far. Regardless, it seems likely that the arsenical-nickelcopper objects produced in the Bronze Age in southeastern Arabia resulted from the use of oxide and sulfide copper ores that were frequently arsenic and nickel rich. The absolute levels of As and Ni reported by the PIXE analyses of samples support such a hypothesis, as do the lack of strong distinctions in arsenic content between AslNi-copper and unalloyed metal (cf. Balthazar 1986:62). The question remains, however, as to whether Tin vs. Nickel

Tin vs. Arsenic r

.V

6.0 A

0 UnaR

Figure 5.2 Nickel and tin (top),andarsenic and tin (bottom)concentrations in Umm al-Nar Period objects analyzed by PIXE.

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Early Metallurgy of the Persian Gulf

the ores likely to produce such copper were deliberately worked in preference to others, and whether the properties of the As-Ni-copper alloy they generated were recognized and exploited after its production. To describe alloys of this sort as "accidentally produced" may be underestimating the knowledge and intelligence of the Bronze Age metal producers of the region. A number of scholars have attempted to address the question of intentionality by examining the use of different alloy types within one metal assemblage. In particular, the use of arsenical copper and tin-bronze has been compared, and in a number of cases inverse relationships have been found (e.g. McKerrell 1978:Figure 13; Mangou and Ioannou 1997:64). In one of the early studies of the properties of these alloys, Charles (1967) concluded that high arsenic copper was intentionally produced, based in part upon strict compositional differentiation between arsenical copper and tin-bronzes, whereby tin-bronzes rarely contained significant arsenic concentrations and vice versa. Such relationships suggest that either the metalworker involved in fabricating the objects was able to recognize and separate alloys of the two kinds, or that they were created by adding arsenic or tin to relatively pure copper. An examination of the presence of arsenic and nickel in the objects analyzed in this volume presents some interesting patterns. The relationship between nickel and tin concentrations in Umm al-Nar Period objects is illustrated in Figure 5.2 (top), while the relationship between arsenic and tin concentrations is shown in Figure 5.2 (bottom). As can be seen, there is quite a strong negative relationship between tin and nickel concentrations. Objects with greater than approximately two percent tin never contain more than approximately one percent nickel, and it could be argued that these limits represent the minimum amount of tin and nickel which could be detected in a piece of metallic copper. In contrast, around onefifth of tin-bronzes contain significant amounts of arsenic (from 1-2.5 percent), with the great majority of these objects coming from the Unar2 assemblage. As it is likely that the AsN-copper used in Bronze Age southeastern Arabia was produced as a result of the ores exploited, the inverse relationship between tin and arseniclnickel concentrations suggests that some form of selection process was undertaken after the production of

the metal. Alternatively, all tin-bronze used in the region may have been obtained in its alloyed form. The trace and minor element patterns in the analyzed tin-bronzes are crucial in the investigation of this question, and they are discussed in the following section.

Tin-bronze For the purposes of this volume, a tin-bronze has been defined as a copper alloy containing more than two percent tin. Following this definition, 40 percent of objects from Umm al-Nar Period contexts analyzed in this volume are tin-bronze. Tin deposits are not known and are unlikely to occur in the basic and ultrabasic rocks which comprise the majority of the northern Oman mountains, where geological studies report tin concentrations in local rocks of the order of approximately 10 ppm or less (Hauptmann et al. l 9 8 8:3S; Cleuziou and Berthoud 1982:18). Thus, objects from southeastern Arabia with more than approximately 0.5 percent tin almost certainly include foreign metal, and the high frequency of tinbronze in the Bronze Age metal assemblages from this region represents a considerable usage of a non-local resource. In the Umm al-Nar Period material, a further 18 percent of objects contain between 0.5-2.0 percent Sn, and must therefore have included some foreign material, perhaps as part of recycling processes. Overall, perhaps 60 percent of the third millennium BCE objects analyzed in this study are likely, based on their tin concentrations, to include some foreign metal. However, the changes in object composition introduced by corrosion (see Chapter Four) make any statements regarding original tin levels in the objects uncertain. While the presence of tin-bronzes can be clearly established, and alloying practices can be tentatively reconstructed, determining the incorporation of foreign metal into locally made objects based upon the measurement of very low tin concentrations in corroded samples is not possible in this study. Archaeometallurgists and archaeologists are interested in answering a number of questions regarding the use of tin-bronze in southeastern Arabia. From a metallurgical point of view, it would be useful to know how this tin-bronze was being manufactured: whether it was a product of an alloying process using metallic copper and tin, or whether it was the product of smelting a mixed furnace charge of copper and tin ores, or whether tin ore

was added to molten copper to produce the alloy. From the perspective of archaeological trade studies, it would be interesting to know how tin was reaching southeastern Arabia: as metallic tin (to be alloyed with local copper), or as pre-alloyed bronze objects or ingots, and what the original source of the tin may have been. Furthermore, the reasons for the adoption of tin-bronze in the region and the factors, which governed its selection, and use for particular object categories are important to comprehend. These issues are discussed below, in light of evidence from the compositional analyses presented in Chapter Four. Evidence for Alloy Production Techniques: Tin Concentrations in Copper and Tin-bronze The tin concentrations of copper objects and tin-bronzes show very different patterns in Bronze Age and Iron Age objects from southeastern Arabia. As illustrated in Figure 5.3, the Umm al-Nar Period objects analyzed by PIXE show a broad range of tin concentrations, with modes at approximately one percent Sn and approximately 20 percent Sn (see also Chapter 4, Figure 4.17). Umm al-Nar Period Objects (PIXE)

lron Age Objects

Figure 5.3 Tin concentrations in Umm al-Nar Period objects analyzed by PIXE (top), and previously-analyzed lron Age objects from southeastern Arabia (bottom). Only objects containing more than 0.1 percent tin are shown.

Discussion of Compositional Results

In contrast, the Iron Age analyses reveal a very distinct mode at around 10 percent Sn, and a strong distinction between tin levels in copper objects and tin-bronzes (only six Iron Age objects contain tin in the 0.5-2.0 percent range). The technological significance of this clear difference is uncertain, but it likely reflects processes of alloy production. The control of alloy composition suggested by the Iron Age data may have been intended to impart specific physical properties to the metal, or following certain technological or cultural traditions (e.g. Lechtman 1988:346). The Iron Age compositional data further suggest that concentrations of alloying elements could be controlled, and that tin or tin ore was probably added separately to copper objects in these periods in a process of deliberate alloying. When linked with the data on the discontinuity of tin concentrations between copper and tin-bronze objects illustrated in Figure 5.3, it would seem clear that the great majority of tin-bronzes found in the northern Oman Peninsula in Iron Age contexts were intentional alloys. Furthermore, the low tin content of the Iron Age copper objects and the high tin content of contemporary tin-bronzes suggest that tin-bronze could be clearly distinguished from unalloyed copper or As/Ni-copper, and that the different types of metal were rarely mixed. Tin-bronze could have been distinguished from unalloyed copper by its working characteristics or by its appearance, which would have been more golden than raw copper, which is reddish (Swiny 1982:75; Moorey 1994:252-253; Hosler 1995). It is also likely that tin-bronze could have been distinguished from As/Ni-copper by appearance, as As/Ni-copper is likely to have been a silvery color. In contrast, the wide range of tin concentrations found in Umm al-Nar Period objects suggests less control over object composition. The common presence of tin at trace levels, at low alloying concentrations, and at very high concentrations, can be explained in a number of ways: through the smelting of mixed furnace charges with varying amounts of copper and tin minerals, through indiscriminate mixing and recycling of copper objects and tin-bronzes (attested in contemporary Mesopotamia: see Zettler 1990:Table l),or as the result of a period of experiment with the properties of tin-bronzes of varying tin concentration. Discrimination between these possibilities is not possible based purely on the evidence presented thus far.

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Early Metallurgy of the Persian Gulf

The pattern of increasing differentiation in alloy compositions through time is visible on a smaller scale within the Umm al-Nar Period objects themselves (see Chapter Four, Figure 4.16). Only one object from A1 Sufouh can be classed as tin-bronze, however roughly one third of the objects contain 0.5-2.0 percent Sn, indicating the admixture or use of foreign tin or tin-bearing metal at some point. The A1 Sufouh data suggest the availability in the region of tin-bronzes, a theory that is supported by analyses of material from the partly contemporary site of Unarl. At this site, seven objects of 18 analyzed are classified as tin-bronzes, however tin concentrations in tin-bronzes are relatively low (five of seven bronzes contain less than 1 0 percent Sn), and a further five "copper" samples contain 0.5-2.0 percent Sn. At the latest Umm al-Nar Period sites of Unar2 and Tell Abraq, tin-bronze is more common than at A1 Sufouh or Unarl, tin concentrations in samples are much higher, and there is a greater distinction between the tin content of copper and tin-bronze objects (although the distinction is not as great as in the Iron Age). Such a pattern might indicate that changes occurred in the way tin and tin-bronze was reaching southeastern Arabia within the Umm al-Nar Period, an issue that is addressed more fully in Chapter Seven. Minor and Trace Element Patterns: Guides to Alloy Production Techniques For the Iron Age, Weisgerber (1988:292) has claimed that minorltrace element patterns, specifically of nickel and arsenic, indicate that tin-bronze was being produced in southeastern Arabia by the alloying of local copper with imported tin. This is because compositional differences between Iron Age copper objects and tin-bronzes are minimal, suggesting that local copper was alloyed with relatively pure imported tin (Prange and Hauptmann 2001; Corboud et al. 1996; Weeks 2000a). As further evidence for the local production of tinbronzes in southeastern Arabia, a close link between the composition of tin-bronze and copper objects can be established by examining the chronological changes in composition in the two groups. A distinct decrease in arsenic and nickel concentrations through time is seen in copper-base objects (see Chapter Four, Tables 4.12 and 4.16), which has been explained above as probably

resulting from the exploitation of different ore deposits in southeastern Arabia. This pattern is seen for the subgroups of both tin-bronzes and copper objects, suggesting a link between the copper used to produce each of the two groups and perhaps indicating the alloying of foreign tin with local copper in the Bronze and Iron Ages. The tin ring from the Tell Abraq tomb is important within the context of this argument, as it provides clear evidence for at least some metallic tin reaching the region in the third millennium BCE. However, there is a general decrease in the amount of arsenical copper in western Asia in the second millennium BCE (Eaton and McKerrell 1976), and foreign material may be inadvertently matching compositional changes observable in local southeastern Arabian metallurgy. However, in contrast to the Iron Age analyses, there are trace and minor element differences between contemporary tin-bronzes and copper objects from the Umm al-Nar Period. Silver and perhaps lead concentrations are frequently higher in tin-bronzes than in copper objects in Umm al-Nar Period material (see Chapter Four, Figures 4.13 and 4.15), while cobalt levels are higher in copper than in tin-bronze (see Chapter Four, Figure 4.6). As discussed above, the range of arsenic and nickel concentrations in copper objects is usually higher than in tin-bronzes. Elements such as As, Ni and CO which frequently have smaller concentration ranges in tin-bronzes may reflect processes of metal selection prior to alloying, as outlined above. Arsenic, nickel and cobalt tend to be correlated in copper produced in southeastern Arabia (see Chapter Four), and the practice of alloying tin with only low AsINi local copper may be reflected also in the low CO concentration of most tin-bronzes. Alternatively, pre-alloyed tin-bronze reaching southeastern Arabia may have had naturally lower levels of As, Ni and CO than the local copper. Again, evidence from LIA will be used to address these issues in Chapter Seven. It is possible that elements that are found in higher quantities in tin-bronzes (silver and perhaps lead), were introduced with the tin during the process of alloying. The EDS analysis of the tin ring from the Tell Abraq tomb indicates more than 1.5 percent arsenic and 0.5 percent silver and copper. Cassiterite (Sn02) is associated with silver mineralization in some tin deposits (Craig

and Vaughan 1994:241), for example those of Bolivia where the tin-silver veins are associated with porphyries of hypabyssal or volcanic origin (Rutley 1988:271). Rapp (197859) also notes that silver may be a diagnostic trace element in subvolcanic tin veins related to finegrained silicic volcanic rocks, where sulfides and sulfosalts of tin and silver may be common. Higher lead and silver concentrations have also been observed in a lowtin bronze from a prehistoric copper hoard from India (Hauptmann 1989:264), with the explanation that the pattern of impurities may have resulted from the use of stannite, which sometimes occurs with galena and silver ores in hydro-thermal veins. Analyses of late Bronze Age ingots from the Mediterranean region indicate very low ( 4 0 ppm) silver concentrations (Begemann et al. 1999:Table A-l). With regard to lead, concentrations of less than 100 ppm Pb in tin ores are commonly reported (Pernicka 1995b:106), as are analyses of ancient tin ingots and objects which show no sign of lead (Maddin 1989:102; Selimkhanov 1978:Table 1; Moorey 1994:301). However, small amounts of lead are associated with tin ores in a number of geological situations (Rapp 1978; Tylecote 1978:Table 4; Gale and Stos-Gale 1985:87-88), and of the tin ingots analyzed from the Late Bronze Age shipwrecks of Ulu Burun, Hishuley Carmel and Kefar Shamir, one has 630 ppm Pb and another 220 ppm Pb (Begemann et a1 1999:Table A-l). Other analyses of tin objects from Bronze and Iron Age archaeological contexts have also revealed the occasional presence of significant amounts of lead in tin objects (Selimkhanov 1978; Muhly 1985a:279; Gale and Stos-Gale 1985:88; Yener and Ozbal 1987:220; Thornton et al. 2002a). An association between tin and lead levels in archaeological bronzes is not unique, as archaeometallurgists have also noted such a relationship in late third millennium BCE material from Daghestan (Gadzhiev and Korenevskii 1984). Thus, it would seem possible that the higher silver and lead concentrations of some of the tin-bronzes analyzed in this volume could reflect the alloying of local copper with tin containing these impurities. However, the compositional differences between copper objects and tin-bronzes offer no conclusive proof as to the techniques of alloy production used in their manufacture, as

Discussion of Compositional Results

123

compositional differences could also have resulted from the use of tin-bronze imported into southeastern Arabia in pre-alloyed form. Such pre-alloyed bronze could have arrived as finished objects or tin-bronze ingots. One example of such an ingot comes from a mid-third millennium context in Mesopotamia, probably from Tell al-Ubaid, and contains approximately nine percent Sn (Moorey 1994:252), while another tin-bronze ingot is said to come from Chanhu-Daro in the Indus Valley, although this compositional attribution is based upon surface appearance rather than laboratory analysis (Mackay 1943:187). If tin-bronze reached southeastern Arabia in the form of finished objects, it may be possible to trace the use of imported tin-bronze objects using typological studies. However, many of the tin-bronze objects analyzed in this volume are either small fragments containing no typological information or fragments of typologically non-diagnostic objects such as simple rings (see Chapter Three). Furthermore, foreign tinbronzes can be easily melted down to produce tinbronzes of distinctively local form, making typological studies redundant. In fact, it is likely that trade in both pre-alloyed bronze (objects or ingots) and in metallic tin was occurring. There is archaeological evidence from the very end of the third millennium BCE that metallic tin was reaching southeastern Arabia, as the tin ring from Tell Abraq testifies. However, the quantity of this material available to local metalworkers is unknown. The scarcity of metallic tin finds from the region is no indicator, as tin finds are scarce in all areas of western Asia in the Bronze and Iron Ages (Maddin et al. 1977:44-45; Charles 1978:25-26; Muhly 1985a; Moorey 1994:301; Lerberghe 1988:254-255), even in regions with documented imports of many tonnes of the material. A number of Mesopotamian textual sources from the third and early second millennia BCE indicate the movement of tin through the Gulf, and mention tin from Meluhha, Magan, and Dilmun (see Chapter Eight). Furthermore, there are textual references to the trade of finished tin-bronze items from Magan (Limet l972:14-17). These references suggest that the "tin trade" involved the trade of both metallic tin itself and finished tin-bronze objects.

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Early Metallurgy of the Persian Gulf

Alloy Use in Different Object Categories A number of studies have demonstrated that, in particular metalworking traditions, certain types of alloys were used for specific object categories. For example, studies of alloy use in ancient west Mexico have determined that utilitarian objects such as axes, needles and awls were made of copper containing tin and arsenic in concentrations of between two and five percent, which would have significantly increased the strength and castability of the resulting alloy (Hosler 1995:101). At the same time, high-arsenic and high-tin copper alloys (containing five to 23 percent Sn or As) were used in the production of bells (Hosler 1988, 1995). The analyses indicated that the properties of colour and sound were more important in alloy selection for bells than mechanical properties such as hardness, as the concentrations of alloying elements were much higher than required purely to optimise mechanical properties (Hosler 1995:lOl). Similar findings with regard to the use of arsenical copper objects with silver surfaces due to inverse segregation are discussed above, and emphasize the many factors which can be involved in alloy production and selection (see also Wheeler and Maddin 1980:99-100; Swiny 1982:75). In a number of works discussing the development of metallurgy, the change from the use of arsenical copper to tin-bronze has usually been seen as resulting from either: The superior mechanical properties of tinbronzes in comparison to arsenical copper (Lechtman 1996). Attempts to recreate the advantageous mechanical properties of arsenical copper once the ore bodies which had led to the inadvertent production of such alloys had been worked out (Muhly 1988; Charles 1980:176). The ability to closely control alloying proportions in tin-bronzes as opposed to the rather haphazard control envisaged for the manufacture of arsenical copper (Charles 1980: 176-177; Lechtman 1996:478). The poisonous nature of arsenic fumes that can be generated by the production and use of arsenical copper alloys (Charles 1967, 198 0, 1985).

Most of these explanations focus upon the mechanical properties of arsenical copper as opposed to tin-bronze, such as strength and toughness. However the preceding examples from west Mexico should indicate that other physical properties of metals can be important in determining the introduction and use of specific alloys. Furthermore, the use of particular types of metal can be related to economic or ideological issues as closely as to the physical properties of the metal. For example, metal production, trade, and use have been linked by a number of scholars to the display of wealth in societies with nascent stratification (e.g. Stech and Pigott 1986:41), and the widespread use of tin-bronze in the Late Horizon Inka settlements of the Andes has been associated with political processes which saw tin-bronze adopted as "the imperial alloy par excellence" (Lechtman 1996:478). The uses to which most early tin-bronze alloys were put have suggested that improved mechanical properties or ease of alloying and casting were not necessarily the most important factors in the introduction and early use of tin-bronze in western Asia (Moorey 1994:252-253; Montero Fenoll6s 1997:17). The examination of alloy use in different object categories, and metallographic evidence regarding the mechanical treatment of different kinds of alloys, are important in arriving at such conclusions regarding early alloy selection and use. In order to address similar questions in a southeastern Arabian context, where relatively pure copper, AsINi-copper and tin-bronze are used simultaneously, the data on the copper alloys used for different object categories are presented below. For the Umm al-Nar objects, alloy use in the object categories of "blades" (21 objects), "pinslawls" (nine objects), "flat fragments" (24 objects), "rings" (20 objects), and "other objects" (nine objects) are given. The category of blades includes fragments of knives, daggers and spearheads such as those found at A1 Sufouh (Benton 1996:Figures 173-186) and Tell Abraq (Chapter Three). Flat fragments could belong to knife or dagger blades, as well as to vessels or other object types. The category of "other objects" includes a number of unidentified fragments or amorphous copper-base lumps, in addition to one possible chisel from Unar2, a rivet from A1 Sufouh, and three fragments from Unarl designated as "tubes" or the like.

As can be seen in Figure 5.4, patterns of alloy use vary greatly in the different object categories analyzed. For the categories of blades and pinslawls, approximately 30 percent of objects are made of relatively pure copper, with a further 50-60 percent of AsINi-copper. Between 1 0 and 20 percent of blades and pinslawls contain significant amounts (more than two percent) of tin. Previous analyses of contemporary blades and blade fragments from Umm an-Nar Island, Hili, Jebel Hafit and Qarn Bint Saud show a similar prominence of AsINi-copper, and only one blade with more than two percent tin (Berthoud 1979; Frifelt 1975a, 1991; Hauptmann 1995). The presence of significant concentrations of zinc and lead must also be noted in some of the Umm an-Nar Island blades (Frifelt 1991:100). The three previously analyzed "needles" from Maysar and Ras al-Harnra (Hauptmann et al. 1988) are of relatively pure copper, showing a lack of tin use similar to the analyses of pinslawls undertaken in this study. In contrast, much more consistent use of tin-bronze is seen in the object categories of rings and flat fragments. Rings, in particular, are most frequently of tinbronze, sometimes containing significant levels of arsenic, lead or silver. Furthermore, four of the six rings categorized as "copper" in fact contain one to two percent tin, and may perhaps be regarded as low-tin bronzes. Tin levels in excess of one percent are thus recorded in 90 percent of analyzed rings. Interestingly, no rings are made of AslNi-copper, while about half of the tin-bronze rings contain arsenic. Previous semi-quantitative analyses of rings from third millennium BCE contexts at Tell Abraq (Weeks 1997) indicated that eight of the 14 objects contained significant amounts of tin (two containing As andlor Ni), while six were of relatively pure copper (none containing in excess of one percent As or Ni). Some of these apparent alloy choices are seen to continue into later periods. For example, tin-bronze continues to be consistently utilized to produce rings and flat fragments in the second millennium; 10 of the 1 4 analyzed Wadi Suq PeriodILate Bronze Age rings from Tell Abraq, Shimal settlement area SX, and Shimal tomb SH102 are composed of tin-bronze, as are 1 2 of 1 5 analyzed flat fragments from contemporary contexts at Tell Abraq and SH102 (Weeks 1997; Weeks 2000a).

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125

Figure 5.4. Alloy use in different object categories.

Furthermore, as tin-bronze was rarely utilized to produce pinslawls in the third millennium BCE, so the pattern continues in the second millennium: of the 12 pinslawls from Wadi SuqILate Bronze Age contexts at Tell Abraq, Shimal settlement area SX, and Masirah Site 38, only two contain significant amounts of tin (Weeks 1997,2000a; Hauptmann et al. 1988). In the Iron Age, with tin-bronze use increasing to incorporate approximately three-quarters of analyzed copper-base objects, these distinctions by artifact type are consequently diminished. Blades, arrowheads and

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heavy braceletslbangles from the IbriISelme hoard (Prange and Hauptmann 2001) and the Qidfa tomb (ImObersteg 1987; Weeks 2000a) are made almost exclusively of tin-bronze. Differences at this time seem more related to the individual site: IbriISelme and Qidfa exhibit the predominant use of tin-bronze in all object categories, whereas settlements such as Muweilah and Tell Abraq (Weeks forthcoming b; Weeks 1997) and the collective tomb assemblage from Bithnah (Corboud et al. 1996:Figure 59) show much lower frequencies of tinbronze use.

Thus, the analyses of objects from A1 Sufouh, Unarl, Unar2, and Tell Abraq suggest that tin-bronze may have been selectively used for particular object categories, reinforcing the results of previous studies of material from Tell Abraq (Weeks 1997). Furthermore, the objects most commonly of tin-bronze are rings, which have a decorative rather than utilitarian function. This may suggest that factors other than the mechanical advantages of the tin-bronze alloy were important in its selection. One such property is the surface appearance of tin-bronze, which is more golden than pure copper or As/Ni-copper. In general, the use of precious or decorative metals such as silver and tin in the manufacture of rings and bracelets in Bronze Age southeastern Arabia (Weeks 1997; Weeks 2000a), is further evidence of the association of these object categories with metals of attractive or unusual physical appearance. Additional evidence for the importance of the appearance of the tinbronze alloy is provided by the use of tin-bronze in the production of beads at the third millennium BCE site of Ra's al-Hadd in Oman (J. E. Reade, personal communication). Copper beads are not known from southeastern Arabia in the Urnm al-Nar Period, but beads of gold and silver are. Alternatively, as jewelry can act as a means of both displaying and storing wealth, the economic value of tin-bronze in comparison to copper, resulting from its scarcity and the distances over which it was obtained, may have been important in its selection for use in rings and bracelets rather than more utilitarian objects (cf. Montero Fenoll6s 1997:17).

Summary The discussion presented in this chapter focused on the impurities of iron and sulfur found in the Urnm al-Nar Period objects, and the concentrations of the potential alloying elements arsenic, nickel, and tin. The presence of sulfur and iron in the Urnm al-Nar Period objects reflects the ores that were used to produce them, the smelting technology employed, and the degree of secondary refining that the raw copper received prior to object fabrication. High sulfur concentrations in the finished objects (see Table 4.5) reflect the presence of copper sulfide (matte) inclusions in the objects. These matte inclusions resulted from the CO-smelting of oxide and sulfur-bearing ores, and the incomplete separation

of metallic copper from the matte that was produced during the typical smelting process employed in Bronze Age southeastern Arabia. The high Fe concentrations of the Urnm al-Nar Period objects (see Table 4.7) can be related in part to the sporadic inclusion of ironbearing sulfide ores in smelting charges, which would have led to the presence of Cu-Fe-S matte inclusions in the finished objects. Additionally, iron-bearing fluxes could have contributed a significant amount of metallic iron to the raw copper produced during a smelt. Such high iron and sulfur concentrations would have had a deleterious effect on the working properties of the raw copper, and a refining stage prior to fabrication (i.e. secondary refining) would have been necessary to produce satisfactory objects. A comparison of the elemental compositions of finished objects and secondary refining waste from archaeological contexts in the Gulf suggests that raw copper produced in southeastern Arabia was indeed refined prior to object fabrication principally to remove impurities of Fe and S. Arsenic and nickel are frequently found in the Urnm al-Nar Period copper-base objects analyzed in this volume at concentrations of one to five percent and occasionally higher. A review of the mineralogical, metallurgical, and technological aspects of As/Ni-copper objects in southeastern Arabia suggests that they are most likely to have been natural alloys inadvertently produced as a result of the types of ores exploited. and the smelting technology employed. Although As and Ni concentrations in the largest copper deposits in Oman, the massive sulfide deposits, are generally very low, the oxidized copper deposits of the lower crustal and mantle sequences of the Semail ophiolite show much higher concentrations of Ni and As. Copper smelted from such deposits would have contained As and Ni as natural impurities. Thus, the significant quantities of As and Ni in the Urnm al-Nar objects are compatible with a southeastern Arabian origin. However, copper ores with significant As and Ni concentrations are also found in geological contexts outside southeastern Arabia, most significantly in some of the copper deposits of the Iranian Plateau. It is therefore clear that reliable conclusions regarding absolute provenance cannot be drawn from the compositional data alone.

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These "accidental" alloys may have had some physical properties (such as hardness, colour, and ease of casting) which allowed them to be distinguished from unalloyed copper after they were produced in the primary smelt. In particular, the inverse segregation exhibited by arsenical (and perhaps nickel) copper alloys suggests that objects from A1 Sufouh with more than approximately three to four percent of combined As and Ni are likely to have had a different surface appearance than most unalloyed copper objects. The evidence for alloy use in different object categories indicates that AsNi-copper was rarely used for decorative objects such as rings, but was commonly found in more utilitarian objects such as pinslawls and blades. Such a differentiation may be indicative of the use of AsINi-copper for its mechanical advantage of hardness, but could also reflect factors such as the relative worth of other alloys like tin-bronze. The examination of the evidence for tin-bronze use in Umm al-Nar Period southeastern Arabia suggests different patterns of alloy production, exchange, and use. Previous analyses are suggestive of the trade in metallic tin to southeastern Arabia by the Iron Age. This is because there are few minorltrace element differences between copper objects and tin-bronzes at this time; there are clear distinctions between the tin content of copper objects and tin-bronzes; and tin concentrations show a normal distribution suggestive of controlled and intentional alloying. The situation for tin-bronzes from the Umm al-Nar Period is not so clear. There are significant minor and trace element differences between copper objects and tinbronzes of this period which could reflect either the alloying of local copper with imported tin or the importation of pre-alloyed bronze objects or ingots. Furthermore, there is no strong distinction between the tin content of copper and tin-bronze objects from the Umm al-Nar Period, particularly in the earlier objects from A1 Sufouh and Unarl. This may suggest that control over alloy composition was minimal, that recycling did not discriminate between alloy types, or that a wide range of tin-bronze alloys were produced for varying reasons. The latter possibility is certainly supported by "recipes" for the production of tin-bronze found in surviving cuneiform documents, which suggest great compositional variability (see Chapter Eight). Archaeological

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and textual evidence indicates that, in this period, both metallic tin and pre-alloyed tin-bronze were being traded through the Gulf. The delineation of alloying practices is complicated by the finding that there are no strict correlations between tin content and the concentrations of other minor and trace elements. For example, tin-bronzes tend to have higher silver and lead levels, but the relationship is not constant, and tin-bronzes can have very low silver and lead concentrations. Indeed, it is unlikely that compositional analyses alone will allow for questions of alloying practice to be solved, as tin and copper of varying composition from multiple sources might be involved, and there was simultaneous trade in both metallic tin and pre-alloyed tin-bronze objects. Regardless of how tin-bronze was actually produced, examination of alloy use in different object categories indicates that tin-bronze was selectively used for objects which had a decorative rather than utilitarian function. In particular, copper-base rings were almost exclusively made of tin-bronze. This suggests that factors such as the surface appearance of tin-bronze, or its greater economic value, dictated how this alloy was used in Bronze Age southeastern Arabia.

6

Lead lsotope Analysis in Archaeology

been drawn with the first applications of radiocarbon dating in archaeology, where discussions regarding basic issues of approach, interpretation and usefulness of the new technique continued over a number of decades (Muhly 1995a:54), before widespread understanding of its practical and logical limitations was achieved. Over that time, and partly as a result of the rigorous examination of its strengths and weaknesses, radiocarbon dating became a cornerstone of archaeological research, and as such it offers a hopeful parallel for the sometimes hotly debated field of archaeological LIA.

Theoretical Basis o f the Lead lsotope Technique

In Chapter Seven, results of the lead isotope analysis (LIA) of more than 40 objects from Umm al-Nar Period tombs in the U.A.E. is presented and discussed. As a background to that discussion, the technique of LIA and its application to archaeological provenance studies is discussed in this chapter. The theoretical basis of LIA and its application to geological studies is addressed first, followed by a detailed discussion of the application of LIA to archaeological questions. Issues addressed in the latter section include the potential complicating factors of isotopic variation within ore deposits, accounting for the presence of lead in bronzes and in tin and cassiterite, and the mixing and recycling of metals from more than one source. The potential significance of these factors for the LIA of material from southeastern Arabia and the Gulf is addressed. The introduction of LIA in archaeology in the 1970s was characterized by initial enthusiasm regarding the potential for addressing outstanding archaeological issues (Gale 1978; Gale and Stos-Gale 1982). This early phase was soon followed by an extended period of robust debate over problems of the interpretation of LIA data, which lasted through most of the 1980s and 1990s. The debate generated a greater degree of clarity regarding the usefulness and limitations of the technique (e.g. Budd et al. 1996; Tite 1996; Scaife et al. 1999), but its acrimonious nature had the unfortunate side effect of generating uncertainty within the broader archaeological community as to the reliability of the technique (e.g. Chippindale 1994). Comparisons to this debate have

The scientific basis of the lead isotope technique has been discussed fully by a number of scholars (see Doe 1970; Gulson 1986; Pollard and Heron 1996 for summaries). Lead isotope analysis involves the measurement and interpretation of differences in the relative abundance of the four stable isotopes of lead in a geological or archaeological sample (Gulson 1986:13). Many metals exist naturally as different isotopes, but lead is uniquely useful for geological and archaeological purposes because it has a relatively large range of natural isotopic compositions which can vary greatly from place to place across the surface of the Earth (Pollard and Herron 1996:302). The four isotopes of lead are referred to by their atomic mass number, and are known as 204Pb, 206Pb, 207Pb and 208Pb. Three of the isotopes of lead (206Pb, 207Pb and 208Pb) are the stable end products of long radioactive decay chains. In contrast, 204Pb is not generated by radioactive decay, and all the 204Pb which is found on Earth was present at the time of its formation (204Pb is actually radioactively unstable, but has an extremely long half-life of 1.4 X 1017 years and is treated as a stable reference isotope, see Faure 1977:202). The radioactive decay schemes for lead involve the elements uranium (U) and thorium (Th). In one series, 238U decays through a number of intermediaries before producing the isotope 206Pb. In a similar manner, the isotope 235U decays radioactively to form 207Pb and 232Th decays to form 208Pb (Faure 1977:Figures 12.1-3). All three isotopes of lead formed in this manner are radioactively stable, i.e. they will undergo no further decay and thus represent the end of the radioactive decay chain.

The lead generated by such decay schemes is known generally as radiogenic, to distinguish it from the 204Pb, 206Pb, 207Pb and 208Pb which was already present at the time of the formation of the earth, known as primeval or primordial lead. All lead on earth is thus a mixture of lead originally present when the earth was formed approximately 4.5 million years ago (primeval lead) and lead subsequently generated by radioactive decay (radiogenic lead) (Gulson 1986:13). In addition, the stable lead isotopes generated from the decay of uranium (206Pb and 207Pb) are often referred to as uraniumderived or uranogenic and the lead produced by the decay of thorium (208Pb) is called thorium-derived or thorogenic (Gulson 1986:25). The usefulness of lead isotope analysis for geological dating is a result of the half-lives of the three radioactive decay schemes, shown below (from Pollard and Herron 1996:312). 238U decays to 206Pb, half life = 4.468 X 109 years 235U decays to 207Pb, half life = 0.7038 X 109 years 232Th decays to 208l?b, half life = 14.01 X 109 years The half lives of the uranogenic and thorogenic lead systems are of the order of billions of years, and are thus ideal for study of rock and ore formation on a geological timescale. The lead isotope composition of rocks and ores varies on a world-wide scale, as the result of a number of processes. Differences in the concentrations of uranium, thorium and lead across the surface of the Earth occurred during its formation and cooling (Pollard and Herron 1996:313) and during the differentiation of the Earth into core, mantle and crustal components (Gariipy and Dupri 1991). Differing ratios of U/Pb and Th/Pb in different parts of the world led to differences in the production of the radiogenic isotopes of lead and hence further differentiation in lead isotope values across the planet (Gulson 1986:Ch. 2). Further differentiation has been caused by processes of ore formation, in which common lead minerals (galena) are separated from uranium and thorium, after which point the isotopic composition of the ore does not change (Pollard and Herron 1996:3 13). Lead isotope compositions of ore deposits are therefore primarily determined by the age of the deposit and the sources of the lead that they incorporate.

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This geological and geographical differentiation of lead isotope compositions forms the basis of the lead isotope technique as applied to archaeological provenance studies. Theoretically, different ore deposits should be characterized by distinct lead isotope ratios, as a result of their different ages and histories of formation. Significantly, these isotopic characteristics should be carried through to any archaeological artifacts that were produced from the ores. This means that ore deposits can be isotopically "fingerprinted", and archaeological objects with matching isotopic characteristics can be related to these specific ore bodies. The simplest case is for objects made of lead, whose isotopic signatures should be very similar to the lead ores from which they were made. However, metals such as copper also commonly contain small amounts of lead (usually less than ca. one percent), as a result of its inclusion in the copper ores from which they were made. The isotopic composition of the lead in the copper objects should also match that of the deposit from which the copper ore was mined, meaning that copper-base objects can also theoretically be provenanced using LIA. Of course, there are many examples of ore deposits that cannot be differentiated isotopically, and many factors like alloying and recycling that make the use of LIA for the purposes of archaeological provenance studies problematic. Nevertheless, the theoretical bases and assumptions of the method have proven robust, and the specifics of its application in archaeology are discussed in the remainder of the chapter. Lead isotope data are usually measured and reported as ratios rather than abundance levels, due to the nature of the measurement technique. Modern samples, (including the Tell Abraq samples analyzed in this volume), are generally measured using a technique known as thermal ionization mass spectrometry (TIMS). A description of the technique is given in Stos-Gale and Gale (1994:99-100). In the measurement of lead isotope composition using TIMS, the greatest experimental precision is achieved by measuring all the individual abundances simultaneously as ratios (Gulson 1986:15; Stos-Gale and Gale 1994:99-lOO). Abundances of individual isotopes can be calculated from the ratios, but the associated error will be greater (Pernicka 1992; Budd et al. 1993a). The samples from A1 Sufouh, Unarl and Unar2 in this

LIA study were analyzed by multi-collector inductively coupled plasma mass spectrometry (MC-ICPMS), for which details are found in Collerson et al. (2002). In geological situations, ratios are most commonly measured in regard to the non-radiogenic isotope 204Pb (e.g. Chen and Pallister 1981; Spooner and Gale 1981; Briqueu et al. 1991; Calvez and Lescuyer 1991). In such a situation, values will be reported for the ratios 206Pb/z@Pb, 207PbI204Pb and 208PbI204Pb. These ratios are used by geologists because they relate to theoretical lead evolution curves used in the calculation of model lead isotope ages for analyzed samples (e.g. Stacey and Kramers 1975; Faure 1977:Chapters 13-14; Koppel and Griinenfelder 1979). In most laboratories around the world, however, the actual ratios measured are 208Pb/206Pb, 207Pb1206Pb and 206Pb1204Pb (Gulson 1986:15 and Appendix One). For archaeological examples, where the geochronological implications of lead isotope data are generally of less significance, the latter ratios are commonly used (e.g. StosGale et al. 1997; Stos-Gale and Gale 1994; Begemann et al. 1989). For examples, see Chapter Seven, Table 7.1. For a visual representation of the data, isotope ratios are commonly plotted on bivariate graphs. The threedimensional nature of the data requires that two bivariate plots are produced to adequately assess the true distribution of a group of samples (e.g. Gale 1999:Figure 2; Budd et al. 1996:169-170). An example can be seen in Chapter 7, Figure 7.1.

