Sedimentology and Ore Genesis: Proceedings of a Symposium, Held During the Sixth International Sedimentological Congress, Delft, 1963

DEVELOPMENTS IN SEDIMENTOLOGY VOLUME 2

S E D I M E N T O L O G Y A N D ORE G E N E S I S

F U R T H E R TITLES IN T H I S SERIES

L . M . J. U. V A N S T R A A T E N , Editor

DELTAIC A N D SHALLOW M A R I N E D E P O S I T S A. H. BO U M A and A . B R O U W E R , Editors

TURBIDITE S F. G. T I C K E L L

THE TECHNIQUES OF SEDIMENTARY MINERALOGY J. C. I N G L E , Jr.

T H E M O V E M E N T O F BEACH S A N D L. V A N D E R P L A S

T H E I D E N T I F I C A T I O N OF DETRITAL F E L D S P A R S G. L A R S E N and G. V. C H I L I N G A R , Editors

DIAGENESIS I N SEDIMENTS R. F. D I L L

S U B M A R I N E EROSION

DEVELOPMENTS I N SEDIMENTOLOGY VOLUME 2

SEDIMENTOLOGY A N D ORE G E N E S I S PROCEEDINGS OF A SYMPOSIUM, HELD DURING T H E

SIXTH

INTERNATIONAL

SEDIMENTOLOGICAL

CONGRESS

D E L F T - 1963

EDITED BY

G. C . A M S T U T Z Director of the Institute of Petrology and Mineralogy University of Heidelberg, Germany Formerly Professor of Geology, School of Mines and Metallurgy University of Missouri, Rolla, Mo., U.S.A.

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1964

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CONTENTS Contents

.....................................

Introduction T ~ Mo. U.S.A.) G. C. A M ~ T U(Rolla, PARTA. REDUZATE DEPOSITS . .

V

.........................

1

.....................

9

. . . .. .

Early diagenetic pyrite in fine-grained sediments and the genesis of sulphide ores L. G. LOVE(Sheffield, Great Britain) . . . . . . . . . . . . . .

11

Apropos du rdle metallogenique de la prkipitation et de I’adsorption skdimentaires .. . . .. . . A. BERNARD (Nancy, France) . . . . . . .

19

.

. .........

..

. ..........

Facies differentiation and controlling factors for the depositional lead-zinc concentration in the W a n geosyncline of the eastern Alps H.-J. SCHNEIDER (Munich, Germany) . . . . .. . . ... .. . . . 29

. ..

. ... .

Lead-zinc deposits in the Calcareous Alsp as an example of submarine-hydrothermal formation of mineral deposits 0. SCHULZ (Innsbruck, Austria) . . . . . . . . . . . . . . . . . . . . . . . . 47

. .

.

L’application des courbes pr6visionnelles a la recherche4 des gisements stratiformes de plomb P. NIC~LINI (Paris, France) ... . . . . . .. . . . . . . ... . . .

..

..

.. .

53

Diagenetic behaviour of sulphides G. C. AMSTUTZ (Rolla, Mo., U.S.A.), P. RAMDOHR (Heidelberg, Germany) and W. C. PARK . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65 (Hamilton, Ont., Canada) I. Shallow water patterns of iron sulphide distribution in the Jefferson City Formation near . . . . . . . . . . . . . . . . . . . . . . . . . 65 Rolla, Missouri . . . . . . 11. Galena localisation in late diagenetic fissures in algal carbonate rock, Elvins Mine, 71 Missouri . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111. Generations of diagenetic crystallization in the Cu-Pb-Co-Ni-deposit of Fredericktown, Missouri.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73 IV. Sphalerite, fluorite and galena as distinct diagenetic crystallization generations of an . . . . . 76 oolitic phase of the Fredonia Formation, southern Illinois fluorspar district. V. The differential localization of sulphides in fossil wood . . . . . . . . . . . . . . 79 VI. Criteria for diagenetic crystallization and deformations in the Mount Isa sulphide beds. . 82

.

.

.

. .

Supergene sulfides and sulfates in the supergene zones of sulfide ore deposits P. ZUFFARDI and I. SALVADORI (Cagliari, Italy) . . . . . . . . . . . . . . . . . . . . . 91 I. Supergene barites from Sardinia . . . . . . . . . . . . . . . . . . . . . . . . . 91 II. Some examples of sulfides of Cd, Hg, Fe, Pb and Zn, regenerated by oxidation-reduction processes in Sardinia. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95 Discussion of papers in Part A.

. .

. . .. .

....................

.........

.

105

.............

107

etude sMimentologique du minerai de fer oolithique de Lorraine L. BUBENICEK (Maizitres-les-Metz, France) . . . . . . . . .

..

1 13

Facies problems of boehmitic and diasporitic bauxites I. VALETON (Hamburg, Germany) . . . . . . . . Discussion of papers in Part B.

. .

. . . . . . . . . . . . .

101

Kohlensauerlinge als eine Eisenquelle der sedimentaren Eisenerze H. HARDER (Munster, Deutschland) . . . . . , . . . . . .

PARTB. OXIDATE DEPOSITS.

. . .

.

. . . . . . .

.

. . . .

. . . . . . . . . . . . . . . . . . 123 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131

VI

CONTENTS

PART C. SULPHATE AND PHOSPHATE DEPOSITS.

. . . . . . . . . . . . . . . . . . . . . 135

Sedimentologie et recherche des gisements ddimentaires marins de phosphate M.SLANSKY(Paris, France). . . .. ... . . .. . .

.... .

. . . . . . . . . . 137

Mineralogisch-geochemische Untersuchungen an Coelestobaryt mit sedimentarem Gefiige H. PUCHELT und G. MULLER(Tubingen, Deutschland) . . . . . . . . . . . . . . .

. . 143

Small scale sedimentary features in the Arkansas barite district (Rolla, Mo., U.S.A.). R. A. ZIMMERMANN and G. C. AMSTUTZ Discussion of papers in Part C.

. . . . . . . . . . . . . . 157 . . . , . . . . . . . . . . . . . . . . . . . . . . . . 165

Rapport de synthkse P.R~UTHIER (Paris, France).

. . . . . . . . . . . . . . . . . . . . . . . . . . . . 167

Index

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177

INTRODUCTION G.

c.

AMSTUTZ]

University of Missouri, School of Mines and Metallurgy, Rolla, Mo. (U.S.A.)

Historically, the relation between sedimentology and the field of ore genesis has been a function of prevailing patterns of thought. Table I offers a brief schematic summary of the trend of thought patterns since Albertus Magnus. Whenever the trend was to search for causes from within, the interest in the wall rock and its genesis was great. When causesfrom without appealed more to the scientists, the rocks enclosing ore deposits, and especially the sediments received little attention. The present generation inherited largely the latter type of thinking; so much so, as a matter of fact, that sedimentary petrology was treated as a step child in petrology courses. An “economic geologist” was not required to have a serious interest in “soft rock petrology”. The ore in “soft rocks” was a priori believed to have come from “hard rocks” at unknown depths, and the magic word which solved all the problems was “replacement”. It is interesting to note that there exists a close relationship between the general cultural trends and the changing patterns of thought in ore genesis displayed by Table I. The tendency to search for causes from without or from within is an archetypal pattern which is inherent in all cultures. The physicist PAULI(1952, pp.112-113) stated: “As regulating operators and builders in this world of symbolic images, the archetypes function precisely as the sought bridge between sense perceptions and ideas, and are thus also prerequisites for the development of a scientific theory”. A basic archetypal pattern present in all earth science theories on genesis is the scheme of interpretation possibilities shown in Table 11. We tend to approach the outcrop and set up an experiment on the basis of preconceived hypotheses - consciously or, more often, subconsciously-and in interpreting the observations, we are prone to use only those assumptions which are indigenous with us. The experimentalist is, therefore, in an even less favorable situation than the field geologist. His experiment is premised on those hypotheses and therefore a double human relativity is involved in the interpretations of experimental results, which, however, does not make them less urgently needed in the physical sciences.This relativity of scientific theories is commonly ignored or even suppressed because it introduces an undesired and subconsciously feared irrationality factor into science and prompts Present address: Mineralogisch-Petroghisches Institut der Universitat, Heidelberg (Germany).

2

G . C. AMSTUTZ

TABLE I RELATIONSHIP BETWEEN THE GENERAL CULTURAL TRENDS AND THE CHANGING PATTERNS OF THOUGHT IN ORE GENESIS

Emphasis on

Historical periods I

Old Greek, Roman, Arabic, Indian and Chinese theories

I

various theories displaying all basic pitterns of thought I

I

r

Albertus Magnus ( I 193/1205-1280)

earth

0 Hg + S + I

metals

and

ore minerals I

everything is congenetic

Congenerat ionists (about 1300-1500)

I

,

Agricola (epigeneticists)

fire is main agent

(1 494- 1555)

water is main agent

Werner, 1749-1 807, and his school)

observational geometric classifications

Von Cotta and Von Groddeck (about 1830-1890) Neo-epigeneticists (PoXepn);, Lindgren in part, Niggli in part) 1960: Detailed spacetime differentiations and determinations (symmetry, i.e., fabric studies, esp. in sediments, of decisive importance)’

main agents

I

I

.

congruent

= syngenetic -t

U

I

non-congruent E epigenetic

Geometric and geochemical distribution patterns (primary fabrics and compositional histograms) inherent to the host rock are first compared before causes from without are assumed.

the scientist to be more than a technician, i.e., to adopt some of the “yvQzt O E C ~ U T ~ V ’ ’ into his work. But, it seems to me that no major advance has ever been made in science which was not at the same time a considerable step towards a better knowledge of man’s own self. The relativity of scientific theories is, however, not only one of time and cultural age, but also one of geographical or rather ethnological environment. These relations are most interesting today, because at international meetings the theories defended reflect cultural patterns of thought. Quite clearly, for example, the immigrated peoples have a tendency to favor epigenetic introduction and replacement theories, just as they 1960, pp.179-186). also favor exogenous gods (cf. AMSTUTZ, The common tendency to repress and ignore these anthropological differences, or to consider them as unscientific, denies to the sciences a great opportunity to develop

3

INTRODUCTION

TABLE I1 BASIC ARCHETYPAL PA’ITERN

Z

ZI

As

syngenetic formation

epigenetic formation

Space’

At=O

At=x

ns=o

possibility Ia (or Al)

possibility IIa (or A2)

B exogenous formation As=n

possibility Ib (or B1)

possibility IIb (or B2)

Time

A endogenous formation

Endogenous = fromwithin (thahost rock or its own source); exogenous = from outside (the host rock or its own source). a Syngenetic at the same time as the host rock; epigenetic = at any later time than the host rock.

-

and mature their own theories. In other words, foreign literature is an extremely valuable source of new thought, and for allowing ones own ideas and thoughts to procede along the “arrow of evolution” of TEILHARD DE CHARDIN (1955). There is always a very close connection between the general cultural pattern and the scientific theories professed by the people living these patterns. It is not accidental that a strong trend has emerged after World War I1 to look more into possible endogenous and syngenetic causes in ore genesis, i.e., the trend away from a priori-assumptions of epigenetic introductions from the outside. As I pointed out in a brief monograph on “syngenesis-epigenesis” (AMSTUTZ, 1959), this evolution of geological thought began in many countries simultaneously and largely independently. It is paralleled or caused by a general trend for more inward interest, i.e., a certain trend away from an overly extroverted and superficial pattern of life. Fig.1 compares the pattern of interpretation built on the myth of “replacement” (Fig.1A) with that of the new trend which prefers causes from within (Fig. 1 B), including at the same time a reasonable amount of interaction between neighboring systems. These figures also illustrate how, actually, ore genesis theories at present go through exactly the same crisis and change as did paleontology one hundred years ago, when Darwin and others proposed to look for factors “from within”, and rejected the exogenous creationistic theories. This process of evolution of thought from epi-exo-patterns to syn-endo-patternsis one which takes place all the time in all fields of human culture, including the sciences. It suffers relapses of course as recently seen when the myth of flying saucers and of meteor impact structures swept around the world and even affected the sci’entists. It is interesting to note that exaggerations in the other direction, i.e., towards syn-endo-

4

G . C . AMSTUTZ

Fig.1. Legend see p.5.

INTRODUCTION

5

patterns are insignificant and always somewhat still integrated (for example the congenerationist theories of Werner and the Farbenlehre of Goethe). This suggests that the gradual disappearence of the overemphasis of the epi-exo-myths is a process of gradual evolution of the human mind as so brilliantly and transparently pictured and analyzed by TEILHARD DE CHARDIN, especially in The Phenomenon of Man (1955). He himself emphasized the importance of the energy “inside of things”, as compared to the “tangentional energy” operating on the outside of things. As shown in Fig.1, the theories on the major base metal deposits reflect this evolution of thought. Instead of assuming a formation through solutions from hidden outside sources, the possibilities of contemporaneous formation as part of rock genesis itself are presently being proposed and investigated. Again, it is interesting to note that the hidden sources for the emanating solutions are almost always at “unknown depth”. The movement away from the myth of the “unknown depths” and the myth of replacement is most interesting and valuable historically because it parallels the general integration of a sound knowledge and acceptance of the realm of the subconscious in the human mind. This acceptance eliminates the need for a mythological compensation in form of a “scientific” theory on emanations from unknown depth or impact from .unknown outer space sources.

Fig.1. Schematic representation of ore genesis theories according to the conventional and the new patterns of thought. A. This figure shows the domination of the myth of epigenetic replacement and of the unknown depth (“deep seated sources”). Epigenetic introduction from the outside is an axiomatic condition for the formation of most ore deposits. This pattern corresponds essentially to the creationistic, preDarwinian beliefs in paleontology. B. This figure pictures the pattern of ore genesis theories according to the new “petrographic” or integrated theory, according to which ore deposits normally formed at the same time and essentially within or very near the observed host rock. Just as man and animals in the evolution theory of paleontology, ore deposits are, in the new theory, considered a normal integral part of rock evolution. Z = igneous intrusive rocks (known!); ZI = igneous extrusive or subvolcanic rocks (known); ZIZ = metamorphic igneous rocks or migmatites; IV = metamorphic sedimentary rocks; V = sedimentary rocks (non-, or partly metamorphic); VZ = introduction from the (unknown) outside assumed; VII = some migration probable, possible, or (?) questionable. List of major types of ore deposits for which a syn-endo as well as an epi-exo origin has been proposed. In sediments and volcanic rocks: I = Arkansas - type barite deposits; 2 = MississippiValley-type deposits (including the barite and fluorspar deposits in the same type of sediments); 3 = Rammelsberg and similar deposits; 4 = magnesite, rhodochrosite and siderite deposits of the Alps and elsewhere; 5 = Kupferschiefer and/or Red Bed copper deposits as well as various disseminated to massive copper-lead-zinc deposits, for example of the Kuroko type; 6 = Blind River, Witwatersrand and similar deposits; 7 = propylitic deposits of copper, gold, and other metals; 7a and 76 = deposits of sulfides, oxides and native elements (Cu, Ag, Au) in or near volcanic rocks (often with spilitic phases); 8 = Mina Ragra type vanadium deposits; 9 = Colorado Plateau or “sandstone type ” Uranium deposits; 10 = Iron deposits of the Lake Superior type; 11 = Ducktown, Broken Hill, Outukumpu, Falun, and similar deposits in metamorphic belts. In and adjacent to igneous rocks: a= porphyry copper deposits in and around intrusions (including the Climax molybdenum deposit); 6 = Granite Mt., Utah, deposits of magnetite; and similar deposits; c = tin deposits in and around intrusions; d = contact deposits, pipe deposits, perimagmatic vein deposits; e = chromite deposits;f = pegmatites.

6

G . C . AMSTUTZ

Fig.2. The geochemical cycles.

This shift of approach brings a more balanced distribution of the mineral deposits along the geochemical cycle or rather cycles (Fig.2). If the new trend is on ,,the right track”, one of the major “laws” of ore genesis will in the future be as follows: each rock has its own natural share of ore deposits, formed at the same time and from within its own sources. This means that the sedimentary part of the geochemical cycle becomes more important than it has been traditionally during the past 70 years. Sediments cannot be considered any longer as “dirty, unimportant soft rocks”, only good if invaded and replaced by magmatic rocks and ore solutions. This is why sedimentary petrology has become extremely important in the study of ore genesis in the last ten or twenty years. Of course, some investigators, clearly ahead of their time, had recognized the situation much earlier. A general acceptance is only following now, and this is why I considered it to be timely to suggest a symposium on ore genesis within the International Sedimentological Congress. Most of the papers in this symposium are purposely phenomenological. Those by this author are deliberately geometric only, an experiment in testing out how far one can go without including geochemical or even experimental results. This restriction was of course also one of space limitations, set by the congress rules. Perhaps the symposium topics embrace too broad a field; and that fact, combined with the spice restrictions for each paper, creates simultaneously an advantage and a

INTRODUCTION

7

disadvantage: to the outsider, the collection of topics appears to have produced a heterogenous conglomerate. But from a basic point of view, historical, geochemical, and geometric, it may prove of value to demonstrate that the same basic laws of sedimentation and diagenesis apply to a large variety of mineral deposits forming in and with the sediments. 1 wish to thank the Organising Committee of the congress for having adopted the suggestion to add this symposium to the congress program. To Professor Faber and the Administration of the Technical University, we owe many thanks for the fine reception at the Technical University of Delft and for the fine hospitality. At the end of the symposium the following resolutions were adopted by the attending members, and it was decided that they should be passed on to the council as suggestions for future congresses.

RESOLUTIONS

(I) The group wishes to thank the officers of the International Association of Sedimentologists .and the Organization Committee of the Sixth International Sedimentological Congress for accepting the idea of a Symposium on Ore Genesis and for their moral and financial support. (2) The group wishes to express its gratitude to the Technical University of Delft and especially to Professor Faber for the invitation to hold the symposium in the Institute of Applied Geology, and for the perfect hospitality they have extended. (3) The group considers the integration of sedimentology in any study of ore deposits in sediments essential to a correct interpretation. A study of the role of sedimentary processes, including diagenesis, is an important field in pure as well as in applied research on the genesis of mineral deposits. (4) In particular, the group also considers the knowledge of sedimentary rocks and processes (in regard to both, the fabric and the geochemical detail) a prerequisite for the understanding of subsequent metamorphic processes and their possible role in the deformation and reconstitution of mineral deposits and host rocks. (5) The group suggests that similar symposia could with advantage be held at future Congresses of the International Association of Sedimentologists.

REFERENCES

AMSTUTZ, G. C., 1959. Syngenese und Epigenese in Petrographie und Lagerstattenkunde. Sehweiz. Mineral. Petrog. Mitt., 39 : 1-84 (English translation:Intern. Geol. Rev., 1961,3 : 119-140,202-226). AMSTUTZ, G. C., 1960. Some basic concepts and thoughts on the space-time-analysis of rocks and mineral deposits in oragenic belts. Geol. Rundschau, 50 : 165-189. PAULI, W., 1952. Der Einfluss archetypischerVorstellungen auf die Bildung naturwissenschaftlicher Theorien bei Kepler. Studien aus dem C.G. Jung-Institut, English translation: Boiling Series, New York, 1952 : 109-194. TEILHARD DE CHARDIN, P., 1955.L e Phinonzene humain. Gditions du Seuil, Paris, 348 pp.

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PART A

REDUZATE DEPOSITS

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EARLY DIAGENETIC PYRITE IN FINE-GRAINED SEDIMENTS AND THE GENESIS OF SULPHIDE ORES LEONARD G . LOVE

Department of Geology, Universityof Shefield, Shefield (Great Britain)

INTRODUCTION

In any discussion on sedimentology and the genesis of sulphide ores, the topic of “syngenetic” ores and their formation is likely to be raised. Much, however, has yet to be learnt about the occurrence and relationships of the sulphides normally found in sediments before some the problems of these ores can be resolved. Both unconsolidated sedimentsand older rocks must be studied in detail, not only to reveal the changes produced by diagenesis but also because in considering ideas about “syngenetic” ores it must be allowed that in the geological past conditions affecting the formation of sulphides may not, quantitatively, have been as at present. Although in fact much important chemical and biochemical work has been done on Recent sediments, one field in particular is much neglected - that involving optically observable detail of sulphides of the finest grain size. The present paper aims at reviewing the author’s recent work on this and introducing some inferences from a more systematic study. Starting with Recent sediments this is still in its early stages and a fuller account will be presented later.

DATA FROM RECENT SHALLOW WATER DEPOSITS

Superficial sediments examined from shallow coastal waters include those from Christchurch Harbour in the south of England and from localities along Long Island Sound, U S A . From both areas silty muds were used, grey to dark grey when dry and containing a substantial fraction passing the 200-mesh B.S.l sieve (76 p). Freshwater lake mud from Queechy Pond, New York, was also used. X-ray examination of the heavy fraction prepared from air dried samples of the wet sediment gave pyrite as the dominant sulphide; marcasite was not found. This pyrite is entirely microscopic and occurs as tiny crystals and spheres. The isolated crystals are dominantly cubes but octohedra and pyritohedra have tentatively been recognised among concentrates. The spheres, because of their distinctive British Standard “Methods of test for soil classification and compaction”.

12

L. G . LOVE

Fig.1. Early diagenetic pyrite spheres in mud. Drawings of typical forms.

appearence, have so far dominated the observations (Fig. 1) and sometimes may indeed represent nearly all the pyrite present. With their remarkably regular spherical form, they show the framboidal texture, this being a close packed aggregation of small individual crystals, again mostly of the cubic habit. Such spheres have been recorded from a number of Recent sediments and from dark shales and other sapropelic rocks of most geological ages. A detailed account has already been given (LOVE, 1963) including a bibliography of recent and earlier research. It is remarkable how the spheres even of Recent sediment can withstand mechanical treatment during separation, although undoubtedly many will break down and add to the number of small isolated crystals, especially at the expense of the proportion of larger spheres. These may be 40 p in size or even more, while small spheres of regular form have been seen as small as 2-3 p under reflected light. Measurements repeatedly demonstrate a tendency towards a unimodal size distribution with the mode somewhere between 4 and 20 p. It has been noticed from many samples that while the maximum and modal sizes of spheres vary from one sample to another, the maximum size of single large crystals, presumably having grown in a solitary state, may approach but not quite reach the modal diameter of the spheres for the same sample. While the controls over the distribution of the sulphide between spherical aggregates of crystals and singly growing crystals have still not yet been inferred, if such an empirical relationship is generallyconfirmed it may be of value in the study of later diagenetic changes and of sulphides in rocks. Larger aggregations, often of the spheres themselves, may even completely fill shells of foraminiferids or give free nodules, up to 1 mm in size. NEEB(1943) saw their origin as test infillings, and in Carboniferous rocks they have also been observed free of shells but none the less showing the distinct form of the infillings of small goniatites. REGN~LL (1961) provides an example of the diagenetic solution of the calcite shell of a foraminiferid infilled with pyrite in a deep sea sediment. Not only may the pyrite occupy this inner space of micro-faunal tests but even more abundantly it may occupy spaces in other, softer, tissues; in many of the sediments individual spheres or groups fill small sacs. If thin and tightly fitting around the pyrite, these sacs may not readily be visible in the microscope but they will always be revealed by quick solution of the pyrite in nitric acid with a few drops of bromine added. From a concentrate of the pyrite rounded, low density, pellicles would be left as a residue. Comparison with the original sediment reveals that these represent an apparently random part of all the microscopic organic debris preserved in the mud, and react similarly to it on staining. Among much unrecognisable other material such items as

DIAGENETIC PYRITE IN FINE-GRAINED SEDIMENTS

13

unicellular algae and cellular wood tissue are represented as well as the tests of diatoms, ostracods and foraminiferids already mentioned. Unless disaggregation and separation of the fraction has had a bigger effect than suspected, the smaller soft cells appear to dominate in containing the pyrite. The occurrence of pyrite spheres within such pellicles is not universal and in some samples examined from Queechy Pond, for instance, the pyrite appears to be almost free from such associations, and this serves to demonstrate that (unless an aerobic phase of decomposition has intervened) a position inside pellicles of organic material is not an essential for the formation of pyrite and, indeed, the larger single crystals normally appear to be free, although the smaller ones may be seen in organic tissues. When organic tissues do contain pyrite both their uncompressed nature and, indeed, the almost superficial position they may occupy in the mud of some localities serves to indicate the very early presence of the pyrite and yet that it is diagenetic in formation. Evidence on this point has been summarised by Low (1963), and earlier by VALLENTYNE (1961) and NAUMANN (1919). Due to its ready breakdown under conditions of weathering and transport, pyrite cannot be regarded as a likely component of the clastic materials making up slowly deposited muddy and silty sediments. A clear statement on the mode of origin of the authigenic sulphide in those sediments is lacking at present although as a generalisationit is safe to say that the sulphide radical is essentially the resultant of micro-biological processes in an anaerobic environment. That this process can occur even though the sediment as a whole does not yet appear to have reached the anaerobic condition may sometimes be demonstrated by the presence of pyrite occurring, for instance, inside shells and other restricted places. Recent studies using the stable isotopes of sulphur (KAPLAN et al., 1963; D m and NAKAI, 1963) trace more clearly some of the stages of the bacterial production of sulphide and confirm that the sulphate and other sulphur compounds in the water body over the sediment are the principal sources of sulphur.

ANCIENT SHALES AND MUDSTONES

In sedimentary rocks apparently free from mineralisation from external sources, sulphides are regularly most common in shales and mudstones: a grey or darker colour and the presence of carbonaceous or bituminous material preserved in the rock are common associations. Many examples have been studied from the Lower Jurassic and Carboniferous systems of Britain and all have revealed those forms of sulphide noted from unconsolidated muds. In those rocks, too, forms of sulphide are present which are not found in superficial muds - larger nodules, veinlets and shell replacements at least some of which may well represent a redistribution of the abundant sulphide present earlier. This is not under discussion here. The microscopic forms already noted also are well seen in ore shales such as the “Kupferschiefer” ,and Rammelsberg “Banderz” of Germany. In all these rocks a further peculiarityof framboidal sulphide spheres may be demonstrated, as was first shown by the author. This is the

14

L. G. LOVE

occurrence of organic matter within the spheres. It must lie interstitially between the individual crystals of the framboidal structure forming a sponge or meshwork which may be revealed and left as a freestanding spherical body by dissolving away the pyrite. Such bodies may be observed in variable proportions and are often very plentiful. They were earlier regarded by the author as microfossils, on the combined characters of regularity of structure and organic composition; while their abundant and exclusive association with pyrite spheres suggested a genetic relationship. Neither of these two inferences is now maintained, for subsequent rigorous study has shown such organic bodies to be mostly absent from pyrite spheres of Recent sediments, where even better occurrences than in rocks might have been anticipated. This is discussed in detail in Low (1963); and similar analytical data on the absence of organic matter is presented by VALLENTYNE (1963). The geologicallymost Recent sediment in which such interstitial organic material has been found abundantly in pyrite spheres is an offshore silt of late Pleistocene age; whether in this and older sediments it was present at the time of formation of the pyrite or entered later is open to conjecture. The evidence of the environment of formation of shales and mudstones bearing plentiful early diagenetic pyrite commonly points to those same conditions under which such sediments are forming at the present day and amplify what is known of them. Little can be added to the author’s earlier assessments (LOVE,1962b) of dominantly fine silty and argillaceous sedimentation, preservation of organic material and, frequently, preservation of fine lamination in the rock, all pointing to conditions favourable to or positively indicative of the establishment of anaerobic conditions. Benthonic faunas are not necessarily affected but burrowing may be inhibited. Geological evidence indicates the great extent and uniformity which some basins of dark mud deposition could attain, perhaps as a result of climatic as well as physiographic influence, but such sediment may now also be found even in the intertidal region and not, as might be expected, only in deep water below the base of wave agitation. HJULSTROM (1935) and INMAN(1949), however, have demonstrated the progressive increase in resistance to erosion by water movement as the grain size of a sediment falls below 180 p. An added factor may be the inter-weaving effect of the live microscopic flora or organic debris at the mud-water interface.

ORE SHALES

Turning more closely to the ore shales, the best documented occurrences of those containing similar sulphides to the framboidal spheres and individual grains under discussion here are the Permian “Kupferschiefer”, the Devonian “Banderz” associated with the Rammelsberg ore bodies of Germany, and the Mount Isa Shale of Lower Proterozoic age of Queensland, Australia (SCHOUTEN,1946b). In each case argillaceous strata of widespread extent are involved, with concentrations of useful

DIAGENETIC PYRITE IN FINE-GRAINED SEDIMENTS

15

metals in more limited areas or as distinct ore bodies. Apart from the latter every resemblance is found to other, “unmineralised”, shale formations. Among the ore concentrations themselves, and particularly in the adjacent rock, pyrite spheres or their relics have been recognised in abundance and provide a distinct link between all the sulphides on the one hand and the characteristics of the host rocks on the other. They do not themselves reveal the origin of the useful ores but their evidence is none the less of significance. In each locality quoted, “replacements” have been illustrated by SCHOUTEN (1946a) of pyrite framboids and other small pyrite crystals by one or more of the metals copper, lead and zinc if not by others and, whatever paragenetic sequence has been postulated and may be found acceptable, indications of a first and particularly prolific pyrite stage have been abundant. This primary pyrite may be traced beyond the areas of valuable mineralisation for considerable distances, as far as the lithology of the rock remains that of a dark shale or dark h e silt; and there can be no doubt, after comparison with other similar rocks in different situations and of different age, that this is a sedimentological feature and not one of later special mineralisation. In the case of the “Kupferschiefer” and its approximate lateral equivalent in England, the Marl Slate, the sulphide spheres in particular show just those associations with organic matter already described from other shales and also close analogy with spheres lying within detrital organic remains of Recent sediment. Internal, interstitial organic material is also abundant, leaving the characteristic sponge-like bodies on solution of the pyrite (LOVE1962a,p.355). The primary pyrite of Mount Isa also shows associations with carbonaceous material (Low and ZIMMERMAN, 1961, p.882) which appears as pellicles from around sulphide grains. When two points of discrepancy are resolved, the material bears close comparison with that from the “Kupferschiefer” sulphide. Firstly, studies recently concluded by the author show that it is distinctly more carbonaceous than its equivalent from sulphide spheres of the “Kupferschiefer” and Carboniferous shales and this difference is variable in the pale, grey substance of the pellicles, whereas those of the “Kupferschiefer” are a rich brown. The chemically determinable difference, indicating “devolatilisation” or carbonisation, may be attributed to the mild degree of metamorphism undergone by the Mount Isa Shale, in fact now a very hard compact rock. Secondly, the peculiar form of the organic material held within the outer pellicle around Mount Isa spheres can now more clearly be seen as a result of the recrystallisation of the pyrite from an original framboidal condition into single regular crystals of much the same total bulk, with the expulsion of interstitial material to a position just within the outer skin. Similar forms will be described by the author from another, non-metamorphic, rock and this particular change does not appear to be one necessarily associated with thermal or dynamothermal metamorphism of the rock. The pyrite spheres from the Rammelsberg “Banderz” have also shown a typical range of carbonaceous material in associations which indicate that this pyrite was a normal part of the original sediment (AMSMZ and LOVE,in preparation). It is on this basic conclusion, that the significant quantities of primary Sulphide of these deposits belong to the normal formation of the shale and its early diagenesis,

16

L. G. LOVE

that this part of the sulphide may be withdrawn from the field of dispute on the origin of sulphide ore occurrences in shales. In itself this produces no solution to the main problem but it does in some degree affect the balance of existing arguments. The introduction of ore metals has been attributed, in the literature, to exhalations or emanations entering the seawaters below which the black mud is not yet deeply buried, if at all, by later sediment, or, alternatively, to hydrothermal uprisings through underlying strata at any later period. It has been thought that it may be the reducing activity associated with the presence of organic material which acts as a trap for the metals, to be retained as sulphides; but as an essential feature of the three deposits discussed is the abundant initial presence of sulphide mineral (pyrite) more emphasis might be placed on this itself being regarded as a significant trap for the ore metals. In some instances, however, the addition of a distinct further generation of sulphide might be inferred from evidence provided by the stable sulphur isotope ratios of different sulphide minerals in the rock (Love, unpublished data). By whichever method eventually shown to have occurred, the time of the surrounding or replacement of the primary pyrite still has to be defined, and it is now shown that this could conceivably have occurred at a period not greatly removed from the time of deposition of the sediment, with no great interval, if other evidence .requires it. Other authors in this symposium are attempting to distinguish the special features of diagenetic and later mobilisation movements of deposits rich in sulphides.

SUMMARY

A preliminary account is given of the microscopic, very early diagenetic, sulphide of unconsolidated Recent muds and of those features by which it may be recognised in rocks. Confirmation by this means of its presence in certain sulphide ore shales can affect explanations of the genesis of the ores, particularly with respect to the time factor, and especially if replacements or different generations of sulphide are suspected. REFERENCES

AMSTUTZ, G. C. and LOVE,L. G., in preparation. DEEVEY, E. S. and NAKAI,N., 1963. Fractionation of sulfur isotopes in lake waters. In: M. L. JENSEN (Editor), Biogeochemistry of Su@r Isotopes. Natl. Sci. Found. Symposium, 1962. Yale University Press, New Haven, pp. 169-178. P., 1935. Studies of the morphological activity of rivers as illustrated by the River Fyris. HJULSTROM, Bull. Geol. Znst. Univ. Upsala, 25 : 221-527. INMAN,D. L., 1949. Sorting of sediments in the light of fluid mechanics.J. Sediment. Petrol., 19 :51-70. KAPLAN, I. R., EMERY, K. 0. and RITTENLSERG, S. C., 1963. The distribution and isotopic abundance of sulphur in recent marine sediments off Southern California. Geochim. Cosmochim. Acta, 27 : 297-331. LOVE, L. G., 1962a. Biogenic primary sulfide of the Permian Kupferschiefer and Marl Slate. Econ. Geol., 57 : 350-366. LOVE, L. G., 1962b. Further studies on micro-organisms and the presence of syngenetic pyrite. Palaeontology, 5 :444-459.