LIA in Archaeology The use of LIA in archaeological research has its origins primarily in the context of provenance analysis (Brill and Wampler 1967; Grogler et al. 1966), although the possibility of authentication studies using LIA has also been raised (Gale 1978530). Geological studies of the technique had demonstrated that a large range of potential lead isotope "fingerprints" could be expected from different types of mineralization formed at different periods in the Earth's history (Gulson 1986:Figure 1.2). The existence of isotopically discrete ore fields from particular regions lead to the speculation that isotope ratios of archaeological objects could be related to these discrete fields, thus providing a provenance for the analyzed object. The transfer of the technique from geology to archaeology required a number of extra assumptions, as

the technique was to be used on objects created by humans rather than naturally produced ores. The primary assumptions were: 1. Isotope ratios remain unaffected by anthropogenic processes. 2. There was no mixing or recycling of metal from different sources. The first assumption has held up well under scientific scrutiny. While fractionation is theoretically possible (Budd et al. 1995c), experimental work indicates that in practical situations fractionation does not introduce errors of greater magnitude than the analytical precision commonly attainable in most laboratories (Barnes et al. 1978:274; Gale and Stos-Gale 1982; Pollard and Heron 1996:324-326; Oxford University Committee for Archaeology 1997). Hence, fractionation seems unlikely to be a significant confounding factor in archaeological LIA. The second assumption listed above is essentially unprovable in archaeological contexts, although a variety of circumstantial evidence has been used to justify models hypothesizing limited metal mixing and recycling in particular archaeological contexts (contrast Muhly 1985b:80-81 with Gale and Stos-Gale 1985:88-90). This issue is discussed in detail below, and its significance for isotopic studies of Bronze Age metallurgy in southeastern Arabia is specifically addressed. Archaeological LIA incorporating these two assumptions developed in a number of discrete stages. The initial research was undertaken by R. Brill and J. Wampler in the early 1960s (Wampler and Brill 1964; Brill and Wampler 1967). Their work was inspired by geological LIA, a field that had by that time a history of roughly 30 years. Early archaeological applications were limited to the study of objects that were made of lead or included large amounts of lead (such as lead glazes and glass). The results of this research were encouraging, in that lead ores from England, Greece and Spain could be isotopically differentiated, and archaeological objects known to have been produced from a particular ore body had isotopic characteristics closely matching those of their parent ores. A similar approach to the isotopic analysis of Roman lead pipes and ingots was undertaken contemporaneously by a number of Swiss scholars, who stressed the potential of the technique when combined with trace-element analyses (Grogler et al. 1966:1168).

Lead Isotope Analysis in Archaeology

13 1

Following the first application of LIA to the analysis of lead objects and lead-containing glasses and glazes, archaeological LIA programs were soon broadened to include silver ores and objects. Silver objects in the ancient world were commonly produced by cupellation from argentiferous galena (PbS), and thus retained a significant percentage of lead (Craddock 1995). This small amount of lead, a result of the composition of the ore body and simple refining procedures, would have the same isotopic characteristics as the galena ore from which the silver was extracted. A large project on Athenian silver sources was organized by scholars from the Max Planck Institut fiir Kernphysik at Heidelberg University and the Department of Geology and Mineralogy at Oxford University, and a significant number of publications on this topic appeared from the late 1970s onwards (e.g. Gale 1978, 1980; Gale et al. 1980; Gentner et al. 1978, 1979180). The analyses were able to demonstrate the importance of Laurion as a silver source for Athens, in addition to the use of a wide variety of silver sources for coinage from Aegina (Gentner et al. 1978:284). It was clear that LIA, when used as one component of a detailed research program incorporating all relevant archaeological, geological and historical evidence, could be an extremely useful technique in provenance studies. LIA of silver sources soon expanded to include material from the Bronze Age (e.g. Stos-Gale and Gale 1982), and from regions other than Attica and Siphnos (Gale and Stos-Gale 1981). The third and most important stage in the development of archaeological LIA was the realization that isotopic analyses could be used to determine the source of the copper used in copper-base objects. Attempts to analyze the variation in isotopes of copper and tin, which seem a priori more appropriate to the study of the provenance of archaeological bronzes, are either in their infancy (Woodhead et al. 1999) or have foundered on the lack of natural heterogeneity within mineral assemblages and the difficulty of differentiating natural and anthropogenic fractionation (McGill et al. 1999; Begemann et al. 1999; Yi et al. 1999). In contrast, the possibility of using LIA to study the provenance of copper and tin-bronze objects was noted from the earliest applications of the technique in archaeology (e.g. Gale

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1978:Table 2). This possibility arose from the fact that small amounts of lead remained in copper and tinbronze objects as a result of the primitive smelting and refining processes that were used to create them (Gale 1978:34; Barnes et al. 1978:274). As this remaining lead was from the copper ore itself, LIA of copper-base objects that had not been intentionally leaded could theoretically indicate the source of the copper in the object. The first paper to present data explicitly on the application of LIA to the provenance of archaeological copperbase objects appeared in 1982 (Gale and Stos-Gale 1982), and marked the beginning of a rapid expansion of the use of LIA in Old World archaeology, particularly in the eastern Mediterranean region. The importance of LIA of ancient copper-base objects arose from the fact that lead and silver occurred infrequently in most archaeological assemblages, and archaeological thought allocated less socio-economic significance to the extraction, exchange and use of these materials. In contrast, the copper trade was thought to have been "a vital factor in the socio-politico-economic organization of every Bronze Age polity" (Muhly 1995a:56; see also Renfrew 1967; Gale 1978; Sherratt 1993, 1994; Tadmor et al. 1995:145), and was regarded as worthy of intensive archaeological research. It is unsurprising that LIA of copper-base material from this region eventually came to focus upon the archaeological leit motif of this trade, the copper ox-hide ingots of the Late Bronze Age (see Stos-Gale 1989:290-292; Stos-Gale et al. 1997; Gale 1991; Budd et al. 1995a, 1995b). The complicated and sometimes heated discussion which surrounded the LIA of this category of object within the last decade (see Budd et al. 1995a, 199513; Gale and StosGale 1995; Hall 1995; Sayre et al. 1995; Muhly 1995a; Pernicka 1995a; Stos-Gale et al. 1997) reflected a growing concern with various aspects of the interpretation of lead isotope data within archaeology. This concern regarding the application of LIA in provenance studies of copper-base objects was reflected in at least two periods of intense academic debate. The first period is represented by articles from Gale and Stos-Gale (1982, 1985) and Muhly (1983, 1985b), to which can be added the work of German research teams presented by Pernicka et al. (1984), Seeliger et al. (1985), and Wagner et al. (1986). The discussion in

these articles investigated such basic issues as mixing and remelting of copper supplies, the production of intentionally leaded bronzes, the possible contribution of lead to a bronze by the addition of tin or cassiterite, and the possible role of polymetallic ore bodies as suppliers of different types of metal. The second major debate is represented by a series of articles and comments in the journal Archaeometry (Sayre et al. 1992; Gale and Stos-Gale 1992; Leese 1992; Pernicka 1992, 1993; Reedy and Reedy 1992; Budd et al. 1993a; Sayre et al. 1993; Gale and StosGale 1993). Issues discussed in this debate reflected the greater maturity of the field, particularly the development of large databases of isotopic analyses. The debate thus covered the nature of samples used to define ore fields, the statistical treatment of lead isotopic data in the removal of outliers and the delineation of ore fields, and the reliability of laboratory measurements of lead isotope ratios. Over the course of the development of LIA in archaeology, a more general discussion has also arisen regarding the legitimate aims and theoretical limitations of such research, particularly an aspect dubbed the "provenance paradigm" (Budd et al. 1996). Although the earliest lead isotope research in archaeology was conducted with the aim of determining absolute provenance for the analyzed objects, it was also realized that outlining isotopic similarities and divergences within an archaeological assemblage, without any assignation of absolute provenance, could be important in the formation of archaeological theories (Brill and Wampler 1967:72). As LIA in archaeology developed, the determination of absolute provenance for archaeological objects was embraced as the logical function of the technique, as examination of any of the analytical reports of the 1970s and 1980s will attest. This was partly a result of the optimism that surrounded the technique in the early stages of its application to archaeological problems, when the possibility of frequent and significant overlaps in ore-fields seemed minimal. However, as the body of available lead isotope data grew, the number of overlaps between ore-fields increased significantly (Pernicka et al. 1990:278), and the potential of the technique to delineate exclusively the sources of the copper used in archaeological

objects seemed to dwindle. Pernicka et al. (1990:278) went so far as to state that "we are in the very ungratifying situation that more measurements lead to more ambiguity!" The emerging difficulties and debates surrounding LIA in archaeology are a result of the growing body of data and the resultant ore-field overlaps: the search for absolute provenance has led scholars to utilize analytical techniques which contain inappropriate geological and statistical assumptions, in an effort to limit the lead isotope fields characterizing the compositional variability within ore bodies. Furthermore, the basic notion that lead isotope data allow strong negative conclusions but only weak positive assignations of source has often been overlooked. Budd et al. (1996:169) suggest that "the interpretation of lead isotope data has not taken place within a framework which reflects the true complexity either of ore deposits, or-perhaps more importantly-of metal supply and circulation in the ancient world". In proposing to move "beyond the tired old idea of provenance", Budd et al. (1996:172-173) note instances in which "detecting change in the pattern of metal procurement and use is more useful than assigning provenance". For example, studies of material from the Bronze Age Aegean sites of Poliochni and Thermi have demonstrated the potential of lead isotope studies to provide information on trade and exchange based on the diversity of lead isotope compositions found at a site (Pernicka et al. 1990:263), to posit changes in trade patterns rather than technology as explanation for changes in overall metal composition at a site (Begemann et al. 1995:123), and to suggest chronological inter-relationships between sites based upon isotopic evidence (Begemann et al. 1992:219). The power of lead isotope studies to conclusively exclude possible ore sources has been used to great (and surprising) effect in studies of early metal use in the Balkans (Pernicka et al. 1993) and southeastern Anatolia (Schmitt-Strecker et al. 1992), where presumed early use of metal from the famous mine sites of Rudna Glava and Ergani Maden respectively has been proven at least partially incorrect. The possibility for isotopic analyses to suggest similarly novel hypotheses in the context of Gulf archaeology would seem to be correspondingly high.

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Issues for Archaeological LIA in the Gulf Region In the following section, the results of geological lead isotope studies in southeastern Arabia are discussed, as they are an important resource for archaeological LIA in the region. Subsequently, general issues important in the interpretation of LIA in archaeological contexts are discussed. These include the isotopic variability of individual ore bodies and the samples used to define them, problems of mixing and recycling, the intentional addition of lead to copper-base objects, the possible contribution of lead by the tin or cassiterite used to manufacture a tinbronze, and the various approaches to displaying and summarizing isotopic data. In all cases, the specific implications of these issues for our understanding of archaeological LIA in southeastern Arabia and the Gulf are discussed. Geological Lead Isotopic Studies of the Semail Ophiolite The lead isotope characteristics of an ore deposit depend entirely upon the geological context in which that ore was formed. For this reason, a great deal of lead isotope analysis has been carried out by geologists interested in establishing the processes involved in the formation of specific ore bodies and in particular classes of ore bodies (e.g. Gulson 1986; Garikpy and Dupr6 1991).Geological research has determined many of the parameters that affect the lead isotope values for specimens from specific geological contexts. These parameters are often the basis for archaeological discussions of lead isotope data, and so the geological use and interpretation of such data is an important issue. Lead isotopic studies in the Oman Mountains have been carried out since the early 1980s and are presented and discussed in numerous papers (Tilton et al. l 9 8 1; Chen and Pallister l 9 8 1;Gale et al. l 9 8 1;Thorpe 1982; Doe 1982; Gale and Spooner 1982; Hamelin et al. 1984; 1988; Lippard et al. 1986: 134-135; Calvez and Lescuyer 1991; Briqueau et al. 1991; Stos-Gale et al. 1997; 103-105). In Oman, analyses have included rock and mineral samples from all the major strata of the Semail Ophiolite, as well as from copper-bearing massive sulfides in the upper volcanic sequence at such important ancient mining sites as Lasail, Bayda and 'Arja. The conclusions drawn from this collected data relate to the mechanisms by which the Semail Ophiolite

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was formed, and the geological time and context of its formation. The early uranium-lead isotopic study by Tilton et al. (1981) established an age for the ophiolite of approximately 95 million years, while Chen and Pallister (1981:2699) concluded, based on comparisons with LIA of samples from mid-ocean ridge basalts (MORB), that the ophiolite was formed from oceanic mantle magma at an oceanic spreading center. Furthermore, lead isotope data for Fe-Cu sulfides from Lasail, Bayda and 'Arja suggested that sulfide ore formation in the upper levels of the ophiolite occurred near the paleo-spreading axis, and involved hydrothermal activity only within the oceanic crust (Chen and Pallister l 9 8 1:27O7). That is, there was no incorporation of radiogenic lead from continental crust sediments during ore genesis. In contrast, the lead isotope analysis of serpentinized peridotite from the mantle sequence of the ophiolite and a galena sample from below the ophiolite nappe suggested that radiogenic lead (from either a continental area or oceanic sediments) could have been incorporated into samples as part of serpentinization or galena-forming processes (Chen and Pallister 1981:2707 'These early lead isotope studies consistently indicated a difference between the isotopic characteristics of the Semail Ophiolite and the Troodos Ophiolite of Cyprus (Hamelin et al. 1984, 1988). In the Semail Ophiolite, there was significant homogeneity in the lead isotope characteristics of sulfides, rocks and sediments, whereas Troodos isotopic compositions were heterogenous and included more radiogenic lead (Hamelin et al. l 9 8 8:229). Differing geodynamic processes were suggested to explain this discrepancy (Hamelin et al. 1988:229). However, more recent lead isotope programs in the Oman Peninsula have changed this picture (Figure 6.1). Analysis of ore samples from sulfide deposits and pelagic sediments associated with two distinct volcanic episodes (V1 and V2) has suggested that "the overall interpretation of the isotopic compositions of the sulphides of the Samail nappe mineralization as being restricted to typical MORB values ...needs to be revised, as does the accepted isotopic distinction between the Samail and Troodos ophiolites and the geodynamic inferences that this implied" (Calvez and Lescuyer 1991:396).

The isotopic data have obvious significance for archaeological studies, even though most of the geological samples analyzed were not copper ores, and some came from different parts of the deposit than those which host the copper. Research has demonstrated that there is no systematic difference between the lead isotope composition of various parts of an ore body (e.g. the gossan, oxidized zone, secondary-enrichment zone or unweathered zone) or between particular minerals in a deposit (Begemann et al. 1989:273-274; Gale and Stos-Gale 1993:256; Pernicka 1993:260; although see Ixer 1999 for a rare, but archaeologically-relevant example of mineral paragenesis at the Great Orme mine in Wales). It follows that the isotopic analyses of pyrite or galena samples from Oman are quite acceptable in the definition of a lead isotope ore-field to examine copper production, as long as they are from the same ore deposit. Based on the geological studies, the range of lead isotopic compositions that might have been expected to characterize copper produced from the massive-sulfide deposits of the A1 Hajjar Mountains has been increased to include more radiogenic values. Secondly, the new data from Oman significantly overlap isotopic data for the copper ore deposits of Cyprus (contra Stos-Gale et al. 1997) and the Taurus Mountains (Yener et al. 1991). While this overlap is of limited significance for archaeological LIA in the Gulf, the discrimination of the use of Omani, Cypriot and Anatolian copper in areas such as Mesopotamia may be compromised. The archaeological significance of the geological LIA from Oman is discussed further in the following sections. Isotopic Variability in Omani Ore Deposits Early archaeological studies incorporating LIA suggested that individual ore deposits should have either a small linearly-related isotopic distribution, representing a "secondary isochron" on an isotopic plot (Gale 1978:537), or a very limited isotopic range (Barnes et al. 1974:6; Gale 1978540). The latter ore bodies are the so-called "conformable deposits" (Faure 1977:235-237; Gulson 1986:30), i.e. ore deposits which were formed at the same time as their host rocks, and which have an isotopic variation of only 0.3-0.5 percent (e.g. Begemann et a1 1989:273-275; Pernicka et

al. 1993:29; Stos-Gale and Gale 1994: 100). Linear arrays in lead isotope data for ore deposits represent "anomalous" or "multi-stage" leads, which have more complicated formation histories (Faure 1977:Chapter 14). A belief in the general conformity of Cypriot copper ore deposits underlies recent efforts to determine the isotopic fingerprint of individual Cypriot mines as opposed to a general "Cypriot field" (Gale 1999; StosGale et al. 1997; Gale and Stos-Gale 1992:314). As stated by Gale ( l 9 9 9 : l l l ) , "the concept of a lead isotope field for a single deposit is useful for the majority of uranium-poor deposits in the Mediterranean region ...the extension of the concept to an island, or a geographical region, is fraught with difficulties". The isotopic spread of the combined Cypriot lead isotope data (approximately two percent) is too large to represent a single conformable deposit, and conceals a more detailed isotopic structure defined by individual mines with very restricted isotopic compositions probably reflecting their conformable nature (Stos-Gale et al. 1997:86). This realization is significant for archaeological LIA in Oman, where copper deposits occur in a virtually identical geological context to those of Cyprus.

Figure 6.1 Lead isotope data for massive sulfide deposits from Oman, in comparison to mid-ocean ridge basalts (MORB).Coastal V1 sites: Lasail, Bayda,'Arja, Daris 1 and Zuha. InlandV1 sites: Raki and Hayl as-SafiLV2 sites: Daris 2 and Maqa'il. MORB boundaries after Hamelin et al. (1988).

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As illustrated in Figure 6.1, the accumulated body of geological lead isotope data from southeastern Arabia indicates a relatively broad range of lead isotope compositions for the copper-bearing massive sulfide deposits of the Semail Ophiolite, with at least two distinct fields (Calvez and Lescuyer 1991). Clearly, the isotopic variation in the Omani ores is the result of numerous conformable deposits, andlor the existence of deposits with anomalous lead isotope characteristics. An examination of the isotopic variability of individual ore deposits from Oman (see Figure 6.2) indicates that ores from the 'Arja mine show a very limited isotopic variation, compatible with a conformable deposit, while the Raki mine has a slightly larger variation which might indicate anomalous leads, and the A1 Ajal deposit has a clearly anomalous linear isotopic signature. Although only a few analyses of material from Daris 1 and Daris 2 have been undertaken (two samples each), they show limited isotopic variability compatible with conformable deposits, whereas ores from Bayda, Lasail and Hay1 as-Safil (two samples each) show anomalous lead isotope characteristics (Calvez and Lescuyer 1991; Stos-Gale et al. 1997). The geological lead isotope studies of ores from the Semail Ophiolite discussed above have recently been supplemented by LIA of ores, processing debris, and artifacts from the Sultanate of Oman undertaken

Figure 6.2 The isotopic variability of copper ores from individual ore deposits in Oman. An ellipse showing isotopic variation of approximately 0.5 percent, the theoretical limit of a conformable deposit, is illustrated in the top left corner.

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e x p licit l y for the purposes of archaeological research. The analyses conducted by Prange et al. (1999:191 and Figure 7) are not fully published, but present data in graphical form on the isotopic characteristics of 16 ore samples from copper deposits in the Semail Ophiolite. The data are reproduced in Figure 6.3, along with the geological isotope data for massive sulfide deposits from the Semail Ophiolite and the A1 Ajal copper-gold deposit. The latter ore deposit is geologically distinct from the Semail Ophiolite, being hosted by significantly older Late Permian rocks of the Hawasina series. The new ore analyses are significant in that they provide a second demonstration (after Calvez and Lescuyer 1991) of "a more complicated formation of ore deposits in the Oman mountain range than previously estimated" (Prange et al. 1999:191). The range of isotopic compositions which characterize copper ores from Oman, and which could potentially characterize Bronze Age copper produced in the region, has been expanded significantly by this research. However, the lead isotope database for Omani copper ores is, as it stands, far from complete. Small deposits from mantle and lower crustal formations of the Semail Ophiolite (see Chapter Two) are poorly characterized, even allowing for the fact that some of the ore analyses presented by Prange et al. 1999 may be from such contexts. Although non-economic in modern terms, such ores were vital to early copper production in southeastern Arabia (see Chapters Two and Five). Additionally, there are no lead isotope analyses of copper ores from Masirah Island, off the southeastern coast of Oman, which are known to have been exploited from at least the early second millennium BCE (Weisgerber 1988, 1991a; Hauptmann 1985:Abb 3). These ores are ophiolite-hosted, and were originally thought to represent a part of the Semail Ophiolite. However, recent geological research has determined that the Masirah Ophiolite is genetically unrelated to the mainland ophiolite (see Chapter Two), and copper from the Masirah Ophiolite is likely to have a different range of lead isotope ratios than that seen for the Semail Ophiolite (Nagler and Frei 1994). Finally, very small copper deposits located within a number of geological units that underlie the Semail Ophiolite (see Chapter Two) remain largely unanalyzed.

The potential importance of these smaller southeast Arabian copper deposits is clear from previous LIA of Bronze Age copper objects from Oman (Prange et al. 1999:Figure 7), the U.A.E (Weeks 1999) and Bahrain (Weeks, forthcoming a), as illustrated in Figure 6.4. While copper objects from late third and early second millennium BCE contexts display a relatively limited range of isotopic compositions (represented by the ellipse drawn on Figure 6.4), contemporary copper ingots from Tell Abraq, Saar and Oman show a much greater isotopic variation and a different distribution. Furthermore, the isotopic composition of at least half of the ingots is incompatible with any of the ores currently analyzed (Prange et al. 1999; Calvez and Lescuyer 1991; Stos-Gale et al. 1997). Comparisons can be drawn with a group of metal samples from Sardinia analyzed by Begemann et al. (2001:Figures 11-13). Like a number of the Gulf ingots, Sardinian objects from the Nuraghe Albuccio hoard show depleted levels of thorogenic 20*Pb, inconsistent with known local or nearby ore sources. Begemann et al. (2001:73) have suggested that such isotopic characteristics are a feature of lead "from a magma source with the lower-than-average thorium/uranium ratio typical of deep-seated magmas". As noted by Prange et al. (1999:191), at the moment it is impossible to determine whether the discrepancies in the isotopic characteristics of ores, ingots and objects reflect the incomplete sampling of Omani ore deposits, or the importation into the Gulf of copper from foreign sources such as Iran or the sub-continent. Needless to say, the presence of foreign copper ingots in southeastern Arabia, the putative "copper mountain of Magan", would be a very surprising discovery with significant archaeological implications.

Figure 6.3 LIA data for copper ores from Oman. An ellipse showing isotopic variation of approximately0.5 percent, the theoretical limit of a conformable deposit, is illustrated in the top left corner.

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copper

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U Ores

Figure 6.4 Isotopic composition of Omani ores, in comparison to copper ingots and finished objects from southeastern Arabia and Bahrain.

Sources of Lead in Copper-base Objects from Southeastern Arabia In the initial stages of LIA of copper-base objects, questions were raised as to the possible intentional addition of lead to copper alloys in the Bronze Age. Lead was argued to be a ubiquitous occurrence in early copper objects, frequently occurring at levels of up to two percent and possibly as high as five to six percent purely as a result of the type of ore smelted and the refining technology used (Gale and Stos-Gale 1985:97). However, an

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intentional addition of lead would undermine one of the basic assumptions of the LIA approach to copper provenance, as the lead in the objects would be sourced rather than the copper. The vast majority of Bronze Age copper-base artifacts from the eastern Mediterranean analyzed isotopically by Gale and Stos-Gale contained less than one percent lead, and were considered extremely unlikely to have been intentionally leaded (Gale and Stos-Gale 1982:12-3; 1985:85-87). Likewise, leaded copper and bronze objects are infrequent in most areas of western Asia in the Bronze Age: very few are found in Egypt until the first millennium BCE (e.g. Cowell 1987; Mommsen et al. 1979), although they appear sporadically in the Levant, Mesopotamia and Iran as early as the fourth millennium BCE (Philip 1991:98-101; Malfoy and Menu 1987; Tallon et al. 1989:142-144; MiillerKarpe 1989:182). The determination of intentionality for leaded bronzes is a complicated question, with many parallels to the problem of defining an "intentional" tinbronze or arsenical copper alloy (see Chapter Five). Significant lead contents may be a result of ore selection and refining technology, but the possibility of deliberate addition and control of very low lead levels (e.g. Hughes et al. 1988:312-313 and Figure 174) or the effects of scrap recycling cannot be ruled out in many cases. It is generally accepted, however, that in contrast to areas such as Atlantic Europe or China, the use of leaded bronze in the ancient Near East and eastern Mediterranean was not important until the first millennium BCE (e.g. Northover 1997:328). None of the objects from A1 Sufouh, Unarl or Unar2 analyzed isotopically in this study contain in excess of one percent Pb, and median lead concentrations are less than 0.1 percent. Lead levels in the 1 7 objects from Tell Abraq analyzed by LIA are also low, even though inaccurately high Pb concentrations for some samples were reported by EDS analysis (Weeks 1997:Appendix A). Corroborative evidence comes from previous analyses of prehistoric copper-base objects from Oman and the U.A.E., which indicate only a handful of objects with more than 1 % lead before the end of the Iron Age (Craddock 1985; Corboud et al. 1996:Figure 59; Weeks 2000a, 2000b; Prange and Hauptmann 2001). Thus, the objects analyzed in this

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study are extremely unlikely to have been intentionally leaded, and those produced of un-alloyed copper should have lead isotopic signatures closely matching those of the copper ores from which they were produced. An exception to this general picture is a group of three copper-base objects from collective graves on Umm an-Nar Island (Frifelt 1975a; Frifelt 1991), which contain both elevated lead and zinc levels. The low lead concentrations seen in the PIXE-analyzed Umm al-Nar Period objects, nearly 80 percent of which contain less than 1,000 ppm Pb, are significant for this study for another reason. These objects are relatively "lead-poor" (as classified by Gale and Stos-Gale 1985), and are highly susceptible to contamination by lead of different isotopic composition coming from alloying components such as tin. The potential contribution of lead from the tin or cassiterite used in producing a tin-bronze object was first discussed by Gale and StosGale (1982:13), who suggested that tin deposits rarely contained any lead. This conclusion was subsequently questioned by Muhly (1983:216), although he was later "prepared to concede that lead is not normally to be found in cassiterite" (Muhly 1985b:80). In general, lead isotope studies in archaeology have sought to demonstrate that there is no significant contribution of lead from the tin in a tin-bronze object (e.g. Pernicka et al. 1990; Stos-Gale 1989). In support of this premise, lead concentrations in tin ores of generally less than 100 ppm are reported, as are analyses of ancient tin ingots and objects which show no sign of lead (see Chapter Five). The analyzed tin objects from early second millennium BCE contexts at Tell ed-Der show no detectable lead, although the analytical technique employed had relatively low sensitivity and results are only qualitative (Van Lerberghe and Maes 1984). However, very little analytical work has been carried out on tin objects from Bronze Age contexts in western Asia (partially because so few are known), so the full range of expected lead values for tin ingots or objects remains uncertain. Some analyses of tin objects from Bronze and Iron Age archaeological contexts have revealed the occasional presence of significant amounts of lead in tin objects (see Chapter Five). In the case of an early tin object from Egypt (Eighteenth Dynasty), the lead concentration (ca. six percent) is high enough to

raise the possibility of a tin-lead alloy (Van Lerberghe and Maes 1984:103), while a bangle from Tepe Yahya Period IVA (ca. 2000-1400 BCE) is of "proto-pewter" comprising 75 percent Pb and 25 percent Sn (Thornton et al. 2002a). Furthermore, small amounts of lead are associated with tin ores in a number of geological situations and potentially significant trace amounts of lead might therefore be expected in some tin objects. Attempts to demonstrate that tin does not contribute to the lead isotope signature of tin-bronzes (e.g. Begemann et al. 1989; Pernicka et al. 1990) have failed to account for the great variability of lead concentrations in copper and tin objects (see Stos-Gale and Gale 1994:104). With highly variable lead levels in copper, and almost certainly in tin also, no strict relationship would necessarily exist between tin levels and isotopic composition. Thus, the demonstrated lack of a relationship does not mean that lead was only coming from the copper and not the tin. In at least one instance, examination of tin and lead levels versus isotopic composition has suggested a contribution of lead from the tin, particularly in bronzes with less than 0.1 percent (1,000 ppm) lead (Gale and Stos-Gale 1985:88). More recent LIA of material from Nuragic Sardinia has also suggested the possibility of lead from tin or cassiterite affecting the isotopic composition of a tin-bronze alloy, although the lack of known tin ingots with lead concentrations high enough to cause such changes is noted (Begemann et al. 2001:66-68). This issue will be addressed in more detail in the following chapter, where the lead isotope data for material from A1 Sufouh, Unarl, Unar2, and Tell Abraq is presented and discussed. Mixing of Metal from Different Sources As noted above, one of the primary assumptions of LIA in archaeology is that metals from different sources have not been mixed together to produce an object. One exception to this rule is the alloying of tin and copper to produce bronze, where it is generally (although not always) thought that insignificant amounts of lead are contributed by the tin and LIA of such objects still indicates the source of the copper in the object (see above). The possibility of intentional production of arsenical copper through admixture of copper with arsenic-bearing ores has also been raised as a problem for LIA (Gale

and Stos-Gale 1982:13; McGeehan-Liritzis l996:162). Although the production of arsenical copper is still a debated issue, there is growing evidence to suggest that most early arsenical copper was produced (intentionally or otherwise) as a result of the admixture of copper and arsenic-bearing ores which occurred together in an ore body, andlor the primitive technology employed in extraction operations (Budd 1993). Arsenic is a common component of metal objects from Bronze Age southeastern Arabia and is found in objects from A1 Sufouh, Unarl, Unar2 and Tell Abraq in concentrations from trace levels to as high as 6 percent (see Chapter Four). Arsenic-bearing ores occur frequently in the copper deposits of the Oman Peninsula and it seems likely that, whether locally made arsenical copper was intentionally produced or not (see Chapter Five), it is unlikely to have differed in its lead isotope composition from locally produced pure copper. It has also been questioned whether ores or metal from geologically distinct sources might have been combined to produce copper ingots. This has been a significant issue for archaeological LIA in the eastern Mediterranean, as the size of the Late Bronze Age oxhide ingots (which weigh ca. 25-28 kg each), has suggested to some authors that they are too large to have been the product of one smelting operation (Budd et al. 199Sa:21). As described in Chapter Two, copper deposits exist in a number of different geological contexts within the Oman Peninsula, and a range of different ores seem to have been exploited from the third millennium BCE onwards. This can be clearly seen in the vicinity of the Umm al-Nar Period settlement at Maysar 1, where copper ores hosted in both mantle and crustal rocks can be found within walking distance of the site (Hauptmann 1985:Abb. 6). Copper from each of these deposits may have distinct lead isotope compositions. Furthermore, we know that the copper ingots produced in the settlement at Maysar are secondary products, involving the agglomeration of smaller pieces raw copper from nearby smelters (Hauptmann 1985:93). It is possible, and indeed likely, that copper mined in the neighborhood of Maysar from geologically-distinct copper ores was brought together at the settlement, smelted to produce raw copper, and subsequently remelted and refined to

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produce ingots and objects. In such a case, the lead isotope signature of the resulting ingot will be intermediate between those of its various components, and it could be difficult to relate the copper in an ingot to the ore bodies from which it was produced using LIA. This potential complication will not necessarily occur at all or even many smelting sites in southeastern Arabia, but will be difficult to isolate without further isotopic studies of mantle-level copper deposits in the region. Mixing also presents itself as a problem if a region or settlement was obtaining its metal from more than one source. For example, LIA of Greek silver coins in the eastern Mediterranean indicated that two sources (Laurion and Siphnos) were prominent, although it has been suggested that mixing of silver to produce the coinage was minimal. This position was also taken in regard to copper use in the region prior to the Iron Age. Gale and Stos-Gale (1982:17) stated: Even in the Late Bronze Age there is likely to have been a tendency to exploit to the limit the few known extensive and accessible sources of rich ores, and while they still yielded rich ore there would have been little incentive to invest time and labour in searching out other sources. The mixing problem may have been overemphasised. In reality it may reduce to the possibility of mixing of metal from only a few sources. Stos-Gale and Gale (1994:lOS) admit that "the possibility of mixing metal used in the production of ancient artifacts is a real one, and should always be taken into account when interpreting lead isotope data", but claim "strong economic and social arguments" in favor of their minimalist position (Gale and Stos-Gale 1985:90; cf. Pernicka l995a:63). Techniques for outlining mixing in lead isotope data have been applied to provenance studies in the eastern Mediterranean and Anatolia (Pernicka et al. 1984; 592-596), although their ability to actually detect instances of mixing has been questioned (Budd et al. 1995a:22). It is clear that a significant number of copper sources were simultaneously exploited in the Oman Mountains from the mid-third millennium BCE onwards (Hauptmann 1985). The geological and archaeological

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isotope studies discussed above indicate that the copper produced at these sites could have been isotopically distinct. The trade routes that allowed the distribution of this material within the Oman Peninsula are poorly known, and it is difficult to reconstruct how many different local copper sources may have been supplying northern coastal sites such as Tell Abraq, A1 Sufouh, and Shimal. Tell Abraq, for example, was very likely acting as a collection point for copper to be traded further north up the Gulf, as suggested by the large pyramidal ingot found in an early Wadi Suq context at the site, and by the role that Umm an-Nar Island filled in this capacity before the foundation of the settlement at Tell Abraq (Frifelt 1995). When the location of Tell Abraq on an important long-distance Bronze Age maritime traderoute is also taken into consideration, the possibility of metal reaching such a site from a plurality of indigenous and foreign sources, each with unknown and potentially distinct isotopic characteristics, would seem to be high.

Metal Recycling Many mixing situations are likely to have arisen not from the combining of raw copper from two or more sources, but from the recycling of scrap metal at settlements distant from primary smelting centers. This issue was discussed in the series of papers by Gale and StosGale (1985) and Muhly (1983, 1985b), and continues to be relevant to archaeological LIA (Budd et al. 1995d; Gale 1995; McGill et al. 1999; Begemann et al. 1999; Yi et al. 1999). Muhly (1983:216) discussed the existence of large "founder's hoards" of scrap metal from Late Bronze Age contexts throughout the eastern Mediterranean, and noted that the potential for significant recycling and mixing of disparate metal sources represented by these hoards required investigation. In response, a number of lines of archaeological reasoning have been used to suggest that metal recycling before the Late Bronze Age was either minimal, or would not have unduly affected the isotopic characteristics of the objects involved. It was suggested that, in Mediterranean contexts: 1. There was little recycling of metal prior to the Late Bronze Age as there are no founder's hoards known from this period (Gale and Stos-Gale 1985:90).

A number of the so-called founder's hoards were sets of possessions "overtaken by catastrophe and never subsequently salvaged" which were never intended for recycling (Gale and Stos-Gale 1985:90). Metal was removed from circulation by interment in burials rather than being recycled (Gale and Stos-Gale 1989:171). Metalwork was preferentially repaired rather than recast as this was a simpler procedure (Gale and Stos-Gale 1989:171). Even if remelting was commonplace, it was argued that it may not have introduced metal from different sources (Gale and Stos-Gale 1985:90) or else it involved the complete recycling of an individual object to produce one object of a similar size (in which case the isotopic integrity of the object would be maintained) (Stos-Gale and Gale 1994:105). While such hypotheses may have validity in certain contexts, it is difficult to overcome the simple arguments posited by Muhly (1985b:80) in support of recycling. Metal was expensive, largely because complicated technology was required to extract it from its ores and because it was commonly traded over long distances. Hence, metal was not readily discarded. When objects broke or were no longer functional, they were collected as scrap for later re-use, as relatively simple pyrotechnological processes (Tylecote 1980) allowed them to be remelted and re-cast. The recycling of metals in ancient western Asia is regarded as commonplace and unquestionable by most scholars studying the region (e.g. Moorey 1994:254 for Mesopotamia), and significant archaeological and textual evidence exists to support such beliefs (Knapp 2000: 43-45; Reiter 1999:169; Muhly 1985b:81; Zettler 1990, 1992:227-230; Chakrabarti and Lahiri 1996:157-159). The great advantage of metal over stone was that, once extracted, it could be formed and re-formed any number of times without a great loss of mass. This fundamental property existed independently of factors such as the ready availability of metal in particular archaeological contexts (cf. Gale and Stos-Gale 1985:89-90), and is likely to have transcended such economic considerations in most cases. Significantly, the reasons used

by Gale and Stos-Gale (1982:l.S-17) to suggest that copper from only a few major sources would have been used at any one site at one time (i.e. the technological complexity of smelting copper ores and the large fuel requirements) also suggest that metal recycling (with its relatively simple technology and smaller fuel requirements) would have been an economically favorable practice. Recycling is not as significant an issue in regions where metal from only one source is used over a long period of time: in such a situation, the isotopic composition of the copper-base objects will not be changed by recycling. However, as has been clearly documented in the preceding paragraphs, multiple, isotopically-heterogeneous copper sources may have supplied the Bronze Age settlements of southeastern Arabia. In such a situation, recycling can significantly complicate the interpretation of lead isotope data for archaeological objects. Quantifying the extent of recycling in the early metal industries of southeastern Arabia is as difficult as for the eastern Mediterranean example given above. The Oman Peninsula witnessed the widespread deposition of large amounts of metalwork in collective graves of Bronze Age, Iron Age and late Pre-Islamic date (Potts 1990a). The consumption of metals in this way, their removal from circulation, is in itself an argument for limited recycling, and the necessity for continued acquisition of newly-won metal. However, the need for new metal may have been ameliorated by grave robbing: it is clear that prehistoric graves in the region were frequently robbed in antiquity for the metal objects they contained, as can be seen on the rare occasions when unrobbed tombs are discovered (e.g. Potts 1990a: 383-386; Potts 2000). The so-called IbriISelme hoard, containing more than 500 copper-base and soft-stone artifacts, is interpreted as the collected plunder of an Iron Age tomb robber, and was almost certainly destined for re-melting (Weisgerber l 9 8 1:232; Hauptmann 1987:214; Yule and Weisgerber 2001). It is difficult to determine at what period after their construction the plundering of these graves may have begun. Furthermore, many excavated tombs in the region appear to have been re-used in periods much more recent than their initial construction, at which time any remaining metal artifacts were removed and presumably

Lead Isotope Analysis in Archaeology

141

re-melted. Thus, metal recycling may have resulted from both tomb robbing and tomb re-use. Most tomb re-use in southeastern Arabia seems to have occurred in the Iron Age or more recently. There is very little evidence for reuse of Hafit or Umm al-Nar tombs in the second millennium BCE (J. Benton, personal communication), but good evidence for Iron Age re-use of collective burial cairns from all preceding periods (e.g. Bibby 1970; Barker 2002; Benton and Potts n.d.). Of course, re-use and robbing can be entirely unrelated events, and assessing periods of tomb plundering based upon re-use is by no means straightforward. Yule and Weisgerber (2001:39), for example, envisage long-term and continuous tomb-robbing activities in the region, noting that "the graves of each successive Pre-Islamic period are better preserved than those of the preceding one [which] may be taken as evidence for the cumulative effects of grave robbing from early times onward". If one was to posit a general theory for the frequency of tomb-robbing for metals in the region then, for a number of reasons, the Umm al-Nar Period is likely to have witnessed considerably less than subsequent millennia. Firstly, there was very little metal to rob in tombs of the preceding Hafit Period. This does not, of course, mean that earlier or contemporary Umm al-Nar Period tombs, richer in metal grave goods, were not robbed. Secondly, a large quantity of newly-won local metal was in circulation in the later third millennium BCE, perhaps as much as a few thousand tonnes (Hauptmann 1985), which may have reduced the need for recycling. Finally, as noted above, there is very little evidence from the Umm al-Nar Period for the re-use (with associated metal acquisition) of tombs from earlier periods. In contrast, if we look at the second millennium BCE, there is very limited evidence for primary metal production in the region (see Chapter Two), even though the deposition of copper-base objects in graves continues in significant quantities. It is at least as probable that the continued use of metal for grave goods reflects a rise in tomb-robbing activities, rather than evidence of continued primary copper smelting, as is sometimes suggested (e.g. Weisgerber 1988:285). When the evidence from the Iron Age is examined, although high levels of primary copper smelting are once again documented, recycling seems very likely because of the practice of tomb re-use discussed above.