DIAGENETIC PYRITE IN FINE-GRAINED SEDIMENTS

17

Low,L. G., 1963. Pyrite spheres in sediments. In: M. L. JENSEN(Editor), Biogeochemistry of Surfur Isotopes. Natl. Sci. Found. Symposium, 1962. Yale University Press, New Haven, pp. 121-143. LOVE, L. G. and ZIMMERMAN, D. O., 1961. Bedded pyrite and micro-organisms from the Mount Isa Shale. Econ. Geol., 56 : 873-896. NAUMANN, E., 1919. Om jarnets forekomstatt i limniska avlagringar. Sveriges Geol. Undersokn., Arsbok, Ser. C: Avhandl. och Uppsat., 289 : 1-47. NEEB, I. G . A., 1943. The composition and distribution of the samples. In: The Snellius Expedition. V. Geological Results. Results. Part 3, Bottom Sampels. Section 2. REGNBLL,U., 1961. On pyrite in deep-sea sediments. Bull. Geol. Znst. Univ. Uppsala, 40 : 305-314. SCHOUTEN,C., 1946a. Some notes on micro-pseudomorphism. Econ. Geol., 41 : 348-382. SCHOUTEN, C., 1946b. The role of sulfur bacteria in the formation of the so-called sedimentary copper ores and pyrite ore bodies. Econ. Geol., 41 : 517-538. VALLENTYNE, J. R., 1961. On the rate of formation of black spheres in recent sediments. Intern. Ver. Theoret. Angew. Limnol., Verhandl., 14 : 291-295. VALLENTYNE, J. R., 1963. A chemical study of pyrite spherules isolated from sediments of Little Round Lake, Ontario. In: M. L. JENSEN(Editor), Biogeochemistry of Suljiur Isotopes. Natl. Sci. Found. Symposium, 1962. Yale University Press, New Haven, pp. 144-152.

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A PROPOS D U ROLE MeTALLOGeNIQUE DE LA PRfiCIPITATION ET DE L‘ADSORPTION SfiDIMENTAIRES

ANDRB

BERNARD

DPpartement des Sciences de la Terre, Universite‘ de Nancy, Nancy (France)

INTRODUCTION

L‘un des arguments force des tenants de l’impr6gnation hydrothermale des sulfures de mdtaux lourds dans les roches stdimentaires consiste A mettre en avant la variCtC des roches supports de ces sulfures. Cette ubiquite n’est-elle pas contradictoire avec un ensemble de conditions skdimentologiques prdcises et relativement restrictives qui devraient prisider au dBp6t de ces roches? Dans le mdme esprit et par opposition, les veritables gisements sidimentaires de m6taux (fer et manganltse, par exemple) n’interviennent-ils pas en effet dans des environments bien particuliers et n’apparaissent-ils pas bien localisds dans les sequences lithologiques? Abandonnant ici l’aspect ndgatif d’une contre-argumentation1,je tenterai plut6t de rksoudre la contradiction appatente que soulthe, A l’encontre de la concentration par voie skdimentaire, l’apparition des sulfures de m6taux lourds dans des roches effectivement trlts varikes et diffkrentes.

ARGUMENTSPRI~LIMINAIRES

Mais auparavant, il convient de nuancer la rigueur des arguments prkcddemment invoques par une conception plus realiste et plus tempirk. Des environnements propices b l’apparition des gisements notoirement skdimentaires de mktaux et de leur position skquentielle Ainsi et par exemple, dans quelle mesure la minette lorraine dipend-elle de son environnement de d6pdt ? On s’attendrait A ce que les couches ferrugineuses apparaissent entre argilites et roches carbonatkes a l’emplacement des ultra-dbtritiques (LOMBARD, 1956). Cette proposition reste vraie, localement, ii l’6chelle mdgascopique, mais elle est insuffisante pour expliquer les recurrences lithologiques de la sCrie aalknienne A Bask par exemple sur l’existence, quelque peu paradoxale pour les hydrothermalistes,des imprkgnations sulfurks de shales argileux et bitumineux.

20

A. BERNARD

Fig. 1. SQquencetype de I’AalQniende lorraine. C‘est entre les niveaux a et b qu’apparait le maximum d‘oolithes ferrugineuses: c’est la couche du mineur. I = Arknite grossikre passant parfois aux rudites. 2 = Arknites moyennes essentiellement ferriferes et caclcaires. 3 = ArQnitesfines surtout calcaires. 4 = Micro-grb siliceux ou calcaires. 5 = Shales argileux ou argilo-siliceux.

l’echelle minikre: en fait, chacune des .strates, bien limit& par des diastkmes nets (“hard-grounds”), prksente un granoclassement inverse (skquence granulomktrique nkgative, Fig.1) qui s’accorde bien avec le caractbre rkgressif de Lias supkrieur de Lorraine et du Luxembourg (BERNARD et BUBENIC~K, 1960). La concentration ferrif6re marine apparait dks lors comme une constquence normale de la skdimentation d’un klkment dktritique particulier, l’oolithe ferrugineuse, et, paradoxalement peutStre, ce minerai doit Stre considkrk comme une ferri-arknite intervenant entre argilite et conglomkrat (crassins de fin de sequence, BUBENICEK, 1961). En bref, en deGa du problbme de l’oolithisation d’hydroxydes ferriques colloldaux dans un milieu littoral (CORRENS, 1939), le phknombne majeur de la genbse du gisement lorrain reste celui de l’apport exceptionnel du metal dans une aire relativement restreinte’; au demeurant, le taux de concentration du fer strictement lik A la skdimentation s’avkre relativement faible si on l’estime par rapport i la teneur moyenne de chaque couche (2-5). I1 est aisk d’elargir cette proposition a bon nombre de gisements stratoldes d’oxydes de fer, de mangankse, de phosphates. . . L‘origine skdimentaire qu’on leur reconnait se justifie essentiellementparce que les caractkres saillants actuels de ces concentrations dkrivent directement de leur sidimentation. 11 serait sans doute plus rationnel d’Ccrire que ces gisements ont 6tk skdimentks, sans prkjuger ainsi de la valeur du taux de concentration strictement lik 9 la skdimentation. Dans cet esprit, la localisation sdquentielle de ces minkralisations stratoldes est bien un reflet direct mais partiel des environnements de skdimentation, relativement nombreux au demeurant, oh se manifeste un L. Bubenicek (communication orale, 1961) explique cet apport exceptionnel par 1’Qmersiondes shales toarciens pyriteux et bitumineux lors de mouvements kpirogkniques affectant I’aire connue au Lias sous le nom de Golfe du Luxembourg.

21

PR~~CIPITATION ET ADSORPTION S~DIMENTAIRES

apport exceptionnel de mktaux ou de produits. On peut juger, en premiere approximation, des taux de concentration propres A chacun de ces environnements, par analogie B leur aptitude 21 diffkrencier les matkriaux normaux de la skdimentation. Sans aucun doute, les milieux marins Cpicontinentaux (et plus prkciskment les environnements ndritiques de boucliers stables) mknagent-ils a ce point de vue la plus grande diversification des lithotopes: ce sont aussi ceux oa Yon rencontre la plupart des gisements stratoldes d’oxydes mktalliques souvent mQme confinks a proximitk des lignes de rivage (ZVEREFF, 1953). L’origine volcanique-exhalative de quelques apports exceptionnels conduit a retenir certains environnements gkosynclinaux (kkratophyriques et spilitiques en particulier) comme propices 21 la skdimentation de telles minkralisations (SCHNEIDERH~HN, 1941; AMSTUTZ, 1958). Ainsi, c’est la localisation palkogkographique qui permettra in fine de poser valablement le probleme de l’origine des apports exceptionnels (dkcharges rhexistasiques, ERHART,1961; apport volcanique-exhalatif-,. . .). Au total et pour ces gisements, la genbse des minerais fait nkcessairement intervenir une suspension aqueuse des oxydes ou des sels mktallifhres sous forme nicellaire (ou colloldale sensu lato) ce qui justifie leur classification c o m e roche ultra-dktritique: leur dkppbt s’apparente alors a une prkipitation au sens chimique de ce terme. Cette attitude est en fait une attitude limite: l’ktude des gisements de fer skdimentaire montre en effet que toutes les dimensions granulomktriques depuis les rudites jusqu’aux lutites doivent Ctre considkrkes, le dkp6t s’apparentant alors purement et simplement A la sedimentation de particules hkritkesl. Ainsi se conc oivent les nuances que l’on doit apporter 21 la stricte localisation stquentielle des mktagknktiques qui ne se comportent pas obligatoirement en ultra-dktritiques. De I‘ubiquite‘des min6ralisations sulfiir6es stratofdes dans les environnements skdimentaires

I1 importe, en ce domaine, de reconnaitre que certaines associations lithologiques hchappent apparemment au contrpble de l’environnement “tectoniques6dimentaire”: je veux parler ici des associations de couches bariolkes et des formations de shales noirs (“red beds” et “black shales associations” de KRUMBEIN et SLOSS,1951). I1 semble en dernihre conclusion (KRYNINE, 1949; TWENHOFEL, 1939) que le potentiel d’oxydo-rkduction du milieu de dkppbt intervienne c o m e le facteur determinant de ces associations: c’est malheureusement un facteur physico-chimique fort peu sklectif des environnements tectoniques-skdimentaires, trop prkciskment dkfinis peut-&re, en fonction de la connaissance qu’on a des milieux de skdimentation actuels, pour &re toujours valablement restituks A partir des documents d’archives que sont pour nous les series skdimentaires, quel que soit le soin qu’on apporte 2i leur dkpouillement. Notons incidemment que les gisements de “red-beds” et de “black shales” comptent parmi les types les plus frkquents de gites sulfurks stratoldes. En d’autres I

Par opposition A nkoformks, cf. MILLOT (1952).

22

A. BERNARD

termes, ce ne sont pas les minkralisations qui sont ubiquistes, mais bien les associations lithologiques qui les supportent.

~ U D EDES PROCESSUS INTERVENANT DANS LA G E N ~ S EDES GISEMENTS STRATO~DESDE

SULFURES

Ayant ainsi limit6 la portte des arguments hydrothermalistes traditionnels, abordons l’ttude des processus intervenant dans la genbse des gisements stratoides de sulfures: ils semblent 8 la fois d8trents et plus complexes. Diffkrents, car les sulfures de mktaux lourds ne constituent jamais de roches: ils affectent pour quelques pour cent la composition de la roche qui les supporte. En termes de gkochimie, c’est par rapport au support rocheux constituk par des kltments majeurs qu’apparait l’anomalie de teneur du gite stdimentaire, les Clkments concent r k n’existant par ailleurs qu’a l’ktat de traces. D’autre part, les mktaux lourds qui cr6ent l’anomalie sont gentralement transportks dans le site skdimentaire sous forme de sels solubles et non d’hydrolysats: il suffit pour s’en convaincre de replacer le plomb, le zinc, le cuivre, . . . dans le tableau des potentiels ioniques de GOLDSCHMIDT (1937). Plus prtciskment, les travaux de KUENEN (1950), de CHOWet PATTERSON (1962) entre autres, montrent que la dkcharge terrigbne du plomb dans les men s’effectue B 99 ,% sous forme soluble. Plus complexes, car il s’agit de sulfures de metaux lourds et que toute concentration reprksente nkcessairement l’intersection dans l’espace et dans le temps des cycles gkochimiques du soufre d’une part, des mktaux lourds d’autre part.

LES PIBGES S~DIMENTAIRES

Nature

Ces prkliminaires s’avbrent insuffisants pour conclure quant aux causes stdimentaires de ces concentrations. Un fait gtologique m’apparait comme le compliment nhssaire de ces propositions: j’ai Btt amend (BERNARD, 1958) 8 constater, dans une province mktallogknique donnk (la bordure triasique et liasique des Cevennes du Sud, France), que tous les gisements sulfurts stratoides de cette couverture de socle stable coincidaient avec des lacunes de skdimentation et, plus gtnkralement, avec des aires de sMimentation ralentie dont la meilleure image est sans doute celle des biseaux stratigraphiques marquant la ptriphkrie des hauts-fonds contemporains de la stdimentation. I1 s’agit 18 de biseaux dits par condensation qui s’opposent aux biseaux stratigraphiques de ligne de rivage, dits biseaux par reduction (GRABAU, 1906). Le rBle skdimentologiquede ces hauts-fonds a t t t particulibrement m i s en tvidence par LEVORSEN (1955) en ce qui concerne les hydrocarbures et je n’oublierai pas

PR~CIPITATIONET ADSORPTION S~DIMENTAIRES

23

d’insister ici sur l’accumulation potentielle de soufre d’origine organique qui dkcoule de cette colncidence. La matkrialisation de cette proposition peut dtre recherchke en Sicile oh les ckltbres gisements solfifbrescoincident prkcistment avec des skries rkduites de hauts-fonds, en 1957). Dans ce cas prkcis, la genBse purement skdimenmilieu kvaporitique (OGNIBEN, taire de cette accumulation de soufre semble prouvke aussi catkgoriquement qu’on puisse le faire aujourd’hui en gkologie par les analyses isotopiques prksentks par DESSAU et al. (1962).

R61e En ce qui concerne les mttaux lourds, l’ttude de la province sousckvenole m’a conduit a esquisser le r81e mktallogknique de ces structures de la manibre suivante. Considirons (Fig.2) un haut-fond contemporain de la skdimentation: les biseaux par condensation qui en rksultent prtsentent une diffkrenciation latkrale, skquentielle, qui est A l’image de la tendance de l’environnement stdimentaire (BERNARD, 1962)l. En d’autres termes, on constate que dans la plupart des milieux Cpicontinentaux, les argilites et les. ultra-dttritiques constituent les stdiments klectifs des hauts-fonds. Plus simplement et rejoignant en cela une remarque de LOMBARD (1956) ces termes reprtsentent les dtp6ts caracttristiques des stdimentations ralenties. La fixation des mktaux lourds en solution, dans ces conditions, s’explique alors trbs simplement en tenant compte des phknomhes d’adsorption. En effet, on sait entre autres que l’adsorption croit quand la granulomttrie des particules adsorbantes dkcroit. Par ailleurs, l’ktablissement de la liaison d’adsorption physique (ou encore de Van der Vaals) depend de la probabilite de rencontre des ions en solution avec les particules adsorbantes en suspension: cette probabilitt augmente avec le temps et la concentration du sel dissous, ce qui introduit pour chaque cas particulier la notion de temps de saturation. Les taux d’adsorption estimts en fonction des valeurs des paramhtres d’environnement rkgissant ce phtnomhe ont ttk relativement bien reconnus par les travaux de ROSHKOVA et SCHTSCHERBAK (1956) et restent parfaitement comparables avec les taux de concentration strictement lits a la skdimentation. Au total, en admettant que la quantitt de mCtaux lourds adsorbks par unit6 de temps et de surface soit la mCme a l’aplomb du bassin et du haut-fond, le taux de concentration qui en rtsulte peut alors s’exprimer par le rapport des puissances2 h/h’. Bien qu’intuitive dans les cas simples, cette proposition meriterait de plus amples dkveloppements. Ainsi, lors d’une transgression epicontinentale, alors que les bassins s’emplissent de dktritiques grossiers, seuls les dktritiques fins et les ultra-dktritiques peuvent persister dans le m&ne temps sur les points hauts en raison de la gravite. La differenciation laterale qui apparait de bassin A haut-fond va bien du conglomerat aux argilites. Laterales ou verticales les sequences ddimentaires sont bien positives ainsi que I’implique la tendance transgressivede I’environnement. Au contraire, la diffkrenciation laerale qui apparait de bassin a ligne de rivage dans un biseau par reduction est toujours negative quelle que soit la tendance de l’environnement. a Les deux epaisseurs de roche ayant ete dkposkes dans le meme temps et contenant suivant I’hypot h k de depart la m6me quantite de metaux lourds, la concentration resulte effectivement de la disparition des roches-supports jouant ici le r61e d’excipient stkrile. C‘est bience qu’exprime le rapport h/h’.

24

A. BERNARD

h’

h

Fig.2. Diffkrenciation latkrale schkmatique d’un biseau skdimentaire de haut-fond en drie grksoargileuse de bassin. On dit qu’il y a condensationdes termes de la drie h dans le terme h’.

Mais ce n’est 18 qu’une valeur minimum car la difftrenciation lattrale de bassin A haut-fond fait apparaitre des stdiments de plus en plus absorbants, multipliant ainsi cette premikre valeur du taux de concentration par un facteur de difftrenciation lattrale D qui tient compte 8 la fois des proprittts adsorbantes croissantes des dCp8ts sur une m&meverticale et du temps d’action plus grand de ces stdiments de hautfond1. Ainsi la structure en haut-fond contemporain de la sedimentation jou-t-elle bien son r61e de pikge des tltments lourds qui s’y fixent de manikre trBs d8krentielle par rapport au bassin. L’Cvolution ulttrieure de ces dtp6ts est facile A saisir: la dkomposition anakrobie des ultra-dktritiques carbonts pendant la diagenkse libkre du SH, qui apparait (ROSHKOVA et SCHTSCHERBAK, 1956) comme un puissant agent de dksorption des mttaux lourds. En bref, la concentration mttallifkre apparait comme syngtnktique si l’expression sous forme minkralogique de sulfures est, elle, diagknktique. La place qui m’est impartie ne me permet pas de citer les autres applications possibles du processus ici dkcrit en environnement de shales noirs marins, tpicontinentaux. I1 est cependant aisk de transposer, 8 quelques modifications prks, ces raisonnements aux stdimentations dttritiques (“red-beds” marins) et carbonatkes (type tri-state, I1 en est ainsi A Figeac, Lot (LAUNEY et LEENHARDT, 1959; Ph. Launey, communication orale, 1962).

PR~~CIPITATION ET ADSORPTION S~~DIMENTAIRES

25

AMSTUTZ, 1962). La stdimentologie des formations continentales homologues reste a Bucider, car, en premitre approximation, elle s’tloigne sensiblement du schkma p r e d e n t sinon en ce qui concerne le r6le de I’adsorption du moins quant au dispositif gtologique qui la favorise. I1 en va de mCme pour certains environnements gtosynclinaux qui prtsentent indubitablement des sympt6mes analogues.

CONCLUSION

En terminant, il serait tentant d’opposer la prtcipitation et l’adsorption stdimentaire en tant que processus de difftrenciation mdtallogknique, rtsolvant ainsi la contradiction soulev& au debut de cet article: tout ne revient-il pas cependant A une question de forme ? Certains gisements pyriteux stratoldes ne reprtsentent-ils pas, gtochimiquement, une concentration ferriftre comparable h celle d’un gisement exploitable parce que le fer y apparait sous forme oxydke?l La precipitation n’apparait-elle pas plus selective que l’adsorption que lorsqu’on l’estime dans une classification granulomttrique, son r61e devenant parfaitement ubiquiste quand on l’estime dans une classificationchimique4cf. diagramme pH-Eh de KROMBEIN et GARRELS, 1952)? A mon sens, le probltme fut ma1 pose et sans doute conviendrait-il de l’envisager comme le fit MILLOT(1952), en d’autres circonstances,h propos des argiles, sous la forme “hkritage et ndoformation”. La nature dttritique ou ultra-dktritique de l’apport exceptionnel de mttaux conditionne la forme de fixation par prtcipitation : heritage; les modalites du cycle superghe du soufre, la fixation par adsorption des ions mktalliques lourds sur les dktritiques fins ou les sels chimiques fraichement prkcipitks, dkterminent I’expression diagknttique des sulfures: ntoformation. L’indkniable interfkrence des stdimentations mdcanique et chimique (POUSTOVALOV, 1940) en fonction des environnements gko-tectoniques de sedimentation nous oblige ainsi h concevoir toute une gamme de possibilitts ou prtcipitation et adsorption iront de pair: gtochimie des argilites, des oxydats (manganhse en particulier), des dolomies, . . . Ce n’est finalement qu’en fonction de structures-pihges et d’apports exceptionnels que l’un (ou I’autre) de ces processus prendra dkcidkment le pas sur l’autre. Quoi qu’il en soit, ils sont tous deux skdimentaires, et cette simple conclusion assortie des rdles mktallogkniques possibles et probables de la prkcipitation et de l’adsorption suffit A mon propos si telle est l’impression qu’en garde le lecteur.

Afin de rtpondre 9 l’argument souvent invoqut par les hydrothermalistes a l’encontre L’industrie siderurgique franGaise ne tira-t-elle pas, au sikcle dernier, l’essentiel de ses &erais des amas pyriteux sous-dvenols, oxydes il est vrai sous forme de chapeaux de fer (Alais, Froges et Camargue)?

26

A. BERNARD

de la genbe stdimentaire des sulfures, argument suivant lequel les sulfures de mttaux lourds interviennent dans des roches stdimentaires t r b diverses l’auteur examine successivement: la position des mttaux lourds dans les sequences stdimentaires, la nature des environnementspropices aux mttallisations sulfurtes, et dbgage, en conclusion, le r61e des pibges stdimentaires (biseau par condensation). Prtcipitation et adsorption stdimentaires apparaissent alors comme des processus de concentration compltmentaires.

SUMMARY

In order to give a reply to the argument often set forth by the hydrothermalists in opposition to the sedimentary genesis of sulfides (argument according to which the sulfides of heavy metals occur in very different sedimentary rocks) the writer successively studies the location of heavy metals in sedimentary sequences and the constitution of surroundings favourable to sulfide deposits, and draws, as a conclusion, the role of sedimentary “traps” (condensated edge). Sedimentary precipitation and adsorption appear then as complementary processes of concentration.

BIBLIOGRAPHIE

AMSTUTZ, G. C., 1958. Spiliticrocks and mineral deposits. Missouri, Univ., School Mines Met., Bull., Tech. Ser., 96 : 11 pp. AMSTUTZ, G. C., 1962. L’origine des gites minkraux concordants dans les roches ddimentaires. Chronique Mines Outre-Mer Rech. Minikre, 308 : 115-126. BERNARD, A., 1958. Contributiona I’lhde de la Provin# me‘tallifkresous-ce‘venole. Thkse, ficole Nationale Supkrieurede Gkologie Appliquee et de Prospection Mhkre, Nancy, 640 pp. Aussi Sci. Terre, 7 (3-4) : 125-403.

BERNARD, A. et BUBENICEK, L., 1960. Remarques sur les skquences skdimentaires de 1’AalCnien de Lorraine. Compt. Rend., 250 : 3353-3355. BERNARD, A., 1962. Seance de clbture, discussions. Colloque sur les Gites stratiformes du Maroc, 1962 -Mines G.601. (Morocco), 20 : 11-39. BUBENICEK, L., 1961. Recherchessur la constitution et la rkpartition du minerai de fer dans 1’Aalenien de Lorraine. Sci. Terre, 8 (1-2) : 5-204. CHOW,T. J. and PATTERSON, C. C., 1962. The occurence and significance of lead isotopes in pelagic sediments. Geochim. Cosmochim. Acta, 26 :263-308. CORRENS, C. W., 1939. Die Sedimentgesteine.In: T. F. W. BARTH,C. W. CORRENS und P. ESKOLA (Redakteure),Die Enststehung der Gesteine, Springer, Berlin. DESSAU, G., JENSEN, M. L. et NAKAI,N., 1962. Geology and isotopic studies of Sicilian sulphur deposits. Econ. Geol., 57 (3) :4 1 M 3 8 . ERHART, H., 1961. Sur la genese de certains gites miniers ddimentaires, en rapport avec le phknomene de bio-rhexistasie et avec des mouvements tectoniques de faible amplitude. Compt. Rend., 252 : 2904-2906.

GOLDSCHMIDT, V. M., 1937. The principles of distribution of chemical elements in minerals and rocks. J. Chem. Soc., 1937 : 655-673. GRABAU, A. W., 1906. Types of sedimentary overlaps. Bull. Geol. SOC. Am., 17 : 567-636. KRUMBEIN, W. C. and SLOSS,L. L., 1951. Stratigraphy and Sedimentation. Freeman, San Francisco, 497 pp.

PRBCIPITATION

ET ADSORPTION S~DIMENTAIRES

27

KRUMBEM, W. C. et GARRELS, R. M., 1952. Origine et classification des ddiments c h e q u e s en terme de pH et de Eh. J. Geol., 60 : 1-33. KRYNINE, P. D., 1949. The origin of red beds. Trans. N. Y. Acad. Sci., 2 : -8. KUENEN, P. H., 1950. Marine Geology. Wiley, New York, 568 pp. LAUNEY, PH. et LEENHARDT, R., 1959. Les brbhes skdimentaires zincares du Sinkmurien du Lot. Bull. SOC.Gkol. France, 7e Ser., 1 : 467-484. LEVORSEN, A. I., 1955. Time of petroleum accumulation. Econ. Geol., 2 : 748-756. LOMBARD,A., 1956. Gkologie stdimentaire. Les SPries marines. Masson, Paris, 722 pp. MILLOT,G., 1952. Hkritage et nkoformation dans la ddimentation argileuse. Congr. Gkol. Intern., Compt. Rend., 19e, Algiers, 1952, 18 : 163-175. L., 1957. Secondary gypsum of the sulphur series Sicily, and the so-called integration. J. OGNIBEN, Sediment. Petrol., 27 : 64-79. POUSTOVALOV, L. V., 1940. Pttrographie des Roches skdimentaires. Gostoptekhizdat, Moscou, 1-2. ROSHKOVA, E. V. et SCE~CHERBAK, 0. V., 1956. Adsorption du plomb dans diverses roches. Tr. Znst. Geol. Nauk, Akad. Nauk S.S.S.R., Geol. Ser., 2 : 13-24. SCHNEIDERH~HN, H., 1941. Lehrbuch der Erzlagerstattenkunde. I . Die Lagerstatten der magmatischen Abfolge. Fischer, Jena, 784 pp. TWENHOFEL, W. H., 1939. Principles of Sedimentation, led. McGraw-Hill, New York, 674 pp. 2ed. : 1950, 674 pp.

ZVEREFF, R., 1953. Donnks rkentes sur quelques gisements manganksifkres de Russie. Ann. Mines, 8 : 31-51.

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FACIES DIFFERENTIATION AND CONTROLLING FACTORS FOR THE DEPOSITIONAL LEAD-ZINC CONCENTRATION IN THE LADINIAN GEOSYNCLINE OF THE EASTERN ALPS HANS-JOCHEN

SCHNEIDER

Institut fur allgemeine und angewandte Geologie und Mineralogie der Universitat, Munchen (Deutschland)

INTRODUCTION

Throughout its entire area of distribution within the eastern Alpine geosyncline, the extremely thick Middle Triassic limestone-dolomite complex contains relatively uniform deposits of lead-zinc ores. This type of deposit is still of considerable economic importance today. In the southern Limestone AIps the most important deposits still in operation are as follows: Gorno and Raibl (Cave di Predil), both in Italy; Mies (Mezica, Jugoslavia); and Bleiberg-Kreuth (Austria). (See Fig. 1). In the northern Limestone Alps also, more than 100 occurrences are known which were in part profitably mined from the end of the Mediaeval Ages up to the beginning of this century. These deposits range over an area of more than 450 km, from Graubunden (Switzerland) in the west to the eastern part of the Austrian Alps. They are especially massed, however, in Alpine ranges at the north Tyrolean-Bavarian frontier from the Lechtal Alps to the Karwendel Mountains. This report deals mainly with the above mentioned part of the northern Limestone Alps, the author having concentrated principally, since 1950, on the ores and country rocks of this region. Geological relationships and genetic problems of these deposits remain, however, unchanged throughout the entire eastern Alps. According to the still recently prevailing classification of ore deposits (e.g., SCHNEIDERHOHN, 1941; FRIEDRICH, 1953), these deposits of the so-called “Bleiberg type” were considered to belong to the group of “metasomatic Pb-Zn ores in carbonate rocks”. They were interpreted to be of apomagmatic-hydrothermal origin caused by a uniform “alpidic metallogenesis” of Tertiary age (TORNQUJST, 1929; PETRASCHECK, 1932, 1945; FRIEDRICH,1937; Dr COLBERTALDO, 1948; CLAR,1953). Based on these conclusions, JICHA (1951) summarized the “hydrothermal paragenesis” of the above deposits in referring them to the Pb-Zn deposits of the Mississippi valley type. The prevailing theory of a hydrothermal-epigeneticTertiary origin of these Alpine deposits, however, has not been universally accepted. SCHWINNER (1942, 1946, 1949) and also HEGEMANN (1949) argued against a uniform Tertiary metallogenksis of the eastern Alps. Especially Pb-Zn ores within the Triassic limestone complex, they

30

H.-J. SCHNEIDER

assumed, must be derived from submarine volcanism during the geosynclinal stage in Triassic times, thus indicating syngenetic origin. Actually the discussed deposits do contain, in nearly all cases, more or less extensive layered ore bodies, but none of these has been sufficiently taken into consideration by earlier investigators. It was just these layered portions of the deposits on which SCHNEIDER (1953, 1954), TAUPITZ (1954), and SCHULZ (1955) did concentrate their investigations by means of modern methods and theories of sedimentology. In the course of their extensive investigations into the deposits of the northern Limestone Alps, they succeeded in proving a syngenetic-sedimentary origin of the layered ores. Their conclusions initiated vigorous discussions (MAUCHER, 1954; MAUCHER and SCHNEIDER, 1957; CLAR,1956; Dr COLBERTALDO, 1956, 1957; PETRASCHECK, 1957, 1960; SIEGL,1956; HEGEMANN, 1957, 1960; DI COLBERTALDO and SCHNEIDERH~HN, 1958; SCHULZ,1959, 1960). Continuing research on problems arising from these discussions, the author, assisted by investigations of his students, was able to arrive at additional conclusions in overlappingfields between sedimentology and geochemistry, concerning the depositional conditions of Pb-Zn ions in marine environments. The general results are given in the following report as a summarizing .digest. As mentioned above, these new ideas may also be taken into consideration for the related Mississippi valley type deposits, as AMSTUTZ(1958, 1959, 1962) has recently shown.

GENERAL CHARACTERISTICS OF THE DEPOSITS

In general, the ore deposits reveal a series of common characteristicswhich are indicative of sedimentary origin. In addition to essential stratigraphical and paleogeographical relationships, the most important marks indicating syngenetic origin are units of layers, bearing distinct and typical sedimentary fabrics. It must be presumed, however, that all types of alteration involved during the Alpine orogenesis, have striven to eliminate primary textures and fabrics of sedimentary origin. Under this supposition, of course, occurrences of fabrics, proving the primary stage, are rarely found. Nevertheless, they may be recognized in nearly every deposit. Paragenesis

The distinguishing feature of the sulfide ore paragenesis is the prevailing “bimetallic character”: sphalerite and galena are quantitatively dominant (Zn/Pb = 2/1 to lO/l). Galena is nearly always the primarily and most intensively recrystallized ore mineral in “replacement textures”. Sphalerite and related gel textures (“Schalenblende”) of a primary stage, however, are preserved sometimes in significant sedimentary fabrics (see Fig.6, 7). Very rare botryoidal schalenblende shows relic patterns of wurtzite, which is mostly alterated to sphalerite.

DEPOSITIONAL LEAD-ZINC CONCENTRATIONS IN THE EASTERN ALPS

31

The above mentioned ore minerals contain a considerable variety of trace elements which have been analyzed recently for geochemical evaluations (SCHROLL,1953, 1955; HEGEMANN, 1960). The irregular content variations of these trace elements, however, have not permitted a direct determination of their origin so far. The FeS, content (pyrite-marcasite) is extensive, but, for the most part, subordinate. Towards the northern range of ore distribution, however, the quantity of iron sulfides increases to an absolute predominance. Therefore, in this northernmost strip of the Bavarian Alps, ore deposits were formerly mined for their iron content only. Galena and sphalerite occur locally only in microscopic traces in this region. A certain portion of the pyrite is preserved everywhere at an early stage which is known to be of micro-organic origin: the so-called “gel pyrite” (pyrite microspheres). Marcasite appears always as a second stage of alteration, replacing primary pyritic textures. Cu-Sb-As containing ore minerals have been found only microscopically as very small inclusions, chiefly in sphalerite and to a lesser degree in galena (e.g., boulangerite, tennantite, chalcocite, chalcopyrite). Due to the small quantity they are without any economicvalue, but their occurrence in a few distinct locations reveals interesting genetic indications (see p.40). The accompanying “gangue minerals” of the layered ore accumulations occur in varying quantities. According to their order of decreasing frequency we find: calcite, dolomite and varying Fe-dolomites, fluorite, quartz, barite, celestite and also anhydrite. Stratigraphical as well as provincial distribution of the “gangue minerals” completes the congruent paleogeographic pattern of ore enrichment (see p.42). In particular fluorite-bearing seams contain well-preserved rhythmic lamination combined with sedimentary fabrics (SCHNEIDER, 1954). Controlling factors for temporary and local enrichments were found to be very complex, as will be shown below. Stratigraphical occurrences and regional relationships

Over the entire extent of the Mesozoic calcareous complex of the eastern Alps, orebearing beds are restricted to a few relatively thin units of the Middle Triassic sequence (see Fig.1): Upper Anisian - maximum 40 m in thickness Lower Ladinian - maximum 50 m in thickness Upper Ladinian - maximum 200 m in thickness and, in addition, occurring only in the southern Limestone Alps, Lower Carnian -from 7 m (Bleiberg) to 75 m (Gorno). The complete Middle Triassic sequence (Anisian, Ladinian plus Carnian) reaches in the main regions of richest ores a maximum thickness of more than 2,000 m! The ore-bearing units intercalated between the enormous calcareous sequences, show all the influences of the extensive alpine folding and over-thrusting. ‘ The ore-bearing layers are nearly always combined with a special facies develop-

32

H.-J. SCHNEIDER

Houptdolomf

Houptdolornft

A

l l l 6

V V V C

- D

t

- E

Fig.1. Ore occurence, volcanism and their time relation during Triassic periode in the eastern Alpine Geosyncline. A : typical deposits of the different areas. 1 = Bleiberg-Ramoz (Graubunden, Switzerland); 2 = Silberberg-Davos (Graubunden, Switzerland); 3 = Sauling-Fiissen (Bavarian Alps, northern border ranges); 4 = Lafatsch-Karwendel (northern Tyrolean Alps, Austria); 5 = Mursee-Mieminger Massif (northern Tyrolean Alps, Austria); 6 = St. Veit-Heiterwand (northern Tyrolean Alps, Austria); 7 = Bleiberg-Kreuth (eastern Gailtal Alps, Austria); 8 = Raibl, Cave del Predil (Giulian Alps, northern Italy); 9 = Auronzo (eastern Dolomites, northern Italy); 10 = GornoDossena (Bergamasc Alps, northern Italy). B : ore bearing units. C : weak evaporitic facies (deposition of dolomite and anhydrite, gypsiferous beds). D : indications of volcanism (tuffaceous shales, agglomeratic breccias etc.). E : tuff layers, porphyritic and basaltic eruptions. (Completed after SCHNEIDER, 1957.)