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Early Metallurgy of the Persian Gulf

Thus, a number of archaeological indices suggest that the amount of recycling undertaken in southeastern Arabia was relatively limited prior to the second millennium BCE. Nevertheless, all isotopic data must be evaluated within a framework that recognizes the basic technological and economic advantages of metal recycling over the winning of new metal. Statistical Treatment and Presentation of Lead Isotope Data Discussion has arisen on a number of issues relating to the statistical treatment of lead isotope data. In particular, concern has been expressed over the statistical determination of the extent of ore-fields, the treatment of outliers to a main isotopic distribution, and the use of multivariate statistics to further delineate ore sources with slightly overlapping isotopic composition. Essentially, the debate was divided into those research groups who favored the use of statistical analyses in the interpretation of isotopic data (e.g. Sayre et al. 1992, 1993; Stos-Gale 1989:279; Stos-Gale and Gale 1994:101), and those who argued that multivariate analyses were either unnecessary (e.g. Pernicka 1993:259) or statistically unjustified (Baxter 1999; Leese 1992:319; Cherry and Knapp 1991:lOO). The debate surrounding the statistical treatment of lead isotope data has clearly changed attitudes to the use of multivariate techniques within the field. For example, recent archaeological publications on the lead isotope characteristics of the Cypriot copper ore deposits have relied on relatively simple interpretation of bivariate scatterplots, noting that statistical approaches "may well obscure rather than help the discussion" (Stos-Gale et a 1997:9 1).A similar reliance on bivariate scatterplots is suggested by Scaife et al. (1999:127), as their proposed kernel density estimations make comparisons between data groups difficult, and are best regarded as a supplement to the simple scatterplot approach, rather than an alternative to it. In general, Scaife et a1 (1999:132) argue that complex statistical approaches in the interpretation of LIA do a disservice to both the data and the perception of LIA within the wider archaeological community: they have failed to clarify archaeological reconstructions of ancient exchange systems and have led t o a general "mystification" of the LIA technique for the general archaeological audience.

In summary, it seems clear that a basic approach in which artifacts can be assigned to ore fields visually using "nearest neighbor" procedures (Cherry and Knapp 1991:100), is the most appropriate for archaeological LIA. Such a minimal approach, whereby orefield boundaries are delineated by enveloping lines around the outer error bars for the data, will be used in this volume for its simplicity and in order to avoid the over-interpretation predicted by some researchers (Pernicka 1993; see also Gale 2001:118). A recent isotopic study of copper and lead ores from the British Isles has used just such an approach, by delineating an "England and Wales Lead Isotope Outline (EWLIO)", which proved useful for the description of patterns in isotopic data (Rohl and Needham 1998). It should also be noted that multivariate analysis is not used in geological applications of LIA, where simple bivariate plots are considered adequate for data representation and interpretation.

Summary The preceding discussion of LIA and its use in archaeology has served to highlight a number of points important to the interpretation of lead isotope data in southeastern Arabian and Gulf contexts. Firstly, conclusions from LIA of Bronze Age material from the Gulf will be limited by the incomplete isotopic characterization of all the important classes of copper deposit in the Oman Peninsula. Although the lead isotope characteristics of the massive sulfide deposits at such sites as Lasail, Bayda and 'Arja are well known, important deposits in lower levels of the Semail Ophiolite and in the Masirah Ophiolite which are known to have been worked in antiquity remain poorly characterized. Secondly, while previous compositional analyses suggest that the intentional addition of lead to copper and tin-bronze objects did not occur with any great frequency in the Gulf region until the final centuries of the first millennium BCE or later, the possible effect of lead from tin or cassiterite used to produce a tin-bronze must be considered. The lead content of copper produced in southeastern Arabia is often exceedingly low, suggesting that even small amounts of lead in tin or cassiterite could significantly perturb the lead isotope composition of a tin-bronze produced from local copper.

Thirdly, as with archaeological LIA in all prehistoric contexts, the extent of mixing and recycling within a metallurgical tradition is almost impossible to quantify. Some circumstantial evidence indicates that recycling of scrap metal may not have occurred on a significant scale in southeastern Arabia until the Wadi Suq Period or the Iron Age. However, given the broad range of geological contexts which were exploited for copper in the ancient Oman Peninsula, the collection and mixing of ores andlor raw copper from isotopically distinct local sources is a definite possibility. When the location of archaeological sites such as Tell Abraq on prominent long-distance maritime trading routes is considered, the utilization at these sites of metal from many sources becomes highly probable. Although the potential of LIA to provide information on the absolute provenance of the copper and bronze used at these sites is limited by the above considerations, its ability to generate useful and interesting archaeological hypotheses is not. A number of studies have demonstrated the potential of LIA to provide important information for reconstructing trade patterns, technological changes and even chronological relationships between neighboring sites, and it is clear that the Bronze Age Gulf data could support similar inferences. It is to these data that we will now turn.

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7

Lead Isotope Data from the Gulf L. R. Weeks K. D. Collerson

with more than a small amount of tin therefore contains a significant proportion of imported metal. The broad compositional groups used in the discussion of the LIA data are therefore determined by the concentration of tin found in the objects. Objects are divided into "copper" (less than 0.5 percent Sn), "copper-low tin" (0.5-5.0 percent Sn), and "tin-bronze" (more than 5.0 percent Sn). These divisions correspond to the three peaks in the tin concentrations of the analyzed Umm al-Nar Period objects illustrated in Figure 4.17. The groups represent metal categories which, in a southeastern Arabian context, have different a priori possibilities of representing the isotopic characteristics of local deposits.

Radiogenic Outliers in the Analyzed Umm al-Nar Period Objects Introduction The objects from A1 Sufouh, Unarl and Unar2 in this LIA study were analyzed by multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) at the Advanced Centre for Queensland University Isotope Research Excellence (ACQUIRE), Department of Earth Sciences, Queensland University, Australia. Objects from Tell Abraq were analyzed in the same laboratory, but by thermal ionization mass spectrometry (TIMS). Details of analytical techniques for MC-ICP-MS, which involve the use of thallium to correct for mass fractionation, can be found in Collerson et al. (2002), while analytical techniques for the earlier TIMS analyses can be found in Appendix One (Section 1.1.5). In the following sections, the isotopic characteristics of the objects listed in Table 7.1 are discussed according to their archaeological and chronological contexts, in addition to being divided into three broad compositional groups. The LIA discussion utilizes different alloy categories than were used for the discussion of compositiona1 results in Chapters Four and Five, where considerations were based on the likely physical properties of the alloys. Geological studies have demonstrated that tin deposits do not occur in the Oman Mountains, where tin concentrations in ore and rock samples are generally less than 10 ppm (see Chapter Five). These considerations suggest that all the tin used in southeastern Arabia must have been imported-either as metallic tin or alloyed with copper as tin-bronze, and that any object

The isotopic data from Table 7.1 is illustrated in Figure 7.1. It includes all Umm al-Nar Period objects from the tombs of A1 Sufouh, Unarl, Unar2, and from settlement and funerary contexts at Tell Abraq. The figure shows a relatively limited linear array of objects with 207PbI 206Pb ratios of 0.800-0.900, with two highly divergent outliers. These outliers, TA699 and TA1614, are tinbronzes from the Tell Abraq tomb, and possess very low 207Pb1206Pb ratios of 0.600-0.700, low 208Pb1206Pb ratios of 1.750-1.850, and very high 206Pb1204Pb ratios of 24.00-26.00. Objects with such lead isotope ratios are generally described as "radiogenic", referring to the fact that their lead isotope compositions have been affected by high levels of uranium andlor thorium in the ores from which they were smelted. Examples of the isotopic systematics of radiogenic deposits are provided by the sediment-hosted lead-zinc ores of the Mississippi Valley (Gulson 1986), while radiogenic copper deposits are found in modern Serbia (Pernicka et al. 1993:Figure 19) and north Wales (Rohl and Needham 1998:176, Pls. 14B, 15B) among other places. Two other objects illustrated in Figure 7.1 can be regarded as outliers to the main distribution. Objects M10-17 (a copper-low tin ring from Unarl) and TA107 (a tin-bronze ring from Tell Abraq) also have relatively radiogenic isotopic compositions, with 207Pb1206Pb ratios of 0.810-0.820. The fact that all of the four outhers are tin-bronze or copper-low tin is significant, as we know from geological studies that they must have

Table 7.1 Lead isotope data for objects from AI Sufouh, Unarl, Unar2, and Tell Abraq Sample

Site

Object

Major

207~bl

2 o abs.

208~b/

2 o abs.

206~bl

2 o abs.

Elements

206~b

error

206~b

error

204~b

error

ASI-2

AI Sufouh

flat fragment

Cu-As-%(low)

ASI-3

AI Sufouh

flat fragment

Cu-As-Ni-CO-%(low)

ASI-5

AI Sufouh

blade edge

CU-AS

M10-41

AI Sufouh

dagger-tanged

Cu

ASTombl d

AI Sufouh

flat fragment

Cu-%(low)-As-Ni

M10-7

Unarl

flat fragment

Cu-Sn(low)

M10-12

Unarl

flat fragment

Cu-As-Ni-Fe

M10-13~

Unarl

flat fragment

Cu-Sn

M10-17 Avg.

Unarl

ring

Cu-%(low)

M10-19

Unarl

ring

Cu-%(low)

M10-22r

Unarl

ring

Cu-Sn-Fe

M 10-38

Unarl

tu belspout

Cu

M 10-39

Unarl

flat fragment

Cu-Sn-Fe

L14N-PIN

Unarl

pinlawl

Cu-As-Ni-Fe

1014.76

Unar2

ring

Cu-Sn-As

1014.1 58

Unar2

ring

Cu-Sn-As

1018-3.93

Unar2

pinlawl

Cu-As-Fe

1018-3.99

Unar2

flat fragment

Cu-Sn-As-(Ni)

1019-3.59

Unar2

flat fragment

Cu

1019-5.71

Unar2

ring

Cu-Sn-As

1023-4.10

Unar2

ring

Cu-%-(Fe)

1019-3.105

Unar2

flat fragment

Cu-Sn-As-Fe

1019-4.1 08

Unar2

pinlawl

Cu-As-Ni

1023-2.110

Unar2

lump

Cu-Sn(low)-Fe

TA107 Avg.

Tell Abraq

ring

Cu-Sn-As-Ni

TA699 Avg.

Tell Abraq

flat fragment

Cu-Sn

TA1217

Tell Abraq

flat fragment

Cu-Sn

TA1227

Tell Abraq

flat fragment

Cu

TA1231

Tell Abraq

spearhead

Cu-Sn(low)

TA1286

Tell Abraq

flat fragment

Cu-Sn

TA 1306

Tell Abraq

flat fragment

Cu-Sn

TA1310

Tell Abraq

ring

Cu

TA1389

Tell Abraq

pinlawl

Cu-Ni-S

TA1426

Tell Abraq

flat fragment

Cu-S

TA 1428

Tell Abraq

pinlawl

Cu-Sn(low)-Fe

TA1459

Tell Abraq

pinlawl

Cu-Sn

TA1461

Tell Abraq

ring

Cu

TA 1467

Tell Abraq

ring

Cu-S-Fe

TA1612

Tell Abraq

pinlawl

Cu-As-Ni-S

TA1614 Avg.

Tell Abraq

ring

Cu-Sn-Fe

TA1648

Tell Abraq

spearhead

Cu-Sn

TA2918

Tell Abraq

ring

Sn-As ring

"Major Elementfare those present in concentrations of greater than one percent, with the exception of tin, which is denoted byUSn"(>5.0 percent tin) and "Sn (low)" (0.5-5.0 percent tin).

146

Early Metallurgy of the Persian Gulf

incorporated at least some foreign metal. The isotopic characteristics of the objects TA107, TA699, TA1614 and M10-17 make the use of this foreign metal abundantly clear, as ores with such lead isotope characteristics are not known from southeastern Arabia (see Chapter Six, Figure 6.3). Although the original provenance of these outlying objects remains uncertain, based upon the isotopic evidence it seems clear that at least some of the tin-bronze reaching Arabia in the third millennium BCE was imported as finished objects, or locally made from imported metal arriving pre-alloyed as tin-bronze. It is interesting to note that three of the outlying objects are rings, given the preponderance of tinbronze usage in this object category in the Bronze Age (see Chapter Five, Figure 5.3). This data may indicate that small, decorative objects such as rings may have been important in the distribution of tin-bronze in the Gulf in the third millennium BCE. Unfortunately, the relative simplicity of these pieces precludes a typological investigation into their point of origin. Of course, such objects may also have been locally manufactured from imported metal. The remainder of the discussion addresses only the objects with 207Pb1206Pb ratios of greater than 0.800, 208Pb1206Pb ratios of greater than 1.990, and 206Pb1204Pb ratios of less than 20.00.

Isotopic Differences by Site The isotopic data for Umm al-Nar Period samples from the U.A.E. are illustrated on a site-by-site basis in Figure 7.2. Most objects fall on a linear array with 207PbI206Pb ratios of approximately 0.835-0.895, 208Pb1206Pb ratios of approximately 2.070-2.150, and 206Pb1204Pb ratios of approximately 17.50-1 8.80. Possible exceptions can be seen in the copper ring TA1310 from Tell Abraq (located in cluster 1 on Figure 7.2), and flat fragments 1019-3.59 and 1019-3.105 from Unar2, that are made of copper and tin-bronze, respectively. All of these objects fall below the main trend line on the 207Pb1206Pb versus 208Pb1206Pb plot, indicating that they are slightly depleted in thorogenic lead in comparison to the remaining objects. The outlying sample M10-17 from Unarl shows more significant depletion of the thorogenic lead component in comparison to the other analyzed Urnm al-Nar Period objects.

0.60

0.65

0.70

0.75 0.80 207 Pbl206Pb

0.85

0.90

0.95

Figure 7.1 LIA data for all Umm al-Nar Period objects from the U.A.E. analyzed in this study.

The earliest objects analyzed in this study come from AI Sufouh, and fall into roughly the third quarter of the third millennium BCE. The five objects from this site include dagger and blade fragments and unidentified flat fragments. They are made of copper and As/Ni-copper, and three of the five objects contain from approximately 0.66-2.0 percent Sn, qualifying them as copper-low tin objects. The LIA of these objects reveals a linear distribution with 207Pb1206Pb ratios of approximately 0.846-0.885, a spread of more than four percent. This is clearly far too large to represent metal from one conformable deposit, and it indicates the use of metal from multiple sources, or possibly the exploitation of one source with a heterogeneous isotopic signature. There are no consistent differences between the categories of copper objects and copper-low tin objects, although the least radiogenic value is for the copper-low tin flat fragment ASI-2 (207Pb1206Pb = 0.88469), and the most radiogenic is for the tanged copper dagger M10-41 (207Pb1206Pb = 0.84658).

Lead Isotope Data from the Gulf

14 7

Figure 7.2 LIA data (207Pb/206Pband 2 0 8 ~ b / 2 0 6ratios ~ b only) for all Umm al-Nar Period objects, arranged by site (outliers TA699,TA1614 not shown).white squares show isotopic data for the site of interest, gray circles show data for the other three sites.

148

Early Metallurgy of the Persian Gulf

Nine objects have been analyzed from the roughly contemporary tomb assemblage at Unarl. These include predominantly flat fragments and rings, in addition to fragments of a pinlawl and a spout. Compositionally, the group includes three copper samples, some with significant concentrations of arsenic and nickel, in addition to three copper-low tin objects and three others of tin-bronze. In contrast to A1 Sufouh, a significant clustering of the isotopic data from Unarl is seen, although there are a number of outlying objects. The major cluster occurs at 207Pb1206Pb approximately 0.85O7208J?b/206Pbapproximately 2.10, 206Pb1204Pb approximately 18.4, and comprises three tinbronzes (M10-13V, M10-22R, M10-39), one copper-low tin object (M10-7),and two copper objects (M10-12, M1038). Of the three remaining samples, the copper-low tin ring M 1 0-19 has a slightly less radiogenic isotopic signature than the remaining Unarl objects (207Pb1206Pb = 0.85542), while the AsINi-copper pin (L14N-PIN)has a more radiogenic signature (207Pb1206Pb = 0.83885), and the most radiogenic characteristics were seen in the copper-low tin ring M10-17 mentioned above. The isotopic spread of the clustered objects at Unarl is just under 0.5 percent, the theoretical limit of a conformable ore deposit, and may represent the concentration in the tomb of metal predominantly from one source. Nevertheless, the isotopic analyses of the remaining objects (M10-17, L14N-PIN, M 1019) suggest the use of multiple metal sources in the creation of the tomb assemblage. A total of ten objects have been analyzed from the Unar2 tomb assemblage, which is dated to the last two centuries of the third millennium BCE. These include four rings, three flat fragments, two pinlawl fragments, and one unidentified lump. Alloy compositions vary from relatively pure copper, to As/Ni-copper, copper-low tin, and tinbronze (often with significant concentrations of arsenic). In contrast to the Unarl assemblage, the Unar2 metal objects show very little evidence of clustering in their isotopic characteristics, displaying rather a linear array. The most radiogenic isotopic values are seen in the two analyzed As/Nicopper pinlawl fragments (1018-3.93,1019-4.108), which show very similar isotopic characteristics (207Pb1206Pb approximately 0.839). These samples are also very similar c o m p o s ~ t ~ o n acontaining ~~y, significant concentrations of The remaining the arsenic and site (flat fragment 1019-33 9 ) is of extremely pure copper,

and has a much less radiogenic signature (207Pb1206Pb= 0.87285). This sample has an almost identical isotopic composition to a flat arsenical tin-bronze fragment from the site (1019-3.105),showing that isotopic homogeneity can occur in compositionally diverse samples. These two flat fragments stand out isotopically from the remainder of the Unar2 assemblage in being relatively deficient in thorogenic lead (208Pb1206Pbapproximately 2.11 0). The remaining objects from Unar2 are all tin-bearing, and form a linear array from the most radiogenic values of 207Pb1206Pb approximately 0.843 (arsenical tin- bronze ring l957l), to the least radiogenic value of any object analyzed in this study, the copper-low tin lump (1023-2.11 0) with a 207Pb1206Pb ratio of 0.89320. No clear evidence for isotopic clustering can be seen in this group of objects, although the tin- bronze ring 1019-5.71 and the tin-bronze flat fragment 1018-3.99 have similar isotopic characteristics. As for the objects from A1 Sufouh and Unarl, the large spread of isotopic ratios of the assemblage from Unar2 (approximately six percent) suggests that multiple sources of metal were used to create the objects found in the tomb. A total of 10 objects from the Umm al-Nar Period tomb at Tell Abraq, and eight from near-contemporary settlement contexts at the site, underwent LIA and this data has been published (Weeks 1999).The objects analyzed include predominantly rings and flat fragments (six of each), in addition to four pinlawl fragments and two spearheads. Alloy compositions include pure copper, AsINi-copper, copper-low tin, tin-bronze, and one tin object. The objects are not those for which compositional data are presented above in Chapter Four, as they come from settlement contexts and the western chamber of the tomb, rather than the eastern tomb chamber. The objects were analyzed compositionally by SEM rather than PIXE, and the results are reported elsewhere (Weeks 1997:Table 14). The Tell Abraq isotopic data show the largest spread of any Umm al-Nar Period site analyzed in this study. As discussed above, this is primarily due to the two highly-radiogenic tin-bronzes from settlement and burial contexts at the site (TA699,TA1614), and another tin-bronze (TA107) that has a significantly more radiogenic signature than the majority of Tell Abraq objects. However, theremaining objects from the site still showsignificant isotopic diversity, with 207Pb1206Pb ratios of approximately 0.834-0.874, a spread of more than four percent.

Within this range, there appear to be three clusters of objects. The first is comprised of four objects with 207Pb1206Pb ratios of approximately O.835,208Pb/206Pb ratios of approximately 2.075, and 206Pb1204Pb ratios of approximately 18.80. Three of the objects (TA1217, TA1286, TA1306) show very similar isotopic compositions, and all are flat tin-bronze fragments from the tomb. The fourth possible member of the cluster (TA1310) is a ring of pure copper (>99percent Cu) from the settlement, however it is lower in thorogenic lead than the tin-bronzes and thus slightly isotopically distinct. The second cluster is composed of four objects (TA1227, TA1426, TA1461, TA1612) from tomb and settlement contexts at the site. All are of copper, although TA1612 contains some arsenic and significant amounts of nickel. The cluster is centered on 207Pb1206Pb ratios of approximately 0.840,208Pb/206Pb ratios of 2.080-2.090, and 206Pb1204Pb ratios of 18.60-1 8.80, and has a spread of approximately 0.2 percent. The third cluster is formed by a group of five objects from tomb and settlement contexts, and various alloys including copper (TA1467), Nicopper (TA1389), copper-low tin (TA1428), tin-bronze (TA1459), and a tin ring (TA2918). The cluster is centered on a 207Pb1206Pb ratio of approximately 0.847, and as for the previous group shows a very limited isotopic spread (approximately 0.4 percent). The remaining two objects from Tell Abraq are a copper-low tin spearhead (TA1231) from the settlement and a tin-bronze spearhead (TA1648) from the tomb (for an illustration, see Weeks 1997:Figure 8), both of which have the least radiogenic isotopic characteristics of the analyzed Tell Abraq material (207Pb1206Pb >0.870,208Pb/206Pb >2.120, 206Pb1204Pb ~ 1 8 . 1 0 ) . The large isotopic spread of the Tell Abraq objects suggests that multiple sources were used in the production of the copper-base objects used at the site, and the clustering of the objects into a few isotopically homogeneous groups may reflect the use of metal from a number of conformable deposits. Two of the isotopic groups show a significant degree of compositional homogeneity-one consisting predominantly of copper objects and the other of tin-bronzes (a group that also shows typological homogeneity). The third cluster shows great compositional diversity, with the five objects representing five different alloy types.

Lead Isotope Data from the Gulf

149

The major isotopic characteristics of copper-base objects from the four sites can be summarized as follows: Linear arrays due to the mixing of lead from different sources are common in each site's isotopic data, in the 207PbI206Pb range of 0.800-0.900. In general, the isotopic data suggest the use at each site of metal from multiple sources, rather than solely one isotopically homogeneous source. An exception might be Unarl, where most objects fall into a relatively limited isotopic range. Highly radiogenic samples are found only at Tell Abraq (TA699, TA1614), although radiogenic outliers are reported from both Tell Abraq (TA107) and Unarl (M10-17). A1 Sufouh and Unarl samples mostly show 207PbI206Pb ratios of greater than 0.845. While Tell Abraq and Unar2 have also produced samples in this range, these sites have also produced numerous objects with more radiogenic 207PbI 206Pb ratios of 0.834-0.845. This may reflect chronological differences in metal supply.

Figure 7.3 LIA data for all Umm aCNar Period objects by alloy category (outliersTA699,TA1614 not shown).

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Differences by Composition (Alloy Group) Although the coastal location of U.A.E. tombs and the strong trade connections found in the excavated material suggest that foreign copper could have been exploited at A1 Sufouh, Unarl, Unar2 and Tell Abraq, the possible use of foreign metal is most clearly an issue in the discussion of the tin-bronzes. In such a situation, it is possible for the isotopic differences between copper objects and tin-bearing objects to provide a useful indicator of the mechanisms by which tin and tin-bearing alloys were traded in the early periods of their use. The LIA data for Umm alNar Period objects analyzed in this thesis is illustrated in Figure 7.3, based upon the compositional groups (copper, copper-low tin, tin-bronze). Some clear differences can be seen, and become more apparent when histograms of the isotopic data are examined (Figures 7.4 and 7.5). Objects of copper, copper-low tin, and tin-bronze all seem to fall upon the same isotopic trend line in Figure 7.3. The majority of objects, including examples from all alloy groups, have 207Pb/206Pb ratios in the 0.834-0.856 range. However, within this range the overlap of objects from different alloy groups is not consistent. As can be seen in Figure 7.4, copper objects (including AsN-copper) show two isotopic clusters: one at 207Pb1206Pb ratios of 0.836-0.842, the other at 207Pb/206Pb ratios of 0.8460.850. Of these two ranges, tin-bronzes and copper-low tin objects are found only in the second, that with less radiogenic characteristics (see Figure 7.5). Only three of 15 analyzed copper objects have 207PbI206Pb ratios higher than 0.850, two of which are AsJNi-copper (ASI-5, M1012), and one of which is of very pure copper (1019-3.59). No copper objects have been analyzed with 207Pb1206Pb ratios of less than 0.836. In contrast, many tin-bearing objects have isotopic compositions outside the 207PbI206Pb range of 0.836-0.850. More than one-quarter of the analyzed tin-bearing objects have 207Pb/206Pb ratios of less than 0.836, including the radiogenic tin-bronzes from Tell Abraq (TA107, TA699, TA1614) and the copper-low tin ring from Unarl (M10-17). Furthermore, half of the tinbearing copper-base objects have 207Pb1206Pb ratios of greater than 0.850, including copper-low tin objects from all sites (ASI-2, ASI-3, ASTombld, M10-7, M10-19, 10232.110, TA123 l),and tin-bronzes from Unarl (M10-22R), Unar2 (1014.76, 1014.158, 1023-4.10, 1019-3.105) and Tell Abraq (TA1648).

Thus, although there is isotopic similarity between a small proportion of copper objects, tin-bronzes, and copper-low tin objects, the significant isotopic variation between the alloy groups suggests that different sources of metal were used to produce them. Of course, the inclusion of foreign metal in tin-bearing objects in the U.A.E. is indicated by the presence of the tin itself. The LIA indicates that some of this imported metal, whether tin or pre-alloyed tin-bronze, was isotopically distinct from the majority of the copper used in the region. There is clear archaeological evidence, in the form of the tin ring from the Tell Abraq tomb (TA2918), that metallic tin was available in the southern Gulf in the late third millennium BCE. Interestingly, the isotopic composition of this entirely foreign metal is very similar to a number of the copper objects analyzed in this study. If we assume that this copper was locally produced in southeastern Arabia, the possibility arises that even entirely foreign tin-bronzes, arriving pre-alloyed as ingots or objects, may be difficult to discern isotopically from local copper. These issues will be addressed in the following sections. Materials that potentially contributed lead to the tinbearing and copper objects are important to assess. Lead levels in the analyzed Umm al-Nar Period objects are generally low, commonly less than 2,000 ppm and frequently much lower (see Chapter Four; EDS analyses of the Tell Abraq material report higher Pb values, but are unreliable, see Weeks 1997:Appendix A). Such low lead levels are unlikely to represent the intentional alloying of lead with copper or tin-bronze, so the lead in the objects is likely derived from the lead in their parent ores (cf. Gale and StosGale 1982:12-13), Thus, objects of unalloyed copper (includingAsINi-copper) analyzed in this study should have lead isotopic signatures closely matching those of the copper ores from which they were produced. In contrast, as tinbronze is an alloy of copper and tin, there is obvious potential for the mixture of metal (or ores) from entirely different sources. In such a case, the lead isotope signature of the resulting tin-bronze may differ from the copper from which it was produced. It is therefore important to assess the amount of lead that might have come from the tin or the copper. As discussed in Chapter Six, the very low lead concentrations of the majority of copper ores and archaeological objects from southeastern Arabia make them extremely liable to contamination by lead-bearing cassiterite, tin or tin-bronze.

Figure 7.4 207Pb/206Pb isotopic composition of Umm al-Nar Period copper objects (including AsINi-copper)from the U.A.E.analyzed in this study (outliersASI-5,1019-3.59not shown).

Figure 7.5 207Pb/206~b Isotopic ranges for Umm al-Nar Period objects analyzed in this study, showing copper objects (lower chart), copper-low tin objects, and tin-bronzes (upper chart).

Two major explanations exist for the isotopic discrepancy between tin-bearing objects and copper samples from the Umm al-Nar Period in southeastern Arabia: 1. The isotopic distribution of the tin-bronzes was affected by lead from the tin, or alternatively 2. The imported tin contributed little or no lead to the tin-bronzes, and the isotopic disparities between the tin-bearing and copper objects indicate that different copper sources were used in their production.

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If the first alternative was the case, we would expect to see the distribution of tin-bearing objects spread away from the field for local copper in the direction of the isotopic signature of the lead in the tin, although there would be some degree of overlap (reflecting instances in which lead levels in the copper have overwhelmed the lead contribution of the tin). There is certainly no direct relationship between tin concentrations and lead isotope characteristics, as some of the most outlying samples contain only low tin levels. However, as outlined in Chapter Six, there is no reason to expect a predictable relationship between tin concentrations and isotopic characteristics, due to the likelihood of highly variable lead levels in tin and copper. The second alternative listed above would suggest that at least some of the tin-bronze was being traded to southeastern Arabia in its alloyed form, either as ingots or as finished objects. In this case, the clear isotopic overlap between the copper and tin-bronze objects could result from the use of foreign metal with a similar isotopic signature to local copper (we have seen already that this is possible, as in the case of the Tell Abraq tin ring TA291 8). Alternatively, the overlap might indicate instances where lead-free metallic tin was alloyed with local copper. Unfortunately, the EDS analyses of the tin ring from Tell Abraq are not of sufficient sensitivity to allow for the accurate determination of the lead concentration of the object. This important information is a priority of future research. The isotopic composition of the Tell Abraq tin ring is similar to that of many objects from the site, suggesting that the effect of the addition of lead from the tin might be minimal in isotopic terms, and also that entirely foreign metal may be indistinguishable from local copper. The tin ring has isotopic characteristics common to a group of Bronze Age samples from A1 Sufouh, Unarl, Tell Abraq and Saar (see Figure 7.3 and below), suggesting a similar origin. As the tin was certainly imported into the region, it may suggest that the isotopically-similar tin-bronzes were also. It must be emphasized that the hypothesized trade mechanisms are not mutually exclusive. It is highly likely that tin was reaching Tell Abraq in a number of formsas the pure metal and as alloyed tin-bronze ingots or objects. Just such a situation seems to have existed in the Bronze Age Aegean and northwestern Anatolia, (see

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below), where items of both exotic alloys and metallic tin were traded. In such a case, it is possible for the typological affinities of the tin-bearing objects from the U.A.E. to be of importance in delineating traded objects. However, the majority of analyzed bronzes are typologically simple (e.g. rings) and provide limited evidence for such pursuits.

Isotopic Comparisons with Bronze Age Objects from the Gulf The isotopic investigation for this study can be compared with the results of a number of other studies of Bronze Age copper-base objects from the Persian Gulf region. These isotopic studies include material from third millennium BCE Oman, the City I1 Period on Bahrain, and the Wadi Suq Period and Late Bronze Age levels at Tell Abraq. The first possible comparison is with the isotopic characteristics of copper ingots from the Gulf region. Eight planoconvex ingots from third millennium BCE contexts in Oman were analyzed by Prange et al. (1999: Figure 7 ) , while three slightly later but typologically similar ingots from Saar on Bahrain have been analyzed by Weeks and Collerson (forthcoming).In addition, an early second millennium BCE pyramidal ingot from Tell Abraq was analyzed by Weeks (1999; see Weeks 1997:Figures 5-6). It has generally been assumed that bun-shaped ingots found in the Gulf region are the product of copper smelting operations in southeastern Arabia, as represented by finds at Maysar 1 and Wadi Bahla, for example (see Chapter Two). The isotopic data for the Umm al-Nar Period objects analyzed in this study are presented in Figure 7.6, along with data for the 12 late-thirdlearly-second millennium BCE copper ingots from the Gulf region. As is immediately apparent, there is very limited isotopic overlap between the two groups. Seven of the 12 copper ingots show major isotopic differences with Umm al-Nar Period objects from the U.A.E. In particular, many of the copper ingots are depleted in thorogenic lead in comparison to the analyzed copperbase objects. As discussed more fully in the following section, these ingots are currently without any isotopic matches among the analyzed ore deposits from southeastern Arabia (Prange et al. 1999: 191; Weeks and Collerson, forthcoming). It must be stressed, however, that archaeological LIA in southeastern Arabia is in its infancy, and further analyses may indeed recover matching ore bodies for these ingots.

Of the five ingots which more closely match the analyzed copper-base objects, three are from early second millennium BCE contexts at Saar and Tell Abraq, and two are from Oman. Unfortunately, the isotopic data for the Omani ingots are not fully published, so the isotopic similarity of Umm al-Nar Period ingots and objects cannot be confidently assessed. Nevertheless, the two ingots from Oman show their closest isotopic parallels with a cluster of copper objects with 207Pb1206Pb ratios of approximately 0.840, and with one tin-bronze object from Unar2 (10195.71). Of the four second millennium BCE ingots for which full data is available (Figure 7.6) there is one clear isotopic match-between an ingot from Saar and the flat copper fragment TA1426 from Tell Abraq. Such results are extremely surprising, given the widespread assumption of the Omani origin of such ingots. Of course, both ingots and objects can be traded over large distances: there is no reason to assume that copper-base objects from Umm al-Nar Period sites in the U.A.E. were made of southeastern Arabian copper, nor indeed to assume that planoconvex copper ingots found in Bronze Age Oman are products of local extractive metallurgy. Such reconstructions have, until now, provided the best explanations of the archaeological evidence. However, the isotopic evidence discussed above casts doubt upon these widely held beliefs. A better match is seen between the Umm al-Nar Period copper-base objects from the U.A.E. and contemporary finished objects and processing residue from southeastern Arabia, analyzed by Prange et al. (1999:Figure 7). These analyses are illustrated in Figure 7.7 (copper objects) and Figure 7.8 (tin-bronzes and copper-low tin objects). Again, the data are not fully published by Prange et al. (1999), so Figures 7.7-7.8 display only the 207Pb1206Pb and 208Pb1206Pb ratios. A number of the analyzed objects and prills analyzed by Prange et al. (1999), none of which contain significant amounts of tin, form a cluster in the 207Pb1206Pb range approximately 0.8 3 7-0.842, coinciding relatively closely with one group of copper objects analyzed in the present study, centered upon a 207Pb1206Pb ratio of approximately 0.840. One other copper prill with less radiogenic isotopic ratios (207PbI206Pb approximately 0.853, 208Pbl 206Pb approximately 2.098) also matches a flat AsINicopper fragment from Unar l (M10-12). Other copper

Figure 7.6 LIA data for Umm al-Nar Period objects analyzed in this study, and Gulf copper ingots analyzed previously (Prange et al. 1999; Weeks and Collerson, forthcoming). A restricted isotopic range is shown, corresponding to the isotopic spread of the copper ingots.

objects and prills analyzed by Prange et al. (1999) have isotopic characteristics different from the objects analyzed in this study. The LIA data therefore indicate that, although multiple metal sources were exploited, settlements across third millennium southeastern Arabia had access to copper with specific isotopic characteristics (207PbI206Pb approximately 0.837-0.842; 208Pb1206Pb approximately 2.075-2.085; 206Pb1204Pb approximately 18.70). This may represent metal from one or a small number of sources, the possible locations of which are discussed below. In contrast, there are no exact isotopic matches between the tin-bearing objects presented in this study and the copper objects and prills analyzed by Prange et al. (1999), as illustrated in Figure 7.8. One tin-bronze ring from Unar2 (1019-5.71) is isotopically similar to cluster of objects and prills at 207Pb1206Pb approximately 0.837-0.842, and one tin-bronze ring from Unarl (M10-

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Figure 7.7 LIA data for Urnm

al-Nar Period copper objects analyzed

in this study,and copper-base artifacts and prills analyzed by

Prange et al. (1 999: Figure 7). A restricted isotopic range is shown.

Figure 7.8 LIA data for Urnm

al-Nar Period copper-low tin and tinbronze objects analyzed in this study, and copper-base artifacts and prills analyzed by Prange et al. (1999: Figure 7).A restricted isotopic range is shown. 22R) has similar isotopic characteristics to a prill from Oman (207PbI206Pb approximately 0.853; 208PbI206Pb approximately 2.09 8). This overall discrepancy may reflect the fact that the analyses of Prange et al. (1999) do not seem to have included objects with significant tin concentrations, highlighting the varying sources of metal used to produce these different alloy categories in southeastern Arabia. A comparison of the Urnm al-Nar Period objects analyzed in this study with objects from Saar on Bahrain is given in Figure 7.9. Two of the copper objects from Saar have isotopic compositions matching copper objects from the U.A.E. tombs, again focused upon 207Pb1206Pb ratios of approximately 0.840. Tin-bronzes from Saar, which are quite distinct isotopically from the copper objects used at the site, show similar isotopic

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characteristics to a cluster of Urnm al-Nar Period objects from the U.A.E. (207Pb1206Pb ratios approximately 0.850). These include two copper-low tin objects (ASTombld, M 10-7), two copper objects (M10-12, M10-38), two tin-bronzes from (M10-13V, M10-39), and the Tell Abraq tin ring (TA2918), and indicate the particular isotopic similarity of Saar tin-bronzes and metal from the Unarl tomb. The Saar analyses are also significant for demonstrating the presence in the central Gulf of metal objects and ingots with depleted thorogenic lead isotope compositions (i.e. low 208PbI206Pb ratios), which also characterize copper ingots from southeastern Arabia (see above). Finally, a comparison can be drawn between the analyzed Urnm al-Nar Period objects from the U.A.E. and the later material from Wadi Suq and Late Bronze Age (LBA) contexts at Tell Abraq (Weeks 1999:Table 1). As illustrated in Figure 7.10, the third millennium BCE copper objects from the U.A.E. and the Wadi Suq PeriodILBA copper objects from Tell Abraq show many isotopic similarities. Although a number of the Wadi SuqILBA copper objects from Tell Abraq have no exact matches with the earlier copper, most copper objects from both groups fall into the 207PbI206Pb range of 0.836-0.853. The Wadi Suq Period objects form a number of clusters, including three objects from the Wadi Suq I11 Period (TA468, TA1041, TA402) with 207Pb1206Pb ratios of approximately 0.837, three objects from the Wadi Suq I1 Period (TA1038, TA1637, TA1359) with 207Pb1206Pb ratios of approximately 0.844, and seven objects from Wadi Suq 11-IV Periods with 207Pb1206Pb ratios of approximately 0.847-0.852. A small number of copper objects with 207PbI206Pb ratios of greater than 0.853 are seen in both Urnm al-Nar Period and Wadi SuqILBA contexts, however their isotopic properties are very different: Wadi SuqILBA objects from Abraq (TA738, TA892) have significantly depleted 206Pb1204Pb ratios in comparison to the non-radiogenic copper objects from A1 Sufouh (ASI-5) and Unar2 (1019-3.59) analyzed in this study. The depleted 206PbI204Pb ratios of the Wadi SuqILBA copper objects from Tell Abraq are much closer to those seen in massive sulfide copper ores from southeastern Arabia, as will be discussed further in the following section on absolute provenance.

Absolute Provenance

The tin-bearing objects from the Urnm al-Nar Period and from Wadi SuqILBA contexts at Tell Abraq are illustrated in Figure 7.1 1. Again, the second millennium BCE objects show some evidence for clustering, notably at 207Pb1206Pb ratios of approximately 0.840 (TA340, TA378, TA994), and at 207Pb1206Pb approximately 0.847-0.850 (TA1194, TA1633, TA896, TA1127, TA1 184, TA1 185). The second isotopic cluster is very similar to that for a number of tin-bronzes and copperlow tin objects from Urnm al-Nar Period Tell Abraq, Unarl, and A1 Sufouh, including the Tell Abraq tin ring (TA2918). As for the copper objects discussed in the preceding paragraph, two Wadi SuqILBA tin-bronzes from Tell Abraq have high 207Pb1206Pb ratios of approximately 0.860 or higher. However, these objects (TA715, TA1043) are very similar isotopically to tin-bearing objects from the Urnm al-Nar Period, and not depleted in 206Pb1204Pb as seen for the non-radiogenic Wadi SuqILBA copper objects.

Comparisons to Omani Copper Ores In Figures 7.12-7.15, the isotopic data for objects from Urnm al-Nar Period tombs in the U.A.E. are compared to the previously existing isotopic data for copper ore deposits in southeastern Arabia (Chen and Pallister 1981; Gale et al. 1981; Calvez and Lescuyer 1991; Stos-Gale et al. 1997:1O3-105), and partially published data on Omani copper ores presented by Prange et al. (1999:Figure 7). As shown in Figure 7.12, there is very limited overlap between the analyzed Urnm al-Nar Period copper objects from the U.A.E. and copper ores from massive sulfide deposits in Oman particularly for the copper mines of Lasail, Bayda and 'Arja in the hinterland of Sohar, which were so important for early Islamic copper extraction (see Chapter Six, Figure 6.1, for the isotopic differences between massive sulfide copper deposits in Oman). Some of the objects show greater isotopic similarity with analyzed ores from the so-called "inland-V1 " massive sulfide deposits (Calvez

Figure 7.9 LIA data for Urnm al-Nar Period objects analyzed in this study, and copper-base artifacts and prills from Saar, Bahrain (Weeks and Collerson, forthcoming). A restricted isotopic range is shown.

Figure 7.10 LIA data for Umm al-Nar Period copper objects analyzed in this studyland copper artifacts and prills from Wadi SuqILate Bronze Age contexts at Tell Abraq (Weeks 1999).

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and Lescuyer 1991), such as those at Raki, although exact matches are absent. This finding is surprising, given the significance that was attached to this type of deposit as the largest in the region, and the evidence for Bronze Age smelting activities found at 'Arja (Hauptmann 1985:116). However, research suggests that smaller deposits from lower levels in the Semail ophiolite rather than the massive sulfide deposits were probably more important for early metallurgy in the region (see Chapter Two). It is likely that such deposits have isotopic characteristics different from the massive sulfide deposits, and the analyses of Prange et al. (1999:Figure 7) have indeed demonstrated the presence of copper ores in Oman with 207Pb1206Pb ratios of approximately 0.840, similar to some of the copper objects analyzed in this study. Unfortunately, the geology of these ores is lacking, so it is difficult to assess the importance of particular ore types or specific ore bodies for Umm al-Nar Period copper extraction in the region. Copper objects with 207Pb1206Pb ratios of greater than approximately 0.850 do not match any currently analyzed ores from the Semail Ophiolite, and are also dis-

Figure 7.1 1 LIA data for Umm al-Nar Period tin-bearing objects analyzed in this study, and tin-bronze artifacts and prills from Wadi SuqILate Bronze Age contexts at Tell Abraq (Weeks 1999).

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tinct from ores of the A1 Ajal copper deposit, in rocks of the Hawasina formation. However, some of the less radiogenic ores summarized by Prange et al. (1999:Figure 7) are likely to be of significance for archaeological LIA. In general, very few lead isotopic analyses of Omani ores have been undertaken, and future analyses may broaden the potential isotopic range of copper produced in Oman. In Figure 7.13, copper-low tin objects from Umm alNar Period tombs in the U.A.E. are illustrated in comparison to copper ores from the Sultanate of Oman. Two objects show similarities to massive sulfide ores when all three isotopic ratios are considered: a pinlawl from Tell Abraq (TA1428) matches closely with a number of ores from Raki and Hay1 as-Safil, and a flat fragment from A1 Sufouh (ASI-3) is isotopically-similar to an ore sample from Zuha, and one from Maqa'il. Other than these objects, isotopic parallels for the remaining copper-low

Figure 7.1 2 LIA data for copper objects from the U.A.E. analyzed in this study; Omani copper ores from massive sulfide deposits (Chen and Pallister 1981; Calvez and Lescuyer 1991; Stos-Gale et al. 1997), from the Hawasina-hostedAI Ajal copper deposit (Calvez and Lescuyer 1991),and; from unspecified deposits (Prange et al. 1999:Figure 7).

tin objects cannot be found among the currently analyzed group of massive sulfide ores. A number of the unspecified ores published by Prange et al. (1999:Figure 7) show isotopic similarities to some of the copper-low tin objects, although full data will be required before a provenance can be suggested with even limited confidence. Three of the copper-low tin objects from Umm alNar Period tombs in the U.A.E. have 207Pb1206Pb isotopic compositions outside the range of any known ores from southeastern Arabia, including a ring from Unarl (M10-17), a flat fragment from A1 Sufouh (ASI-2), and a copper-low tin lump from Unar2 (1023-2.11 0). Even when their 207Pb1206Pb ratios are similar to ores from southeastern Arabia, copper-low tin objects from the U.A.E. appear to have higher relative 206Pb1204Pb ratios, and thus identification of local sources is equivocal. As illustrated in Figure 7.14, a similar pattern is observed for tin-bronzes. When not entirely outside the

207Pb1206Pb range of known ores from Oman (e.g. TA107, TA699, TA1217, TA1286, TA1306, TA1614), they seem to be enriched in 206Pb1204Pb relative to the ore samples (e.g. all Unar2 tin-bronzes). A close match with a massive sulfide ore can be seen for only one tinbronze, a pinlawl from Tell Abraq (TA1459), which is isotopically similar to an ore sample from Raki. One tinbronze from Unar2 (1014.158) also has similar isotopic properties to one of the unspecified Omani ores analyzed by Prange et al. (1999), although all ratios are not available for comparison. It is helpful to examine more closely the isotopic distribution of objects of AsINi-copper, as illustrated in Figure 7.15. As discussed in Chapter Five, As-Ni-copper is an unintentional or "natural" alloy that is highly likely to have been locally produced in southeastern Arabia. That is, under the kinds of smelting conditions known to have characterized the Bronze Age, the geology and

Figure 7.1 3 LIA data for copper-low tin objects from the U.A.E. analyzed in this study, and Omani copper ores from massive sulfide deposits (Chen and Pallister 1981; Calvez and Lescuyer 1991; StosGale et al. 1997),from the Hawasina-hosted AI Ajal copper deposit (Calvez and Lescuyer 1Wl), and from unspecified deposits (Prange et al. 1999: Figure 7). Outlier M10-17 not shown.

Figure 7.14 LIA data for tin-bronze objects from the U.A.E. analyzed in this study, and Omani copper ores from massive sulfide deposits (Chen and Pallister 1981; Calvez and Lescuyer 1991; Stos-Gale et al. 1997),from the Hawasina-hosted AI Ajal copper deposit (Calvez and Lescuyer 1ggl), and from unspecified copper deposits (Prange et al. 1999: Figure 7). Outliers TA107,TA699 and TA1614 not shown.

Lead Isotope Data from the Gulf

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Figure 7.1 5 LIA data for copper-base objects with As and Ni concentrations greater than 1 percent analyzed in this study, and Omani copper ores from massive sulfide deposits (Chen and Pallister 1981; Calvez and Lescuyer 1991; Stos-Gale et al. 1997),from the Hawasina-hosted AI Ajal copper deposit (Calvez and Lescuyer 1Wl), and from unspecified copper deposits (Prange et al. 1999: Figure 7). Outlier TA107 not shown.

mineralogy of many copper deposits in southeastern Arabia indicate that objects high in impurities of As and Ni could have been naturally produced from them. As can be seen in Figure 7.15, objects with more than one percent of As and Ni have a relatively restricted range, with 207Pb1206Pb ratios in the 0.83 8-0.855 range. One exception is the tin-bronze ring TA107 from Tell Abraq, which has a radiogenic 207Pb1206Pb ratio of 0.8 1800. Given that As-Ni-copper is unlikely for mineralogical reasons to have been produced from the massive sulfide ores of Oman, it is not surprising that there are very few isotopic matches between these groups. Only the flat fragment ASI-3 from A1 Sufouh has isotopic characteristics similar to a massive sulfide ore, in particular a sample from the deposit at Zuha. Object ASI-3 is unusual in possessing very high cobalt levels (1.2 percent CO) in addition to approximately 2.8 percent Ni and 6.2 percent As.

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In contrast, a number of As-Ni-copper objects show isotopic similarities to Omani copper ores analyzed by Prange et al. (1999), especially those with 207Pb1206Pb ratios of approximately 0.840. This group is composed entirely of pinlawl fragments, and includes Cu-As-Ni alloys from Unarl (L14N-PIN), Unar2 (1019-4.108) and Tell Abraq (TA1612), and a Cu-As alloy (1018-3.93) from Unar2 (this pinlawl has just under one percent Ni). Two arsenic-bearing tin-bronze rings from Unar2 (1014.158, 1019-5.71) also have isotopic characteristics similar to the ores analyzed by Prange et al. (1999). The full publication of the ore data from Oman is required before the isotopic similarity of these Omani ores and AsINi-copper objects can be properly assessed. In particular, the types of copper deposits that the German team analyzed must be considered. Although close isotopic matches with local Omani ores cannot be found for all AslNi-copper objects, the analyses provide tentative support for the hypothesis that AslNi-copper found in southeastern Arabian contexts is a local product, as proposed based on the mineralogical and technological considerations outlined in Chapter Five Overall, close isotopic matches between analyzed objects and Omani ores can only be seen in a handful of cases. In some instances, such as the highly radiogenic objects discussed earlier in this chapter, the attribution of the metal to non-Omani sources seems very likely. In other cases, it is difficult to distinguish between the possible use of foreign metal and the effects of the non-representative nature of the local ore database. The database is limited in both the number of analyses undertaken, and in the variety of geological contexts from which copper ores have been collected and analyzed. Comparisons to Non-Omani Ores Isotopic evidence from other areas of western Asia and adjacent regions is relatively limited, but can nevertheless be used to suggest possible source areas for the Umm al-Nar Period objects from the U.A.E., if a foreign origin is argued. Iran and India are the two most obvious candidates given the strong trade connections between these regions and southeastern Arabia documented in the Bronze Age archaeo-

logical record. Potentially important metal supply areas with demonstrable contemporary copper production, such as Baluchistan and Afghan Seistan (e.g. Dales 1992),unfortunately remain isotopically uninvestigated. Moreover, isotopic analyses from Iran and India are very limited, and rarely undertaken with the provenancing of archaeological copper-base objects in mind. Thus, the following discussion represents a very preliminary investigation of this issue. Ores and slags from India have been analyzed by Hegde and Ericson (1985)and Srinivasan (1999),and they are largely related to lead deposits and their associated smelting remains, with a geographical focus in Rajasthan. However, some copper ores have been analyzed isotopically, and based on these data and the trends suggested by the analyzed lead deposits, an Indian origin for the U.A.E. objects appears unlikely. Many Indian ore deposits, and especially those of Rajasthan, are hosted in geologically-old rocks of Precambrian age. This is reflected in the isotopic composition of the ores and associated slags that commonly have 207Pb/206Pbratios of greater than 0.900, (see Figure 7.16). Two exceptions can be seen in the data, one of which is from the Cu-Pb-Zn deposit at Ambaji in northern Gujarat, while the other ore is from Ambadongar in the Deccan. The Ambaji ore, however, is clearly depleted in thorogenic lead in comparison to the archaeological objects analyzed. It thus seems an unlikely source for the Umm al-Nar Period copper-base objects from the U.A.E. However, the number of copper objects from the Gulf (particularly ingots) with depleted thorogenic isotope ratios should be borne in mind when assessing the potential importance of this deposit, as should Carter's (2001)evidence for Gujarati pottery at Saar in the early second millennium BC. The Ambadongar deposit is much less likely to be significant for discussions of Bronze Age copper use in the Gulf region, due to its outof-the-way location and the lack of evidence for early exploitation of the deposit. Turning to the evidence from Iran, some isotopic data is available for copper ores and prehistoric slags from the Iranian Plateau, based on recent archaeometallurgical research by a collaborative Iranian-German team (Chegini et al. 2000), and geological research at the Sar Cheshmeh copper mine, Iran's largest (Shahabpour and Kramers 1987). As can be seen in Figure 7.17, the analyzed Iranian copper ores and slags from the Kashan region have 207Pb1206Pb ratios of less than 0.843, and

show a similar range to the analyzed sulfide concentrates from rocks hosting the Sar Cheshmeh deposit. There are no exact isotopic matches between the Iranian and southeastern Arabian groups, with Sar Cheshmeh samples in particular having relatively depleted 206PbF04Pb ratios in relation to the U.A.E. objects. The two analyzed midthird millennium copper slag samples from Tepe Sialk and Arisman show general isotopic similarity with a number of U.A.E. objects, including a copper object from Tell Abraq (TA1426) and an arsenical tin-bronze from Unar2 (1018-3.99). The significance of the Veshnoveh ore sample is difficult to determine, as its stated 207Pb1206Pb ratios and those illustrated in the report are significantly different (compare Chegini et al. 2000:Figure 23 and Table 3). Nevertheless, it suggests that Veshnoveh ores

Figure 7.16 LIA data for Umm al-Nar Period objects analyzed in this study, and Indian ores and slags (Srinivasan 1999; Hegde and Ericson 1985).Outliers TA699 and TA1614 not shown.

Figure 7.17 LIA data for Umm al-Nar Period objects analyzed in this study, lranian copper ores and slags (Chegini et al. 2000:Table 3), sulfide concentrates from the Sar Cheshmeh mine (Shahabpour and Kramers 1987), and lranian lead ore and slag (Stos-Gale 2001:Table 4.1). Limited isotopic range shown.

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dence for contact between the Gulf and western Arabia in the third millennium BCE, and currently no evidence for the exploitation of Saudi Arabian copper deposits at that time. Better isotopic parallels for the U.A.E. objects can be found in more northerly and westerly regions of western Asia, including Anatolia and the southern Levant (see Figure 7.19), for which copper production is documented by at least the third millennium BCE (e.g. Hauptmann 2000:Abb. 33). However, the evidence for contact between these areas and the Gulf region in the Bronze Age is absent, making the use of Anatolian or Levantine copper in southeastern Arabia highly unlikely. Likewise, the similarity of the isotopic composition of copper from southeastern Arabia and Cyprus has been addressed by Prange et al. (1999:191), and reflects the similar age and geological context of the copper ores from the two regions. This metal is very unlikely to have been used in the southern Gulf, at least in the Umm al-Nar or Wadi Suq Periods. However, distinguishing the use of isotopically and compositionally similar Cypriot and Omani copper in second millennium BCE Mesopotamia may be very difficult (see Chapter Six). Figure 7.18 LIA data for Umm al-Nar Period objects analyzed in this study, and Saudi Arabian copper ores (Stacey et al. 1980) and tinbearing granites (Du Bray et al. 1988).

Tin-Bronze in Wider Western Asia: Important Lead Isotope Studies

may be more radiogenic than most of the copper objects from the U.A.E. analyzed in this study. The slag analyses do indicate that, when more LIA of Iranian copper ores and slags have been undertaken, distinguishing isotopically between metal from Oman and Iran may be problematic. This possibility is further indicated by the isotopic composition of various lead ores and slags from across Iran (Stos-Gale 2001) illustrated in Figure 7.17. Although not strictly useful for provenancing copperbase archaeological objects, these analyses demonstrate that ore bodies with a wide variety of isotopic characteristics can be expected in Iran, many of which may isotopically match ores from southeastern Arabia. Looking further afield, there are numerous copper and tin deposits in the Arabian shield. However, the isotopic characteristics of these ores (Stacey et al. 1980; Du Bray et al. 1988) are incompatible with the LIA of the Umm al-Nar Period objects from the U.A.E. (see Figure 7.1 8). Furthermore, there is little or no archaeological evi-

Sizeable programs of isotope analysis have been conducted on material from the Aegean and northwestern Anatolia. These data proved unexpectedly important for assessing the significance of the Gulf LIA data for wider studies of western Asian trade in the Bronze Age. The analyzed material comes from the Early Bronze Age (EBA) sites of Poliochni, Thermi and Kastri in the Aegean, and from Troy and the Troad in Anatolia. These sites show use of tin-bronze by the mid-third millennium BCE, and have been exceptionally important in discussions of the development of tin-bronze technology and the tin trade in the eastern Mediterranean and western Asia (see Chapter Eight). The results of these isotopic studies are summarized below, and their relationship to Bronze Age material from the Gulf is investigated. Lead isotope analyses of EBA metal artifacts from Kastri and Troy have revealed that these objects show great isotopic diversity, with 207Pb/206Pb ratios from approximately 0.830-0.900, a spread of more than eight percent. It has been suggested by Stos-Gale et al.

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(1984:28) that five separate ore sources, ranging in age from Pliocene (2-33 Ma) to Precambrian (700-900 Ma), provided the copper and tin-bronze that was used at these sites. Tin-bronzes fall into all five "source" groups, but dominate those with lead isotopic model ages beyond known ores from the Aegean, eastern Mediterranean or Anatolia. Very similar patterns are visible in LIA of other EBA material from Troy and the Troad (Pernicka et al. 1984; Seeliger et al. 19851, Poliochni (Pernicka et al. 1990) and Thermi (Begemann et al. 1992; 1995; Stos-Gale 1992). The isotopic analyses are regarded as evidence that, during the third millennium BCE, tin-bronze was traded into northwestern Anatolia and the Aegean from as yet unknown external sources. Furthermore, trace element data for objects from Thermi indicate that tin-bronze was imported pre-alloyed as ingots or objects, and "was not produced by adding imported tin to locally produced copper" (Begemann et al. 1992:220). Isotopic data also show that, in addition to tin-bronze, "exotic" copper and brass was reaching sites such as Kastri and Troy in the third millennium BCE, from areas outside the Aegean or Anatolia (StosGale et al. 1984). It is clear that some metallic tin was also reaching the region, as indicated by the tin bangle from Thermi, and as might be expected given the mention of metallic tin in a number of mid-third millennium BCE written sources from western Asia (see Chapter Eight). The ultimate source of this "exotic" metal remains uncertain. Given that a number of the Aegean tinbronzes are isotopically incompatible with any Anatolian source, various authors have suggested that Precambrian copper and tin deposits in the Arabian Peninsula and Egypt (Stos-Gale et al. 1984:29) or Afghanistan (Pernicka et al. 1990:290; Pernicka 1995b:107-108) may have been used. There is neither archaeological evidence for contact between the Saudi Arabian region and the Aegean at this time, nor evidence for the exploitation of Saudi Arabian copper and Egyptian tin ores in the third millennium BC (see Chapter Eight). Significantly, the available isotopic evidence from Saudi Arabian copper deposits (Stacey et al. 1980) indicates that they did not supply the metal used at EBA sites such as Troy, Poliochni and Thermi.

i

2m02

Anatolianl~e~ean Ores O

Figure 7.19 LIA data for Umm al-Nar Period objects analyzed in this study, in comparison to ellipses representing the isotopic characteristics of ores from Anatolia, the Aegean, Feinan and Timna. Ellipse boundaries drawn after Hauptmann (2000: Abb. 33).

Furthermore, if the Thermi bangle is regarded as representative (Pernicka 1995b:108; Sayre et al. 1992), its isotopic ratios suggest that proposed tin sources in the Taurus Mountains, in particular Kestel and Goltepe (Yener et al. 1989; Yener and Vandiver 1993a), did not supply the tin that was used in EBA contexts in the region. The question is slightly more complicated for the tinltungsten-bearing granites of Saudi Arabia and Yemen (see Chapter Eight). An actual tin ore deposit (at Silsilah) is only associated with one of these granites, but cassiterite occurs in small quantities as an associated mineral in three other deposits (Du Bray et al. 1988:Table 1).N o lead isotope data are available for the cassiterite ores themselves, only for their host granites. If the data from the granites are an accurate reflection of the isotopic composition of the cassiterite ores they host, then it seems clear that tin from western and central Saudi Arabia was not supplying the EBA Aegean or Anatolia. However, cassiterite ores are frequently lead-poor and uranium-rich (Gulson and Jones 1992), meaning that the isotopic signature of the cassiterite may not match that of the host granite. In this discussion, the scant evidence for the early exploitation of these ores is significant, and suggests that western Arabia was an unlikely tin source for EBA Anatolia and the Aegean. Unfortunately, the possible production of early Aegean and Anatolian tin-bronze from Afghani sources cannot be investigated using LIA data, as none is available from geological or archaeological studies.

Lead Isotope Data from the Gulf

16 1

The LIA of objects from Poliochni, Thermi, Kastri and the Anatolian mainland has served to complicate discussions of the EBA tin trade in the Aegean, and has broadened immensely the areas in which potential tin and tin-bronze sources must be sought. In this context, it is interesting to note that the third millennium tin-bronzes from the U.A.E. show a very similar isotopic composition to EBA tin-bronzes from the Aegean region, as illustrated in Figure 7.20. The Gulf tin-bearing objects follow very closely the linear pattern of the tin-bronzes from northwestern Anatolia and the Aegean, and show a similarly broad a range of values.

Highly radiogenic tin-bronzes similar to those from Umm al-Nar Period contexts at Tell Abraq are occasionally reported from northwestern Anatolia and the Aegean (e.g. Seeliger et al. 1985:Abb. 31). It should also be noted that a similar isotopic pattern seems to occur in a number of EBA objects from the central Anatolian site of Kaman-Kalehoyiik (Hirao et al. 1995:Figure l l ) , in mid-third millennium BCE tinbronzes from Velikent in Daghestan (Kohl et al. 2002:127) and in some Luristan tin-bronzes (Begemann et al. 1989:Figure 30.5), although the Luristan data are not fully published.

Figure 7.20 LIA data for tin(and zinc)-bearing objects from the Aegean and northwestern Anatolia, in comparison to tin-bronzes and copper-low tin objects from the U.A.E.analyzed in this volume.

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Early Metallurgy of the Persian Gulf

The isotopic similarity between the Tell Abraq and Aegean tin-bronzes may indicate that the tin-bearing metal being used at Kastri, Poliochni, Thermi, Troy, and Umm al-Nar Period sites in the U.A.E. was obtained from the same source(s). There are a number of other reasons for believing such an hypothesis, which are discussed in detail in the following chapter.

LIA: Summary of the Main Findings Isotopically heterogeneous metal was used in each of the four metal assemblages investigated, with the possible exception of the objects from Unarl. This probably indicates the simultaneous exploitation, at each individual site, of metal from multiple sources. Further differences are seen in the isotopic ranges of metal objects from each tomb assemblage, which probably reflect variation in sources resulting from the chronological differences between the sites. In addition to this chronological variation, isotopic variability can be linked with composition, in particular the tin-content of the objects. This is perhaps not surprising, as tin is clearly a metal foreign to the geological milieu of southeastern Arabia. Overall, about one-quarter of the analyzed Umm al-Nar Period objects lay outside the isotopic range of any Omani copper ores as currently known, and all have tin concentrations over 0.5 percent. The presence of a number of highly radiogenic tinbronzes and copper low-tin objects demonstrates the import of pre-alloyed tin-bronze (probably in the form of finished objects) into southeastern Arabia. In contrast, a group of objects (207Pb/206Pbratios of 0.836-0.842,208Pb/206Pb ratios of 2.070-2.0907206Pb/ 204Pb ratios 18.50-1 8.80) which includes material from all four assemblages and from other sites in southeastern Arabia and the central gulf shows a significant degree of isotopic homogeneity. Although these objects show no isotopic matches with Omani massive sulfide ores, they are isotopically similar to a few Bronze Age copper ingots from the Gulf and one Omani ore sample. This group may represent one "kind" (isotopically speaking) of Omani copper available in the Gulf. Furthermore, the broad isotopic range of the analyzed Omani ores (207Pb/206Pb approximately 0.838-0.872) coincides with isotopic characteristics of most of the Umm al-Nar Period objects, which suggests

that many of them may have been made of Omani copper. Although there are very few exact matches between the objects analyzed in this study and Omani ores, this may reflect the limited database of Omani ore analyses. The similarity of the Bronze Age analyses from the four sites to later material from Tell Abraq might also support a local origin, i.e. it could reflect the continued use of local sources exploited in the Umm al-Nar Period into the second millennium. Alternatively, isotopic similarities may simply reflect the recycling of third millennium metal, or continuity in foreign sources. However, one object of undoubtedly foreign origin, the tin ring from Tell Abraq, has isotopic characteristics compatible with Oman. This tells us that some foreign metal is likely to be isotopically indistinguishable from Omani ores. Furthermore, as a group, the isotopic characteristics of the tin-bronzes show many similarities to those found in other areas of Bronze Age western Asia, particularly the Aegean region and northwestern Anatolia. If tin sources are very scarce, one or a very limited number of sources could have supplied a very large area, and such isotopic matches could be a reflection of shared provenance. In general, conclusions about absolute provenance are very much open to debate. This is primarily due to the incomplete and possibly unrepresentative nature of the Omani ore database. However, the fact that isotopic similarity does not necessarily equal shared provenance-a basic tenet of isotopic analysis-must also be borne in mind. The archaeological implications of the various exchange transactions suggested by the lead isotope data are addressed in the following chapter.

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8

Tin and Tin-Bronze in Early Western Asia

Introduction As tin is a non-local resource in most regions of western Asia, questions regarding the ultimate source of this raw material have long been asked by archaeologists, archaeometallurgists and ancient historians. The mechanisms and routes by which tin and tin-bronze were exchanged throughout Bronze Age western Asia and beyond have also received significant attention (e.g. Muhly 1973a; Larsen 1976). After all, what is a Bronze Age without bronze? Nevertheless, a review of the archaeological evidence for early tin-bronze use forced P.R.S. Moorey (1982:87) to conclude that "the significance of tin in the third millennium B.C. in the economy of the Near East is very easily overrated.. .a dearth of analyses, and the consequent danger of over-emphasizing isolated ones, makes any conclusions hazardous". Such a statement was justified at the time of its writing, more than two decades ago, when the early tinbronzes from northwestern Anatolia, Mesopotamia and Iran seemed, like the proverbial good men, both few and far. However, recent programs of archaeometric analysis and the isotopic analyses presented in the previous chapter indicate a more widespread use of the alloy than previously known, as well as the possibility of a far-flung trade in tin and tin-bronze from a very limited number of sources. At the same time as such findings demand explanation in terms of trade routes, technology, and ideology, they also have the potential to add to our understanding of the interconnectedness of regional economies that seems to characterize Bronze Age western Asia.

The determination of the ultimate sources of tin used in the Bronze Age is a provenience problem of slightly different nature to many dealing with the metals trade, due to the extremely limited occurrence of workable tin deposits within or adjacent to western Asia. As geological evidence on the occurrence of tin in the Old World has improved, and the plethora of western Asiatic tin-deposits discussed in early archaeological reports (see Muhly 1973a; 1985a) have vanished under the scrutiny of modern research, the problem of tin sources is increasingly visible as a primarily geological concern (although see Moorey 1994:299 for the limitations of the geological data). Such an approach is not possible for many other metals in use in Bronze Age western Asia, such as copper or iron, deposits of which occur much more frequently within the region (e.g. Pigott 1999b:Figures 4.6, 4.12). Hence, evidence from modern geological surveys provides the framework within which theories regarding the provenance of tin in early western Asia are evaluated. Information from early written sources dealing with the tin trade can also be incorporated into provenance studies, in addition to evidence for the occurrence of tin and tin-bronze in the archaeological record provided by archaeometallurgical studies. Interestingly, it is the combination of these different strands of evidence that has largely led to the search for tin sources in western Asia being regarded as problematic. Archaeological, metallurgical and textual sources have suggested explanations for the provenance of tin which are, superficially, conflicting. However, a close examination of the evidence reveals long-standing but questionable archaeological assumptions, the modification of which allows for the formulation of a consistent explanation for the early use of and trade in tin and tin-bronze. In the following chapter, the evidence from geology, historical sources, and archaeometallurgical analyses is collated and discussed, in order to arrive at an understanding of the sources that may have supplied tin and tin-bronze to the Gulf region in the Bronze Age. The chapter concludes with a reconsideration of the tin problem in the light of broader developments in metallurgy, exchange systems, and socio-political complexity in western Asia. The locations of the archaeological and metallurgical sites referred to in the following discussion are given in Figure 8.1.

Tin Deposits in Western Asia and Surrounding Regions At one time or another, workable tin deposits have been claimed to exist in various regions of Anatolia, Mesopotamia, Iran, Syria and the Levant, Egypt, and the Arabian Peninsula, among other places (Muhly 1973a, 1985a; de Jesus 1 9 8 0 5 1 ff.). Many of these claims, for example the alluvial tin of the Kesserwan District of Lebanon (Wainwright 1934; Lucas 1934:213), have failed to withstand the scrutiny of detailed geological research (de Jesus 1980:53). Likewise, an hypothesized tin source in northern Mesopotamia, based upon price equivalencies for tin in Bronze Age cuneiform sources (Heltzer 1978:108-1 l ) , clearly does not take account of the geological information which would preclude such a deposit (Muhly 1985a:249-250). Furthermore, a number of areas of western Asia which do have tin deposits can be excluded

as potential sources for the tin used in the Bronze Age, based upon the lack of evidence for early exploitation of the deposits, or lack of evidence for contemporary local use of tin and tin-bronze. It is clear that tin deposits do not exist in Syria, Lebanon, the Levant or Mesopotamia, but other regions of western Asia have possible tin deposits that require more detailed discussion, as presented below. Egypt and the Arabian Peninsula Significant granite-hosted and alluvial cassiterite deposits have been recorded at a number of places in the Eastern Desert of Egypt (Rapp et al. 1999:153-154; Wertime 1978; Muhly 1978; 1993b:244-248 and Figure l ) , and more recently in the western Arabian Peninsula in both Saudi Arabia and Yemen (Du Bray 1985; Du Bray et al. 1988; Kamilli and Criss 1996; Overstreet et al. l 9 8 8:411-413). The Egyptian deposits were surveyed by

Figure 8.1 Map of Asia, showing archaeological sites, metallurgical sites, and ore deposits discussed in Chapter 8.

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J. D. Muhly, T. A. Wertime and G. Rapp in 1976, who noted the presence of tin-tungsten mineralization in the form of "high-temperature hydrothermal vein deposits forming mineralized zones that are 1,200-2,500 m long, 450-650 m wide, and up to 1.5 m thick" (Muhly 1993133244). Alluvial cassiterite is present and replenished regularly by rainstorms in the wadis of Abu Dabbab, Nuweibi, Igla, El Mueilha and Homr Akarem (Rapp et al. 1999:Figure 3; Muhly 1993b:246). All of these locations have been worked for tin within the last century (Rapp et al. 1999:154). Another tin deposit exists further to the south, in the Khartoum province of Sudan ( Garenne-Marot 1984:107). In the Arabian peninsula, a tin deposit is associated with only one of the so-called Sn-W granites of the region, the Silsilah deposit in the Fawarrah pluton, although cassiterite occurs in small quantities as an associated mineral in three other deposits (Du Bray et al. 1988:Table 1).At Jebel Silsilah, cassiterite is found as disseminated grains in partly and completely greisenised rock, and as elliptical pods of cassiterite-rich greisen. The latter consist of 60-90 percent cassiterite in a quartz-topaz matrix, while samples from the two most intensely mineralized greisens contain from 0.1 to several percent tin (Du Bray et al. 1988:153 and Table 7; Kamilli and Criss 1996:1423). Overall, the deposit has been described as "generally low-grade" (Du Bray et al. 1988:153), and the potential for modern extraction is regarded as economically marginal (Kamilli and Criss 1996:1432). Penhallurick (1986:l.S) reports that "the source grade and volume, geomorphology and climate, are not conducive to tin placer possibilities" at Jebel Silsilah. For a number of reasons, it is unlikely that Egyptian and Arabian tin deposits provided the tin that was used in Bronze Age western Asia or the Aegean. One of the most powerful arguments against their use is that Egyptian craftsmen seem to have made little use of tinbronze before the second millennium BCE (see below). Furthermore, in the Middle and New Kingdoms, tin seems to have been traded into Egypt by way of Eastern Mediterranean and Levantine polities (Garenne-Marot 1984:107-108; Muhly 1973a). The situation is similar for the Arabian tin ores, which are associated with deposits of copper and gold, but which show no signs of

exploitation prior to the first millennium BCE (Glanzman l 9 8 7: 146; Fleming and Pigott 1987; Wertime 1978:6). An analysis of slags from the first millennium BCE site of Hajar Ar-Rayhani in the Yemen Arab Republic demonstrated the association of copper and tin ores in smelting installations, although tin-bronze does not always appear to have been successfully produced by the local metalworkers even in this period (Fleming and Pigott l 9 8 7: 174). Further evidence against the use of Arabian or Yemeni tin was discussed above (Chapter Seven), based upon lead isotope studies. Other tin deposits claimed to exist in Arabia, such as those of Oman listed by Lamberg-Karlovsky (1967: l49), have not been recorded in extensive geological surveys of the region. Anatolia Copper, iron, silver and lead are plentiful in Anatolia, and the geological preconditions necessary for the occurrence of tin ores are met in a number of regions of the country, such as the Troad and the Taurus Mountains (Muhly 1985a:277). Correspondingly, claims for the occurrence of tin deposits within Anatolia have been relatively common. For example Muhly (1995b: 1507) states that "a source of tin in the Troad remains a very attractive possibility, especially because of the very early use of tin in the area", and Renfrew (1967:13) and de Jesus (1978:37-8) have expressed similar views. Cassiterite has been recorded in southeastern Anatolia in the KestelICelaller region (Yener et al. 1989; Kaptan 1995:200) and stannite is known from Sulucadere/Bolkardag and Sogukpinar near Bursa (Yener and Ozbal 1987:222-223; Kaptan 1995:201 and Figure 1).Numerous minor occurrences of tin minerals have been recorded in Anatolia (Kaptan 1995:Figure 1; Yener 2000:71-72), but the three sites mentioned above are the largest known from more than 130 years of geological research into tin sources in the region. None of these sources is of modern economic value (Kaptan 1995:198), and the exploitation of these sources in ancient times is also debated, as discussed below. The occurrences of stannite at Sulucadere and Sogukpinar are regarded by a number of scholars as unlikely to have ever provided tin, principally due to the relatively high silver and gold values in the deposits, the

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complexity of the ores and, in the case of Sulucadere, the tiny size of the deposit (Hall and Steadman 1991:221-222; Pernicka et al. 1992:92-93). Thus, the investigation of potential Anatolian tin deposits has concentrated upon the site of Kestel in the Taurus Mountains of southeastern Turkey, which allegedly operated as a tin mine in the Early Bronze Age (Yener 2000:72 ff.; Yener and Ozbal 1987; Yener et al. 1989; Yener and Goodway 1992; Willies 1990; 1992; Yener and Vandiver 1993a). The mine, containing more than 1.5 km of shafts and galleries used discontinuously from Chalcolithic to Byzantine times, contains very low concentrations of cassiterite (0.1-1.0 percent Sn) which are said to be the non-economic remains from Bronze Age mining activities (Yener 2000:73, Figure 15; Yener and Vandiver 1993a:215). The Kestel mine is believed to have been worked after ca. 3000 BCE, with an expansion from the EBI-I1 period onwards (Yener and Vandiver 1993a:214), and to have ceased production by approximately 2000 BCE (Earl and Ozbal 1996:289). The geologist associated with the Kestel project has estimated a potential production of hundreds of tonnes of tin concentrate from the mine (Willies 1991:79; 1992; 1993:263). Associated with the Kestel mine is the nearby Early Bronze Age site of Goltepe, where the mined cassiterite was processed through a complex series of concentration, crushing and smelting stages to produce metallic tin (Yener and Goodway 1992; Earl and Ozbal 1996; Adriaens et al. 1999). The site is characterized by the presence more than 5000 stone crushing tools and almost one tonne of clay crucible fragments with metallurgical accretions on their interior surfaces (Yener 2000:74, Figure 24; Earl and Ozbal 1996:289, 298). A number of deposits of powdered ore have been recovered from Goltepe, and are thought to represent different phases of ore-production at the site (Adriaens et al. 1999). Although it is suggested that they represent the high tin-containing material from Kestel that was "selectively transported to Goltepe for ore dressing and smelting" (Adriaens et al. 1999:83), the ore powders show very low levels of tin, generally less than one percent (with an average of 0.2 percent Sn; Earl and Ozbal 1996:295). There is evidence that some of the excavated powders were waste samples that had undergone heating

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processes, and it is further noted that the analyses have demonstrated "the presence of a metallic tin phase, which could be concentrated by simple metallurgical processes" (Adriaens et al. 1999:88; Earl and Ozbal 1996:297). Settlement at Goltepe reached its peak in the EBII-I11 period (Yener and Vandiver 1993a:214) and the crucible fragments from the site are dated to the span of the Early Bronze Age through their stratigraphic contexts and by radiocarbon and thermoluminescence determination~(Yener and Vandiver 1993a:216, 222; Vandiver et al. 1993; Earl and Ozbal 1996). However, the true importance of these sites remains a contentious issue, with various scholars arguing that the Kestel mine was more likely to have been a source of gold or auriferous lead (Hall and Steadman 1991:229; Pernicka et al. 1992:95; Sharp and Mittwede 1994) or perhaps iron (Muhly 1993b:25 l-252), rather than tin. The most recent reports of the early mining and smelting operations at Kestel and Goltepe acknowledge that gold winning may also have been associated with tin extraction, and that the mining operation may indeed have been initiated in the search for gold (Yener 2000:73; Earl and Ozbal 1996:289,295). The possibility that Kestel was mined for iron ores is thought to be excluded by an examination of the techniques used to process the haematite ores at Goltepe. Earl and Ozbal (1996:296) regard the fine grinding of tin-bearing haematite to small particle size as much more indicative of attempts to extract tin and gold from the haematite than to produce iron. The tin concentrations reported from the ores remaining in the Kestel mine are generally very low, leading to claims that tin is present in the mine only as a trace element, and would have been impossible to detect (Muhly 1993:247; Hall and Steadman l991:218). Although Yener and colleagues have claimed that the low tin levels now found at Kestel represent the cut-off grade below which Bronze Age extraction was not possible (approximately one percent Sn; Willies 1990:94; Yener and Vandiver 1993a:215), the analyses presented by Adriaens et al. (1999) suggest that ores with tin concentrations of less than one percent were commonly processed at Goltepe. This fact is important in considering the estimates for overall production given by Willies, which were based in part upon the idea of the "cut-off grade" and which may be significantly too high as a

result. Pernicka et al. (1992:95) regard Willies' estimates as "unrealistic" given the type of mineralization and the ore grades reported from the Celaller region. Willies (1992:lOl) has defended the proposed production levels, citing evidence for the total volume of ore that could have been extracted from the known galleries at Kestel and stating that "even at sub-one-percent-levels of tin, there seems no reason to reduce the estimate". The tin extraction process postulated for Kestel and Goltepe has been criticized as unrealistically complicated for a Bronze Age operation (Muhly 1993b:251; Hall and Steadman 1991:222). The complexity of reconstructed mining techniques at Kestel employing fire-setting is regarded by some scholars as unparalleled in the early production of tin, and more likely to have been the result of later mining activities (Muhly 1993b:25 1).The reconstruction of ore processing at Goltepe by Yener and colleagues (Yener and Vandiver l993a:23 5-23 6; Earl and Ozbal 1996), involving tin concentrations which are so low as to be unobservable until the later stages of production, is also criticized as it is difficult to imagine how such an extraction process may have originated (Muhly 1993b:251). However, the scientific analyses of the crucible fragments from Goltepe provide strong support for the production of tin at the site (Yener and Vandiver 1993b:257-258). Yener and Vandiver (1993a:Table 4; 1993b:257) report compositional analyses of 24 crucible accretions showing average tin-oxide concentrations of 30 percent (although analyses of 28 crucible accretions by Earl and Ozbal (1996:298) reveal only four samples with more than one percent tin, and a maximum concentration of 3.65 percent Sn). In addition, the vanning, concentration and refining reconstructions undertaken by Earl and Ozbal (1996) seem plausible, even if somewhat "tortuous" (as noted by Muhly 1993b3246). The experimental smelts produced very small amounts of metallic tin with high iron concentrations (up to ca. 42 percent Fe; Earl and Ozbal 1996:300), which could be collected and amalgamated by slag crushing and remelting of the tin metal prills. The reconstructions can, however, be criticized on the basis of the tin concentrates used for smelting: these contained 10-15 percent tin (Earl and Ozbal 1996:300-301), much higher concentrations than were found in any of the archaeological powder samples

from Goltepe. Of course, it could be argued that the crushed ore samples found at Goltepe represent waste products from the refining process, rather than concentrated crucible charge for smelting. Additional circumstantial evidence for the production of tin at Goltepe is provided by the appearance of tin-bronze objects at the site in Early Bronze Age contexts. Six of eight copper-base objects from the settlement contain more than five percent Sn, which Earl and Ozbal (1996:Table 6 and 302) consider as surprising given the largely "industrial" nature of the site. In comparison, other examples of early tin-bronze from central Anatolia (see below) occur in contexts more reflective of high status, such as the rombs of Alaqa Hiiyiik and Horoztepe (see below). Such evidence is, of course, open to many different interpretations. For example, a site that was producing gold, as has been claimed for Kestel, would seemingly have had enough wealth to obtain tinbronze. The potential significance for western Asia of the tin extraction processes proposed for Kestel and Goltepe is discussed further below.