ment of the country rock (called “Sonderfazies” by SCHNEIDER, 1954; see p.33). A significant geological feature of the time interval between Upper Anisian and Lower Carnian within the eastern Alpine geosyncline is the constant occurrence of submarine volcanism of an early initial stage (CORNELIUS, 1941; SCHWNNER, 1949). Its centre is situated in the southern Limestone Alps and in the Dolomites where, moreover, the climax was reached. Important traces can be observed in the northern Limestone Alps also. There are widely spread tufaceous layers and local eruptions of basic to intermediate character (VIDAL,1953; SCHNEIDER, 1954). Volcanic activity in the northern Limestone Alps decreases from uppermost Anisian to the Lower Ladinian, whereas in the southern areas it continues until Lower Carnian times (see Fig. 1). There, voluminous porphyritic extrusions fall within the Middle Ladinian. It is a typical feature of the layered ore enrichments, however, that

DEPOSITIONAL LEAD-ZINC CONCENTRATIONS IN THE EASTERN ALPS

33

they are never combined directly with volcanic beds, although they do contain indications of present activity of volcanism. Since the climax of Triassic geosynclinalvolcanism, as well as the greatest number of the large Pb-Zn deposits, is found in the southern Limestone Alps, there is apparently a close genetic relationship between volcanic activity and the maximum supply of ore matter. In the northern portion of the geosyncline, on the other hand, weak volcanism is accompanied generally by ore enrichments of lesser degree. The Pb-Zn deposits of this region are concentrated in a few areas scattered throughout the entire northern Limestone Alps. It is in these areas that centres of (weak) volcanism may be observed. Another essential feature of mid-Triassic times is the evolution of huge plateau reefs showing a wide spread of lagoonal environment. These provided perfect locations for the sedimentary enrichment of Pb-Zn ores, which took place in connection with hydrothermal supply during volcanic activity. Structures of the ore bodies As described in current literature, the ore occurs predominantly as more or less massive

accumulationsin short unconformable veins and also in larger “replacement bodies”. These types of ore-bodies are of major economic interest. In addition, however, the ore occurs in far lesser concentration in conformable layers and lenticular bodies which, in general, contain a sprinkling of ore mixed with various types of country rock. The local predominance of the unconformable, metasomatic, ore enrichments has led to the prejudiced and erroneous belief that all such features could be indicative of hydrothermal epigenetic(-hypogene) origin only. Replacement fabrics are, in fact, very common but they prove only that replacement has taken place. They do not indicate the nature and geological time of supply. Occasionally, such replacement fabrics are closely associated with sedimentary fabric relics in various stages of transition (see Fig.5). Such examples, on the other hand, indicate local transfer of ore matter during all stages of diagenesis. By this epigenetic supergene mobilization secondary phases of ore enrichment reached a point where they became of economic importance. These processes and structures are, however, within the scope of this report, of secondary interest only. The layered ore-bodies are associated by avariegated country rock which contains, in addition, anabundance ofvarious sedimentaryfabricsand structures.These must beconsidered as the most important criteria for primary syngenetic enrichment of ore matter.

FACIES DEVELOPMENT AND SEDIMENTARY FABRICS OF ORE-BEARING UNITS

Within the normal sequence of carbonate deposition, bedded ore is limited to only a few horizons, showing a remarkable development of certain sediment types. Deviations from the predominant and monotonous carbonate deposition comprise the so-called “special facies”. It consists of the following types:

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H.-J. SCHNEIDER

Fig.2. Common rock type of the “backreef” facies of the upper Wetterstein Limestone. In the basal

part interbedded laminae of calcilutite and dololutite (“quiet water stage”), cut off by prevailing pisolitic resediments (e.g., limy chunks, oolites, algal pellets, fragments of Dasycladacee. All terminal envelopes of the fragments are dolomitized! (“turbulent water stage”, low graded bedding). The dolomite content of the cement is increasing towards the top of the layer. Polished section,stained by Alizarin Red (calcite = dark parts). Schneeferner-Kopf,Wetterstein Mountains, Bavaria.

(I) Well-bedded pure dolomite, passing into rhythmically laminated dolomitecalcilutite. (2) In connection with type I, locally predominant development of the “backreef facies” takes place. All the related lithological elements are to be observed (e.g., composite pisolites, algal pellets, coquina, dolomitic mudstone breccias, biogenetic detritus, different types of calcarenites, etc.; see Fig.2). (3) Laminated bituminous dolomite-calcilutite, passing into bituminous clayey laminae (different types of carbonaceous gyttja). (4) Greenish beds of marl (tufaceous marl?), occurring often as matrix of sedimentary (agglomeratic) darkish to black, marly limestone breccia (see Fig.8). (5) Fluorite (showing definite sedimentary fabrics), also quartz and barite, with celestite and anhydrite as minor components (see Fig.3,4). (6) Fine-grained pyrite, sphalerite and galena, combined with types 3 and 5. Sphalerite, in particular, is well-preserved in polar laminations and rhythmic beds as in type 3 (see Fig.6). (7) Fe-, and Zn (Pb)-sulfide ores in gel textures (e.g., “Schalenblende I”) often redeposited in coarse fragments (“sedimentary ore breccias”; see Fig.7). In addition to these lithological components, the beds reveal numerous sedimentary

DEPOSITIONAL LEAD-ZINC CONCENTRATIONS IN THE EASTERN ALPS

35

structures and fabrics in regular mutual combination. This definite combination is also indicative of depositional conditions: (a) General features of a widely spread “quiet water deposition” in carbonaceous environment (rhythmic and polar lamination, algal pellets aad crusts, “quiet water oolites”, etc.), locally passing over into euxinic sediments (combined with ore deposition, type 6) or passing into weak evaporitic units (deposition of dolomite, lesser amounts of anhydrite and celestite). (b) Intercalation of thin layers within a few horizons indicative of a weak volcanism: greenish marl beds and agglomeratic breccias, type 4, and sedimentary sequences of fluorite, quartz, ore minerals, etc. (type 5). (c) Local development of flat submarine relief (pockets, basins, channels, etc.,

Fig. 3. Rhythmic bedding of fluorite, calcilutite-calcarenite, organic matter and few ore grains, combined with graded bedding. The fluorite is enriched within the dark (pelitic) top of each rhythmite. The rhythmitic sequence is cut off by a penecontemporaneous phase of resedimentation (calcareous “black breccia” at the top). Upper Wetterstein Limestone, Gute-Hoffnungs-Zeche near Mittenwald, Bavaria. Polished section.

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H.-J. SCHNEIDER

Fig.4. Depositional lamination of fine-grained idiomorphic fluorite (dark) and calcarenite (light), disconnected into tabular fragments during early diagenesis (stage of compaction). Orientated specimen, stained dry-peel (mm-scale left side). Upper Wetterstein Limestone; opening adit Gassenalm, Wetterstein Mountains, Bavaria.

I

1

Fig.6. A fragment of compacted calcareous mud (C), free of ore, has sunk into a “still hydroplastic” bituminous limy slick with laminae of fine-grained sphalerite (black): load cast! The pebble belongs to a graded breccia fan, which is composed of calcarenite and calcirudite (light), detrital sphalerite grains and bent chunks of “Schalenblende I” (Zn, dark grey): turbidity currents! This sequence is covered over by mm-rhythmitic laminae of bituminous calcilutite (black), interbedded again with fine-grained sphalerite (grey). Orientated specimen 3 (location see Fig.5), polished section. Fig.5. Several small sedimentary ore-bodies are transformed by degrees into one larger “metasomat-

ic” ore body through secondary mobilization. Relict patterns of the primary depositional stage are preserved (see location I and Fig.6, 7). I = Primary ore pockets: depositional lamination of bituminous calcilutite, fine-grained sphalerite (traces of galena) and layered “Schalenblende I”. Crossbedding and glide-folding of ore and country rock with transition into glide breccias (slump structures); 3 :see specimen Fig.6; 4 : see specimen Fig.7. II = Metasomatic pattern (replacement textures) of rind-like mammocks of recrystallized, coarse-grained “Schalenblende 11” and galena Pb)combined with predominantly coarse-grained calcite. Upper Wetterstein Limestone, Lafatsch mine/880 m-layer; Karwendel Mountains, northern Tyrol.

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H.-J. SCHNEIDER

Fig.7. Glide breccia (“ore-and-limemud breccia”) causing load casts on a rhythmic interbedding of bituminous calcilutite (black) and sphalerite arenite (grey). C = calcareous mudstone, free of ore; Zn = flag of extremely fine-grained sphalerite in limy matrix. Orientated specimen 4 (location see Fig.S), polished section.

ranging from decimetre to metre size), combined with erosion unconformities, crossbedding, cut-snd-fill structures, etc. (see Fig.5, 8). ( d ) Closely associated with these structures are mud cracks, glide folds, and convolute bedding of all types of sediment mentioned previously (1-7). (e) All possible passages to resediments of those types mentioned in a are encountered: coarse- and fine-grained breccias consisting predominantly of carbonate detritus, partly mixed with ore fragments of all sizes in limey or marly matrix and often very similar to “turbidity currents” (graded bedding, load casts, etc.; see Fig.6,7).

DEPOSITIONAL LEAD-ZINC CONCENTRATIONS IN THE EASTERN ALPS

39

m I &

I ? ’ ’ ’ ‘ ’

50 cm H.-J. Schneider, 1963

I

Fig.8. Typical cut-and-fill structure of upper Wetterstein Limestone; “Sonderfazies” in an area with low ore mineral contents. Dark bituminous breccia (S) of former lime mudstone in a (tuffaceous?) greenish grey, marly calcilutite matrix, embedden pocket-like into backreef layers. The slump structure is bedded over by a layer of green marly limestonewith lenses of recrystallized celestite (C)at the top. Outcrop Maggeswand near Fischbach-Inn, Bavarian Alps.

.

The structures of bedded ore matter, considered together with facies differentiation of the country rock therefore allows a reconstruction of the depositional conditions. This will be exemplified by the Ladinian members of the northern Limestone Alps.

THE EVOLUTION OF THE LADINIAN REEFS IN THE NORTHERN LIMESTONE ALPS

(“WETTERSTEINKALK”) AND CONNECTED ORE DEPOSITS

The northern branch of the Ladinian geosyncline reveals a paleogeographicalpattern. The most characteristic representative of the Ladinian stage is a thick limestonedolomite sequence named “Wettersteinkalk”. The areas of its maximum development coincide significantly with the areas of maximum occurrence of the ore. The recifal origin of the “Wettersteinkalk” was recognized very early and has been confirmed by recent research. The corresponding sediments of the forereef basins are represented predominantly by clayey-marly “Partnachschichteny’.In spite of strong alpine tectonic activity, which, to a great extent, has separated these two important units of facies, local facial transitions are still preserved. Over the entire area, reef building tendency increased constantly from the Lower to the Upper Ladinian. Thus, the depositional area of the forereef basins became constantly narrower in corresponding proportions (see Fig.9). The facies development of the Ladinian reefs may be restored on the basis of recent detailed research. In part, it appears to be very similar to the depositional environment of the Great Bahama Bank (e.g., NEWELL and RIGBY,1957). Due to the main features,

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there exists close parallelism to the Permian reef complexes of the Guadalupe Mountains (NEWELL et al., 1953). In general, the “Wettersteinkalk” complex reveals the character of extensive plateau reefs, separated into marginal belts of barrier reefs and central backreef lagoons. The ecological features, however, were constantly changing throughout the stratigraphical sequence. Therefore, the development of the entire Ladinian reef complex may be divided conveniently into three stages, which are approximately congruent to the three stratigraphical divisions familiar to field geologists. The lower division is chiefly massive, consisting of pure dolomite in many regions. Diagenetic alterations are prevalent, as shown, for example, by poorly preserved coral colonies. Significant is the diagenetic filling of former reef cavities by carbonate matter (so-called “Grossoolithe”), indicating an intensive recrystallization (“chemical intern deposition”). Although not nearly as distinct as in the upper division, there is a noticeable separation between bioherms or barrier reefs and lagoonal backreefs. Stratified units, which bear the initial signs of the “special facies”, and also ore sediments, occur in limited quantity. The major amount of ore, however, is here accumulated in typical diagenetic replacement bodies within the cavernous sections of the reef. The ores are obviously the product of direct precipitation from rising, rather high-temperatured, hydrothermal solutions, as the resulting Pb-Zn ores contain microscopic particles of the Cu-Sb-As paragenesis mentioned previously. Moreover, a low content of partly recrystallized quartz is characteristic for the related country rock while fluorite is missing. The middle division of the “Wettersteinkalk” forms a well-layered, thick, and predominantly very monotonous sequence. Guides for the altered environment and key fossils are lime-secretingalgae (Dasycladacee), fragments of which are accumulated in extensive lentils. Most probably an increased down-sinking of the entire reef area tended to eliminate the previous reef pattern. Augmented depth of the sea above the sunken platforms, good aeration, and sufficient light caused the sudden and prolific growth of blue-green algae. This huge limestone complex contains no ore. Within the comparatively thin upper division, again facies differentiation took place in an even more distinct way than in the lower one. Marginal barrier reefs (bioherms, mostly coral colonies) are found only rarely, whereas the typical backreef facies extends widely over the shallow reef surface. The tendency to deposition in shallow water environments increased, leading to stagnation locally. In flat basins, development of weak evaporitic facies took place (finely-bedded dolomite, passing laterally into mud cracks, occasional occurrence of celestite and anhydrite, etc.). Within these areas also an euxinic environment spread especially in pools, pockets and narrow troughs (bituminous calcilutite with sulfide ores). The most remarkable event of this “stagnant stage” is the sudden occurrence of submarine slides (glide-folding, convolute bedding) and resediments of varying sizes (mixed mudstone and ore breccias, etc.). In the close vicinity of these sedimentary units there appear traces and indications of volcanism (see p.34, types 4,5 and 7). In the Gorno area, for instance, these agglomeratic breccias are combined with actual volcanic pipes and tuff layers.

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41

Fig.9. The evolution of Ladinian plateau reef type, diagrammatic section. 1 = uppermost “Alpine Muschelkalk”; wavy-clumpy, thinly bedded bituminous limestone with chert nodules; 2 = andesitic green tuffs (ash and crystal tuffs, few lapilli) with thin layers of marl and limestone; 3 = “Partnach Mergel”, clayey marls, shales with lenses of layered limestone (like 4 ) (Ladinian basin facies); 4 = “Partnachkalk”, bituminous, marly, layered limestone units (Ladinian basin facies); 5-8 = different types of “Wettersteinkak” (Ladinian reef facies); 5 = massive limestone and dolomite, partly cavernous or relictic patterns of bioherms (often coral colonies); 6 = well layered grey limestone (mainly calcarenite) with debris and colonies of algae (Dasycladacee), single algal patch reefs; 7 = predominantly thinly layered limestone with intercalations of the “Sonderfazies” in special sequences (backreef units, tufaceous marls, slump structures, ore sediments etc.); 8 = late diagenetic alteration of the cavernous reef body by recrystallization of dolomite, quartz and different Fe-dolomites; 9A = Pb-Zn sulfide ores with sedimentary fabrics; 9B = Pb-Zn sulfide ores primary enriched in metasomatic replacement bodies, locally associated by small amounts of Cu-Sb-As minerals.

These processes, however, lasted for short intervals as the sediments concerned are intercalated only to a proportionally lesser extent into the main limestone sequence. Characteristicfor these intercalations is the fact that they often recur and repeat themselves with any combinations of the various types of facies. Regarding the areas of this development, therefore, a direct quantitative ratio may be observed between the development of the “special facies” and the maximum quantitative occurrence of ore.

DISCUSSION OF THE GENESIS

Except for the extreme components of the “special facies”, i.e., the ore sediments, “Wettersteinkalk” is in many respects similar to the recently discussed reef complexes mentioned above. The peculiarities of the Ladinian reefs, however, are the results of their position within a temporarily mobile orogeosyncline and its related volcanic activity. In the northern Limestone Alps, volcanic activity alternated during Ladinian times.