Iran and the Caucasus Suitable geological conditions for the occurrence of tin exist in various parts of Iran, and this fact has led a number of scholars to suggest that tin deposits might be found within the country. For example, J. D. Muhly (1973b:409) suggested in 1973 that "a mineral zone running roughly from Hamadan to Tabriz seems to fit all the evidence for the Near Eastern tin trade as it exists today", although the supporting evidence for the occurrence of tin in this mineralized zone was unpublished (Muhly 1973a:261 and Chapter IV note 158). Further references were made to possible tin deposits in northeastern Iran near Meshed and in the Elburz region (Muhly 1973a:260). However, as Moorey (1994:299) has noted, tin is not mined in Iran today, nor is there any evidence for medieval extraction of this material. Detailed surveys of northwestern Iran by Iranian, American and French geological teams have revealed no significant traces of tin mineralization (Wertime 1978:3). Only two tin-bearing deposits in Iran are currently cited with any conviction: the minor occurrences of primary and placer cassiterite in the far east of the country in the Dasht-i Lut (Stocklin

Tin and Tin-Bronze in Early Western Asia

1 69

et al. 1972:58; Rothenberg 1982:267-268; Pigott 199913381; Vatandoust 1999:Figure 2), and the copper-tin-gold prospect near Deh Hosein in central western Iran (Momenzadeh et al. 2002). The Dasht-i Lut deposits may relate to the tin of Drangiana (modern Seistan) mentioned by Strabo (15.2.10). However, Wertime (1978:4) has reported that his survey of the region in 1976 revealed no traces of workable cassiterite or stannite, and his doubts as to the occurrence of significant tin deposits in Iran are shared by Penhallurick (1986:19-20). In contrast, the ore deposit at Deh Hosein shows evidence for large-scale extraction. However, this extraction is limited to the early first millennium BCE and the deposit is primarily of copper (chalcopyrite, malachite, azurite, tenorite) with maximum tin levels of only ca. one percent (Momenzadeh et al. 2002). Although the site has been suggested as possibly important for the production of Iron Age Luristan bronzes, it is unlikely to have been significant for the Bronze Age tin trade: the exclusive extraction of minor cassiterite from the deposit does not seem possible, and the production of a consistent natural tin-bronze by the smelting of mixed copper and tin ores has not yet been demonstrated archaeologically. A number of references can be found to tin deposits in the Caucasus, and cassiterite was supposedly worked at the archaeological site of Metsamor in Armenia in the thirteeth century BCE and perhaps earlier (e.g. Crawford 1974:242-243; Burney and Lang 1971:68). However, more recent assessments of the evidence from Metsamor and other areas of the Caucasus have tended to indicate that claims for tin sources are not supported by geological evidence, and should be considered unproven (Penhallurick l986:18-19; Moorey 1994:300). Although I. R. Selimkhanov (197857) is adamant that tin deposits are not to be found in the area, Kavtaradze (1999:86) reports that geologists have recorded "twenty deposits with tin content" in western Georgia. None of these deposits, however, contained any evidence for ancient exploitation, and the meaning of the phrase "tin content" is unclear. We do not know the grade of the deposits if they are in fact of cassiterite, and it is possible that the tin ores are only a minor mineral com-

17 0

Early Metallurgy of rhe Persian Gulf

ponent in deposits largely consisting of other base metal ores (such as in the copper-tin deposit at Deh Hosein). As such information is not currently available for the Georgian deposits, their potential significance for Bronze Age tin extraction remains uncertain. Afghanistan and Central Asia The sources of the tin used in third millennium western Asia have often been sought in regions with welldocumented sources of tin that lie outside western Asia itself. For the metal industries of Mesopotamia and Iran, tin is often posited to have come from further to the east. It is therefore significant that extensive tin deposits, both granite-hosted and alluvial, are known from many areas of Afghanistan (Berthoud et al. 1977; Rossovsky et al. 1987; Pigott 1996, 1999a:Figure 9; Economic and Social Commission for Asia and the Pacific [ESCAP] 1996:32-37). All the primary tin mineralization in Afghanistan is associated with skarns, fault zones or pegmatites, and a number of low-grade placer deposits are known (ESCAP 1996:32). In addition to the major tin occurrences in Afghanistan, 44 tin mineral occurrences and numerous tin mineral showings are widely distributed throughout the country (ESCAP 1996:37). Research by a French tcam has isolated tin deposits near ancient copper mines southwest of Herat (cf. ESCAP l996:32), while tin-bearing sands regarded as "easily beneficiated by panning" were recorded in the Sarkar Valley (Cleuziou and Berthoud 1982:16 and Figure 2; Berthoud et al. 1977). Details of the majority of tin deposits recorded in Afghanistan by Russian geologists are summarized by Rossovsky et al. (1987) and by Stech and Pigott (1986:44-45), who note the common association of cassiterite with copper, lead and gold, and deposits with greater than five to six percent tin (see also ESCAP 1996:32). While the area is emerging as one of the most likely sources for the tin used in Bronze Age western Asia (Moorey 1994:301) and South Asia (Kenoyer and Miller 1999:118), it has been observed that, aside from the overwhelming geological evidence, "there is no other substantive evidence to suggest it as a source for ancient Near Eastern bronze production" Pigott (1999a:118). The little evidence that exists for early use of tin-bronze in the region is discussed below.

Tin deposits in central Asia proper were brought to the attention of archaeologists working in western Asia by the publications of Masson and Sarianidi (1972:128) and Crawford (1974:243, citing Kuzmina 1966), who noted the occurrence of tin deposits "on the Zeravshan River about halfway between Bukhara and Samarkand". The exploitation of the mines was said to date back to the Middle Bronze Age (ca. 2000-1600 BCE), but the possibility of earlier workings was not ruled out (Crawford 1974:243; see also Cleuziou and Berthoud 1982:16-1 7). This occurrence, and the proposed Middle Bronze date, has been confirmed by important recent work undertaken in the region by scholars from Germany, Uzbekistan and Tajikistan (Alimov et al. 1998; Boroffka et al. 2002). This work has isolated a number of tin occurrences between Bukhara and Dushanbe, at the sites of Karnab, Lapas, Cangali and Mushiston (Alimov et al. 1998:Abb. 1). The Karnab mineralization is regarded as a typical example of a granite-related tin deposit, with tin present as cassiterite in quartz veins in a granite intrusive complex. Other tin mineralization at Karnab, formed by contact-metasomatic processes at the contact between quartz veins and marble, is considered less important for ancient extraction processes (Alimov et al. 1998: 164). Tin concentrations in samples from Karnab are relatively low (ca. 1.3 percent Sn or less), and relatively high sulfur levels are recorded due to the presence of associated arsenopyrite, pyrite and sphalerite (Alimov et al. 1998:164 and Table 1).There is evidence for mining operations at Karnab radiocarbon dated to the first millennium BCE (Alimov et al. 1998:170-179; see also Penhallurick 1986:25-28), and mining as early as the second millennium BC is indicated by the presence of Andronovo sherds in the lower levels of the mine (Boroffka et al. 2002:145, 147; Parzinger 2000:249). It has been suggested that ancient mining may have concentrated upon the richest areas of tin mineralization at the site and that the remaining ore is of a lower grade than that which was actually extracted (Alimov et al. 1998:166). Nearby the Karnab mine site is a seasonal Andronovo settlement with evidence for some smallscale metalworking activities, including the use of tin ores and the possible production of tin-bronze (Boroffka et al. 2002:149-153; Parzinger 2000:250).

Mushiston is a hydrothermal ore deposit with numerous, relatively thin ore veins situated between dolomitized limestones of the Upper Silurian-Lower Devonian Kupruk-formation and the schists of the Upper Devonian Akbasai-Formation (Alimov et al. l998:166). The deposit is unusual in that it contains significant quantities of both copper and tin, with the primary mineralization consisting of stannite (Cu2FeSnS4)with associated cassiterite, arsenopyrite, pyrite, chalcopyrite and tetrahedrite (Alimov et al. l998:166). The deposit also has a significant oxidation zone with rich secondary mineralization including malachite with infrequent azurite, alongside cassiterite, varlamoffite (Sn02.nH20)and Mushistonite ( C ~ s n ( 0 H )(Alimov ~) et al. 1998:167; Boroffka et al. 2002:141-142). Tin and copper concentrations in both the primary and secondary mineralization zones are very high, ranging up to 50 percent Cu and 34 percent Sn (Alimov et al. 1998:Table 2). However, there is great variation in the concentration of these two elements in the 18 samples analyzed, with compositions varying between almost pure copper ore and almost pure tin ore, and many ratios in between (Alimov et al. 1998:167). The Mushiston deposit is considered to be of potentially great importance for the early production of tinbronze in the region, as the smelting of the mixed ores from the site is likely to have led to the production of a natural tin-bronze (Alimov et al. 1998:166, 184). Mixed copper-tin ores were available in one of the recently examined Mushiston mining galleries, which were worked by at least the middle of the second millennium BCE according to radiocarbon determinations and finds of Andronovo pottery (Alimov et al. 1998:185, 190). Parzinger (2000:250) has claimed radiocarbon determinations from Mushiston date as early as the second half of the third millennium BCE, but as yet the dates are unpublished. Alimov et al. (1998:170) note that, for both modern and ancient mining operations, considerations of logistics and infrastructure are just as crucial to the viability of a mining operation as overall ore grades. They therefore emphasize their belief that, although analyses indicate that Mushiston is a much richer ore body, a number of factors including the elevation (ca. 3,000 m asl) and inaccessibility of the Mushiston deposit make Karnab a more viable mining operation.

Tin and Tin-Bronze in Early Western Asia

17 1

A number of other important metal deposits have been recorded in the region. The mine of Kaznok (about one km east of Mushiston) also contains copper and tin mineralization, but of a form only accessible through modern mining techniques (Alimov et al. 1998:169). The lead-zinc-silver occurrence of Chirgasang and the lead-zinc deposit of Kaninukra lie to the west of Mushiston, where there is evidence for mining and slag from lead smelting that probably relates to medieval silver production (Alimov et al. 1998:169). Ruzanov (1979) reports tin deposits to the southwest of Samarkand and along the Kok-Su River, known to have been worked in the early centuries CE and perhaps much earlier. Penhallurick (1986:25-26) describes other tin deposits in the Ferghana Valley region.

India Tin deposits occur in a number of Indian provinces, including Maharashtra, Karnataka, Bihar, Rajastan, and Gujarat (Chakrabarti and Lahiri 1996:25-26 and Map 2; Asthana 1993:278). Hegde (1978:40-41, Figure 2) further notes the possibility of alluvial cassiterite deposits in the Kaptagod, Aravalli and Chota Nagpur Hills, and more recent research in Haryana has identified a significant tincopper deposit at Tosham (also called "Tusham"; see Seetharam 1986; Kochhar et al. 1999; Chakrabarti 2002). The Hazari Bagh deposits of Bihar are the largest in India (Penhallurick 1986:21), while the smaller sources in Rajastan and Gujarat (and now at Tosham) have been regarded as more significant for early metallurgy due to their proximity to the Indus Valley (Asthana 1993:278). There is very little archaeological evidence for the early exploitation of these deposits, although Chakrabarti and Lahiri (1996:25-26) have drawn attention to British colonial descriptions of pre-industrial cassiterite extraction at Bastar in Madhya Pradesh, and Paharsingh and Nurungo in Bihar. Muhly (1985a:283), though allowing for the occurrence of significant alluvial cassiterite deposits in Madhya Pradesh, states his belief that Indian tin deposits are likely to have been an important source only for local metallurgy. Certainly, there is no strong archaeological evidence for the exploitation of Indian tin sources in the Bronze Age, but the same can be said for copper mining in the region, which was almost certainly taking place by the third millennium BCE (Chakrabarti and Lahiri 1996:192-196).

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Europe For Anatolia, the Aegean and the Eastern Mediterranean, tin deposits in the western Mediterranean (e.g. Sardinia and Iberia), or in western Europe (e.g. the Erzgebirge Mountains and Brittany), have often been regarded as potential sources (Muhly 1985a:285-287). Tin is also known to occur in the area of the former Yugoslavia (McGeehan-Liritzis and Taylor 1987), and the well known tin deposits in Cornwall are also a possible source in later periods (Muhly 1985a). The tin occurrences at the sites of Cer, Bukulja and Srebrenica in the former Yugoslavia (McGeehan-Liritzis and Taylor 1987:289-290) are lode deposits, while placer deposits of stream tin also occur at Cer. The placer deposits are considered large enough to be of potential commercial value, although no details are given on the grade of the alluvial deposit and no archaeological evidence for ancient working has been recovered (McGeehan-Liritzis and Taylor 1987:290). Further to the west, the large tin deposits of the Erzgebirge have been worked since at least the twelfth century CE (Taylor 1983:295). Bronze Age tin production in the region has often been hypothesized (e.g. Penhallurick 1986:71-79), however this possibility was rejected by Muhly based partly on the fact that primary tin ores in the Erzgebirge are hosted by hard granite and could not have been mined at such an early stage (Muhly 1973a:27). In response to Muhly's arguments, Taylor (1983) has given a detailed description of the geology of the Erzgebirge, highlighting the presence of placer deposits which would have been workable during the Bronze Age (see also Roden 1985:74; Rapp et al. 1999). Circumstantial evidence for Bronze Age tin production in the Erzgebirge region is provided by the local utilization of significant amounts of tin-bronze after ca. 2000 BCE (Tylecote 1987:39), and the proximity to the tin deposits of Late Bronze and Iron Age settlements situated in locations non-ideal for agricultural subsistence (Bouzek et al. 1989). It has been suggested that the lack of many early settlements in the tin-bearing regions of the Erzgebirge might be explained by the transport of extracted tin ores to more distant settlements for smelting (Roden 1985:74). The lack of convincing evidence for the Early Bronze Age exploitation of alluvial cassiterite in the Erzgebirge is highlighted by Niederschlag et al. (2002),

and supported by recent LIA of ores and objects from the region (Niederschlag et al. 2003). Additionally, Muhly (1985a:289-290; 1987:103-104) provides a significant argument against the early exploitation of these deposits by noting that Classical and later sources never refer to tin from Bohemia. The significant tin deposits of northwestern Spain and Portugal (Muhly 1985a:286; Tylecote 1987:38) were worked at least as early as the Iron Age and perhaps earlier (Roden 1985:72; Giardino l995:3 12-3 16), and correspond to the tin producing areas of Galaecia and Lusitania described by Pliny the Elder and Strabo. The extraction of alluvial cassiterite is indicated by Pliny's note (Natural History XXXIV.156-157) that tin is found "in the surface strata of the ground which is sandy and of a black color. It is only detected by its weight, and also tiny pebbles of it occasionally appear, especially in dry beds of torrents". Likewise, Strabo (Geography 3.2.9) records that the tin-bearing soil of northwest Lusitania "is brought by the streams; and the women scrape it up with shovels and wash it in sieves woven basket-like". Tin is also said to occur in the provinces of Murcia and Almeira in southeastern Spain (McGeehanLiritzis and Taylor 1987:288). The tin deposits of Brittany are known to have been worked in the prehistoric period (Penhallurick 1986536-94; Roden 1985:66-71), and may have been an important source for the eastern Mediterranean world from the later second millennium BCE (Muhly 1985a:287). Evidence for the ancient exploitation of tin deposits in the Massif Central of France is lacking (Penhallurick 1986:86). The main cassiterite deposits in Italy are found in Tuscany, with smaller occurrences known in Etruria (Muhly 1985a:285; Roden l985:72-73; McGeehanLiritzis and Taylor 1987:288-289). The grade of the Tuscan deposit (ca. 0.4 percent Sn) has seen it described as "wildly uneconomic" for production even in the middle of the twentieth century CE (Tylecote 1987:38), although much richer ores in the area are reported by Roden (1985:73). Extensive mining during the Second World War has destroyed any evidence that may have existed for early tin extraction in the region (Roden 1985:72). Analyses of copper-base objects from northern Italy have indeed revealed the presence of a small number tin-bronzes in third millennium BCE contexts (Eaton

1977), and one copper object with a possible coating of metallic tin (Angelini et al. 2002), however the Italian deposits are likely to have been significant only for local use at most (Penhallurick 1986:80-82). Likewise, a number of minor tin deposits are known in southern Sardinia, particularly in the Iglesias region (Tylecote et al. 1983; McGeehan-Liritzis and Taylor 1987:289). There is no evidence for the early working of the Sardinian deposits (Beagrie 1985: 166; Giardino 1995:309), and the find of a crucible containing oxidized fragments of a tin ingot from the Nuraghic site of Forraxi Nioi cannot be dated earlier than the Late Bronze Age (Tylecote et al. 1983; Muhly 1985a:286). The abundant tin deposits of Cornwall have been discussed in numerous papers dealing with early tin and tin-bronze use (see Penhallurick 1986:148 ff. for a detailed discussion), and it is certain that they were exploited from at least the end of the third millennium BCE. J. D. Muhly (1973b3409-412; 1980:40; 1985a: 287-288) envisages Cornish tin and Baltic amber reaching the eastern Mediterranean in the later Bronze Age, with definite evidence for such a trade from at least the sixth century BCE onwards. However, it is extremely unlikely that Cornish tin was being used in Bronze Age western Asia, for reasons related to both the chronology of tin-bronze use in Britain and the distance of the source from western Asia.

Archaeological Evidence for Early Tin-Bronzes Tin-bronzes, defined variously as copper alloys containing over one, two or five per cent tin, first appear in a number of areas of western Asia in the later fourth or early third millennium BCE. The archaeological evidence for early tinbronze use has been summarized and discussed in numerous scholarly works (e.g. Muhly 1973a, 1985a, 1993b; Eaton and McKerrell 1976; de Jesus 1980; Yakar 1984; Montero-Fenollos 1997) and only an outline is presented here, alongside important recently documented occurrences and relevant re-interpretations of the evidence. In Mesopotamia, the earliest tin-bronzes are found in the Early Dynastic I (ED I) period at the Y cemetery at Kish, and occur in tombs which probably represent the burials of elite members of the society. Eight of 23 analyzed copper-base objects from Kish contain one percent tin or more (Stech 1999:63; Moorey and Schweizer 1972;

Tin and Tin-Bronze i n Early Western Asia

1 73

Miiller-Karpe 199l),but tin-bronzes remain uncommon in the region until the ED I11 period (ca. 2600-2350 BCE), when they form a significant percentage of the copperbase objects found in the Royal Cemetery at Ur (Stech 1999:Table 3.1; Miiller-Karpe 1991:Table 1).Tin-bronze does not appear to have been so common at other Mesopotamian sites:Moorey (1994:253) notes that analyses of material from Tepe Gawra revealed no tin-bronze before Level V1 (Akkadian to post-Akkadian), and that the alloy was scarce even at this time (see also Muhly 1987a:285 for differences between Ur and Tepe Gawra). As Stech (1999:64) has observed, the introduction of tinbronze at certain Mesopotamian sites "did not occasion its entry into general circulation" within the alluvium. Early third millennium BCE tin-bronzes are also found at sites further to the west and north. A cache of six human figurines from Level G at Tell Judaidah in the Amuq which dates to the early third millennium BCE contains some of the earliest known examples of tin-bronze (Braidwood and Braidwood 1960:296-3 15,516-519; Stech and Pigott 198652).Although the date of the Judaidah figurines has been questioned (see Seeden 1980:8; Yakar l984:7O; Hall and Steadman 1991:227), a few tin-bronzes are found in other Level G deposits from Tell Judaidah, reinforcing the evidence for early tin-use at the site (Yener and Vandiver 1993:97). Until recently, very few tin-bronzes of similar date were known from other Syrian sites, despite extensive references to tin and bronze in the mid-third millennium BCE texts from Ebla (see below), and Stech and Pigott (198652)regarded the earliest "reliable" occurrence of tin-bronze as the late third millennium example from Tell Sweihat (see also Maddin et al. l98O:ll3). However, 1 6 tin-bronzes (mostly decorative pins with up to 19 percent Sn) dating to the EDI period have recently been recovered from a tomb at the site of Tell Qara Quzaq on the northern Euphrates in Syria (Montero 1995; Montero Fenoll6s 1997:1 6 and Figure 1; Montero Fenoll6s and Montero Ruiz 2000:Lam. 5.1). Early or mid-third millennium tinbronzes are also reported from southeastern Anatolia at Tarsus (Esin 1969; Yener and Vandiver 1993; Muhly 1993b:240), where six of 25 analyzed EBII objects contain more than one percent tin, with an average of 4.4 percent Sn (DeJesus 1980:Graph 8; Muhly 1993b1240; cf. Yener and Vandiver 1993b3256).

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Early Metallurgy of the Persian Gulf

Further evidence for early tin-bronze use comes from Early Bronze Age (EB) I1 and I11 contexts in the central Anatolian sites of Ahlatlibel, Mahmatlar, Alaqa Huyuk and Horoztepe (Esin 1969; Muhly 1993b:240-242). While the absolute chronology of the Bronze Age in Anatolia is much debated, the EBII period in central Anatolia probably begins in the second quarter of the third millennium, and extends to ca. 2300 BCE (Yakar 1984:73; cf. Miiller-Karpe l 9 9 l : l l l ) . From the EBII period at Ahlatlibel eight tin-bronzes are recorded out of 20 analyses (de Jesus 1980:Graph 2), while EBII Mahmatlar had seven tin-bronze objects (Muhly 1993b:240). Nineteen of 40 analyzed objects from EBII Alaqa Hiiyiik were tin-bronze (de Jesus 1980:Graph 3), while 32 of 56 analyzed samples from EBIII Horoztepe proved to be of tin-bronze (de Jesus 1980:Graph 5). All these figures are based upon a definition of tin-bronze as containing more than one percent Sn. Additionally, Yakar (1984:73) makes mention of the production of tin-lead pewters in Anatolia at this time, although he cites no references. The distinctly regional character of Anatolian tin use in the EBA is indicated by analyses of objects from sites such as Ikiztepe on the Black Sea coast, which have revealed a more limited use of tinbronze in the later third millennium (Bilgi 1984; Gedik et al. 2002). However, even at Ikiztepe, where the analyses (Bilgi 1984:73) are said to indicate that "copper is alloyed only with arsenic", 14 of 101 analyzed copperbase objects contain more than two percent tin, with a further four objects having 0.5-2.0 percent tin. These tin-bronzes come from Late Chalcolithic, EBII, EBIII and late third millennium BCE contexts at the site, and moreover are characterized by higher levels (often more than one percent) of zinc and lead, and lower levels of arsenic, than the remaining objects at the site (an interesting impurity pattern matched by some contemporary Transcaucasian tin-bronzes; see Edens l995:56). Evidence of significant tin-bronze use is also found in third millennium contexts in northwestern Anatolia, at the sites of Troy and Beshiktepe (Pernicka et al. 1984; de Jesus 1980:134-135), and at a number of nearby Aegean settlements which show strong Anatolian connections in their material culture, such as Poliochni on Lemnos (Pernicka et al. 1990), Thermi on Lesbos (Begemann et al. 1992; 1995; Stos-Gale 1992) and

Kastri on Syros (Stos-Gale et al. 1984). These tinbronzes were thought to have been among the earliest in the western Asia, dating to the first half of the third millennium BCE, but more recent debate has tended to date them towards the third quarter of the third millennium (Manning 1995:Figure 2; J. E. Coleman 1992:276; Mellink 1992:219; Muhly et al. 1991:215 ff.). The florescence of tin-bronze use at Troy occurs in the Troy I1 period (where 61 percent of objects contain more than one percent Sn), although one example of tin-bronze is claimed to occur in a Troy I context (de Jesus 1980:134-135; but see Muhly 1985a:283-284 for problems with the chronological attribution of this piece). The material from Thermi is particularly interesting, as Thermi Towns I-V are usually considered to be contemporary with Troy I and early Troy 11, and the limited tin-bronze use at Thermi (three objects from 33 analyses) is thus clearly datable to the second quarter of the third millennium BCE (Manning 1995:Figure 2; Yakar 1984:83; Muhly 1985a:284; Begemann et al. 1992:220-221). A further five tin-bronzes at Thermi are recorded from the so-called "Potter's Pool" deposit, which may date to the Troy I1 period rather than Troy I (Begemann et al. 1992:221). Thermi has also provided the earliest example of metallic tin in the region, a bangle from Level IV (Begemann et al. 1992). The chronological attribution of other claimed early examples of tin-bronze in Anatolia, such as those from Mersin, have been clearly refuted (Yakar 1984:60; Muhly 1985a:284), while two examples of tin-bronze from the Greek site of Sitagroi (Level IV) are likely to be contemporary with the Thermi examples (Begemann et al. 1992:223). Tin and tin-bronze are found more sporadically in other areas of western Asia before the end of the third millennium BCE, with the majority of metal assemblages reflecting instead the use of pure or arsenical copper (Eaton and McKerrell 1976:Table 9; Moorey 1982:97-98). Tin is used for only a handful of objects in third millennium Egypt and the Levant (Lucas 1934:177-1 78; Eaton and McKerrell 1976; Maddin et al. 1980:117; Cowell 1987; Muhly 1993b:243), and the late date for the introduction of tin-bronze into Egypt is supported by analyses of the blue and green pigments used for wall paintings. Such pigments were manufactured from copper-base scrap metal, and their composi-

tion indicates an absence of tin-bronze before the rule of Thutmosis I11 in the fifteenth century BCE (El Goresy et al. 1995; Schiegl 1994:95). Such evidence is open to other interpretations (for example technological, economic, or ideological preferences for copper scrap over tin-bronze scrap in the manufacture of pigments) but seems to match quite well with the chronological changes in alloying suggested by the analyzed objects from the region. In Iran, early tin-bronzes occur with significant frequency only at the site of Susa. The analyses of Malfoy and Menu (1987:Table D) indicate that tin-bronze first appears consistently at Susa in the Susa IVA2 period (equivalent to the EDIIIB period in Southern Mesopotamia) and the frequency of tin-bronze use remains below 10 percent of objects until the late third millennium BCE, when 15 percent of Susa VA objects (three of 20) are of tin-bronze. The real beginnings of tin-bronze use date to the Susa VB phase, in the early second millennium BCE, when more than 60 percent of objects are of tin-bronze (64 of 98 analyses). Isolated examples are known from later fourth-early third millennium BCE contexts at Susa (Moorey 1982; Stech and Pigott 1986:42-43), although the chronological attribution of some of these pieces has been questioned (MiillerKarpe 1991:111).Elsewhere in Iran, one arsenical tinbronze is recorded from Giyan Period IV, which dates broadly to the mid-third millennium BCE (Berthoud 1979). Besides these early examples, a more consistent use of tin-bronze is recorded for the late third and early second millennia BCE at Tepe Godin (period 111) and Tal-i Malyan in the Kaftari phase (Pigott 1996:461; Pigott 1980:107; Pigott et al. 2003). Other Iranian sites such as Tepe Sialk, Tepe Hissar, Shahr-i Sokhta, Shahdad and Tepe Yahya show predominant use of arsenical copper in the third millennium (Pigott 1999a, 199910; Vatandoust 1999:Table 2; Thornton et al. 2002a). As Pigott (1996:460) has noted, tin-bronze does not become the dominant copper alloy in Iran until the Iron Age (see also Pigott 1980:105; Moorey 1982:87). The evidence for the early occurrence of tin-bronze in the Caucasus region is similar to that from Iran. The summary of alloy types used in the early metal industries of Asia and Eastern Europe provided by E. N. Chernykh (1992:Figure 6) indicates that tin-bronze appears in

Tin and Tin-Bronze in Early Western Asia

17 5

conspicuous amounts in the Trans-Caucasus and Caucasus only towards the end of the third millennium BCE. However, in one subterranean tomb at the site of Velikent in Daghestan, 15 of 195 analyzed copper-base objects (ca. eight percent) were found to contain more than one percent Sn (Gadzhiev and Korenevskii 1984). Kohl et al. (2002) now date the Velikent catacomb tombs to the early-middle third millennium BCE based upon radiocarbon determinations, thus making these tin-bronzes among the earliest recorded for the Caucasus and among the earliest in wider western Asia. Further isolated examples of contemporary or even earlier tin-bronzes from the Caucasus region are reported by Kavtaradze (1999:71), who nevertheless suggests a gradual introduction of tin-bronze in the later third millennium BC, followed by its adoption as the predominant copper alloy in material from the Trialeti kurgans in the terminal thirdlearly second millennium. Significantly, the early use of tin-bronze south of the Greater Caucasus has been linked to the presence of a small number of lapis lazuli items which appear in the region in the later third millennium BCE (Apakidze 1999:Abb. l),and to a significant increase in the amount of gold found at Transcaucasian sites from the Middle Bronze Age (Edens 1995:60). An origin of all three materials in Afghanistadcentral Asia has been suggested, utilizing a trade route that brought raw materials from Afghanistan via Turkmenistan, thence across the Caspian Sea or perhaps through Iran, north of the Elburz Mountains, to the Trans-Caucasian region. Apakidze (19 9 9 5 13) envisioned the Afghani raw materials as subsequently being transported along the large river valleys south of the Greater Caucasus to the eastern Black Sea coast, from where they were traded to more westerly regions such as northwestern Anatolia and the Aegean. Such a reconstruction has also been suggested by Edens (1995:60-61), and is obviously of significance for the discussion of tin sources presented here. Analyses of copper-base objects from central Asia also indicate that the frequent use of tin-bronze is a relatively late innovation. In Turkmenistan, the earliest bronze object comes from a Namazga IV (ca. mid-third millennium BCE) context at the site of Aktepe (Ruzanov 1999:104), but bronze remains infrequent in the

176

Early Metallurgy of the Persian Gulf

subsequent Namazga V period at the major sites of Anau, Namazga and Altyn-depe (Ruzanov 1999; Salvatori et al. 2002; Terekhova 1981:319-320; Pigott 1996:461; Egor'kov 2001). Analyses of third millennium BCE copper-base objects from Sarazm on the Zeravshan River in Tajikistan, in the immediate vicinity of the previously-discussed central Asian tin sources, revealed only unalloyed copper (Isakov et al. 1987; Pigott 1996:461). A similar lack of tin-bronze is seen in eastern Bactria at the settlement of Shortughai (Berthoud et al. 1982:Table C; Francfort 1989:208). The real beginning of tin-bronze metallurgy in central Asia can be placed in the early second millennium BC, in the BMAC or Namazga V1 phase (Hiebert 1994:Figure 10.1). At this time, bronze becomes the dominant alloy at sites in southern Uzbekistan, Tajikistan and Turkmenistan, although apparently not in the Kopet Dagh region or the Murghab oasis (Ruzanov 1999:104; Hiebert 1994:160; Hiebert and Killick 1993). Bronze use is also significant among the adjacent steppic (Andronovo) peoples in the second millennium BCE (Ruzanov 1999). This could reflect either contact between these groups and the bronzeusing sedentary agriculturists of the central Asian oases, or the direct involvement of Andronovo peoples in tin mining in the Zerafshan valley, as suggested by the Andronovo pottery from the tin mines at Karnab and Mushiston (Alimov et al. 1998:Abb. 29; Boroffka et al. 2002). The situation seems noticeably different further to the south in Afghanistan, although very few analyses have been undertaken. Important evidence comes from Mundigak, where a small number of analyses indicate that tin-bronze was used from the middle of the fourth millennium BCE, although the absolute dates are debated (Stech and Pigott 1986:47). Unfortunately, a number of possibly early tin-bronzes from Snake Cave in Afghanistan analyzed by Caley (197171972a,b)cannot be assigned a clear chronological range. The Afghani evidence is paralleled by the occurrence of tin-bronzes at a number of sites in Pakistani Baluchistan excavated by Sir Aurel Stein. Six of seven "prehistoric" samples from the sites of Shahi-Tump, Mehi, Siah-damb and Segak analyzed by Desch were of tin-bronze (Ullah 1931a: 488). The material from Shahi-Tump and Siah-damb

(also known as Nundara) seems clearly to belong to the first half of the third millennium BCE (Possehl 1999595; Besenval 1997) and Asthana (1993:277-278) allocates all of these finds to the pre-Harappan period. Tin-bronze use is also attested at Indus civilization sites. Of the 177 objects analyzed from MohenjoDaro and Harappa, 30 percent show tin concentrations of greater than one percent (Agrawal 1984:164). A chronological change in alloy use is also seen, as tin-bronze is much more abundant in the later levels of Mohenjo-Daro (23 percent of objects) than in the earliest phases at the site (six percent of objects) (Agrawal 1984:164; see also Ullah 193la:484). Seven of 1 3 tools analyzed from Rangpur contain more than two percent Sn (Agrawal 1984:164), while a tabulation of metal alloys used in prehistoric India (Lahiri 1995:Table 2 ) indicates that tin-bronze was also used at the Indus sites of Kalibangan, Lothal, Rojdi, Chanhu-Daro and Surkotada (see also Chakrabarti and Lahiri 1996:36-65; Kenoyer and Miller 1999). Ingots of tin-bronze are also said to have been found at Mohenjo-Daro (Mackay 1943: l 8 7 ) , although the attribution is based only on the color of the metal rather than compositional analyses. Both Agrawal (1984:164) and Asthana (1993:278) have speculated that the infrequent use of tin-bronze in the Indus region reflects the scarcity of tin available to local metalsmiths, and Asthana notes that tin and tinbronze are very rare for more than a millennium in post Harappan contexts in the region (see also Yule 1989). Such a pattern of use suggests that the wideranging trade contacts developed in the Harappan period were responsible for the arrival of tin-bronze at Harappan sites, which would indicate the utilization of tin sources from outside the Indus region (Asthana 1993:278). In contrast, Chakrabarti and Lahiri (1996:207) argue strongly against such technologically deterministic and evolutionary interpretations of early alloying. They suggest that social traditions of "purity" and the conservation of raw materials, observed ethnographically and through ancient texts, may better explain the variable pattern of copper and copperalloy use in South Asia since the Bronze Age. These issues will be further elaborated upon in the following sections of this chapter.

Returning to the Gulf, it is unfortunate that virtually no analyses of third millennium BCE metal objects from the central Gulf region have been undertaken. Although copper-base objects and fragments have been reported from Tarut Island (Piesinger 1983:190) and copper-base objects, crucibles and copper-working residues are known from City Ib levels at Qala'at al-Bahrain (Hrzrjlund and Andersen l994:370-38 l ) ,they remain largely unanalyzed. Only material from the subsequent City I1 period at the Qala'at, the Saar settlement (Weeks forthcoming a ) and graveyard (Prange et al. 1999), and the Barbar temple (McKerrell 1977; Heskel, undated) has been chemically studied. The earliest analyses were of 30 metal objects from the Barbar Temple (wrongly attributed to the site of Qala'at al-Bahrain) undertaken by H. McKerrell (1977: 167). The absence of tin-bronzes among these objects was taken used to suggest that there was no significant tin trade through the Gulf in the very late third or early second millennium BCE (McKerrell 1977: 167). Further analyses of material from the Barbar Temple (Heskel, unpub.) tend to support such a view, with tin concentrations of one percent or higher recorded in only five of more than 100 analyzed samples (all five objects were axes). The seeming infrequence of tin-bronze use at Barbar may, however, partly reflect the samples that were available for analysis. Most were sheet fragments or nails used to decorate the temple and seem to have been preferentially made of pure copper, perhaps for ideological reasons similar in conception to those outlined in the preceding paragraph. Less than 40 of the Barbar Temple analyses are of finished objects that are not sheet fragments or nails, and the ratio of tin-bronze to unalloyed copper among this group is consequently somewhat higher. Nevertheless, a similarly low rate of tin-bronze use is reported by Prange et al. (1999:191 and Figure 6), where only two objects from about 40 analyses of second millennium Bahraini material contained in excess of one percent tin, with a maximum concentration of six percent tin in an object from the Saar grave field. In contrast, analyses of five objects from Bahrain tumuli presented by Peake (1928:454) revealed that they were all tin-bronzes with high tin concentrations. At least one of these objects was a socketed spearhead from Mackay's excavations at the 'Ali cemetery (Reade and Burleigh 1978:82) which has exact typological ~arallels

Tin and Tin-Bronze in Early Western Asia

177

in the late third to early second millennium BCE in southeastern Arabia (Potts 1990a, 2000). It is likely that the other items analyzed came from either Mackay's excavations or those of Mr. and Mrs. Bent at 'Ali in 1889 (Reade and Burleigh 1978), and also date to the early second millennium rather than to ca. 1200 BCE as proposed in the original article (Peake l928:454). Peake's analyses are therefore good evidence for tin-bronze use on Bahrain in the City I1 period, and are supported by analyses of objects from the Saar settlement, where a further five tin bronzes were recorded in a group of 19 analyzed finished objects (Weeks, forthcoming a). In summary, there is no evidence at all regarding alloying practices in the third millennium BCE in the central Gulf, while analyses of early second millennium BCE material indicate a limited use of tin-bronze. Finally, as summarized in Chapter Two, a number of analytical studies have revealed little evidence for the use of tin-bronze in southeastern Arabia prior to the second millennium BCE (Hauptmann et al. 1988; Prange et al. 1999),whereas recent analytical programs and the data presented in this volume provide ample evidence of tinbronze use in the northern Oman Peninsula in the Umm al-Nar Period (Weeks 1997:20-22). Two of three recently analyzed objects from a burial context at Aztah near Salalah, in the Dhofar province of southern Oman, are also of tin-bronze (Yule 1999). The chronological attribution of these objects to the third millennium is uncertain, and it is difficult to know whether they should be grouped with material from the Oman Peninsula or South Arabia, as the typological parallels with material from Asimah in Ras al-Khaimah cited by P. Yule (1999: 91) are not particularly convincing. Archaeological surveys indicate that the southernmost location of Umm alNar cultural materials is Masirah Island, suggesting that the Aztah finds are more likely to reflect a South Arabian metallurgical tradition. Very little is known of South Arabian metallurgy in the third millennium BCE, although the Aztah data can be compared with recent analyses of a hoard of Bronze Age objects from the site of al-Midamman near the Red Sea coast (Giumlia-Mair et al. 2002). Analyses of these objects, typologically dated to a broad Early-Middle Bronze Age range (third to second millennium BC), revealed the presence of a number of low-tin bronzes (Giumlia-Mair et al. 2002:Table 1).

17 8

Early Metallurgy of the Persian Gulf

Texts Referring t o the Bronze Age Use and Trade of Tin The earliest textual sources from western Asia have proven critical for the reconstruction of ancient trade and exchange in metals. As a relevant illustration of this point, one might consider the metals trade between Mesopotamia and Dilmun, so clearly reconstructed through textual sources by A. L Oppenheim (1954), W. F. Leemans (1960) and others. As summarized by B. Foster (199759): Buying and selling metals in commerce can now be documented continuously from the latter half of the third millennium through the Old Babylonian period. Sumerian and Babylonian merchants went to Dilmun to buy copper and tin, while traders from Dilmun came to Mesopotamia, for example, to Sargonic Umma, Lagash, and Agade, as well as to Susa when it was under Sargonic rule. Contacts between Dilmun and archaic Uruk push the possibilities of such contact back half a millennium, while contacts with north Syria at various times extend the geographical horizon of such trade far beyond Sumer ...As the evidence accumulates, the continuity of this trade is impressive in its consistency. The importance of textual sources is particularly clear in the case of the early use and trade of tin in western Asia. As discussed above, archaeological evidence for objects of metallic tin is extremely limited prior to the midsecond millennium BCE, whereas references to tin and tinbronze in textual sources are frequent. Textual evidence for the use and trade of tin has been discussed in detail by J. D. Muhly (1973a, 1973b) and others (e.g. Limet 1960; Malamat 1971; Larsen 1976,1987; Waetzoldt 1981; Joannes 1991; Archi 1993), and is summarized below. From Bronze Age written sources, words for tin are known in Sumerian, Akkadian, Hittite, Egyptian and Ugaritic (Muhly 1985a:279; see also Muhly 1973a: 240-247). For Mesopotamia, the first distinction between copper (urudderii) and tin-bronze (zabadsiparru) appears in cuneiform texts from the EDI period at Ur, while the earliest mention of metallic tin (AN.NA/annakum) is found in EDIVIII texts from Fara (Limet 1960). Contemporary with the appearance of tin-bronze in the Royal Cemetery

at Ur there are references in texts from Palace G at Ebla to the mixing of various ratios of "washed" copper (agar5(-gar5)la6aru)and tin to produce bronze (Waetzoldt and Bachmann 1984; Archi 1993), and similar recipes are found in the late nineteenth century BCE texts from Mari (Muhly 1985a:282). The most common copper-tin ratios mentioned are from 6:l to 10:l (e.g. Muhly 1973a:243-4; Waetzoldt 1981:371, 375-376; Limet 1993:104-5; Reiter 1999:169), although ratios producing alloys with less than one percent Sn are also reported as are ratios producing alloys with 20 percent Sn (Limet 1985:204; Archi 1993:619-625; Muller-Karpe 1991). Textual references to the Mesopotamian tin trade are largely found in two collections of cuneiform texts, from the central Anatolian site of Kultepe (ancient Kanesh) and from Mari on the Euphrates, which date to the late nineteenth and early eighteenth centuries BCE. These texts document a trade in which tin was moving exclusively from east to west. Arriving in Mesopotamia from the east, metallic tin was transhipped up the Euphrates to Mari, or overland to Assur. From Assur the tin (in addition to Babylonian textiles) was transported via donkey caravan to various Assyrian trading colonies such as KaneshIKiiltepe in Anatolia, where it was traded for silver and gold (Larsen 1976, 1987). From Mari, the tin was traded further west to sites in Syria and Palestine (Dossin 1970; Malamat 1971), and perhaps as far as Crete (Malamat 1971:38; Muhly 1985a:282). The absolute quantities of tin documented in the Kanesh sources (ca. 13.5 tonnes over approximately 50 years, see Larsen 1987:5 1)are significantly higher than those recorded in the Mari texts, which are often of the order of only a few kilograms (although a single tablet from Mari, A.1270, discusses the distribution of 16 talents 10 minas [ca. 485 kg] of tin, see Dossin 1970; Malamat 1971). The original sources of this tin are unknown, as many of the place-names mentioned in the texts can refer only to way-stations along the trade routes, rather than the actual tin sources themselves. The Kanesh texts refer to tin coming overland through the Zagros Mountains to Mesopotamia from northwestern Iran (Muhly 1973a:306), while Mari seems to have obtained its tin in ingot form almost exclusively through diplomatic gift exchange with Susa and Anshan (Limet

1985; Joannes 1991; Potts 1999a:169 and Table 6.2), although the cuneiform evidence is limited (Reiter 1999:171). As stated by Larsen (1987:50), "Assur and Susa ...represent the pipes through which tin was channeled into the Middle Eastern system" in the early second millennium BCE. The elite spheres in which tin seems to have circulated probably reflects the observation by Reiter (1999:171) that "the import of all kinds of metals even for kings depended heavily on good political relations with the countries which produced these metals or which functioned as thoroughfares". Claims for an eastern source of tin are supported by other textual evidence. For example, the Sumerian poem "Enmerkar and the Lord of Aratta", an epic myth of the third millennium known from later copies, mentions a period in which there was no trade between Uruk and the semi-mythical land of Aratta which lay beyond the Zagros in Iran. The cessation of this trade meant that Uruk did not have access to the gold, silver, copper, tin, lapis lazuli and "mountain stones" of Aratta (Kramer 1952, 1977:61). This association of tin, lapis lazuli and also carnelian found commonly in third millennium Mesopotamian texts is taken to indicate that tin had a similar origin to these goods (e.g. Kramer 1977:61; T. F. Potts 1994:155). Extensive geological and archaeological studies indicate that the lapis lazuli used in western Asia is most likely to have come from Badakhshan in Afghanistan (Herrmann 1968), although smaller deposits in Baluchistan (Delmas and Casanova 1990) or those in Iran mentioned in medieval sources (Moorey 1994:86) cannot be ruled out. Carnelian is likely to have been obtained from a number of Indian sources in Gujarat and elsewhere, or possibly in Iran (Tosi 1980:448-449; Asthana 1993:275; Moorey 1994:97). Both lapis lazuli and carnelian are referred to in Mesopotamian cuneiform sources as coming from the land of Meluhha (Heimpel 1993:54), a trade which was conducted via the Gulf (Muhly 1973a:307). Furthermore, Stieglitz (1987:45) and Pinnock (1985; 1988:108-llO) suggest that the lapis lazuli used at Ebla in the third millennium BCE traveled via the Gulf and Dilmun. In addition to its tin, Mari also obtained lapis lazuli from Susa in the early eighteenth century BCE, which may reflect the significant overland contact between Susa and Bactria at this time (Potts 1999a:169).

Tin and Tin-Bronze i n Early Western Asia

17 9

One text from the reign of Gudea of Lagash mentions that, in addition to lapis lazuli and carnelian, tin was also traded to Mesopotamia from the land of Meluhha. The relevant passage (Cylinder B, column XIV, lines 10-13) states that "Gudea, the Governor of Lagash, bestowed as gifts copper, tin, blocks of lapis lazuli, [a precious metal] and bright carnelian from Meluhha" (Wilson 1996; see also Muhly 1973a:306-307). This is the only specific cuneiform reference to the trade of tin from Meluhha (see Possehl 1996:141 for doubts over the association), however further evidence for a tin trade through the Gulf is provided by late third and early second millennium BCE texts mentioning tin from Magan (Cohen 1975:28) and Dilmun (Waetzoldt l 9 8 1:366-367; Moorey 1994:298; Foster 1997; see Stieglitz 1987:44 and Muhly 1995b:1506 for uncertainties regarding the use of the term "Dilmun" in the Ebla texts). A pre-Sargonic text from Lagash published by B. Foster (1997) and described as "a Sumerian merchant's account of the Dilmun trade" mentions obtaining from Dilmun 27.5 minas (ca. 14 kg) of an-na zabar. This phrase can be literally translated as "tin bronze", and Foster suggested the possible reading "tin (inlfor?)bronze". As there are additional textual references to the trade of finished tinbronze items from Magan (Limet 1972:14-1 7), there is some degree of historical support for the hypothesized trade in tin-bronze suggested by the LIA of the Gulf objects (Potts 1999b; also Chapter Seven).

Summary of Archaeological, Geological and Textual Evidence The evidence presented above for the early use of tinbronze has been used by a number of scholars as a guide to the sources of tin used in Bronze Age western Asia. Thus, the archaeological evidence for significant Early Bronze Age tin-bronze use in the Aegean and the Troad, central Anatolia, northern Syria and Mesopotamia was seen as evidence for the contemporary exploitation of tin deposits somewhere in (probably northwestern) Anatolia (e.g. Renfrew 1967; Eaton and McKerrell 1976; Yener and Vandiver 1993; Muhly 1995b:1507). A Troadic tin source has been ruled out by geological research, which has established the existence of tin deposits in Egypt, Arabia, Afghanistan, central Asia,

18 0

Early Metallurgy of the Persian Gulf

Europe, and probably the Taurus Mountains, but not in northwestern Anatolia. A range of evidence indicates that, of these verified tin sources, those in the Eastern Desert of Egypt and the western Arabian Peninsula were not utilized in the third millennium BCE. Furthermore, the use of European tin in the EBA Aegean, once considered likely (e.g. Muhly 1985a:285), now seems improbable due to relatively late adoption of tin-bronze in mainland Europe (Niederschlag et al. 2003:62-64). The extant archaeological, geological and historical evidence indicates that the tin used in third millennium western Asia most likely came from sources in southern Anatolia, Afghanistan, and central Asia. Certainly, the use of Taurus tin within EBA central Anatolia seems likely, although this has not yet been conclusively demonstrated. Claims of third millennium BCE tinsmelting operations at Goltepe seem stronger for weathering a period of intense scrutiny and debate. However, the use of Taurus tin beyond central Anatolia, on any significant scale, is not recorded in the surviving textual sources from Mesopotamia, and the LIA of the third millennium tin objects from Thermi and Tell Abraq indicates that tin from KestelJGoltepe was not used in their manufacture (see Chapter Seven). Additionally, the LIA of contemporary tin-bronzes from the Aegean region has indicated that they are probably not made of Anatolian metal. Thus, although a tin source in the Taurus Mountains fits the distribution pattern of early tinbronzes quite well, the isotopic evidence indicates clearly that more than one tin source supplied western Asia in the third millennium. Afghanistan and the Indo-Iranian borderlands have been tentatively suggested as the source regions for the tin-bronze used in the EBA Aegean (Pernicka et al. 1990:290; Pernicka 1995b:107-108), based upon geological considerations and the geo-chronological implications of Aegean lead isotope data. The fact that the isotopic characteristics of the Aegean tin-bronzes are so similar to those from the Gulf analyzed in this study adds further weight to the hypothesis of an eastern source for these early alloys. Although the great distances involved in such a trade have been regarded as problematic by some authors (Renfrew 1967:13; de Jesus 1980:59), the isotopic evidence is consistent with that from early second millennium BCE textual sources,

which testify to the large-scale overland trade of tin into Mesopotamia from beyond the Zagros Mountains and its subsequent export in large quantities into central Anatolia. Significantly, a number of scholars regard the surviving texts from Kanesh as reflecting only one short period in a trade relationship with Assur that existed already by the third millennium (Muhly 1993b32.52; Larsen 1977:119-120). The possibility of tin coming from these eastern sources is supported by the occurrence of many tin deposits in modern-day Afghanistan, Uzbekistan and Tajikistan, although evidence for tin extraction is currently limited to the central Asian sites of Karnab and Mushiston, and goes only as far back as the second millennium BCE. Yener (2000:75) has argued cogently against a "onesource-for-all" model of the third millennium tin trade, and does not regard the proposed tin mining and processing in the Taurus Mountains as inconsistent with the importation of large amounts of tin into Anatolia (cf. Belli 1991). Taurus tin production is thought to have CO-existedwith large-scale exchange of foreign metal in the third millennium (Yener et al. 1989:203; Yener and Vandiver 1993:212), before the eventual "devastation" of Anatolian tin mining operations by the availability of "purer, already packaged, readily-available tin" from the Old Assyrian trade (Yener 2000:7.5). Yener's arguments regarding multiple tin sources are well made, and it is clear that the evidence from KestelIGoltepe provides only a part of the information needed for a complete understanding of the Bronze Age tin trade. Obviously, the question remains as to the sources that were supplying the "large-scale metal exchange" discussed by Yener and others. The eastern sources noted above are clearly significant candidates, especially when the tin sources used in a region such as the Gulf are under consideration. Having confirmed the likelihood of a long-distance tin trade in third millennium western Asia, however, the evidence for the use of the Afghan and central Asian sources remains equivocal. In particular, the evidence for early tin-bronze in these regions is sparse, due to the limited number of analytical programs, and chronological attributions of the analyzed objects are often doubtful. As noted above, the evidence for extraction of tin in the third millennium BCE is also absent. Such factors

have added weight to arguments hypothesizing the importance of Anatolian tin sources. In particular, the evidence for EBA tin-bronze use in Anatolia is much stronger than in the east, there is some archaeological evidence for third millennium tin extraction in the Taurus Mountains, and the textual references to the use of eastern tin in Greater Mesopotamia are concentrated in the early second millennium BCE. However, the combined evidence from archaeology, geology, and historical sources suggests the significance of eastern sources for the tin trade in both the third and second millennia BCE. In particular, for regions such as Baluchistan, the Indus Valley, and the Gulf, which show significant third millennium tin-bronze use, the exclusive use of tin or tin-bronze from Afghanistan and central Asia seems highly likely. Textual sources are scarce, but highlight the trade through the Gulf linking Mesopotamia with Meluhha, Magan and Dilmun as the most common source of tin in the later third millennium BCE, after an earlier overland Iranian tin-lapis-carnelian trade hinted at by the epic tale of Enmerkar and the Lord of Aratta. The trade routes which may have brought this eastern tin (and perhaps also Taurus tin) to the Gulf region in the third millennium BCE are investigated in more detail in the following section.

Tin-Bronze in the Gulf: Patterns of Acquisition The presence of tin-bronze objects at A1 Sufouh, Unarl, Unar2 and Tell Abraq in the second half of the third millennium BCE raises interesting questions with regard to the means by which this material reached southeastern Arabia. As outlined above, the absolute source of the metal is likely to have been far to the north and east in Afghanistan or central Asia. Tin or tin-bronze from such a source, like the other material of undoubted central Asian origin has been found in southeastern Arabia and the central Gulf, could feasibly have reached the Gulf along a number of routes. The first possibility that must be considered is that tin and tin-bronze were obtained through direct contact with central Asia. The limited amount of archaeological material of central Asian origin found in southeastern Arabia includes footed vessels of Bactrian type from a grave in the Wadi Suq and the Umm al-Nar tomb at

Tin and Tin-Bronze in Early Western Asia

18 1

Tell Abraq (Frifelt 1986:133 and Figure 33; Potts 2000:127), and a copper-base goblet from a late third millennium BCE grave at Asimah in Ras al-Khaimah (During Caspers 1992:s and PI. 4d; Vogt 1995:129 and Figures 54:3 and SS). An interesting attestation to the use of Indo-Iranian or central Asian materials in southeastern Arabia is provided by a third millennium alabaster vessel with very strong Indo-Iranian parallels, which bears the inscription "Naram-Sin, king of the four world regions, a vessel from the booty of Magan" (Potts 1986:282 ff., Tav. XXIV). Other objects with clear central Asian parallels include a small soft-stone flask from Tomb A at Hili North (Cleuziou and Vogt 1985:255-257 and Figure 4.5) and two decorated ivory combs from the Umm al-Nar tomb at Tell Abraq (Potts 1993d; Potts 2000:127; Potts 2003b). The ivory combs from Tell Abraq are part of a larger collection of ivory objects from the tomb which show strong Indus parallels in addition to Bactrian connections, a point whose significance is addressed further below. Objects of possible central Asian origin have also been found in the central Gulf, where one of the more numerous categories of evidence is footed goblets, known from graves at 'Ali, Sar al-Jisr and Dhahran (During Caspers l992:Pls. 1, 4; Edens 1993:Figure 29.5:s-12). Comparable sherds are reported from settlement contexts on Failaka and at Qala'at al-Bahrain (During Caspers 1994:37). A bronze goblet from a grave at Hamala North on Bahrain, very similar to the example from Asimah mentioned above, has also been paralleled with BMAC material (During Caspers 1992:8 and P1. 4d). From the "foundation deposit" of the Barbar Temple I1 comes an anthropomorphic tinbronze mirror handle which bears comparison to Bactrian examples, although some elements of its conception differ (Heskel undated; During Caspers 1992:10 and Figure 7c-d; During Caspers 1996:s 1). Furthermore, the bronze bull's head from the Barbar Temple has been compared to a late third millennium BCE example from Altyn-Depe in central Asia (During Caspers 1976:32), although parallels could also be drawn with Mesopotamian material of Early Dynastic date. Finally, three alabaster vessels from the same deposit have strong Indo-Iranian parallels (Potts 1986:284, Tav. XXXI).

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However, while pottery with central Asian parallels is found in the Gulf, there is very little additional evidence to suggest the presence of central Asian people in the region. Exceptions to this situation include a stamp seal of Murghabo-Bactrian type that was recovered from a grave at Hamad Town on Bahrain (Crawford and a1 Sindi 1995) and a cylinder seal from Hamad town that shows iconographic parallels with the Dasht-i Lut region of eastern Iran (Denton and al-Sindi 1996). The latter seal is particularly interesting, as it seems to have been manufactured on Bahrain and incorporates elements of both eastern Iranian and Dilmun glyptic. Denton and alSindi (1996:191-192) regard the seal as belonging to an eastern Iranian expatriate resident in Dilmun in the early second millennium BCE. Such evidence is, however, far too ambiguous to support a general claim of "Bactrians" in the Gulf in the Bronze Age. Archaeological evidence from the Gulf is significantly different to that from the Indo-Iranian borderlands, where sizeable collections of intrusive BMAC material indicate either periodic direct contact with central Asian people or their actual presence (Hiebert and Lamberg-Karlovsky 1992; Kohl and Pottier 1993). The first significant use of tin-bronze at Tepe Yahya has in fact been quite explicitly linked by the excavators of the site to the presence of an ethnic Bactrian element in the early second millennium population (Thornton et al. 2002a, 2002b). In general, it seems much more likely that the central Asian material in the Gulf, including tin or tinbronze, arrived by way of intermediaries. The central Asian materials from the Gulf cannot be understood in isolation, as they form only a small portion of the exotic goods found in Bronze Age sites in the region that testify to contacts with Mesopotamia, Iran, Baluchistan and the Indus region, and the existence of a complex trade network capable of transporting goods thousands of kilometers. The potential complexity of the trade contacts in the Gulf is demonstrated by the Ur version of the myth of "Enki and Ninhursag", composed around 2000 BCE, which indicates that eight countries transported their wares to Dilmun:Tukrish, Meluhha, Marhashi, Magan, the "Sealand", Zalamgar, Elam and Sumer (Kramer 197759). The archaeological evidence for foreign material in the Gulf has been presented in numerous places as a basis for general discussions of the Bronze Age Gulf

trade (e.g. Edens 1992; Potts 1993b, 1993c; Cleuziou 1982, 1984, 1992; Cleuziou and Tosi 1989; Franke-Vogt 1993, 1995; Vogt 1996; Possehl 1996; Weisgerber 1986; Zarins 1989). The data are summarized below, in two sections related to the southern and central Gulf regions respectively, with the aim of delineating the routes by which tin and tin-bronze may have reached the region. Tin for Southeastern Arabia The first possible intermediary in the tin trade to be considered is Mesopotamia, as evidence for Mesopotamian contact with Magan is extensive. Mesopotamian pottery has been recovered in numerous Umm al-Nar Period settlement contexts (Frifelt 1991, 1995; a1 Tikriti 1985; M6ry and Schneider 1996:83; Potts 1990b; Mkry 1996:170) and in tombs (Mkry 1997:187 and Figure 12; Potts 2000:51-52; Phillips 1997:Figure 2.1). On Umm an-Nar Island, vessels lined with Mesopotamian bitumen have been recovered, in addition to numerous bitumen fragments (Frifelt 1995:226), and bitumen fragments from Raysal-Jinz RJ-2 are also shown by atchaeometric studies to be of Mesopotamian origin and transported in Mesopotamian vessels (Cleuziou and Tosi 1994:756-757; Mkry 1996:170). Mesopotamian influence in the Umm alNar Period is also indicated by the cylinder seal recovered from the A1 Sufouh tomb (Benton 1996:Figure 197). While almost certainly of local manufacture, this A1 Sufouh seal and two other cylinder seals from Hili North tomb B and Ajman tomb B (Benton 1996:165) suggest economic relations with the cylinder-seal using cultures of Mesopotamia or Iran. The number of archaeologically-attested objects of southeastern Arabian origin in Mesopotamia is very much smaller, and includes around a dozen se'rie re'cente soft-stone vessels from contexts spanning the late third and early second millennia BCE (Reade and Searight 2001:Figures 1-10; Potts 1990a:108-109), while a handful of examples of skrie tardive have been found in early second millennium BCE contexts at Ur and al-'Ubaid (Potts 1990a:252; Reade and Searight 2001:Figures 11, 12). Cleuziou (1986: 148) originally suggested, based on archaeological evidence, that southeastern Arabia experienced a change in external orientation in the Bronze Age:strong ties with Mesopotamia existed at the

beginning of the third millennium BCE, but its influence lessened to be replaced by contacts with the Indus in the late third millennium (see also Cleuziou and Tosi 1989:37; Edens 1993; Franke-Vogt 1993; Vogt 1996). Thus, at exactly the time when tin-use in southeastern Arabia increased (i.e. from 2300-2000 BCE), the archaeological evidence of Mesopotamian contact is significantly more scarce than previously, and secondary to the evidence for contemporary exchange with southeastern Iran and the Indus. However, a more recent consideration of the evidence by Cleuziou and Miry (2002:286, 290) has led them to suggest that the deposition of Mesopotamian pottery in Oman in funerary and settlement contexts at least partially reflects arbitrary social and ideological factors, and cannot be regarded as an accurate index of the exchange between the two regions. A much different picture of Mesopotamian-Gulf interaction is seen when the surviving cuneiform evidence is examined (Oppenheim 1954; Leemans 1960; Pettinato 1972; Heimpel 1987), as contacts between Mesopotamia and Magan are recorded only from the Sargonic Period onwards, with a peak of interaction at the very end of the third millennium BC. Such contacts could, in theory, have been responsible for the introduction of tin-bronze in southeastern Arabia, as tin and tin-bronze were used in Mesopotamia from the early third millennium BCE onwards (see above). Nevertheless, the texts do not support such a hypothesis. This is because the range of traded materials listed in the texts is consistently limited to the local agricultural and manufactured products of the Mesopotamian al1uvium:perishable organic products such as oils, cereals, wool and garments. There are very few references to metals reaching southeastern Arabia from Mesopotamia. Copper, tin and gold are traded to Mesopotamia through the Gulf, and only silver is occasionally provided to Mesopotamian merchants for exchange in the Gulf region. It is possible, however, that the surviving texts do not provide a complete record of the materials exchanged between southeastern Arabia and Mesopotamia. The occasional trade of metal artifacts from Mesopotamia to Oman in the Umm alNar Period, for example as gifts between the individuals undertaking the trade, therefore remains a possibility.

Tin and Tin-Bronze in Early Western Asia

18 3

A more likely northern intermediary in the movement of tin between central Asia and the southern Gulf is Iran. As discussed above, cuneiform evidence suggests that a significant portion of the tin reaching Mesopotamia in the early second millennium BCE seems to have been channeled through Elam and Anshan. Moreover, metallurgical analyses from Susa indicate that tin-bronze was used there from the mid-third millennium, although the frequency of tin use was not high until the early second millennium BCE. The archaeological evidence for contact between the Gulf and southwestern Iran is rather slim. From the final centuries of the third millennium BCE, Kaftari ware has been recorded in Umm al-Nar Period tomb assemblages at Unar2 (Carter 2002) and at Tell Abraq (Potts 2003a). Connections can be traced into the second half of the second millennium BCE, through the presence of a number of Middle Elamite sherds and a cylinder seal of Middle Elamite style in Wadi Suq layers at Tell Abraq (Potts 1993b:434-435). Likewise, some material of Gulf origin seems to have been circulating in Elam by the second half of the third millennium BCE. Although the majority of it is from Dilmun rather than Magan (see below), Omani soft-stone vessels of both se'rie re'cente and se'rie tardive have been found at Bandar Bushire (Pizard 1914:Pl. VIII), and sirie ricente soft-stone vessels have been found at Susa (Potts l99Oa: 110; Potts 1993b:434). Of course, Omani copper could have been the main item of trade between the two regions, and analyses of copper-base objects from the Gulf region undertaken by the CNRS, France, have been used to suggest that Susa was indeed obtaining southeastern Arabian copper by the mid-third millennium BCE (see Chapter Two). In general, the archaeological evidence from southeastern Arabia and the metallurgical studies of tinbronze use at Susa suggest that Elam would have been a more likely supplier of tin to the Gulf in the second millennium BCE rather than earlier, an idea which is investigated further below. However, the increase in tinbronze use at Kaftari phase Tal-i Malyan and the presence of Kaftari vessels in the tombs at Tell Abraq and Unar2 may indicate a role for this region in Gulf tinbronze use. V. Pigott (personal communication from W. Sumner) argues that, given the limited distribution of

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Kaftari material outside the Marv Dasht, the evidence for contact between Anshan and the Gulf is relatively strong. This trade could have been conducted through ports such as Liyan, at Bandar Bushire, which show clear material connections to both the central and southern Gulf and Kaftari period Malyan (PCzard 1914). Of course, Kaftari period Malyan could in fact have been receiving its tin or tin-bronze from the Gulf trade, rather than vice versa. As a result of these uncertainties, the possible role of southwestern Iran in the Gulf tin and tin-bronze trade remains unclear. By far the bulk of evidence for third millennium contact between Iran and the Oman Peninsula involves material from southeastern Iran and neighboring areas of Pakistani Baluchistan. Although finds of se'rie ancienne (Intercultural Style) soft-stone in southeastern Arabia are very limited (Potts 1990a:76-77; Ziolkowski 2001), at least three types of imported southeast Iranian gray-ware pottery are found abundantly in later Umm al-Nar grave assemblages. These include painted black-on-gray vessels with parallels at Bampur, Shahr-i Sokhta and Khurab, which archaeometric studies indicate were imported from southeastern Iran (Cleuziou 1982, 1984; Cleuziou and Vogt 1985:267-269; Blackman et al. 1989:66), as well as incised gray-wares which were both imported and copied locally in southeastern Arabia (De Cardi et al. 1976:118-122; MCry 1991, 1997; MCry 1996:170). Such vessels are found as early as the mid-third millennium BCE in the region, but are much more common towards the end of the Umm al-Nar Period (Blackman et al. 1989:66; MCry 1996:170). The third type of Iranian pottery is represented by two burnished gray-ware vessels found in the tomb at Tell Abraq (Potts 2000:124). A number of alabaster vessels from the Tell Abraq tomb are also likely to have originated in southeastern or eastern Iran (Potts 2000:125). Omani material in southeastern Iran is much rarer, but a number of Umm al-Nar pottery sherds and fragments of sirie ricente soft-stone are reported in later third-millennium BCE contexts at Tepe Yahya (Potts 1990a:103, 110), and an Omani softstone vessel was also found at Shahdad Cemetery B (Hakemi 1997:72 and 205). It is clear that southeastern Iran and southeastern Arabia were in close contact throughout the third millennium BCE, and particularly in the latter half of that

period. Based on this evidence, a relatively straightforward north-south movement of tin andlor tin-bronze through the Indo-Iranian borderlands to the Gulf could be hypothesized. However, the evidence for third millennium tin-bronze use in southeastern Iran is very limited (see above), with the Tepe Yahya sequence particularly illustrative of the late adoption of tin-bronze in the region. In contrast, much more evidence for tin use is available from early to mid-third millennium sites in neighboring areas of Baluchistan, and the central Asian connections of both southeastern Iran and Baluchistan in the late third millennium are clear (Hiebert and LambergKarlovsky 1992; Kohl and Pottier 1993). Thus, Baluchistan could theoretically have been a significant source of tin and tin-bronze for the southern Gulf region, although there is no positive proof of this hypothesis. The final intermediary in the Gulf tin trade which must be considered here is the Indus Valley, as studies of n metallurgy indicate significant tin-bronze use in the region in the later phases of the mature n period (see above). The n site of Shortughai (Francfort 1979, 1984, 1989) in Afghanistan is a prime and often cited example of the means by which central Asian materials such as lapis lazuli were obtained by the ns, although no tinbronze is found there. During Caspers (1994523-525) has noted that the presence of central Asian materials in the Gulf coincides with an increase in the amount of Indus Valley material in the region, and has suggested that "the Indus Valley presence in the Arabian Gulf towards the close of the third millennium B.C. could, at least partly, be responsible for the introduction of Murghabo-Bactrian material into the region". During Caspers' reasons for the hypothesis are sound: there were direct connections between the Indus and central Asia (Francfort 1984:174; Hiebert 1994:13), and a strong Indus trade with the Gulf in the third millennium. The chronology of Indus contacts with the Gulf is also important in the evaluation of this hypothesis, as a clear intensification in Indus-Oman relations is seen towards the end of the third millennium BCE (Cleuziou 1992; Frifelt 1995: 238-239; Vogt 1996:127). Thus, the Indus presence in the Gulf is seen to intensify at the time when tin-bronze first appears in significant quantities in southeastern Arabia in the tombs at Unar l,Unar2 and Tell Abraq.

Southeastern Arabian archaeological finds in the Indus Valley are extremely rare, and include one softstone vessel of se'rie re'cente style from Mohenjo-Daro (Cleuziou and Tosi 1989:Figure 12; Chakrabarti 1998: 306) and one from Lothal (Miry 1996:171). Of course, the most important raw material that may have been exchanged between the two regions is copper (see Chapter Two), although the evidence for this trade is unfortunately ambiguous. In contrast, the archaeological evidence for Indus material in southeastern Arabia is considerable. For example, black-slipped storage vessels of Indus origin are found in numerous settlement contexts in southeastern Arabia in the second half of the third millennium BCE (Blackman and Miry 1999:Figure 2; Mkry and Blackman 1999:173; Vogt 1995,1996: 123-124; Frifelt 1995: 165-168; Cleuziou 1984; De Cardi 1997; Potts 1993c, 1994). Decorated Indus pottery is more common in tomb assemblages, such as Tombs A and N at Hili (M6ry 1997:Figures 11, 12; A1 Tikriti and Miry 2000:21 l),and continues to be found in southeastern Arabia into the early second millennium BCE (Potts 1994; Kennet and Velde 1995:87, 92-93; De Cardi 1988:46 and Figure 11). Additional Indus-related finds from southeastern Arabia include stamp seals (Weisgerber l98 1:218:Abb. 53, 1984; Cleuziou 1992:97), cubical stone weights (Potts 2000:128; De Cardi 1988), and ivory combs and figurines (Cleuziou 1996:97; Potts 1993d, 1994:Figure 53.6, 2000:102, 131; cf. Possehl 1996:141). Of course, the most numerous class of goods imported into southeastern Arabia from the Indus is beads. Examples in etched carnelian (Vogt l996:ll3; Benton 1996:Figures 149-150; Cleuziou and Vogt 1985: Figure 5; Vogt 1996:113; Potts 2000:131; Edens 1993: 348), gold, and silver (Potts 1994:620; 200054) are found in tomb assemblages throughout the Oman Peninsula and have very close parallels to Indus finds. Most significantly for this study, typological analyses suggest that Indus copper-base objects, including spearheads and flat axes, were also imported in southeastern Arabia (Mkry and Marquis l998:217, Figure 7; Potts 1990b:Figure 36; Weisgerber 1980b:Abb. 78; Frifelt 1975:Figure 46) Indus contact with southeastern Arabia is observable not only by imported Harappan goods, but also by locallyproduced objects which show Harappan influences. Such

Tin and Tin-Bronze in Early Western Asia

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items include the thumbnail-impressed pottery found at Maysar 1 and Hili 8 (Cleuziou and Tosi 1989:40; Potts 1990a:103; Vogt 1996:120), and deeply concave handle lids such as found at Umm an-Nar Island (Edens 1993: 341; although Frifelt 1995:178 and Figures 245-247 suggests an actual Indus origin for these pieces). Other changes in ceramic technology which are seen to occur in southeastern Arabia at the end of the third millennium BCE, such as string-cut bases and the use of rope or cord to wrap large vessels prior to firing, are thought to indicate influence from the Indus or Indo-Iranian regions (Cleuziou and Vogt 1985:272-274; Vogt 1996:ll9-120). T. F. Potts (1994:28 1)has suggested that the distribution of tin in third millennium western Asia was controlled by the Meluhhans. This hypothesis is based upon the pattern of early tin-bronze use in the region, and particularly its dearth in highland Iran, which Potts sees as reflecting differential access to maritime trade through the Gulf. Certainly, the archaeological evidence for contact between southeastern Arabia and the Indus Valley indicates that Meluhhan tin and tin-bronze might have been accessible to the inhabitants of southeastern Arabia. However, the review of the archaeological evidence for foreign material in Magan suggests that central Asian tin and tin-bronze could also have been traded to southeastern Arabia via Iran or Baluchistan. These regions show the strongest contacts with southeastern Arabia in the last third of the third millennium BCE in addition to significant levels of interaction with the putative source areas the Indo-Iranian borderlands and central Asia. Admittedly, the evidence for tin-bronze use in the Indus in the third millennium BCE is much stronger than that for most areas of Iran, but the recent analyses of material from Kaftari Period Malyan indicate significant tin-bronze use, and Kaftari vessels have been found in the tomb assemblages at both Tell Abraq and Unar2 where tin-bronze is frequently used. However, as nowhere between Fars Province and the Indo-Iranian borderlands seems to have been using tin-bronze at this time, the possibility of Malyan obtaining its tin via an overland trade with the east seems small. In short, an Indus origin for the tin used in the Gulf region, and perhaps also in southwestern Iran, seems the most likely situation.