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There is proof of the last eruptions by effusive rocks and tuff beds in the lower division only. In the Middle Ladinian division, all indications of volcanic activity are missing. During the same period of time the reef complexes sank further below sea level, showing relatively uniform, non-differentiated, depositional environment. On the contrary, the upper division reveals frequent and short intervals of eventful changes of the sedimentary conditions. These periodical alternations of depositional environments were caused by intervals of generally wide-spanned uplift of the reef complexes. During this time, a significant differentiation took place, initiating the development of typical backreef areas with local increasing stagnation. The intervals of general extensive uplift of the reef complexes were, oddly enough, combined with interstratal flowage, glide folding and resedimentation of ore-and-mud breccias like turbidity currents. These structures of suddenly occurring mudstone movements within the very flat relief of the platforms can be interpreted only as effects of episodic tremors and shocks at the sea bottom. Such movements have apparently been caused by volcanic activity. The close relationship between the development of the “special facies” and the general effects of volcanism is stressed by tufaceous, greenish marl beds, associated agglomeratic breccias, and, above aU, by the appearance of thin bituminous layers containing fluorite-rhythmites; the last-named can only be interpreted as a product of submarine hydrothermal supply (SCHNEIDER, 1954). The primary precipitation of the Pb-Zn sulfide gels took place in close genetical association with the localized precipitation of fluorite. Pools, craters and pockets with weak euxinic environment were active spots of primary sedimentary enrichment of ore. From such localities in many cases the ore has been redeposited penecontemporaneouslyby mechanical transport as mentioned above. There is no doubt about the presence of hydrothermal springs scattered over certain areas of the reef surface. Thus, there is the possibility of precipitation of ore matter from ascending thermal solutions in lower parts of the reef complex. Such “epigenetichypogene” depositsare marked by the appearance of a Cu-Sb-As paragenesis (see p.3 1). The paths, used by the ascending solutions, were retained permanently, as indicated by vertical recurrences of layered ore bodies, especially of so-called “ore-bearing craters”, sometimes over maximum distances of nearly 200 m. Considering the entire sedimentaryseries of the Ladinian in respect of the stratigraphical and paleogeographical distribution of the Pb-Zn mineralization, two fundamental features will be evident: (I) Mineralization in general is restricted to those divisions which indicate a penecontemporaneous, weak, volcanic activity. (2) Sedimentary mineralization in special is primarily bound to the reef complexes and, moreover, secondarily restricted to a few intercalations (“special facies”, see pp. 33-34). Taking into account the distribution of ore deposits, one fact is remarkable: the sediments of the forereef basins (i.e., the “Partnachschichten”) do not contain any comparable ore enrichment. The metal ions, supplied by hydrothermes, have probably

DEPOSITIONAL LEAD-ZINC CONCENTRATIONS IN THE EASTERN ALPS

43

been scattered over the entire euxinic basins in geochemical amounts. The effective environment for external sedimentary enrichment of ore matter was limited by the extension of strong carbonate deposition within reef platforms. It may be taken into consideration, therefore, that during distinct short intervals marked by intercalations of “special facies”, two basic factors of development have met. The first one may be assumed to be the permanent (?) hydrothermal supply as discussed above; the second factor is, presumably, the development of a hypersaline and weak euxinic environment, which took place only at short intervals. The synsedimentary local enrichment of the typical bi-metallic ore matter is based on the significant geochemical behaviour of the lead and zinc ions. As CISSARZ (1930) and RICHTER (1947) have pointed out within the Permian “Kupferschiefer” series of Germany, a strict separation into two groups of metals was apparently caused by differing behaviour of metal ions under various conditions in sedimentary environments. The first group, characterized by the combination of Cu-MoV-Ni-Co, etc., was enriched within units of highly bituminous shaly layers, well known as “Black Sea facies”. The second group, on the contrary, revealed a combination of three metals only: lead, zinc and cadmium. This group was concentrated solely within an intercalated carbonaceous (dolomitic!) unit. The inverse behaviour of these two metal groups during the primary precipitation is linked to different pH values of the depositional environment. The Pb-Zn-Cd group especially tends to precipitate under weak alkaline conditions (lower degrees above pH = 7). These conditions were given during Ladinian times specifically within the intervals of hypersaline and weak euxinic development at certain localities of the backreef area. The sulfur ions, needed for the precipitation as sulfides, may have been produced in a sufficientamount by actions of bacteria, presumably by sulfate reducing strains. The environment of the stagnant backreef offered sufficient organic matter as well as hypersaline conditions. The ascending hydrothermal solutions may procure metal ions of the “coppergroup” too, as proved by a few minor deposits. The dominint sedimentaryconditions, however, did separate and enrich the Pb-Zn-Cd group only. The author thinks that, by a complex mechanism, the sedimentaryorigin of a special type of lead-zinc deposits in carbonate rocks could now be understood by facts which had not been takeninto consideration so far. This mode of sedimentaryorigin,initiated by hydrothermal supply in the course of submarine volcanism, may be obscured in many a recrystallized ore deposit.

SUMMARY

Over the entire area of the Triassic geosyncline of the eastern Alps, the thick midTriassic limestone formation contains in general four lead-zinc bearing horizons. Apart from the more common replacement ore bodies, there remain layered parts which exhibit many criteria for a syn-sedimentary origin. From the many complex

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problems of genesis, only the facial development of the Ladinian members within the northern Limestone Alps is discussed; however the same is true for the entire area. Both the layered carbonate beds with and without primary sulfidic ore matter reveal sedimentary structures and fabrics, which cannot be interpreted as mimetic replacements, as was previously maintained. These are e.g., graded bedding (geopetal fabrics!), cross-bedding, load casts, mud cracks passing over into different types of “ore-and-mud breccias”. Flat submarine slides are documented by various intercalations, mainly combined with “cut-and-fill structures”. Moreover, the paleogeographical conditions are marked by the evolution of extended reef complexes and the appearance of submarine volcanism. It is concluded that the environment leading to Pb-Zn-sulfide deposition is bound to the Ladinian reef facies. The forereef basins are represented by the argillaceous “Partnach-Schichten”, which contain Pb-Zn scattered in geochemical amounts only. The syn-sedimentaryseparation and enrichment of Pb-Zn (Cd) is controlled by hypersaline and (local) weak euxinic conditions restricted to the backreef facies, moreover, by various redepositional effects. The weak Ladinian volcanism, belonging to the initial stage of the Alpine geosyncline, is assumed to be the hydrothermal source for the ore.

REFERENCES

AMSTUTZ,G. C., 1958. The genesis of the Mississippivalleytype deposits, U S A . Experientia, 14 :235. AMSTUTZ, G. C., 1959. Syngenese und Epigenese in Petrographie und Lagerstattenkunde. Schweiz. Mineral. Petrog. Mitt., 39 : 1-84. English translation in Intern. Geol. Rev., 3 :119-140,202-226, AMSTUTZ, G. C., 1962. L‘origine des gites minkraw concordants dans les roches skdimentaires. Chronique Mines Rech. MiniPre, 308 : 115-126. Ossmz, A., 1930. Qualitativ-spektralanalytische Untersuchung eines Mansfelder Kupferschieferprofiles. Chem. Erde, 5 : 48-75. CLAR,E., 1953. uber die Herkunft der ostalpinen Vererzung. Geol. Rundschau, 42 : 107-127. CLAR,E., 1956. Bemerkungen hu Entstehungsfrage der kalkalpinen Pb-Zn-Erzlagerstatten. Mitt. Geol. Ges. Wien, 1955,48 : 17-28. CORNELIUS, H. P., 1941. Zur magmatischen Tatigkeit in der alpidischen Geosynklinale. Be*. ReichsstelIe Bodenforsch., Zweigstelle Wien, 1941 : 89-94. DI COLBERTALW, D., 1948. The lead and zinc deposit at Raibl in Friuli. Intern. Geol. Congr., 18th, London, 1948, Rept., 7 : 1-15. DI COLBERTALDO, D., 1956. Raibl 6. un giacimento di origine magmatica. Rend. SOC.Mineral. Ital., 12 1-23.

DI COLBERTALW, D., 1957. Sulla nuova ipotesi dell’origine sedimentaria dei giacimenti alphi tipo Bleiberg. Rend. Soc. Mineral. Ital., 13 :205-212. DI COLBERTALDO, D. und SCHNEIDERH~HN, H., 1958. Die Blei-Zinklagerstatte von Raibl. Neues Jahrb. Mineral., Monatsh., 1958 :217-224. FRIEDRICH, 0. M., 1937. uberblick iiber die ostalpine Metallprovinz. Z. Berg-, Hiitten- Salinenw. Deut. Reich, 85 ; 241-253. FRIEDRICH, 0.M., 1953. Zur Erzlagerstlttenkarte der Ostalpen. Radex Rundschau, 1953 : 371-407. HEGEMANN, F., 1949. Die Herkunft des Mo, V, As und Cr im Wulfenit der alpinen Blei-Zinklagerstatten. Heidelberger Beitr. Mineral. Petrog., 1 : 690-715. HEGEMANN F., 1957. Geochemische Untersuchungen zur Entstehung der alpinen Blei-Zink-Erzlagerstatten in triadischen Karbonatgesteinen. Berg- Hiittenmann. Monatsh. Montan. Hochschule Leoben, 102 :233-234.

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HEGEMANN, F., 1960. Uber extrusiv-sedimentareErzlagerstatten der Ostdpen. 11: Blei-Zinkerzlagerstatten. Erzmetall, 13 : 122-127. JICHA,H. L., 1951. Alpine lead-zinc ores of Europe. Econ. Geol., 46 : 707-730. MAUCHER, A., 1954. Zur “alpinen Metallogenese” in den bayerischen Kalkalpen zwischen Loisach und Salzach. TschermaksMineral. Petrog. Mitt., 4 :454-463. MAUCHER, A. und SCHNEIDER, H . J . (Redakteure), 1957. Entstehung von Blei-Zinkerzlagerstatten in Karbonatgesteinen -Berg- Hiittenmiinn. Monatsh. Montan. HochschuleLeoben, 102 :225-256. NEWELL, N. D., RIGBY, J. K., FISCHER, A. G., WHITEMAN, A. J., HICKOX, J. E. and BRADLEY, J. S., 1953. ThePermian Reef Complexof Guadalupe Mountains Region, Texas and New Mexico. Freeman, San Francisco, 236 pp. NEWELL, N. D. and RIGBY,J. K., 1957. Geological studies on the Great Bahama Bank. SOC.Econ. Palaeontologists Mineralogists, Spec. Publ., 5 : 15-72. PETRASCHECK, W., 1932. Die Magnesite und Siderite der Alpen. Sitz. Ber. Akad. Wiss. Wien, Math. Naturw. KI., 141 : 195-242. PKTRASCHECK, W., 1945. Die alpine Metallogenese. Jahrb. Geol. Bundesanstalt (Austria), 1945 : 129-149.

PETRASCHECK, W. E., 1957. Die Gesichtspunktefiir eine hydrothermale Entstehung der kalkalpinen Blei-Zinklagerstatten. Berg- Hiittenmiinn. Monatsh. Montan. Hochschule Leoben, 102 :229-233. PI~ASCHECK, W. E., 1960. Die alpin-mediterraneBlei-Zinkprovinz.Erzmetall, 13 :199-204. WCHTER, G., 1947. Palaogeographische Grundlagen fur die Erschliessung des deutschen Kupferschiefers. Technik (Berlin), 2 : 366-368. SCHNEIDER, H.-J., 1953. Neue Ergebnisse zur Stoffkonzentration und Stoffwanderung in Blei-ZinkLagerstatten der nordlichen Kalkalpen. Fortschr. Mineral., 32 :26-30. SCHNEIDER, H.-J., 1954. Die sedimentareBildung von Flusspat im Oberen Wettersteinkalk der nordlichen Kalkalpen. Abhandl. Buyer. Akad. Wiss.,Math. Naturw. KI., 66 : 37 pp. und H.-J. SCHNEIDER (Redakteure), SCHNEIDER, H.-J., 1957. Diskussionsbeitrage. In: A. MAUCHER Entstehung von Blei-Zinkerzlagerstatten in Karbonagesteinen - Berg. Hiittenmiinn. Monatsh. Montan. Hochschule Leoben, 102 : 238-240,242-244. SCHNEIDERH~HN, H., 1941. Lehrbuch der Erzlagerstiittenkunde. Fischer, Jena, 1 :858 pp. SCHROLL, E., 1953. Uber Minerale und Spurenelemente, Vererzung und Entstehung der Blei-ZinkLagerstatte Bleiberg-Kreuth, Karnten in Osterreich. Mitt. dsterr. Mineral. Ges., Sonderh., 2 : 60 pp. SCHROLL, E., 1955. Uber das Vorkomen einiger Spurenmetalle in Blei-Zink-Erzen der ostalpinen Metallprovinz. Tschermaks Mineral. Petrog. Mitt., 5 : 183-208. SCHULZ, O., 1955. Montangeologische Aufnahme des Pb-Zn-Grubenrevieres Vomperloch, Karwendelgebirge, Tirol. Berg- Hiittenmiinn. Monatsh. Montan. HochschuleLeoben, 100 :259-269. SCHULZ, O., 1959. Beispiele fur synsedimentare Vererzungen und paradiagenetische Formungen im alteren Wettersteindolomitvon Bleiberg-Kreuth. Berg- Hiittenmiinn. Monatsh. Montan. Hochschule Leoben, 105 : 1-11. SCHULZ,O., 1960. Die Pb-Zn-Vererzung der Raibler Schichten im Bergbau Bleiberg-Kreuth (Grube Max).Carinthia 11, Sonderh., 22 :93 pp. SCHWINNER, R., 1942. Tektonik und Erzlagerstatten in den Ostalpen. Z. Deut. Geol. Ges., 94 :169-175. SCHWINNER, R., 1946. Ostalpine Vererzung und Metamorphose als Einheit? Verhandl. Geol. Bundesanrtalt, 1946 : 52-61. SCHWINNER, R., 1949. Gebirgsbildung, magmatische Zyklen und Erzlagerstatten in den Ostalpen. Berg- Hiittenmiinn.Monatsh. Montan. Hochschule Leoben, 94 : 134-143. SIEGL,W., 1956. Zur Vererzung der Pb-Zn-Lagerstatten von Bleiberg. Berg- Hiittenmiinn. Monatsh. Montan. Hochschule Leoben, 101 : 108-111. TAUMTZ,K. C., 1954. Erze sedimentarer Entstehung auf alpinen Lagerstatten des Typs “Bleiberg”. Erzmetall, 7 : 343-349. TORNQUIST, A., 1929. Die Vererzungsperiodenin den Ostalpen. Metall Erz, 26 : 241-246. VIDAL,H., 1953. Neue Ergebnisse zur Stratigaphie und Tektonik des nordwestlichen Wettersteingebirges und seines notdlichen Vorlandes. Geol. Bavarica, 17 : 56-88.

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LEAD-ZINC DEPOSITS IN THE CALCAREOUS ALPS AS AN EXAMPLE OF SUBMARINE-HYDROTHERMAL FORMATION OF MINERAL DEPOSITS OSKAR SCHULZ

Mineralogisch-Petrographisches Institut a‘er Universitat Innsbruck, Innsbruck (Osterreich)

The discussion on the genesis of the Pb-Zn deposits in the “Calcareous Alps”, particularly in the Ladinian Wetterstein Limestone was revided in 1954 (SCHNEIDER, 1954; TAUPITZ,1954; MAUCHER, 1954; HEGEMANN, 1948, 1960; see SCHULZ,1960 a, b). The Raibl Beds, which are the Carnian units of the Triassic, contain ore minerals and are of special interest. The studies comprised a partial mapping of the mine, a tectonic analysis, and macroscopic and microscopic fabric analyses of the country rock and of the ore bodies. The following results were obtained from studies which were completed in the summer of 1958: The Raibl Bed which is approximately 200 m thick comprises three beds of shale, each of them approximately 20 m thick. These beds divide the dolomite strata into a first (lower) and a second (upper) intercalated dolomite horizon. The workable ores are found in the lower dolomite. The rocks, mainly mm-laminites, comprise partially recrystallized dolomite-pelite and contain bitumen, FeS,, and clay minerals. In the stratigraphic profile, the distance of the ore bodies from the central shale beds is 11-24 m. In some cases also a second ore bed is found at a distance of approximately 4-7 m from this shale. Both ore bodies are sometimes connected; their beds are approximately conformable, with some deviations and the ore grade varies in strike and dip. Relative to the country rock, the main ore bodies (6.5 m thick at the most) are, strictly speaking, “epigenetic”. They fill a relief cut obliquely into the sediment that was to a certain extent diagenetically hardened. Some cavities are displayed by this relief which is due to submarine earthquakes, accompanied by mechanical erosion and chemical leaching. As a result, the beds are broken up into huge mosaics of varying depths down to several metres. It is assumed that certain substances were supplied simultaneously or subsequently by submarine thermal springs and that, after deposition of sphalerite, quartz, small amounts of iron bisulphide and possibly also of galena, a mechanical deposition took place of these mainly idiomorphic grains, together with dolomite pelite, clay substance, and bitumen, partly as mm-rhythmic laminites. The chemical deposition of schalenblende, galena, and fluorite as well as metasomatism play an important part. Resedimented breccias can be observed mainly in the lowest portions of the sediments filling the relief. Geopetal and polar fabrics are observed frequently. Hence, it can be concluded that mechanical depohtion of the ore pelite took place prior to the alpine tectonic displacement of the strata.

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Fig.1. “Funnel” cut (I) in the footwall beds of dolomite rocks (2) today having a dip angle of 78”.The cut is filled geopetally with mechanically accumulated ore mineral and clay laminae, partly with conformable beds of Schalenblende. The lamination of the “funnel sediment” and the coarse stratification of the dolomite are parallel. The figure shows the tectonic tilting of the primary geopetal arrangement. (Mine-wall “Max” mine, Kreuth.)