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Tin for the Central Gulf At the moment, the only real evidence for the availability of tin in the central Gulf in the third millennium BCE is the reference from Ebla t o the use of Dilmun tin, and a text from pre-Sargonic Lagash that refers to obtaining an-na zabar from Dilmun. The uncertainties associated with these references have been discussed earlier. The lack of analyses of copper-base objects from third millennium BCE contexts in the central Gulf is a major lacuna in our understanding of the Gulf metals trade, and prevents a reliable discussion of the tin and tinbronze trade through the region before the early second millennium BCE. Indus contacts seem particularly pervasive by this time (the City I1 Period) at the Qala'at alBahrain, and include items such as seals with Indus inscriptions and weights derived from the Indus system (Edens 1993) which were used for the administration of aspects of the Gulf trade. (Harjlund and Andersen 1994:474). Carnelian beads and ivory form the Qala'at are likely also to have come from the Indus (Bibby 1986; Harjlund 1989; H~zrjlundand Andersen 1994:470-473) and Indus material has been recovered at contemporary sites on Bahrain, including the graves at 'Ali (Frifelt 1986:129-131 and Figure 32) and the Saar settlement (Carter 2001). Further to the north, Edens (1993:346) has suggested that a number of seals from Failaka demonstrate strong "greater Indus" connections that continued into the early second millennium BCE. Contemporary Dilmun-related material in the Indus region is extremely limited, but includes a Dilmun seal found at Lothal (Rao 1963). In the second millennium BCE, Dilmun's exchange ties with more northerly areas such as Mesopotamia and Elam were also close. The small number of Kaftari (Zarins 1989:82) vessels in the central Gulf is supplemented by a limited array of other finds. Notably, four Dilmun seals have been excavated at Susa (Amiet 1986), in addition to a number of locally-manufactured seals with elements of Dilmun glyptic, and a cuneiform tablet bearing a Dilmun seal impression (Potts l999a: 179). Furthermore, analyses of the bitumen used at the Saar settlement in the early second millennium BCE indicate that it was Iranian in origin (Connan et al. 1998 cite possible sources in Luristan, Khuzistan and Fars). The once-hypothesized presence at Susa of a temple to the

Dilmunite god Inzak has now been refuted (Potts 1999a:169), but the use of personal names associated with Inzak by Elamite residents, and the offering of a gift or tribute of silver to Susa by Dilmun in the late 18th century BCE (Potts 1990a:226-228) remain as indications of the contact between these two regions. -Furthermore, in the northern Gulf there is significant archaeological evidence for Elamite contact with Failaka in the second millennium, in the form of Elamite pottery and cylinder seals at tells F3 and F6 (Potts 1990a:274 note 78). Further south, red-ridged Dilmun pottery has been found on the coast of Iran at Bandar Bushire (Pizard 19l4:Pl. VIII). Regardless of the quantity of finds in Dilmun and Elam, their nature suggests that contacts between the two regions were based on mercantile activity. The Elamite connections with Failaka in particular suggest that this region must be considered as a potential supplier of the tin and tinbronze used in early second millennium Dilmun. The use of "Elamite" tin in Dilmun might also correlate with changes in the trade routes used to transport eastern tin to western Asia over the course of the Bronze Age. As discussed above, the overland trade of eastern luxury goods that characterized the early third millennium seems to have been reduced in importance with the incorporation of Meluhha into the Gulf trade by the later third millennium. T. F. Potts (1994:277-290) has discussed the increasing role of the Gulf in the supply of eastern raw materials and luxury goods to southern Mesopotamia over the course of the third millennium, and the possibility that the overland trade route through highland Iran and the Gulf sea-route were essentially mutually exclusive exchange systems. With the collapse of the Indus civilization some time around 1900 BCE, the trade in eastern luxuries may have reverted to near-exclusive use of the overland routes. Significantly, Susa is regarded by Potts as one of very few sites which may have participated in both exchange networks (T. F. Potts 1994:280), and it may have been well placed to profit from the loss of Meluhha from the Gulf trade in the early second millennium BCE. Materials of central Asian origin once traded via Meluhha now had to be obtained through the overland trade with Iran, and the strong Bactrian connections at Susa in the early second millennium

attest to the role of Susa in the westerly distribution of eastern goods (Potts 1999a: 179). Certainly, all the references to the tin trade through the Gulf (the tin of Dilmun, Magan and Meluhha) belong to the third millennium BCE, whereas the large-scale tin trade of the second millennium involving Assur and Mari seems to have involved tin which reached Susa and Mesopotamia via overland routes. The significant increase in tin-bronze use at Susa in the early second millennium BCE (Malfoy and Menu 1987:Table D ) may be a further reflection of this change in acquisition patterns, and the contemporary use of tin on Bahrain may indicate contacts with Susa rather than the more easterly regions which supplied tin to the Gulf in the third millennium. In this context, it is interesting to consider the material from the foundation deposit of Barbar Temple 11: the alabaster vessels, bronze bull's head and mirror handle have parallels in the Indo-Iranian or central Asian regions (Potts 1990a:204-205; Crawford and a1 Sindi 1995:3; cf. Mortensen 1986:184), and may also have arrived through northern exchanges with Elam.

Reconsidering the "Tin Problem" The early tin trade has long been regarded as problematic because of apparent discrepancies between the distribution of early tin-bronzes, the textual evidence for tin trade routes, and the limited geological evidence for the location of tin deposits suitable for Bronze Age exploitation. As outlined above, the evidence from archaeometallurgy and geological studies has improved dramatically over the last twenty years, and archaeologists are no longer forced to rely upon the distribution pattern of the earliest tin-bronzes as a proxy indicator for the location of ancient tin sources (cf. Renfrew 1967:13; Muhly 1973a:170; de Jesus 1978:37-38). Thus, tin sources in the Troad need no longer be hypothesized, as the EBII tin-bronzes of the Troad and the Aegean, once thought to represent the earliest in the region, are in fact contemporary or later than tin-bronzes in Greater Mesopotamia and elsewhere. Modern programs of compositional and isotopic analyses have conclusively supported these findings, by demonstrating the non-Anatolian origin of the metal in the earliest tin-bronzes of the Troad and the Aegean region (see Chapter Seven).

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From the very first, the Mesopotamian evidence for tin-bronze use has illustrated the limited influence that the geographical distribution of tin ore deposits had on the utilization of tin-bronze soon after this alloy was first produced. Basic geological considerations indicate that the early and mid-third millennium tin-bronzes in metalpoor Mesopotamia were obtained through long-distance trade (Stech and Pigott 1986:40-4 1).Moreover, surviving cuneiform evidence from Mesopotamia indicates that its tin sources lay to the east, and that in the early second millennium BCE this tin was traded from Mesopotamia into central Anatolia. It is increasingly clear that investigating how, why, and by which elements of society the tin-bronze alloy was adopted is as important to understanding its early trade as where it was used and in what quantities (cf. Philip 1991; Stech and Pigott 1986). Only by addressing such factors can the "problematic" distribution patterns of early tin-bronzes and Bronze Age tin sources be reconciled. In the following discussion, the possible ideological and socio-political aspects of early tin-bronze use in western Asia are investigated, beginning with southeastern Arabian evidence. Tin and Tin-Bronze as Prestige Goods in the Gulf A large and growing body of data from both the Old and New Worlds indicates that the earliest copper-base alloys were often produced and selected based upon such properties as physical appearance and scarcity rather than purely on mechanical properties of strength, hardness, or ease of working and casting (Levy and Shalev 1989:358; Miiller-Karpe 1991:112; Moorey 1994:253; Hosler 1995; Tadmor et al. 1995; Hayden 1998:27). For example, the physical appearance of tinbronze has been regarded as important in the initial adoption of this alloy in upper Mesopotamia. Speaking of material from the early third millennium site of Qara Quzaq in Syria, Montero Fenollos (1996:20) stated: Su be110 aspect0 exterior, frente a1 m i s vulgar del cobre arsenicado, explica la presencia en una misma tumba de alfileres de bronce, unos simples ornamentos personales, junto a armas de cobre, donde hubiera sido m i s 16gico el empleo de la aleaci6n cobre-estaiio. [Its beautiful outer aspect, as opposed to arsenical copper, explains the presence in the

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same tomb of tin-bronze pins, simple personal ornaments, next to copper weapons, for which the use of the copper-tin alloy would have been more logical.] A similar argument can be made for early tin-bronze use in the Gulf. As discussed in Chapter Five, there were considerable differences in the alloy types used to produce different object categories in Umm al-Nar Period southeastern Arabia. In particular, 90 percent of rings analyzed in this volume contained in excess of one percent Sn, whereas objects such as pins/awls and blades showed a much lower frequency (less than ca. 20 percent) of tin-bronze use. It seems clear that the advantageous mechanical properties of tin-bronze were not the reason for its adoption. If this were the case, the use of tin-bronze in utilitarian object categories, such as blades or pins/awls would have been expected. In Chapter Five, it was suggested that this discrepancy reflected the preferential use of tin-bronze for decorative rather than utilitarian objects in Bronze Age southeastern Arabia, based upon its golden color in comparison to reddish copper, andlor the greater value of the alloy, due to its inclusion of exotic tin. Both factors may have made tin-bronze more appropriate for adornment and display than unalloyed local copper. While still allowing for the importance of the surface appearance of tin-bronze in its initial adoption in southeastern Arabia, a more elaborate argument is presented in the following paragraphs. Although surface appearance may indeed have marked this alloy as distinct and could have caused it to be valued differently than copper, it is suggested below that its golden color was simply one among a suite of properties, both materially and socially determined, that distinguished tin-bronze from contemporary copper-base alloys. This argument recognizes the fact that in prehistoric contexts, metals and metal objects possessed unique, socially-defined properties partly divorced from their material characteristics. These properties are, thus, not amenable to identification and quantification by archaeometric analysis such as those employed in this volume. In particular, I wish to examine the possible role of tin-bronze as a prestige material in the Bronze Age Gulf. The role of "luxury" or prestige goods in prehistoric economic and political development has been emphasized by a number of scholars (Kohl 1975:47; Schneider

1977; Renfrew 1986; Sherratt and Sherratt 1991; Hayden 1998). Following theoretical models developed primarily in anthropology (e.g. Mauss 1966; Sahlins 1972; Dalton 1975; Ekholm 1977), the control of the long-distance trade in prestige goods has been linked to the construction and maintenance of political power in societies with developed or nascent hierarchies (e.g. Friedman and Rowlands 1977; Frankenstein and Rowlands 1978; Hodder 1982:204; Kristiansen 1986; Larsson 1986; Kipp and Schortman 1989; Earle 1997; McGlade 1997). According to such theories, prestige goods act not only as important markers of status, but also have a role to play in generating and legitimizing political, economic and other forms of hierarchy (e.g. Renfrew 1986:144; Appadurai 1986:34). The point is succinctly expressed by Earle (1997:144): "power rests on materialized ideologies". The importance of luxury or prestige materials, that is their potential to generate and legitimize political power, is linked to both their scarcity and their symbolic or ideological content (Hodder 1982; Helms 1986, 1993). Scarcity arises from a number of factors, including limited natural occurrence (for raw materials) andlor restricted loci of production (for raw materials and finished artifacts), in addition to the great distances involved in the acquisition of such goods. Their symbolic and ideological content would have reflected bogh the distances from which the goods were obtained, as well as the ideologically-charged contexts in which they were consumed at their destinations (Helms 1993; LambergKarlovsky 2001:280). Furthermore, implicit in the theoretical formulations outlined above is the notion that the long-distance exchange of prestige goods took place within restricted social and political spheres, i.e. between the elites of the societies in contact (Earle l997:198; Helms 1993:3-4; for a western Asian example, see Pinnock 1988 regarding Ebla). The significance of long-distance exchange in prehistory has been down-played by a number of scholars (e.g. Wallerstein 1993:294; Leemans 1977:s-6), due to the small scale of the trade and its limitation to goods of a "luxury" nature, which Wallerstein regarded as nonsystemic to early economies. However, if the generation, maintenance and legitimization of socio-political relationships relied upon obtaining luxury goods, they

are better regarded as necessities, and the admittedly small scale of the trade in such goods is perhaps not as important as its role. Following Polanyi (1975:135), luxuries can be seen as simply necessities for the rich and powerful. This concept is emphasized by Appadurai (1986:38), who states "I propose that we regard luxury goods not so much in contrast to necessities (a contrast filled with problems), but as goods whose principal use is rhetorical and social, goods that are simply incarnated signs. The necessity to which they respond is fundamentally political." It is interesting to note Adams' comments on this trade (1974: l 4 9 ) , which he regarded as possessing "considerable socioeconomic force ...in spite of its being largely confined to commodities of very high value in relation to weight and bulk because of high transport costs, and in spite of its directly involving only a small part of the population" (my italics). If this statement is assessed from the theoretical perspective discussed here, it would seem that the prestige goods trade was important precisely because of these factors. Thus, we can see that prestige goods have three important attributes:they are scarce, charged with symbolic content, and circulated with restricted spheres of exchange. It is these three factors that have led archaeologists and anthropologists to attach such significance to long-distance exchange in early economies. The particular role of metals as prestige goods in Bronze Age exchange systems has been discussed by a number of authors (e.g. Renfrew 1986; Sherratt 1976, 1994; Sherratt and Sherratt 1991:360-361; Hayden 1998:27-28). For example, Sherratt and Sherratt (1991:354) state that items such as exotic metalwork may "embody concepts of value and purity which have a power which is more than just a consequence of their relative scarcity". Although many examples of the use of gold and silver could be cited in this context, it is important to note that other metals such as copper, tin and copper alloys could also have been regarded in such a manner in Bronze Age contexts. As has been noted numerous times in this volume, tin is a foreign object in Gulf archaeological contexts. The analyses discussed in this volume, in addition to a handful of cuneiform sources, indicate that both tin and prealloyed tin-bronze (the latter probably traded as finished

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artifacts) were available through the Gulf trade that connected Mesopotamia with the societies of Dilmun, Magan and Meluhha. Based upon objects recovered from archaeological contexts in the Gulf and the evidence of Mesopotamian texts, it is clear that this trade dealt largely in materials that can be regarded as prestige goods (e.g. Edens 1992:122; Crawford 1996). Such goods included gold, silver, textiles, ivory, lapis lazuli, carnelian, various types of wood, and exotic vessels of pottery and stone (Heimpel 1987, 1988; Potts 1990a, 1993b; Ratnagar 1981). The association of tin and tinbronze with these materials in the Gulf trade is one factor that suggests it may have had a prestige status in Bronze Age southeastern Arabia. In addition to their rarity and intrinsic worth, Edens (1992:122) has noted that the raw materials of the Gulf trade "carried heavy burdens of ideological significance" when they reached their Mesopotamian destinations, where they were consumed as part of cultic or elite practices. A similar regard for these materials almost certainly prevailed in southeastern Arabia and Mkry (1997:171) has suggested that the deposition of so much foreign material in burial contexts in southeastern Arabia suggests the retention of a "strong symbolic meaning" for objects obtained through the Gulf trade. Moreover, the participation of southeastern Arabia in the Gulf trade almost certainly led to a spread in the ideology of elite consumption and notions of "appropriate" prestige goods among the societies participating in the trade. This reflects the fact that, in all societies, the value of raw materials and finished products is chiefly a matter of convention (e.g. Renfrew 1972:370). For example, Sherratt (1994:337-338) regards the development of Bronze Age exchange networks in Europe as dependent in part upon the emergence of a common ideology of consumption reflected in the existence of "internationally recognized 'role/status kits"' of prestige materials. Sherratt's ideas echo the claim by Stech and Pigott (198656) that tin was part of a "material complex", incorporating also lapis lazuli and gold, that was important in the display of power in third millennium Mesopotamia (see also Muhly 1985a). Thus, the symbolic value of tin-bronze in southeastern Arabia was probably shaped by both local and broader regional ideologies of consumption, in particular those possessed

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by the elite elements in Mesopotamian society that created the principal demand for the prestige goods traded through the Gulf. The simple fact that tin-bronze came to the Gulf from a great distance not only added to its ideological worth (e.g. Lamberg-Karlovsky 2001:280), but also ensured that it circulated in limited spheres of exchange within southeastern Arabia. This is because the Gulf trade seems to have been organized in such a way that it was highly susceptible to monopolistic control (cf. Peregrine 1991:2). Such control was possible because there were only a few points of articulation between the internal southeastern Arabian exchange system and the trade of prestige goods through the Gulf, at coastal trading sites such as Umm an-Nar Island, Tell Abraq, and Ra's al-Jinz (e.g. Frifelt 1991:128; Carter 2001:196). It is almost certain that foreign connections at these sites, and the goods they introduced into southeastern Arabia, were monitored and controlled by local elites (Cleuziou and Tosi 1989:33). As a result of such exchange mechanisms, tinbronze may have been regarded as a highly different material to unalloyed or local copper. In addition to its golden color, and its rarity, access to the alloy was limited ideologically and practically to the elites in southeastern Arabian society. Using the theoretical construct outlined above, at the same time as the use of tinbronze demonstrated an elite person's access to the fruits of the Gulf trade, this access and the prominent display that went with it helped to legitimize their authority in the eyes of the wider community. The conspicuous consumption of tin-bronze through its preferential incorporation into items of jewelry, such as rings and bracelets, supports such a notion for early tin and tin-bronze use in southeastern Arabia. Such an explanation contrasts strongly with previous hypotheses regarding alloy use in Bronze Age southeastern Arabia, which have focused predominantly on the mechanical properties of early copper-base objects. Specifically, the apparent lack of tin-bronze in Bronze Age southeastern Arabia was explained by the prevalence of arsenic and nickel-bearing copper in the local metal industries. This natural alloy of As/Ni-copper probably had similar working properties to tinbronze, meaning that from a material perspective tin-

bronze did not "need" to be adopted (Hauptmann 1987:217; Hauptmann et al. 1988). However, more recent analyses of material from Oman have suggested that AsINi-copper occurs more frequently in the Wadi Suq Period than the third millennium BCE, and that its appearance coincides with the first significant (though limited) use of tin-bronze (Prange et al. 1999:Figures 5-6). However, the results of this study and of analyses undertaken on Umm al-Nar Period material by Berthoud (1979), Hauptmann (1995) and Hauptmann et al. (1988) indicate that the co-occurrence of As/Ni-copper and tin-bronze also characterizes third millennium BCE metallurgy in southeastern Arabia. This CO-occurrence of alloy types, and particularly the preferential use of tin-bronze in the production of decorative items, argues against interpretations of early alloying in southeastern Arabia focused purely upon mechanical properties. In summary, the arguments presented above are based upon two considerations: firstly, the actual use that was made of the tin-bronze alloy in southeastern Arabian metalworking industries and, secondly, anthropologically-derived theories which stress the socio-political importance of the long-distance exchange of prestige goods. Thus, the possibility that tin-bronze was adopted in southeastern Arabia due to its improved mechanical properties seems to be ruled out by the preferential use of tin-bronze in decorative rather than utilitarian items. One possible explanation for the use of tin-bronze in the later Umm al-Nar Period is that the external appearance of the alloy, its golden color, was important in its adoption. However, theoretical considerations indicate that the importance of the non-material, socially-defined characteristics of tin-bronze in Bronze Age contexts in the Gulf should not be underestimated. It seems highly likely that tinbronze, due to its scarcity and its source in the Gulf prestige goods trade, had ideological/symbolic qualities and a socio-political value that locally-produced copper and AsINi-copper could never have possessed. The adoption of tin-bronze in southeastern Arabia was no doubt conditioned by these ideological considerations as much as by consideration of the mechanical and casting improvements offered by the alloy, or its physical appearance.

Tin and Tin-Bronze in Wider Western Asia: Technology, Ideology, Trade Routes In contrast to earlier technologically-based explanations for the development of alloying practices in western Asia, scholars have recently suggested that the adoption of tin and tin-bronze in third millennium metal industries was governed more by their prestige status than their mechanical properties. The strongest statement to this effect was made by Stech and Pigott (1986; see also Stech 1999; Pigott 1999c), but realization of the possible prestige status of tin-bronze in third millennium Mesopotamia can be seen as early as the work of Moorey and Schweizer (l972:185). Early tin use in Iran is also considered by Moorey (1982:98) to have been conditioned by more than just technological considerations. He notes that "it may be doubted that, outside the great Elamite urban centers, tin-bronzes were common in Iran much before the middle of the second millennium B.C. and, even in Susa, social and economic factors may have controlled their production and distribution". The potential role of these factors in the early use of tin-bronze across western Asia is considered in the following paragraphs. In Mesopotamian contexts, the hypothesized "prestige" status of tin and tin-bronze has been suggested not only by the distances which were involved in the tin trade and the association of tin with clearly prestigelluxury materials such as lapis lazuli and gold (e.g. Muhly 1973a), but also by the kinds of objects that tin-bronze was used to manufacture and the archaeological contexts in which it was concentrated. The enormous distances to the tin sources have been clearly established by geological research, with the even the nearest potential source in the Taurus Mountains located more than 1,000 km from southern Mesopotamia, and the more likely sources in Afghanistan and central Asia well over 1,500 km distant. In Mesopotamia, the preference observable in the material from the Royal Cemetery at Ur for using tin-bronze to produce vessels (Muller-Karpe 1991, 1994:71) has been explained as reflecting the prestige status of the alloy, because the mechanical advantages of employing tinbronze to produce vessels are unclear (Stech 1999). Likewise, Moorey and Schweizer (1972:185) have noted the preferential use of tin-bronze for vessels and clothing pins, and suggested that its display or "luxury" value

Tin and Tin-Bronze in Early Western Asia

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seemed more important in third millennium Mesopotamia than its "natural advantages" of hardness and easier casting. Similar patterns are seen outside Mesopotamia. As noted above, tin-bronze is used only for toggle pins at Qara Quzaq on the upper Euphrates, while tools and weapons from the site are of arsenical copper (Montero Fenoll6s 1996, 1995:Figure 1; Montero Fenoll6s and Montero Ruiz 2000:Lam. 5.1). Likewise, the early tin-bronzes from Velikent in the Caucasus are all decorative items (toggle pin, rings, bracelets) rather than tools or weapons (Kohl et al. 2002: 124; Gadzhiev and Korenevskii 1984). Looking at the context of the early tin-bronzes in western Asia, the deposition of many early Mesopotamian, Anatolian and Caucasian tin-bronzes in high-status burials is additional evidence for the prestige nature of tin in the third millennium BC. As observed by Stech (1999:66), the distribution of tin-bronze is far from uniform:a great deal of the third millennium BCE tin-bronze known from Mesopotamia and Anatolia is concentrated in the elite burials of Kish (Y Cemetery), Ur, Alaqa Hiiyiik, and Horoztepe. Thus, the great distance to the tin sources, the contexts of tin-bronze use, and alloying patterns point to the fact that tin-bronze was a prestige material in Greater Mesopotamia. However, the evidence from other regions with early tin-bronze use is much more equivocal with regard to the prestige status of tin and tin-bronze. In the Indus Valley, there seems to be little differentiation between the uses of tin-bronze for utilitarian or display objects. As conveniently summarized by Kenoyer and Miller (1999:142), while some bangles, button and beads are of tin-bronze, so are many axes, knives, and chisels. Likewise, at Aegean sites with early tin-bronze use, the new alloy is used to produce a range of objects, from those which can be clearly classed as items of display or prestige (e.g. vessels, toggle pins, and "frying pans"), to objects whose display status is uncertain (e.g. daggers and flat axes), and simple utilitarian items such as awls, chisels and punches (Pernicka et al. 1984:Table 4; StosGale et al. 1984:Tables 2-3). Thus, while tin-bronze seems in a number of cases to be preferentially utilized for items of display, its use for specific object categories is never exc1usive:some tools and weapons are made of tin-bronze, and many non-utilitarian items are not.

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Furthermore, the tin-bronzes of northwestern Anatolia and the Aegean and the Indus Valley are commonly found in settlement contexts, rather than in elite burials as in Mesopotamia and central Anatolia. In some cases, however, the settlement contexts are far from "commonplace" or domestic. At Troy, for example, the tin-bronzes are from the citadel complex and were found as part of large caches of objects, or "treasures", that also included precious metals. In contrast to the situation in the Aegean region, caches of metal objects from Harappan sites are generally of gold and silver only, with copper-base objects found predominantly in normal household or rubbish contexts (Kenoyer and Miller l999:l3 1-132). An exception is seen for copper-base vessels, which are found more commonly in hoards than in settlement contexts. These differences in context of deposition may indicate that precious metals and metal vessels "were used more overtly to define wealth, status, and power" in the Indus region than copper-base tools and weapons (Kenoyer and Miller 1999:132). Moreover, the find contexts and distribution patterns of copperbase objects at Indus sites are regarded as potentially significant. Specifically, the lack of concentrations of copper-base tools in workshops or hoards has been taken to indicate that copper-base tools were widely available or accessible within Indus sites. This may reflect the fact that metal use was not closely associated with elite elements of society. Of course, such statements are speculative, and the data on which they are based is open to alternative explanations (Kenoyer and Miller 1999:133). More information on the factors affecting the adoption of tin-bronze is provided by examining metallurgical traditions in the regions where tin-bronze does not seem to have been utilized in any significant quantities in the third millennium BCE. In a Near Eastern context, the most conspicuous examples of this phenomenon are the Iranian Plateau and Egypt, both of which had developed metal industries and urban communities and yet relied almost exclusively upon copper and/or arsenical copper until the late third or early second millennia BCE. A first factor to be considered is that of trade routes, which no doubt influenced the access to the new tinbronze alloy at sites across western Asia. The virtual lack of tin-bronze in third millennium BCE Egypt is perhaps easier to explain than its absence in Iran, as Egypt

lay at the very end of what was an extremely long-distance trade route, and there is little evidence for the contemporary use of tin-bronze in the neighboring Levant. Nevertheless, a maritime tin trade to Egypt seems to have been well established by the early second millennium, when eastern tin (i.e. from sources to the east of Mesopotamia) was regularly obtained through Middle Kingdom contacts with the Syrian littoral at Byblos (Muhly 1973a:332). Although similar trade connections existed in the Old Kingdom, they do not seem to have brought much tin or tin-bronze to Egypt, even though Afghan was utilized in Egypt, somewhat sporadically, from the early third millennium (Muhly 1973a:318). However, ideological factors could also explain the dearth of tin-bronze in third millennium Egypt. For example, Lucas (1934:178) has noted that, while the Middle Kingdom is the period when tin-bronze really begins to be used frequently in Egypt, analyses of the material from the tomb of Tutankhamun reveal more copper objects than tin-bronzes. Significantly, particular object categories, such as the implements of shawbti figurines, seem to have been preferentially made only of relatively pure copper. Such differentiation suggests that notions of appropriate alloys for particular types of objects, or of ritual purity, may have existed, and constrained the use of particular alloys in early Egypt. Turning to the third millennium Iranian Plateau, the very rare occurrence of tin-bronze in the region is more difficult to explain, especially if tin was coming overland from Afghanistan or central Asia. One explanation could be that tin was, in fact, not coming from these eastern sources at all. The textual evidence from Mesopotamia has always led scholars to look for tin deposits in northwestern and central western Iran (e.g. Muhly 1973b:409), and a possible tin or tin-copper source has been recently discovered in Luristan, at Deh Hosein. The utilization in Mesopotamia of tin from such a region would help to explain the lack of tin-bronze at sites on the Iranian Plateau and further to the east, if the tin was traded only to the southwest. However, as outlined above, the significance of the Deh Hosein coppertin deposit is yet to be adequately assessed. Basic data regarding the possible production of natural tin-bronzes from the ores are as yet unpublished and, most importantly, production at Deh Hosein seems to have been

concentrated in much later periods than those under consideration here. Nevertheless, the very recent discovery of the site indicates the possibility that small tinbearing deposits remain undiscovered, even in regions as well surveyed as the Zagros. Although the Deh Hosein extraction seems unrelated to the issue of Bronze Age tin sources, and more easterly regions have emerged as the most likely third millennium tin producers, the site highlights the limitations of the geological knowledge upon which much of the present discussion is based. If tin was in fact coming to Mesopotamia from the Indo-Iranian borderlands, we must imagine that it was either not traded through central and eastern Iran, or that when it was, none was utilized in local metal industries. Alternative routes to an overland Iranian Plateau trade include a southern trade through the Gulf, or a northern route across the Caspian Sea. The possibility of a southern tin and tin-bronze trade through the Gulf is supported by the results of the present study, although the absence of analyzed third millennium BCE objects from the central Gulf is still a significant lacuna in our knowledge. As discussed above, such a trade route could explain the known distribution of tinbronze in southern Mesopotamia and at Susa, and indeed this has been proposed by T. F. Potts (1994:281). This southern maritime route was already long-established in the supply of copper and other goods to southern Mesopotamia and, by avoiding Iran altogether, possessed a number of advantages in cost and speed. Possehl (1996:189) has described the MesopotamiaMeluhha trade as an "end-run" around southeastern Iran which facilitated the procurement of larger quantities of material, more suitable for the scale of demand generated by contemporary Mesopotamia, than could be provided by the overland route. Of course, once tin and tin-bronze reached Mesopotamia, they could have been further dispersed to the west (i.e. the Troad and the Aegean) via overland trade through Anatolia. The higher tin-bronze frequency in the Troad than in central Anatolia is not a significant stumbling block to an overland trade hypothesis, if one regards the trade as directed more towards some consumers than others, rather than being simple down-theline exchange. Nevertheless, the possibility of an alternative northern trade route across the Caspian Sea is hinted

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at by archaeological evidence from the Caucasus, the Aegean, and the Troad. For example, the coastal/island concentration of tin-bronze in the Aegean and the Troad has suggested to some scholars that a maritime trade across the Black Sea may have brought eastern tin into the Aegean (Muhly et al. 1991; Muhly 1999:18-19; Apakidze 1999). The predominant use of arsenical copper at the site of Ikiztepe on the Black Sea coast (e.g. Gedik et al. 2002) has proven problematic for proponents of such a tin trade route, but analyses indicate that about 15 percent of the analyzed copper-base objects from Ikiztepe contain significant amounts of tin. As noted above, the possibility of a Black Sea trade in tin is further supported by the finds of tin-bronze and lapis lazuli in third millennium Transcaucasia (e.g. Kohl et al. 2002; Kavtaradze 1999; Apakidze 1999; Edens 1995:56), which raise the possibility that tin from the Indo-Iranian borderlands may have been shipped west via a Caspian route, or that it may have traveled overland through northernmost Iran, along the southern shores of the Caspian Sea. The utilization of such a route might explain the absence of tin-bronze in eastern Iran, although its absence at a northeastern site such as Hissar is still hard to explain if the tin was coming from Afghanistan. In contrast, central Asian tin from the Uzbekistan-Tajikistan border region could well have traveled to the west by a route that ran north of the Kopet Dagh and Elburz Mountains. In contrast, if tin and tin-bronze were traded across the Iranian Plateau, then technological or ideological explanations must be proposed for their absence in Iranian metal assemblages. A technological explanation might be supported by the evidence for a developed arsenical copper metallurgy at most third millennium BCE sites in eastern and central Iran, including Tepe Hissar (Pigott 1982:Table 3), Shahr-i Sokhta (Hauptmann 1980; Pigott 1999b), Sialk (Berthoud 1979), Shahdad (Vatandoust 1999), and Tepe Yahya (Heskel and Lamberg-Karlovsky 1980; Thornton et al. 2002). Using this reasoning, the arsenical copper used at these sites probably had similar material characteristics to tin-bronze, and the new alloy was not utilized as it offered no mechanical advantages over the alloys already in use and was no doubt more difficult and costly to obtain. However, analytical studies have

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demonstrated the CO-occurrenceof pure copper and many varieties of binary and ternary copper alloys in metal assemblages from sites across western Asia, and the use of these alloys in ways that do not exploit their mechanical potential. Such findings suggest that the technological advantages of alloys over pure copper may not always determine the nature of metal use at Bronze Age sites. Moreover, explanations which suggest scarcity of alloying elements as an explanation for synchronic and diachronic alloy variability may also be underestimating the significance of ideological factors in early metal use. As noted by Chakrabarti and Lahiri (1996:207), the assumption that "what is considered to be technologically superior must also be culturally preferred" is often not justified by the available archaeological, metallurgical and ethnographic data. An alternative interpretation for the dearth of tinbronze on the Iranian Plateau is offered by Pigott (1999b:83). He regards tin and tin-bronze as prestige goods, and suggests that "the rarity of tin may have promoted its status among the Sumerians while the people of the Iranian Plateau may have remained un-influenced by such pressure". However, lapis lazuli from Afghanistan or Baluchistan reached Iran in significant quantities, as seen for example at Shahr-i Sokhta (Lamberg-Karlovsky and Tosi 1973:46) and Hissar (Bulgarelli 1979). Lapis lazuli was also a status material in Mesopotamia, and one wonders why the distribution patterns of lapis and tin, both probably from a similar source region, are so different. Furthermore, although the great majority of lapis lazuli that reached Shahr-i Sokhta was traded further west rather than used locally (Lamberg-Karlovsky and Tosi 1973:46), it is still highly visible in the archaeological record of the eastern Iranian sites. Tin-bronze is not, and one may question whether this material was ever, in fact, traded overland through the Indo-Iranian borderlands in the later third millennium BCE. Other ideological and symbolic factors may have a role in explaining the non-utilization of tin-bronze in third millennium Iran. One factor suggesting this is Pigott's (1999b:84) description of the "remarkable technological conservatism" of metallurgical production at Hissar. Such conservatism may not be a reflection of technological retardation, but rather of strong ideological or ritualistic beliefs dictating the use of metal from a

particular mine site, or metal produced in a specific way, or of a specific alloy type (cf. Chakrabarti and Lahiri 1996:206-207; Hosler 1995; Budd and Taylor 1995). Where complicated extraction technology was most likely learnt and passed on within a ritual context (Budd and Taylor 1995:139) and by analogy with natural and social processes (Childs and Killick 1993:325), practical barriers to the adoption of new extraction or alloying technologies and non-local metal are likely to have existed. Furthermore, elements of social reproduction and identity may have been tied to metal production, exchange, and use (e.g. Childs and Killick 1993; Philip 1991; Hosler 1995). Such factors may have led to the development of a highly conservative but reliable extraction technology, and strong sanctions against "experimenting" with the practical aspects of extraction. Moreover, once metal was extracted from its ore, it and the artifacts produced with it no doubt functioned as material markers of ethnicity, status, religion, and wealth, in addition to their more "obvious" roles as tools, weapons, and raw materials for trade (Childs and Killick l993:33 1). As has been noted by a number of archaeologists (e.g. Chakrabarti and Lahiri 1996:207; Budd and Taylor 1995), such ideological considerations are antithetical to many evolutionary schemes of early metal production, which focus upon technological advances dependent upon the freedom or drive to innovate (e.g. Wertime 1973). Although the ideological aspects of early metallurgy are probably unknowable from an archaeological perspective, this does not mean that their potential significance can be disregarded or diminished. Among communities that extracted their own copper-base raw metal, such as those of the Iranian plateau, the adoption of the new and foreign metal tin-bronze may have been incompatible with local cultural traditions of metal manufacture and use. Just as in the Gulf, where tin-bronze appears to have had a socially-defined ideological worth that local AsINi-copper could not possess, so on the Iranian Plateau tin-bronze may not have been compatible with the social and political contexts in which local arsenical copper was produced and used. The discussion presented above points to a high degree of regionalism in alloying practices across western Asia. Examples of the use of tin-bronze for ideological purposes of status display or elite consumption seem

to characterize some metalworking traditions (e.g. the Gulf, Mesopotamia, and central Anatolia), while technological conservatism or differing ideological sanctions may have prevented the adoption of tin-bronze in other areas (e.g. Iran and Egypt). In other regions, such as the Aegean and the Indus Valley, the factors that influenced early alloying practices remain uncertain. Thus, the archaeological evidence does not reflect a simple evolutionary development of fabrication technology based upon observation of and experiment with the mechanical properties of copper and its alloys. Moreover, it is abundantly clear that such overarching "technological" explanations for the development of early alloying cannot simply be replaced by correspondingly broad theoretical conceptions incorporating ideologies of elite consumption. Rather, early alloying practices reflect the interaction of a multitude of both enduring and historically contingent forces; from mechanical and physical properties, to the stability of trade routes for metals and alloying components and variations in the socio-political and ideological contexts of metal production, exchange and use.

Tin and Tin-Bronze in Early Western Asia

19 5

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Summary and Conclusion

Aims Reiterated This study began with relatively restricted aims, specifically the investigation of whether the Bronze Age inhabitants of Tell Abraq were unique in southeastern Arabia in terms of their access to metallic resources. This possibility was suggested by previous analyses of material from the site, which demonstrated the routine use of tin-bronze in the Umm al-Nar Period. This alloy had not previously been found with any frequency in third millennium BCE contexts in the Gulf, and given the geological setting of southeastern Arabia, was clearly imported to Tell Abraq from a considerable distance. The hypothesis that Tell Abraq may have had greater access to foreign metals than contemporary sites in southeastern Arabia was supported by additional circumstantial evidence. This included the prominent position of the site on the southern shores of the Gulf and its size in relation to contemporary coastal sites, in addition to material evidence from Tell Abraq attesting to widespread exchange relations with regions to the north and east. Tell Abraq7sunusual pattern of metal use seemed to reflect the role played by long-distance exchange in shaping metal-working crafts in southeastern Arabia, a region otherwise famous for its large-scale, indigenous, Bronze Age copper production. However, the ability to assess the uniqueness of the Tell Abraq metal assemblages was impaired by the extremely limited number of analyses of contemporary copper-base objects that were available for comparison. That is, it was possible that the Tell Abraq analyses appeared anomalous simply due to the lack of relevant comparable data.