Nine distinct periods of purely external, syngeneticmechanical and chemical deposition of ore laminae, equally not displaced and of small thickness only, can be observed. The ore lamination is caused by mm-rhythmic variations of the qualitative content of ZnS grains, quartz, fluorite, dolomite pelite and sparry carbonate, or else by a variation in the grain sizes. In addition, clayey bituminous laminae and, in certain cases, resedimented microconglomerate beds also contribute to the inhomogeneous parallel fabric. Lateral and vertical transitions were found from ore rhythmites into dolomite pelite rhythmites. These transitions are characterized by a general decrease in the sphalerite, quartz, and fluorite content, and an increase in the dolomite pelite content. Typical mechanical depositional fabrics, such as polar lamination, diagonal- and cross-bedding, resedimented microconglomerates, and paradiagenetic movements of the ore laminae and the ore sediments of the main orz body, with formation of para-

LEAD-ZINC DEPOSITS I N THE CALCAREOUS ALPS

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diagenetic deformation breccias which are in part inhomogeneity breccias, are observed frequently. Para- and postdiagenetic recrystallization and chemical redepositions of sulphides as well as of fluorite, carbonate and small amounts of quartz, can be proved. The ore bodies have no prevalent linear direction within the stratification. For other regions this is, however, not excluded. There are no primary depth differences. Genetically, the deposit is designated best as “extrusive-sedimentary”, i.e., it has to be taken into account that during its first process of formation, precipitations took place from an extrusive Carnian hydrothermal source of substances. Mainly submarine, mechanical and chemical depositions contributed to the formation of the ore bodies. Further study deals with the investigation into the conformable strata of ore bodies

Fig.2. Space-rhythmic mm-lamination due to polar mechanical external deposition of‘ZnS grains (b1ack) and quartz (white). The dark grey beds also repeating rhythmically are rich in dolomite p e h and clay substance (thin section).

0. SCHULZ

Fig.3. Section from a gradual transition of ore laminae (below) to dolomite pelite laminae (above), (polished sections). ScaIe = 1 cm.

in the stratigraphically Lower Wetterstein Dolomite (Ladian Stage of the Triassic). There are indications for a submarine hydrothermal supply of substances at the time when this sediment was formed. Although schalenblende and coarse-crystalline sulphides predominate in these deposits, relics of quartz-fluorite-sphalerite rhythmites could be found which can certainly be ascribed to the mechanical sedimentation ion the surface of the bottom of the sea. These space-rhythmic ore laminae are interbedded with marl and dolomite rhythmites. They are connected by gradual transitions, and all these primary fabrics are, at some places, replaced by schalenblende, including colloform types of galena and fluorite. According to the fabric analyses, the formation of colIoform fabrics and of coarse crystalline ore is regarded as mainly paradiagenetic. The primary fabric and the colloform fabric were deformed by folding, brecciation and slumping. Moreover, similar typical mechanical deposition fabrics like those of the ore

Fig.4.W p e t a ! mechanical internal deposition in a microcavity within the Schalenblende fabric: at the bottom of the cavity mainly ZnS (black) and quartz grains (white). The remaining part of the cavity (above) is filled with fluorite (white) chemically deposited internally (thin section).

Fig.5.The repetition of the two beds can be explained by small scale thrust faulting, as could be seen from the section 1plane of the figure. Space-rhythmic lamination with sphalerite, wuttzite, galena, uartz, fluorite, dolomite pelite, clay substance. Light grey beds above: rich in ZnS. Black beds: rich in

iuorite. Grey beds below: rich in carbonate pelite and quartz. Scale strip = 1 cm (polished section).

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deposits of the Raibl Beds can be found. In addition to fabrics indicating external processes there are also fabrics that point to paradiagenetic processes, both in the ore deposit proper and in the barren country rocks. The fissures in the region studied are to be regarded as later faults, and not as feeder channels of ore solutions. Belteroporic migration of ore solutions along fine partings of the rocks and a diffusive metasomatic mineralization, can also be observed on a restricted local scale. Hence, the hydrothermal supply of ore matter causes, at least at some places, an extrusive sedimentary, submarine deposition of ore minerals and, at the same time, intrusive epigenetic mineralization in the lower sediment. The results obtained in the studies herewith summarized, lead thus to essentially the same hypotheses concerningthe origin of the main ore horizons of Bleiberg-Kreuth which are contained in the Upper Wetterstein Limestone (Ladinian Stage of the Triassic). Data concerning this subject are given in the papers SCHULZ(1960a, b) in which some of the figures of this article have already been published.

SUMMARY

Fabric analyses of Carnian and Ladinian sediments in the Pb-Zn-mine BleibergKreuth (Austria) substantiate the conception of the submarine-hydrothermal origin of the deposit with partially extrusive-sedimentary deposition of ore minerals.

REFERENCES

HEGEMANN, F., 1948. Uber sedimentare Lagerstatten mit submariner vulkanischer Stoffmfuhr. Fortschr. Mineral., 21 : 54-55. HEGEMANN, F., 1960.Die Entstehung der kalkalpinen Blei-Zinkerzlagerstatten. Neues Jahrb. Mineral., Monutsh., 7-8 : 170-185. MAUCHER, A., 1954. Zur “alpinen Metallogenese”in den bayrischen Kalkalpen zwischen Loisach und Salzach. Mineral. Petrog. Mitt., 4 (14) :454463. SCHNEIDER, H.-J., 1954. Die sedimentare Bildung von Flusspat im Oberen Wettersteinkalk der nordlichen Kalkalpen. Abhandl. Buyer. Akad. Wiss., Math. Naturw. KI., 66 : 1-37. SCHULZ, O., 1960a. Die Pb-Zn Vererzung der Raibler Schichten im Bergbau Bleiberg-Kreuth (Grube Max), als Beispiel submariner Lagerstattenbildung.CarinthiuZZ, Sonderh., 22 : 93 pp. SCHULZ, O., 1960b. Beispiele fiir synsedimentare Vererzungen und paradiagenetische Formungen hn alteren Wettersteindolomit von Bleiberg-Kreuth. Berg- Hiittenmiinnische Monafsh. Monfan. Hochschule Leoben, 105 (1) : 1-11. K. CH., 1954. Erze sedimentarer Entstehung auf alpinen Lagerstatten des Typs “Bleiberg”. TAUPITZ, 2. Erzbergbuu MetaIlhiittenw., 7 (8) : I.

L'APPLICATION DES COURBES PREVISIONNELLES A LA RECHERCHE DES GISEMENTS STRATIFORMES DE PLOMB P . NICOLINI

Bureau de Recherches Giologiques et Mini&es, Paris (France)

INTRODUCTION

Dans un precedent travail (NICOLINI, 1962), nous avons pose le problkme: A savoir si les conclusions dCgag6es a propos de la localisation du cuivre dans les courbes prkvisionnelles peuvent &re &endues aux autres substances et notamment au plomb-zinc. Nous avons citk, a ce propos, un gisement du Missouri oil les courbes sont assez voisines de celles du cuivre. D'autre part, nous ne savions pas si l'association cuivreplomb-zinc 6tait necessaire, a Mansfeld par exemple, pour que le plomb et le zinc se situent dans les memes types de courbes que le cuivre. Des travaux recents nous permettent s'apporter un certain nombre de prkcisions a ce sujet.

QUELQUES EXEMPLES DE LOCALISATION DU PLOMB DANS LES S ~ R I E SS~DIMENTAIRES

L'exemple des CPvennes: Les gites de plomb de la rPgion de Florac-Meyrueis (France) Dans la rkgion de Florac-Meyrueisdes concentrations plombifkres sont connues dans le Mksozoi'que. (a) Les faciks de grbs feldspathiques continentaux, plus ou moins grossiers, du Trias renferment des mineralisations pinkoncordantes assocites A de la barytine. (6) Un niveau de calcaire dolomitiquejaune de Charmouthien et accessoirement un ou plusieurs niveaux de 1'Hettangien renferment des mineralisations stratiformes. Cette rkgion est donc interessante, du point de vue gitologique, car on y trouve associ6es A la fois des concentrations stratiformes et des concentrations penkoncordantes. L'examen des courbes previsionndles representees Fig. 1, montre ce qui va suivre. Les concentrations les plus importantes de plomb se trouvent dans des sequences lithologiques brutalemmt positives, que la roche encaissante soit constituee par des clastiques (Trias) ou par des chimiques (Lias), les sequences moins brutalement positives (Hettangien) renferment tgalement des min6ralisations plombifkres, mais celles-ci prksentent une moins grande continuitt ou des teneurs plus faibles selon le cas.

54

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-.I I

I

Fig.1. Courbes prkvisionelles de la rkgion Florac-Meyrueis (Lozkre). Echelle 1 : 2.000. A. &ages. B. Coupe. C. Courbe lithologique : I = conglomkrats; 2 = conglom6rats grkseux; 3 = grks grossiers; 4 = grks a grain moyen; 5 = mames; 6 = mamo-calcaires; 7 = calcaires f mameux; 8 = calcaires dolomitiques. D. Cycles de ddimentation: 1 = ddiments de premier cycle; 2 = skdiments de second cycle. E. Couleurs: r = rouge;j = jaune; 6 = b1anc;g = gris, bleu, vert; n = noir. F. Milieu de ddimentation: c = continental; rn = marin. G. Cycles biorhexistasiques: b = biostasie; r = rhexistasie. H. Courbe pr&isionnelle Pb: I = favorable aux gites stratiformes sensu stricto; 2 = favorable aux gites pknkconcordants; 3 = barytine.

La courbe de cycles de sedimentation CC), indique une premibre apparition du plomb, dans la serie stratigraphique, dans la zone de passage des stdiments du premier aux stdiments du second cycle (Trias), mais aussi un Btalement des concentrations plombifkres dans le second cycle (Lias). La courbe des couleurs (E), montre que le plomb se situe, comme la barytine, plus volontiers dam la partie gauche de la courbe, c'est-8-dire dans des stdiments ddposts en milieu 8 tendance oxydante. Ceci constitue un caractkre distinctif des gisements de plomb et des gisements de cuivre, ces derniers se situant gentralement dans les parties positives des courbes de couleur (ndgatif oxydant, positif rtducteur). On sait, par ailleurs, que la barytine stratiforme est plus souvent associde 8 du plomb qu'8 du cuivre.

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55

Les minkralisations stratiformes de plomb (et de cuivre 6galement) se trouvent dans des sediments dkposks en milieu marin, les minkralisationspknkoncordantes dans des skdiments dkposts en milieu continental. La courbe F met bien en Gvidence ces relations entre le milieu de sedimentation et la morphologie des concentrations. Le plomb, mais ii un degrk moindre que le cuivre, se situe dans des phases biostasiques des cycles biorhexistasiques (courbe G) mais souvent au voisinage de “microphases” rhexistasiques, soulign6es par la prksence de barytine dans des sediments jaunes ou rouges. Une derniBre colonne de la Fig.1 ( H ) situe les minkralisations dans l’ensemble des courbes. On voit que si la minkralisation plombifkre obkit i une certaine rkpartition skdimentologique, elle prksente, dans l’khelle stratigraphique un ktalement beaucoup plus important que le cuivre dans les gisements stratiformes du monde (NICOLINI, 1962). On voit aussi, que la premikre “skquence plombifkre” (Trias) ne surmonte pas une s6quence en I c o m e cela se produit gknkralement pour le cuivre. Mais nous avons montrk (NICOLINI, 1962) que la rubkfaction du socle, qui est ici trBs intense, peut avoir, dans une certaine mesure, la mQmesignification qu’une skquence en I.

C

A

2

Fig.2. Crktack du Gabon. hhelle 1 : 1.OOO. Z = organismes; ZZ = niveau brkhique. A . Courbe lithologique: I = conglomkrat; 2 = arkose grossikre; 3 = arkose moyenne-fine; 4 = gtks argileux; 5 = argilite; 6 = mame; 7 = cdcaire. B. Cycles: 1 = premier cycle; 2 = second cycle. C. Couleurs; r = rouge; b = b1anc;g = gris, vert; n = noir. D.Niveaux minkralih.

56

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Autres exemples de gftes de plomb Gftesdu Crktack &tier gubonais Des indices de plomb ont t t t m i s en 6vidence avant la dernikre guerre mondiale dans la serie continentale de Cocobeach attribute au CrBtacB. Rtcemment ces indices ont tt6 dtcrits par ARNOULD et al. (1962), et accessoirement Nicolini (CARRIEet al., 1962). La galkne est diss6minte sur une grande epaisseur de la strie, mais plus volontiers localiske dans des grks feldspathiques grossiers gris. Comme dans la Lozkre, le plomb se localise dans les stquences brutalement positives (Fig.2) et apparait dans la zone de passage des sediments du premier aux stdiments du deuxikme cycle. Le milieu est trbs riche en matibres organiques, bois carbonists ou matikres bitumineuses. De la barytine est connue, dans la serie de Cocobeach, debordant geographiquement les zones mineralisees et les annowant en quelque sorte. A la d86rence du Trias de Lozbre, les sediments mintralises reposent directement sur le socle, sans intermkdiaire de surjace rubkJiPe. Gisements de plomb du Missouri Apropos de l’analogie de types de stquences entre certains gisements de cuivre et de plomb, nous avons cite les gisements de plomb situes au sudouest de la ctlkbre “lead belt” du Missouri (NICOLINI,1962). Dans cette region, le plomb est localis6 dans la formation de Bonneterre qui correspond (i une skquence franchement positive, sans phase nkgative (sauf au sommet m6me de la formation) et qui se poursuit par une stquence oscillante (Formation de Davis) (Fig.3). Comme dans les stquences cuprifkres, la mintralisation surmonte une stquence en I, mais se trouve localiste au voisinage de paleoreliefs, ce qui indique en soi une rtduction d’tpaisseur de cette sequence en I. L‘etalement de la mintralisation dans la stquence positive -la S6rie de Bonneterre -est un phenombne frequent dans les gisements de plomb. Ici l’ttalement particulikrement important de la mineralisation peut s’expliquer par la longueur anormalement tlev6e de cette sequence positive. Gisements de plomb-zinc du Maroc Zellidja A Zellidja, la mintralisation est incluse dans des dolomies liasiques reposant par l’intermaiaire d’un conglomtrat dolomitique sur le socle de schistes vistens. L‘ensemble peut 6tre assimile A une stquence brutalement positive, A l’kchelle du l/l.OOOk ou du 1/2.000k malgre certaines variations pttrographiques dans le dttail. A ouli-Mibladen Des travaux gtologiques rtcents sur ces gisements sont dGs A BOULADON (1960), DIOURI(1962), EMBERGER (1962) et FELENC (1962).

APPLICATION DES COURBES PR~VISIONNELLES

Socle

57

+++

Fig.3. Gisements de plomb du Missouri (U.S.A.)

h

Cretace Ji

E!

Cias Trias SCCk

-

+ + +

1

h

Plomb

g

Earytiw

Fig.4. Schemade la Srie de Mibladen (d’aprksles renseignements tirks des rapports de FELENC, 1962).

58

P. NICOLMI

La mintralisation la plus importante est localiste dans des niveaux carbonatts, en association avec de la barytine. LA encore, il semble que le plomb se trouve dans des stquences brutalement positives. Mais il se pose un probltme de coupure stratigraphique Trias-Lias, probltme qui peut modifier l’allure de la courbe. Aussi n’avons nous represent6 qu’un schtma de l’tvolution lithologique (Fig.4).

Gisement de Mansfeld ( AIlemagne ) Ce gisement est surtout cCltbre pour le cuivre, mais renferme tgalement une trks belle mintralisation stratiforme en plomb-zinc, situte un peu au-dessus du “Kupferschiefer”. Ici le plomb et le zinc, encaissts dans un shale noir, sont localists dans une stquence brutalement positive, du Zechstein marin, tvoluant entre des conglomtrats et des roches saliftres. La Fig.5 indique la position des mintralisations dans I’tvolution stdimentologique

1I

Fig.5. Courbes prtvisionellesdu gisernent de Mansfeld (Allemagne). A. Courbe lithologique: I = conglomerates; 2 = grks; 3 = argilites; 4 = calcaire; 5 = sel. B. Cycles: I = premier cycle; 2 = second cycle. C. Couleurs: r = rouge;j = jaune; b = blanc;g = gris, vert; n = noir. D. Milieu: c = con-. tinental; m = marin. E. Biorhexistasie: b = biostasie; r = rhexistasie. F. Niveau mineralid (I).

des stries (A et B), dans leurs variations de couleur (C) et en fonction de leur tvolution palkogtographique ( D et E). En fait, selon que l’on considtre l’ensemble Zechstein-Trias, nous avons une s6quence oscillante positive favorable pour le cuivre, ou bien si l’on considkre le Zechstein comme un tout (coupure entre le Zechstein et le Trias), la skquence est brutalement positive et par constquent favorable au plomb et au zinc. On pourrait multiplier les exemples dans le monde de la localisation prtftrentielle du plomb dans l’tvolution des stries stdimentaires.