In order to investigate this issue, analyses of objects from three other tomb assemblages in the northern U.A.E. were undertaken. The compositional analyses from A1 Sufouh, Unarl, and Unar2 utilized the technique of Proton-Induced X-ray Emission analysis (PIXE), and were supplemented by the analysis of a newly excavated group of objects from the Tell Abraq tomb using the same technique. These new analyses form the core of the present volume and they have facilitated an improved understanding of alloying technology and raw material exchange patterns over the second half of the third millennium BCE in the northern Oman Peninsula. Furthermore, as the ultimate origin of the tin and tinbronze used in Bronze Age western Asia remains uncertain, the study of the Umm al-Nar Period artifacts has provided important insights into an archaeological issue of concern to Bronze Age western Asia as a whole. The data from the four Umm al-Nar Period sites have, however, allowed for the investigation of more than the Bronze Age tin trade, and the issues addressed in this volume have expanded well beyond the scope of the project as initially conceived. A discussion of copper production in Bronze Age southeastern Arabia represented one primary addition, and provided information of fundamental importance for the interpretation of the new compositional data. The review of technological and mineralogical aspects of Bronze Age copper mining and smelting in Oman indicated that specific alloys recorded in Umm al-Nar Period tomb assemblages reflect the geological milieu of the Oman Mountains, and the comparison of the two data sets has allowed an assessment of the likelihood of their local manufacture. More generally, and moving away from technological issues, a discussion of the organization of copper production in Bronze Age southeastern Arabia and the impact that this may have had on contemporary society was also presented. Just as the evidence for tinbronze at Tell Abraq and in other U.A.E. tombs reflected patterns of trade in wider western Asia, so too primary copper production in southeastern Arabia responded to both internal and external socio-economic factors. In previous studies, the apparent periodicity of copper production in southeastern Arabia has been strongly linked with changes in the external demand for the copper of Magan. However, the discussion presented

in this volume indicates that internal demand for Omani copper, as well as changing socio-economic configurations in Bronze Age southeastern Arabia, also played a significant role in the development of primary smelting operations. The compositional analyses of objects from the four Urnm al-Nar Period sites were supplemented by lead isotope analyses (LIA) of a sub-set of the objects. These data provided important evidence regarding the relative and absolute provenance of the metals used to produce the copper-base objects, and raised many issues with regard to the mechanisms and routes by which clearly foreign tin and tin-bronze reached the Gulf. Comparisons of the LIA of the four U.A.E. sites to isotopic data for artifacts from other regions, such as Anatolia and the Aegean, also raised interesting questions regarding the significance for wider Western Asia of the early tin-bronze exchange in the Gulf.

Summary of Major Results The analyses of the A1 Sufouh, Unarl, Unar2 and Tell Abraq assemblages indicate a number of variations in metallurgical technology and alloy use. Objects of unalloyed copper are used at all four sites, as are copper-base alloys including As/Ni-copper (containing approximately one to six percent arsenic andlor nickel) and tin-bronze ( > 2percent Sn). However, while the types of alloys used in southeastern Arabia are relatively limited, the frequency of alloy use changes dramatically over the half a millennium (ca. 2450-2000 BCE) covered by the tomb assemblages. Thus, As/Ni-copper was particularly prominent in the earlier Urnm al-Nar objects from A1 Sufouh, but was rare in the latest tomb assemblage from Tell Abraq. In contrast, tin-bronze appears with greater frequency in the later third millennium BCE:a few tinbronzes with low tin concentrations (0.5-5.0 percent Sn) are recorded at A1 Sufouh and Unarl, whereas more than half of the objects from the latest Urnm al-Nar assemblages from Unar2 and Tell Abraq were manufactured of tin-bronze, often with greater than 1 0 percent Sn. A number of objects, particularly from the Unar2 tomb, are ternary alloys with significant concentrations of both tin and arsenic. Other complex alloys are rare, but include one example each of the Cu-As-Pb and CuSn-Pb ternary alloys (with one to two percent Pb), and one example of a Cu-As-Ag alloy (with 2.3 percent Ag).

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Returning to the basic aim of this study, analyses of copper-base objects from the four Urnm al-Nar Period sites in the U.A.E. indicate that the alloying practices recorded at Tell Abraq in previous studies by the author (Weeks 1997) are not unique in the northern Oman Peninsula. The patterns of metal-use at Tell Abraq show numerous parallels to contemporary Urnm al-Nar Period sites in the U.A.E. A strong contrast remains, however, between the results of the present study and those undertaken on contemporary material from southeastern Arabia (Prange et al. 1999). The strongest compositional differences in the U.A.E. objects analyzed in this volume are between the A1 Sufouh and Tell Abraq assemblages. These tomb assemblages sit at the opposite ends of our half millennium span, and their observed compositional diversity might reflect this chronological separation. However, the compositional variability of the assemblages is not complete, as statistical analyses have indicated that the copper objects from each of the tomb assemblages were relatively similar in terms of their minor and trace element compositions. In contrast, the tin-bronzes from Unarl, Unar2 and Tell Abraq were relatively distinct from each other in terms of their overall composition. The discussion presented in Chapter Five focused on the impurities of iron and sulfur found in the Urnm alNar Period objects, and the concentrations of the potential alloying elements arsenic, nickel, and tin. The presence of sulfur and iron in the Urnm al-Nar Period objects reflects the ores that were used to produce them, the smelting technology employed, and the degree of refining that the raw copper received prior to object fabrication. The high iron and sulfur concentrations would have adversely affected the working properties of the raw copper, and a refining stage prior to fabrication (i.e. secondary refining) would have been necessary in order to produce satisfactory objects. Evidence of such refining practices has been found in abundance at Bronze Age settlements in the Gulf region, including sites such as Bat, Hi1 8, Tell Abraq, Saar, Qala'at al-Bahrain, and Failaka. A review of the mineralogical, metallurgical, and technological aspects of the production of As/Ni-copper objects in southeastern Arabia suggests that they are most likely to have been natural alloys inadvertently produced as a result of the types of ores exploited and the

smelting technology employed. Thus, much as with iron and sulfur, arsenic and nickel are present as natural impurities in southeastern Arabian raw copper. The difference is that these impurities had advantageous rather than deleterious effects on the mechanical properties of the resultant metal. The advantageous properties of these "accidental" alloys, including increased hardness, attractive color, and improved castability, most probably allowed AsJNi-copper to be distinguished from unalloyed copper after it had been produced in the primary smelt. The evidence for alloy use in different object categories indicates that AsJNi-copper was rarely used for decorative objects such as rings, but was commonly found in more utilitarian objects such as pinslawls and blades. Such a differentiation may be indicative of the use of AsJNi-copper for its mechanical advantage of hardness, but could also reflect factors such as the relative worth (in economic and ideological terms) of other alloys like tin-bronze. Examination of alloy use in different object categories indicates that tin-bronze was selectively used for objects which had a decorative rather than utilitarian function. This suggests that the surface appearance of tin-bronze, or its greater value (however defined), may have dictated how this alloy was used in Bronze Age southeastern Arabia. Evidence from the compositional analyses was, however, inconclusive regarding the techniques used to manufacture the tin-bronzes found at A1 Sufouh, Unarl, Unar2, and Tell Abraq. The LIA presented in Chapter Seven indicated that at least some of the tin-bronze used in southeastern Arabia was traded to the region already in its alloyed state, perhaps in the form of small finished objects. In contrast, the discovery of a tin ring in the Tell Abraq tomb indicates that alloying of metallic tin with local copper could also have been undertaken in the region in the Umm al-Nar Period. Although the significant quantities of arsenic and nickel in the Umm al-Nar objects are compatible with a southeastern Arabian origin, copper ores with significant As and Ni concentrations are also found in geological contexts outside Oman. Reliable conclusions regarding absolute provenance cannot, therefore, be drawn from the compositional data alone. In this study, issues of provenance were investigated using both compositional analyses and the LIA of a subset of the objects analyzed

by PIXE. This approach was critical in assessing the potential provenance both the AsJNi-copper objects and the tin-bearing objects from the four tomb assemblages. The significant isotopic diversity of the objects analyzed in this study suggests very strongly that multiple sources of metal were utilized in the northern Oman Peninsula in the Umm al-Nar Period. Comparison of the data from individual sites suggests that each had access to some metal from different sources than available to the other sites. Nevertheless, there are a range of isotopic compositions (207PbJ206Pb ca. 0.837-0.843, 208PbJ206Pb ca. 2.070-2.090, 206Pb1204Pb ca. 18.60-1 8.80) that seem to characterize copper objects found at Bronze Age sites in both Oman and the Central Gulf. Thus, although the isotopic data indicate multiple metal sources for Gulf sites, copper from one source may have been a significant supplier to the Gulf region in general. The most obvious candidate for this source is a mine or mines in southeastern Arabia, a region whose large copper output in the third millennium has been amply demonstrated. Moreover, some of the copper ingots from southeastern Arabia that have been isotopically analyzed fall into this range of "common" isotope ratios. However, many of the plano-convex copper ingots found in Oman and one from the Central Gulf site of Saar have unusual isotopic characteristics that are unmatched amongst the objects analyzed in this study. Thus, the likelihood of an Omani origin for many Gulf objects is difficult to determine. Although only a small number of ore analyses exist against which to assess the results in this volume, the LIA clearly indicated that at least some of the analyzed objects were produced from metal sources outside southeastern Arabia. In particular, the radiogenic isotopic signatures of some of the tin-bronze objects from Tell Abraq and Unarl suggest a foreign source for the alloy. Likewise, a number of tin-bronzes and copper-low-tin objects from A1 Sufouh, Unar2 and Tell Abraq have 207PbJ206Pb ratios less radiogenic than those encountered in the southeastern Arabian ores so-far analyzed. Of course, the tin content of these objects alone indicates that they incorporate at least some foreign metal, and so their isotopic divergence from copper objects analyzed here could reflect either the use of entirely foreign metal, or the perturbation of the isotopic characteristics of local copper by lead-bearing metallic tin.

Summary and Conclusion

1 99

These outlying objects, exclusively tin-bronzes or copper-low tin objects, make up about one quarter of the 42 copper-base objects that underwent LIA. The remaining objects show a small number of clear isotopic matches with Omani ores, but nevertheless fall into the (very broad) isotopic range of southeastern Arabian copper deposits (207Pb/206Pb ca. 0.838-0.872). Given the limited nature of the ore database as it currently stands, it is impossible to determine whether the lack of isotopic matches between U.A.E. copper-base objects analyzed in this study and Omani ores reflects a separate provenance, or merely the limited number of analyses of appropriate ore sources. Certainly, the isotopic signature of the metallic tin ring from Tell Abraq and isotopic similarities between U.A.E. objects and third millennium BCE tinbronzes from other areas of Western Asia suggest that the tin-bronzes may be composed entirely of foreign metal, and that this metal may be difficult to distinguish isotopically from Omani copper ores. The ultimate source of the tin in the U.A.E. tinbronzes almost certainly lay to the east or northeast of Iran, in Afghanistan, Tajikistan or Uzbekistan. Geological research and archaeometallurgical studies in Central Asia have demonstrated the presence of many tin deposits, and some evidence for their having been worked by the early second millennium BCE. The situation in Afghanistan is less clear, due to the inaccessibility of the region for research over the past few decades. However, the combination of early tin-bronze use and abundant geological evidence for cassiterite deposits in a number of areas of the country make Afghanistan a prime candidate for a source of tin used in the Gulf region and other areas of Bronze Age Western Asia. This metal probably reached the Gulf through a number of intermediaries, and the archaeological evidence from southeastern Arabia points particularly to trade with the Indus Valley, and possibly Iran, as the immediate source of Gulf tin and probably also tin-bronze. The above claims do not represent a rejection of the evidence for tin extraction that has been found in the Taurus Mountains of Turkey, but merely a reflection of the kinds of cultural contacts that seem to characterize the polities of the southern Gulf region. Clearly, any discussion of tin production and exchange in wider Western Asia must deal not only with the potential eastern sources, but also with those in Anatolia.

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Generally, the evidence for the inconsistent adoption of tin-bronze across Western Asia suggests that, in addition to considerations of technology and trade routes, "ideological" aspects of early metal use often conditioned the adoption of the new alloy. Indeed, it is clear that technological changes, such the adoption of a new, harder, more easily cast and worked alloy like tinbronze, were mediated at every stage by cultural values. To co-opt a phrase used by Hamilton (1991), tin-bronze is best thought of as a "cultural alloy", whose adoption and use was conditioned by the social contexts in which it was produced, exchanged, and utilized.

Prospects for Future Research Much of the discussion presented in this volume has served to highlight the limitations in our understanding of early copper production in southeastern Arabia. In particular, the current understanding of primary copper extraction as having gone through distinct periods of intensification and decline requires close scrutiny. A complete understanding of Bronze Age copper production in southeastern Arabia will require investigation of both the earliest metallurgy in southeastern Arabia in the Hafit and early Umm al-Nar Periods, as well as metallurgical activities in the Wadi Suq Period and Late Bronze Age. The Hafit Period has produced significant evidence for the use of copper-base objects but virtually no evidence for contemporary copper smelting. Determining whether these early copper-base objects are foreign or local products (as usually assumed) is of critical interest. Analyses of objects from Hafit period sites may be crucial in determining whether Hafit Period copper-base objects were imported, or if they represent the development of copper extraction technology in southeastern Arabia through direct adoption from neighbouring regions such as Iran, or a process of stimulus diffusion. Finding and studying evidence for Hafit Period copper smelting will be of the greatest significance. Smelting sites such as that at al-Batin recorded by Yule and Weisgerber (1996:141), with TL dates around the middle of the third millennium BCE and a slag typology different to that seen at later Umm al-Nar Period sites, are a hopeful indication that evidence for early smelting will be recovered in the archaeological record of southeastern Arabia.

Obtaining secure evidence for primary copper extraction in the Wadi Suq Period will require intensive investigation of the very few sites, such as Masirah Island, that show some evidence of Wadi Suq Period exploitation. The investigation of even one such site could radically alter our understanding of this critical period of copper production and trade in the Gulf region. However, efforts must also be made to determine the exact chronological range of the numerous Omani smelting sites designated "Bronze Age" because of their slag typology. Although dating of such sites can be difficult, programs of TL dating (Haustein et al. 2003) may aid in their interpretation. Compositional and isotopic analyses of contemporary Wadi Suq copper-base objects from tomb assemblages (e.g. Qattarah) will also be important in reaching conclusions about second millennium copper smelting in southeastern Arabia. Determining the organization of Bronze Age (and later) copper production in southeastern Arabia should also be a major focus of future research. Understanding the impact of copper production on the Bronze Age population southeastern Arabia necessitates an understanding of the way in which copper mining and smelting were integrated with other social and economic activities. In investigating this issue, detailed field reconnaissance at large extraction sites such as Wadi Salh 1 and Tawi Ubaylah will be critical. Our current treatment of these sites as homogeneous, indivisible, large-scale collections of extraction residue, means that they are mute regarding the ways in which Bronze Age communities organised production. In order to understand production at such sites, factors such as the scale, context, concentration and intensity of extractive processes (Costin 1991) must be investigated. Attention must also be paid to the variability of production regimes that characterized Bronze Age southeastern Arabia. Thus, relatively small sites like Wadi Fizh 1, where copper extraction is integrated within the context of village subsistence farming, require investigation of their productive processes as much as the larger sites mentioned above. Such approaches will allow archaeologists to move from a primarily technological understanding of early metallurgy in southeastern Arabia towards a more behavioral interpretation of the archaeometallurgical evidence. The large output of copper from Bronze Age

Oman, for 4,000 tonnes of copper is indeed a very great amount, must be contextualised in terms of individual and group human behaviors. How much copper was smelted and how this was accomplished technologically are important archaeometallurgical questions. However, more complex and intractable archaeological problems remain to be addressed. These include an understanding of who controlled copper production in Bronze Age Oman, both in organizational (political) terms and in terms of access to the technical (i.e. ritual) knowledge that lay at the heart of copper extraction. Such questions raise others, for example the status of those involved in the mining and smelting of copper in Magan. Such issues will no doubt prove difficult to unravel, but nevertheless they lay at the heart of any understanding of the ways in which mining and smelting were integrated with political, economic, and subsistence activities in Bronze Age southeastern Arabia. With regard to other problems, the question of metal sources and exchange will only be satisfactorily investigated through greatly expanded programs of LIA of Omani sources, and sources in the neighbouring regions of Iran, Pakistan, India and Central Asia. Very important preliminary research along these lines is being undertaken by.the German mining Museum in Oman (Prange et al. 1999) and in Iran (Chegini et al. 2000), as well as by other groups (e.g. Stos-Gale 2001; Srinivasan 1999). Of course, such isotopic analyses will only be one component of archaeometallurgical research at important Bronze Age primary production sites across the Indo-Iranian borderlands. Finally, despite the significant advances that have been made over the last decade in the knowledge of the tin sources used in Bronze Age western and central Asia, a definitive understanding of early production centers and exchange mechanisms has not been achieved. The basic foundations for the discussion of this issue will continue to be provided by field research at putative tin sources in Anatolia, Uzbekistan, and Tajikistan. It is to be hoped that related research will soon be possible in Afghanistan, given the enormous significance of this region for the resolution of the "tin problem". In the Gulf region, our understanding of early alloying practices would be considerably improved by the analysis of copper-base objects from third millennium contexts in

Summary and Conclusion

20 1

the Central Gulf. Few assemblages of such date are known, but material from Tarut Island and from City I contexts at Qala'at al-Bahrain can be cited, whose study would be extremely enlightening for the discussion of early tin and tin-bronze exploitation. As noted above, all of this metallurgical research must be interpreted with an understanding of the social relationships that determined the ways in which tin and tin-bronze were produced, exchanged, and utilized. Although we may never be able to satisfactorily address some of these questions in an archaeological context, their influence in the shaping of the archaeometallurgical record is clear. Indeed, the realization of the social embeddedness of technological systems has been one of the most significant theoretical developments in archaeometric research in the last few decades. Although the explanations that can be offered by studies synthesising metallurgical, archaeological, historical and ethnographic data are often tentative, limiting our conclusions to issues of materials science can only marginalise archaeometric studies within the wider discipline of archaeology. Striving to explain human behavior, and to embed our explanations of technological systems in social processes, must remain the goal of the archaeometallurgist.

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Appendix 1 Analytical Techniques and Data Treatment

A.l Analytical Techniques A.l . l . PIXE Sample Preparation Samples taken for analysis were usually small, pre-existing fragments. If a sample had to be removed from a larger object, a fine-bladed handsaw was used. For PIXE analyses, samples with dimensions of greater than approximately five mm were taken. Samples were almost inevitably heavily corroded. For analysis, material from the center of the sample was exposed by abrasion, and polished using wet-and-dry sandpaper grades 320, 600, 800, and 1,200. The samples were cleaned in distilled water and mounted on Cr-coated iron brackets on the long target stick just prior to analysis. A.1.2. PIXE Instrumental and Analytical Details (courtesy of Dr. Grahame Bailey) 1. Samples, mounted on a long target stick, were positioned at the center of an evacuated target chamber and bombarded with 2.5 MeV protons from ANSTO's 3MV accelerator. A schematic of the SR2 target chamber is illustrated in Figure A.1. 2. Gamma rays and X-rays, produced from proton interactions within the target material, were counted simultaneously by two detectors positioned at angles of 135 and 225 degrees from the incident proton beam direction. 3. The gamma rays were counted by a large, 67 mm diameter intrinsic Ge detector situated outside the chamber. This detector was surrounded with 20 mm of lead shielding to reduce contributions from the natural background. 4. The X-rays were counted by a small 4 mm diameter Si(Li) X-ray detector, placed close to the target, and situated inside the target chamber vacuum to minimise attenuation of low energy X-rays. The X-ray detector, which is constructed with a fixed 25pm Be entrance window, was fitted with an additional pinhole filter. The pinhole filter consisted of a combination of thin 47pm Mylar disc, attached to a 1.68 mm thick perspex disc, which had a small pinhole drilled in the center. The Mylar filter, in combination with the inherent Be filter, is required to prevent

Figure A.l SR2 target chamber schematic.

scattered protons from the target surface reaching the sensitive volume of the X-ray detector. The pinhole filter is used to reduce the counting rate in the X-ray detector to manageable levels (set at a figure of about five percent dead time) by preferentially attenuating low energy X-rays from the light elements such as A1 and Si, which are often present in samples in high concentrations. 5. Samples were exposed to a fixed proton charge, together with a number of standards and carbon blanks, which allows for calibration of the two detectors. 6. The calculation of element concentrations from the X-ray spectra was done using the ANSTO PIXAN X-ray analysis software package, which has be adapted for use on a fast unix-based computer (Clayton et al. 1987).

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A.1.3. Sensitivity, Precision, and Accuracy of the PIXE data The sensitivity of the PIXE technique is represented by a quantity known as the Minimum Detectable Level (MDL), which is calculated for each quantified element in each analyzed sample. The MDL is the theoretical minimum amount of an element that can be discerned by the PIXE analytical technique, and is dependent upon the atomic weight of the individual element, the compositional matrix of the analyzed sample, and the particular instrumental set-up employed in individual laboratories (Fleming and Swann 1986). The effect of atomic weight on the MDL for a particular element is illustrated in Figure A.2, which shows the average MDLs for every element for the Umm al-Nar samples analyzed in this volume. However, matrix effects can also be observed in these data. The MDLs for the three elements closest to copper (CO, Ni and Zn) are

Atomic Number and MDL

100000

Pm SnL

S.

10

15

20

25

30

35

40

45

50

55

Atomic Number Figure A.2 The relationship between PIXE sensitivity and atomic number.

higher than elements of similar atomic weight, which reflects the difficulty in measuring low concentrations of these elements in high-copper samples. MDLs can vary greatly between laboratories as a result of instrumental set-up. For example, the MDL for silicon in this analytical program is commonly between one and two percent, whereas the MDL for arsenic is generally less than 100 ppm. Detection limits for these elements at the MASCA laboratory, University of Pennsylvania, are 1 7 ppm and 160 ppm respectively (Fleming and Swann 1986: 146). The large difference in Si detection levels between the laboratories results from the use of a pinhole filter for the ANSTO analyses (see section A. 1.2, point 4 ) which severely attenuates the low-energy electron signal from light elements such as A1 and Si. The MDL values presented in Chapter Four for each element are a statistical simplification of the large amount of raw MDL data collected during PIXE analyses, and represent an average MDL value calculated from the MDL data for all the analyzed samples. However, significant variations can be seen between samples from different sites, which reflect the differing performance of the ANSTO PIXE system on a day-today basis. The higher the concentration of a particular element above the MDL, the better the precision that can be associated with the measurement. The relationship

between MDL and precision for samples from Tell Abraq analyzed on the ANSTO PIXE system is illustrated in Figure A.3. As can be seen, values below the MDL, although frequently produced by the quantification software, are highly unreliable. Percentage standard deviations are commonly in the range of 40-10,000 percent at concentrations below the MDL. At levels of one to three times the MDL, percentage standard deviations are generally in the 15-40 percent range. At concentrations of more than about five times the MDL, precision is better than ca. 210 percent for most elements. As noted in section A.1.2 (point S), each analytical run involved the calibration of the PIXE detectors using standards of known composition, which are used to correct for possible systematic errors such as offset in the target current measurement. The standards used for the

0.01

0.1

1

10 100 St. Dev. (%)

1000

10000

Figure A.3 The relationship between PIXE precision and element concentration.

Appendix 1

205

analyzeds of archaeological samples were two ANSTO in-house geological standards GSR3-A and GSR3-B. The overall experimental error of the ANSTO PIXE system is ca. 210 percent (Dr. R. Siegele, ANSTO, personal communication). A.1.4. Problems Measuring Chromium Concentrations As noted in Section A.l .l,archaeological samples were mounted on chromium-coated iron brackets for PIXE analysis at ANSTO. Following the analysis of the majority of samples presented in Weeks (2000a), an interesting pattern was found in the Cr concentrations. The Cr data for all objects analyzed in Weeks (2000a) are illustrated in Figure A.4. They show a strongly bimodal distribution with modes at 0-500 pprn Cr and 4,500-5,000 pprn Cr. Examination of the published analyses of Bronze Age and Iron Age copper-based objects from Western Asia indicated that Cr concentrations of greater than ca. 2,000 pprn were extremely rare, and close scrutiny was subsequently given to the Cr data provided by the ANSTO PIXE system. To test the validity of the ANSTO results, 8 samples with high concentrations of more than 5,000 pprn Cr were re-analyzed using mounting brackets coated with nickel rather than chromium. One sample with relatively low Cr concentration (ca. 160 ppm) was also re-analyzed on the different brackets. The results proved conclusively that the high Cr concentrations recorded in the initial analyses were spurious. All samples with high Cr concentrations reported Cr levels of less than 200 pprn upon re-analysis. The sample with low Cr concentration of ca. 160 pprn was found to contain ca. 70 pprn Cr upon re-analysis. Upon

0-500 1000- 2000- 3000- 4000- 5000- 6000- 70001500 2500 3500 4500 5500 6500 7500 Cr ( P P ~ )

Figure A.4 Chromium concentrations in all analyzed PIXE samples.

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Early Metallurgy o f the Persian Gulf

consultation with ANSTO technical staff, it seems likely that the spurious Cr concentrations resulted from problems in proton-beam alignment, whereby a part of the beam was hitting the bracket holding the archaeological sample rather than just the sample itself. The possibility that some of the iron recorded in analyzed samples was a by-product of poor beam alignment was also considered. PIXE compositional analysis of a Cr-coated iron bracket suggested that the possible iron contamination was approximately 10 percent of the Cr contamination. This finding allowed for the correction of iron concentrations given by the PIXE analyses using the formula: Femodified = Feoriginal - 0.1 Cr All Fe concentrations presented in this volume have been corrected in the above manner prior to normalisation. Such findings are obviously of importance for previous PIXE analyses undertaken at ANSTO. As an example, the high Cr concentrations reported in the analysis of pre-Islamic copper-based coins from Arabia (Grave et al. 1996b) are almost certainly false. The findings suggest that the nickel-coated brackets employed at ANSTO should be used in preference to Cr-coated brackets, as the aperture through which the beam can pass is larger on the Ni-coated brackets (10 mm as opposed to five mm). The larger aperture of the Ni-coated brackets reduces the possibility of contamination through poor beam alignment. A.1.5. LIA Sample Preparation and Analytical Details (courtesy Prof. Ken Collerson) TIMS: All archaeological objects from Tell Abraq were analyzed at the facilities the Advanced Center for Queensland University Isotope Research Excellence (ACQUIRE) of the Department of Earth Sciences, University of Queensland, using TIMS. Small shavings from each artefact were retrieved and stored in clean teflon SavillexB beakers. Each sample was cleaned using deionised water and acetone in ultra sonic bath prior to dissolution with hot HC1-doped 7 N H N 0 3 . Following evaporation to dryness on a hot plate at -75 "C shavings were converted to chloride using 7pl of 6 N HC1. Samples were taken up with 3pl HBr for loading on ion-exchange columns. Lead separations were carried out using standard HBr-HCl chemistry on columns filled with 100 m1 AG-1~8,200-400mesh anion exchange resin using procedures of Tilton (1973).

Purified Pb fractions were dissolved in H3PO4 and a small fraction was loaded with silica gel on single degassed Re-filament. Isotopic compositions were measured at 1,350 degrees C and the data were corrected for instrumental mass fractionation of l % o per atomic mass unit using the values of Todt et al. (1996).This value was established by measuring multiple loads of a NBS-981 standard solution during the data acquisition. Procedural blanks during the study ranged from 100 pg to 65 pg Pb.

A.2. Data Treatment A.2.1. Normalization The PIXE data values were calculated using PIXAN, a computer-based spectrum interpretation and quantification program developed at ANSTO (Clayton et al. 1987). The raw data produced by the quantification software have been modified prior to analysis and discussion. All data have been "normalized", whereby elemental data for each individual sample are manipulated so as to sum to a uniform value, which in our case is 100 percent (or one million parts per million). Such a process is useful when raw data sums for individual samples can range from (in extreme cases) 500,000 to 1.5 million parts per million (ppm), as normalization can make otherwise incomparable compositional analyses directly comparable. Other normalization processes have also been used on sample data generated by PIXE, due to the compositional changes introduced through processes of sample corrosion. PIXE analyses revealed the occurrence of a number of elements which are likely to be present only due to the contamination of the archaeological objects after their deposition, and which are not representative of their original composition. The process of corrosion can not only change the concentrations of elements relative to those seen in the original, but can introduce wholly foreign material such as surrounding soil and mineral particles and corrosive salts (Scott 1991: Figures 65, 67). In the case of the samples analyzed in this study, the elements silicon, chlorine, calcium and potassium are the major indicators of the intrusion of soil and mineral particles into the sample matrix or the formation of bronze disease within the sample. Additionally, titanium, vanadium, manganese, bromine and strontium data also

reflect contamination. The median level of total contamination in the analyzed objects is eight percent, and the ninetieth percentile value is 22 percent. In all cases, the PIXE data for nine corrosion-related elements (Si, Cl, K, Ca, Ti, V, Mn, Br, Sr) have been removed prior to normalization, and normalized compositional values are thus presented only for those elements which would have comprised the metal object in its original state. There is a great deal of debate about the relative advantages and disadvantages of data normalization, but the technique is used for all data discussed in this volume (as advised by the scientific staff responsible for PIXE analysis at ANSTO-Dr. Grahame Bailey, personal communication 1997). Craddock (1976) argues strenuously against such normalization procedures, particularly when applied to compositional data for corroded samples. He states (1976: 96) that such normalization assumes "the corroded metal had the same composition as the original metal", and notes that there is no justification for such an assumption. However, as almost all the objects analyzed in this study are corroded, no analytical technique will succeed in providing fully quantitative data. In such a case, normalization procedures possess the advantage of allowing for better comparability between analyses which, no matter how accurate or precise, are only a guide to the original composition of the objects in question.

A.2.2. Statistical Summaries A brief note is required on the data summaries and charts presented in Chapter Four. In all cases, the data for individual elements are summarized statistically by giving the median and the tenth to ninetieth percentile range. These measures are preferred to other statistics such as the average and the standard deviation because the data are in almost all cases far from normally distributed. Averages and standard deviations can be strongly affected by outliers within the data, and generally provide misleading summaries of group properties if utilized on non-normally distributed data. Statistical summaries better reflective of group properties can be achieved with the removal of outlying data, but this is potentially a very subjective process (Freedman et al. 1991: 95-96, 101). The selective removal of outliers can be avoided through the use of

Appendix 1

207

the median rather than the average as a measure of centrality, as it is less affected by outlying data. Percentiles are preferred to standard deviations as a measure of dispersion for a similar reason; standard deviations contain little descriptive power in situations where the data are strongly asymmetrical. The particular use of the tenth to ninetieth percentile range to describe the dispersion of the data is arbitrary, but offers a reasonable middle choice between the absolute range of the data (which can be strongly affected by outliers) and more commonly cited percentile-based measures of dispersion such as the interquartile range, which represents only the middle 50 percent of the data dispersion. A.2.3. Previous Analyses Summarized The summarized previous analyses of Umm an-Nar objects (2700-2000 BCE) incorporate material from Umm an-Nar Island (Berthoud 1979; Frifelt 1975a, 1991; Hauptmann 1995), Hili, Jebel Hafit and Qarn Bint Saud (Berthoud 1979), Maysar 1, Maysar 4 and Maysar 25 (Hauptmann et al. 1988), and Tell Abraq (Pedersen and Buchwald 1991). Analyzed ingot and raw copper fragments (2700-2000 BCE) come from Maysar 1, Wadi Bahla (Al-Aqir), Umm an-Nar Island and Ra's al-Hamra (Hauptmann 1987, 1995; Hauptmann et al. 1988; Craddock 1981). The previous analyses of Wadi Suq and Late Bronze Age material (2000-1300 BCE) incorporate objects from Masirah Island, Maysar 9, and Suweiq (Hauptmann et al. 1988), Shimal settlement area SX and Shimal tomb SH102 (Weeks 2000a). A significant amount of previously-analyzed metal comes from tomb assemblages of mixed Wadi Suq to Iron Age date (2000-300 BCE). Summarized analyses include those from Shimal tombs 1 and 2 (Craddock 1985), Sharm (Weeks 2000b), Jebel Buheis and Al-Qusais (Weeks 2000a) and Qattarah (Abu Dhabi National Oil Company: n.d.). Previously anal~zedIron Age material (1300-300 BCE) comes primarily from the IbriISelme hoard (Prange and Hauptmann 2001; Hauptmann 1987), the Qidfa tomb (Im-Obersteg 1987; Weeks 2000a), the collective tomb at Bithnah (Corboud et al. 1996), the settlement of Muweilah (Weeks: forthcoming b), Tell Abraq (Pedersen and Buchwald 1991), and the site of Maysar 9 (Hauptmann et al. 1988).

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A.2.4. Frequency Histograms Data are summarized graphically in Chapter Four in the form of frequency histograms (e.g. Figure 4.1). The histograms are presented in either percentage terms or ppm on a logarithmic (base 10) scale, with each order of magnitude divided into four geometric intervals corresponding to the squares of the fourth root of 10 (=1.78).As an example, the divisions from 0.1 through to 10 percent on Figure 4.1 are divided into the ranges 0.101-0.178, 0.179-0.316, 0.317-0.562, 0.563-1.0, 1.01-1.78, 1.79-3.16, 3.17-5.62, and 5.63-10.0. On the histograms, the bar delineated by gray stippling ing represents all samples for which the elemental concentration was below the MDL. This MDL column is placed on the histogram at the position it would occupy in the frequency distribution. Thus, for sulfur with a MDL of ca. 0.1 percent, the MDL column is in the 0.056-0.1 percent range (see Figure 4.1).

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Early Metallurgy of the Persian Gulf

Index

'Arja, 12, 20, 22, 25-27, 29, 32-33, 42, 54, 110, 119, 134-136,143,155-156

Anatolia, 3, 16-17, 41, 113, 116, 133, 135, 140, 152, 160-163, 165-169, 172, 174-176, 179-181, 192-193, 195, 198 Anau, 176 Andronovo, 171, 176 Assur, 179, 181, 187 Bactria, 65, 176, 179, 181-182, 185, 187 Bahla, 39, 56, 152, 208 Bahrain, 1, 5, 14, 43, 64, 67, 74, 84, 88, 107, 113 Bayda, 12, 22, 26, 28, 33, 42, 57, 110, 134, 136, 143, 135, 155 carnelian, 15, 60-61, 65, 67, 179-181, 185-186, 190

Cyprus, 12-13,17,22,52-53,111,

134-135,161

Dilmun, 1, 4, 14-16, 22, 37, 41, 43, 57 Dushanbe, 171 Ebla, 15, 174, 179, 180, 186, 189 Elam, 182, 184, 186-187 Failaka, 14, 182, 186-187, 198 Goltepe, 161, 168-169, 179-180 Gujarat, 15, 159, 172, 179 Hafit, 1, 3, 8, 24, 36, 55, 82, 125, 142, 200 Harappa, 37, 41, 177, 185, 192 Hili, 21, 25, 36, 42, 52, 54-57, 78, 82, 94, 96, 113, 118, 125, 138,182-183, 185-186, 188, 195, 198,208 Indus, 1, 3, 4, 15, 22, 34, 36-37, 41, 44, 46-47, 49, 50, 53-54, 58

Iran, 1-2, 16, 20-21, 36-37, 43, 55, 58, 60-61, 64, 67, 110, 111, 116, 127, 138, 158-159, 166, 169-170,175, 179 Italy, 172 KaneshIKiiltepe, 179, 181 Kargaly, 40

Karnab, 171, 176, 181 Kastri, 160-163, 175

Kish, 18, 173, 192 lapis lazuli, 15, 60, 67, 176, 179-180, 185, 191-191, 193-194 Lasail, 12,22, 25-26, 28, 33, 42, 53-54, 57, 110, 119, 134-136, 142-143, 155 Levant, 6 , 112, 138, 160, 166 Lothal, 37, 177, 185, 186 Magan, 1, 14-16, 21-22, 37, 41, 43, 51, 57, 124, 137, 180-184, 186-187, 190, 197,201 Mari, 17, 179, 187 Masirah Island, 1, 10, 13-14, 17, 22,24-25, 27-31, 37, 39 Maysar, 46-50, 52, 88, 108, 111, 119, 125, 139, 152, 186, 208 Mediterranean, 17, 123, 132, 135, 138-141, 160-161, 167, 172-1 73 Meluhha, 14, 15, 37,41, 124, 179-182, 186-187, 190, 193 Mesopotamia, 1, 3-4, 14-18, 21, 36-37, 39-41, 43, 45, 51, 55, 57-58, 64,66, 107, 123-124, 135, 138, 141, 160, 165-166, 170, 173-175,179-183, 186-188, 190-194 Mohenjo-Daro, 176, 185 Mundigak, 176 Mushiston, 18 1 Namazga, 176 Old Assyrian trade, 181 ox-hide ingot(s), 132, 139 Poliochni, 133, 160-163, 174

Qara Quzaq, 174, 188, 192

Ra7sal-Jinz, 38-39, 50, 52, 55, 183, 190 Rajasthan, 159 Raki, 12,25-26,43, 53,57, 110-111, 135-136, 156-157 Ricardo7s Law of Comparative Advantage, 38-39, 52 Saar, 74, 76, 78, 82, 84, 88, 90, 10-108, 113, 152-154, 156, 160, 177-178, 186, 198-199 Samdah, 20, 22, 26, 28, 30, 54

248

Early Metallurgy of the Persian Gulf

Sarazm, 176 Sar-Cheshmeh, 159 Saudi Arabia, 1, 15, 160-161, 166 Shahdad, 36, 116,175,184,194 Shahr-i Sokhta, 20, 116, 175, 184, 194 Shortughai, 174-1 85 Sialk, 159, 175, 194 Snake Cave, 176 Susa, 175, 179, 184, 182, 187, 193 Tal-i Iblis, 36 Tal-i Malyan, 176, 184 Talmessi, 110, 116 Tarut Island, 14, 177, 202 Tell ed-Der, 138 Tell Judaidah, 174 Tepe Gawra, 174 Tepe Ghabristan, 36 Tepe Hissar, 36, 116, 175, 194 Tepe Yahya, 116,139, 175,182, 184-185,194 Thermi, 57, 153,160-163, 174-175 Transcaucasia, 174, 176, 194 Troy, 160, 161, 163, 174, 175, 192 Umm an-Nar Island, 38, 54-57, 73, 82-86, 90-91, 94, 96, 125,137, 183, 186, 190,208 Ur, 15-16, 173, 179, 182-183, 191 Velikent, 162, 176, 192 Veshnoveh, 159 Yemen, 161, 166 Yugoslavia, 172

Index

249