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59

SIMILITUDES ET DIFF~RENCESENTRE LES COURBES PREVISIONNELLES POUR LE PLOMB ET POUR LE CUIVRE

Courbes Iithologiques

Le fait, que la plupart des gites stratiformes sensu strict0 de cuivre se trouvent dans des roches clastiques ou argileuses la plupart des gites de plomb-zinc dans des roches carbonattes, laisse supposer une localisation sequentielle differente du cuivre et du plomb. Les exemples cites plus haut montrent, en effet, que, si les horizons renfermant des mineralisations cuprifbres sont represent6 par des sequences oscillantes positives surmontant une sequence en I, les skquences 6 plomb sont brutalement positives et la skquence en I sous-jacente n’est pas nkcessairement prhente. Au contraire, dans une region donnde, il semble que les chances de trouver des concentrations plombifkres croissent lorsque la longueur de la sequence en I sous-jacente diminue. On peut citer A ce propos le Trias c6veno1, mineralid en plomb lorsque la sequence en I est nulle ou faible (pas ou peu de Permien), mineralis6 en cuivre lorsque la sequence en Z sousjacente devient trbs longue, dans le Bassin de Lodbve par exemple. Le cas des gttespb&oncordants est un peu d86rent: si la mineralisation qu’elle soit cuprifkre ou plombifbre, se trouve dans des roches-h6tes analogues, generalement clastiques, cette mineralisation se trouve dans des sequences differentes brutalement positives pour le plomb, oscillante positive pour le cuivre (la localisation sequentielle du cuivre penkconcordant est cependant moins rigoureuse que la localisation s6quentielle du cuivre stratiforme). En r6sum6: (a) Le cuivre et le plomb se trouvent tous deux, dans des skquences positives donc dans des phases transgressives. Mais les oscillations des sequences cuprifires indiquent une transgression plus saccadke, plus rythmee, le mouvement transgressif est plus net, sans retour A des microphases regressives dans le cas du plomb. (b) La presence d’une skquence en I, n’est pas nkcessaire pour qu’il existe une mindralisation stratiforme plombifbre, mais cette sequence en I est parfois presente: au Missouri et 51 Mansfeld par exemple. A Mansfeld, l’association du cuivre au plombzinc coincide avec la presence d‘une sequence en I . Dans le Missouri, la localisation du plomb autour des paltoreliefs du socle indique dkj51 une tendance A la reduction d’ipaisseur de la sequence en I. La sequence en Z traduit deux sortes de ph8nomBnes: ( I ) Un phenombne de comblement avec superposition monotone des mQmesstdiments: grande epaisseur de conglomerats par exemple 51 White Pine (U.S.A.). Ce phenomknepeut correspondre 51 un remplissage Bolien, 51 un ependage de piedmont, etc. (2) Un ph6nomBne de subsidence saccadke, oscillations faibles sur une grande Cpaisseur entre deux termes petrographiques trbs rapproches (grBs fins argileux et pClites argileuses par exemple): cas du Saxonien du Bassin de LodBve. Dans le premier cas -comblement - la mobilit6 du fond du bassin pedt Qtrenulle et la sidimentation peut s’expliquer par de simples variations du couvert vCg6tal sur le

60

P. NICOLINI

continent (biorhexistasie) ou par une elevation du niveau du continent ayant declenche une erosion brutale. Dans le second cas, subsidence saccadbe, la mobilite du fond du bassin est vraisemblable. Autrement dit, l’absence frequente, de sequence en I sous-jacente aux sequences plombifbres, indique que le depat des roches-hates du plomb correspond h une “histoire gtologique” plus simple que l”‘histoire gtologique” des roches-hates du cuivre et que le plomb htrite moins en quelque sorte que le cuivre du “passe geologique” des sediments antkrieurs au d6pBt de la r6che-h6te.

Cycles de sgdimentation Le terme de “cycle de sedimentation” est utilise dans le sens de STEWARD et FISCHER (1961). Nous avons montre que le cuivre se localise, dans les gisements stratiformes, vers la limite des sediments du premier et du second cycle. Les quelques concentrations plombifbres que nous avons eu l’occasion d’etudier montrent Cgalement que, dans une skrie sedimentaire, le premier niveau ii mineralisation stratiforme vraie ou penkconcordante, se situe vers la limite des sediments du premier et du second cycle. Cependant, d’autres niveaux plomb@res peuvent encore apparaitre, au-dessus, dans les sediments de second cycle, sans que l’on retrouve de rtccurences de sediments du premier cycle, dans la strie. Toutefois, si nous reprenons les courbes trades dans la figure no 1, nous constatons la presence d’une reccurence du premier cycle, sous le banc miniralist, vers la bordure du bassin, bien que ces sediments du premier cycle n’apparaissent pas dans la zone minkralisee mCme.

Couleurs Nous observons une localisation du plomb moins rigoureuse que la localisation du cuivre dans la courbe des couleurs. Nous avons vu que, dans une serie de couleurs variees, le cuivre se trouve prtferentiellement dans les sediments gris, verts, noirs, h l’exclusion des rouges. Le plomb peut se trouver comme ii Mansfeld, par exemple, dans des sediments noirs, riches en matibres organiques et deposes en milieu generala ment trbs dducteur, mais ce metal existe aussi dans des sediments deposes dans des conditions vraisemblablement oxydantes’. Dans le Crktace Gabonais, les sediments noirs, gris foncks et verts, paraissent dans l’ensemble, moins riches en plomb que les sediments blancs ou gris clairs. On cite aussi de nombreux exemples de mineralisations plombifbres dans des sediments rouges, au voisinage de hard-grounds, par exemple, notamment lorsque ces mineralisations sont associks h la barytine. Le potentiel d’oxydo-reduction originel n’est pas toujours aid il determiner. I1 faut tenir compte egalement des colorations trompeuses - mangankse, magnetite, etc. - qui n’indiquent pas nkessairement un milieu reducteur. L’altbration mbtkorique des roches modifie Bgalement la couleur originelle, lorsque l’ttat du fer se modifie.

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Milieu de skdimentation

Le type de stquence mintralisk indique, du point de vue paltogkographique que les mineralisations plombo-zincifbres ont plus de chances de se trouver dans des transgressionspluspousskes que le cuivre. Le problbme est de savoir si le plomb et le zinc se situentplusprbs des anciennes lignes de rivages que le cuivre. Ceci parait verifit dans de nombreux cas. BERNARD et FOGLIERINI (1963) ont montrt que les gisements stratiformes triasiques de France se rtpartissent en bordure des anciens rivages du continent. Le milieu proprement dit de sedimentation a une importance dtterminante sur les concentrations mintrales, que ces concentrations soient cuprifbres ou plombo-zinciRres. L‘exemple du Permien d’Europe oh des facibs analogues (shales noires) sont tour A tour steriles ou mintralisks en cuivre selon que le milieu de sedimentation de ces shales est continental (Autunien franqais) ou marin (Zechstein a1lemand)l. En ce qui concerne le plomb et le zinc, on connait des concentrations a la fois dans les sediments continentaux et dans les sediments marins, mais les concentrations les plus importantes semblent prtsentes dans des stdiments marins. A ce point de vue, le Pb-Zn a une plus grande latitude A la fois stdimentologique et paltogtographique que le cuivre. La latitude de la pyrite est encore plus grande. Le milieu de stdimentation est caracttrist, d’autre part, par son potentiel d’oxydoreduction. La nature des dtbris vtgttaux inclus dans les stries nous donne une id& de ce potentiel d’oxydo ou de sous kvolution: bois carbonists en milieu rkducteur, bois silicifies en milieu oxydant ? Bio-rhexistasie

Les Fig. 1 (Lozbre) et 5 (Mansfeld) indiquent que les mintralisations plombifbres peuvent se trouver soit dans des phases rhexistasiques soit dans des phases biostasiques. En fait, il semble que les caractbres morphologiques des gisements permettent, une fois de plus, d’ordonner les observations: les mintralisations strutiformes vraies se trouvent dans des phases biostasiques (Charmouthien de la Lozbre, Mansfeld, Mount Isa) tandis que les mineralisations pPnPconcorduntes se localisent dans des phases rhexistasiques (Trias de la Lozbre). Ceci semble valable aussi bien pour le cuivre que pour le plomb.

CONCLUSIONS

Nous avons vu que le cuivre et le plomb se trouvent tous deux dans des sequences En milieu continental peuvent exister des sites pbkconcordants de cuivre, souvent associb au vanadium ou A l’uranium, mais rarement des gisements exploitables.

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P. NICOLINI

positives mais que la sequence du plomb est moins oscillante - et mCme n’oscille pas - et qu’il n’est pas ntcessaire d’oberver une sequence en “I” sous-jacente aux sequences plombifkres. En d’autre termes, le plomb et le cuivre se trouvent dans des phases transgressives, plus franches pour le plomb, et n’ayant pas nkcessairement un “passe sedimentaire”. Les metalloginistes ont explique certainesparagensses, certaines associations mindrales par des affinitks physico-chimiques des dements (temperature de formation des mineraux, temperature de fusion des metaux, rayons ioniques, affinites chimiques, etc.). Mais, si l’on replace les minerais dans les courbes prdvisionnelles, on constate que certaines associations minerales s’ordonnent en fait, dans un encaissement sedimentologiques particulier a chaque metal ou a chaque groupe de metaux. I1 ne faut pas Cvidemment negliger le c6te physico-chimique de la gitologie mais certaines associations minerales insolites ou plus exactement la presence de certains minerais dans des milieux insolitesl devient moins aberrante si le minerai n’est plus BtudiC en tant que tel, mais en fonction de son contexte gitologique et notamment s6dimentologique. Les differences observees dans les localisations sequentielles du plomb et du cuivre correspondent bien a la rarete des concentrations stratiformes de Cu-Pb-Zn ayant un intergt Cconomique dans le monde. Le cas de Mansfeld fait exception; cependant, dans ce gisement allemand, les faciks Cu et les faciks a Pb-Zn sont en fait separb, et la sequence lithologique est intermediaire entre une sequence cuprifkre et une sequence plombifkre. Un problkme peu Btudie est le problkme du passage, dans un m&mebassin, de sequences cuprifkres des sequences plombifkres. I1 s’agit la autant de variations paleogeographiques que de variations sedimentologiques, les deux &ant likes. Ceci a une importance fondamentale dans les previsions de recherche. Ceci nous conduit parler de la latitude deformation des minkaux, latitude a la fois stdimentologique et paleogeographique. Nous avons montre (NICOLINI,1962) que, si les sulfures de Cu, Pb, Zn se trouvent concentres dans des sediments deposCs sous climat a tendance chaude et en milieu marin ou lagunaire, la pyrite beaucoup plus ubiquiste, peut se trouver a peu prks dans tous les types de paleoclimats et milieux (sauf peut-&re en milieu Bolien). Sur le plan sdimentologique, nous observons A peu prks les m&mesphenomknes: le cuivre se trouve, en milieu marin et dans des skdiments deposes sous climat A tendance chaude, lorsque les conditions sedimentologiques favorables apparaissent pour la premisre fois, dans une serie s6dimentaire2.Les concentrations plombifkres apparaissent &galement lorsque les conditions sedimentologiques sont favorables pour la premikre fois dans la s6rie stratigraphique, mais d’autres concentrations peuvent ainsi exister, si les mt?mes conditions skdimentologiques se reproduisent dans le temps. Cependant, lorsque l’effet socle-couverture tend a s’attenuer, c’est-A-dire lorsque la distance du socle au La pyrrhotine dam des argiles non mktamorphiquesde Sicile, par exemple TAMAYO (1955). I1 peut exister parfois dew ou trois niveaux minkralids en cuivre, mais ces niveaux sont gknkraleDent tres rapprochk stratigraphiquementet sont i n c h dans la m&medquence lithologique.

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63

niveau considtrt comme favorable est trop tloignte, la mintralisation plombiftre peut stre absente. La pyrite, dont la latitude stdimentologique est tres grande, se retrouve dans tous les types de stquences, mais gtntralement plus abondante dans les sequences favorables au cuivre ou au plomb dans une province minerale donnte, et cette pyrite dtborde gtographiquement les zones mintralistes notamment en plomb-zinc. Elle deborde aussi, stratigraphiquement, les niveaux mintralists en sulfures de Pb, Zn, Cu. Dans une certaine mesure, elle peut, par condquent, “annoncer” les zones 9 minerais utiles, un peu comme la barytine annonce les zones i plomb-zinc dans certaines provinces mintrales.

Les recherches de l’auteur ont permi de montrer que les gisements stratiformes de cuivre se trouvent localisis dans un environnement stdimentologique particulier: premitre stquence oscillante 9 tendance positive, surmontant une longue stquence en I dam les courbes lithologiques de LOMBARD (1956); niveaux verts, gris ou noirs dans les stries de couleurs varikes, etc. Cette ttude est destinte 9 montrer dans quelle mesure les conclusionsmises en tvidence pour le cuivre, peuvent &re appliqutes i l’ttude des gisements stratiformesde plomb. En fait, les min6ralisations plombifbres se localisent gtneralement dans les stquences brutalement positives, que celle-ci soient prtctdtes ou non par une sequence en I. La localisation dans les roches de couleurs dttermintes est moins rigoureuse que pour le cuivre. Les mintralisations plombiftres sont d’autre part replactes dans l’tvolution bio-rhexistasique de ERHART (1956) et dans l’tvolution des cycles de stdimentation.

SUMMARY

The author considers examples of stratiform lead concentrations (from France, U.S.A., Africa) and compares them with stratiform copper deposits. Lead and copper are both found in positive sequences with those of lead being often less oscillating. The subjacent I sequence may be absent. Sedimentological context may explain aberrant occurrences of ore or of ore associations. Cu, Pb and Zn are concentrated in sediments deposited under warm conditions. In marine or lagunal milieu Cu appears restricted to the first appearance of favourable conditions in a given basin, whereas Pb may recur with recurring favourable conditions, except when the distance to basement is too great. The ubiquitos pyrite is generally more abundant in sequences favourable to Cu-Pb, possibly extending into the Pb-Zn milieux and also into the Pb, Zn, Cu sulfide zones. Pyrite announces zones of economic minerals in the way that barytine announces lad-zinc zones in certain mineral provinces.

64

P. NICOLINI BIBLIOGRAPHIE

ARNOULD, M., CARRIE, J. et KNUP,J., 1962. Rapport inedit Bur. Rech. Gtol. Minitres sur le plomb du Crktack gabonais. BERNARD, A. et FOGLIERINI, F., 1963. AperCu sur le Trias m&alliftre en France. En: Colloque sur le Trias de la France et des rdgions Iimitrophes -Mdm. Bur. Rech. Gdol. Mini&es, 15 : 635-650. BOULADON, J., 1960. Sur les mineralisations en Pb-Zn et en Sb de la pkriphkrie du Mt. Lozere. Bull. SOC.Gdol. France, 2 :906-914. CARRIE, J., KNUP,J. et NICOLINI, P., 1962. Observations sur les Mindralisations en Pb-Zn du Crdtacd gabonais. Bur. Rech. Geo1. Minitres, Paris, 40 pp. (inedit). DIOURI,M., 1962. Renseignementsinedits. EMEERGER, A., 1962. Renseignementsinkdits. H., 1956. La Genbe des Sols en tant que Phdnomdnegdologiques.Masson, Paris, 88 pp. ERHART, FELENC, R., 1962. Rapport inedit. LOMBARD, A., 1956. Geologie sddimentaire.Les Sdries marines. Masson, Paris, 722 pp. NICOLINI, P., 1962. L'utilisation des donnks ddimentologiques dans l'etude et la recherche des gisementsstratiformes. Etablissement des courbes previsionnelles.Chronique Mines Rech. MiniPres, 309 : 156167. STEWARD, J. M. et FISCHER, R. P., 1961. Copper, vanadium and uranium deposits in sandstones. Their distribution and geochemicalcycles. Econ. Geol., 56 (3) :509-520. TAMAYO, E., 1955. Sur la presence de pyrrhotine de nkofonnation dans les argiles ddimentaires de Sicile. Bull. SOC.Gdol. France, 5 (4-6) : 375-379.

DIAGENETIC BEHAVIOUR OF SULPHIDES G.

c.

A M S T U T Z ~ ,P . R A M D O H R , F . E L B A Z

and w. c .

PARK

School of Mines and Metallurgy, University of Missouri, Rolla, Missouri (U.S.A.) ; MineralogischesInstitut, Universitat von Heidelberg, Heidelberg (Germany) ; Department of Geology, University of Missouri, Rolla ,Missouri (U.S.A.) ; Department of Geology, McMaster University, Hamilton, Ontario (Canada)

INTRODUCTION

In the following six short papers, phenoinena of diagenetic behaviour of sulphides are reported which bear a close similarity and relation to each other. In all cases, the sulphides are shown to be associated with distinct diagenetic patterns; in some cases, even to the extent of being located at definite loci, which inevitably suggests that they crystallized at definite stages during the gradual formation of the respective sedimentary rocks. Each one of the short papers represents a preliminary summary on extensive detailed work. The purpose of presentation at this time is to draw attention to certain phenomena and their distinct genetic meaning, which, although widespread and well known in sedimentary petrology, have not been used as yet in the interpretation of sulfide ore deposits.

I. SHALLOW WATER PATTERNS OF IRON SULPHIDE DISTRIBUTION IN THE JEFFERSON CITY FORMATION NEAR ROLLA, MISSOURI

( G . c. AMSTUTZ)

Megascopic observations

The Quarry Ledge Member of the Ordovician Jefferson City Formation 11 km south of Rolla, Missouri, on both sides of Highway 72, contains the sulphide patterns to be discussed in this paper. A shallow marine environment is indicated by the presence of sun cracks and perhaps also by ripple marks and crossbedding at different horizons. The beds containing the sulphides to be described consist of dolomitic limestones with partial vertical variations to sandy and clayey portions. The rock is quite massive and the layering is often seen only from the layered arrangement of sulphides or from stylolite seams, as seen in the figures. The distribution patterns of sulphides are conspicuous and the great variety of forms invites an analysis of the diagenetic history. Present address: Petrographisch-Mineralogisches Institut, Universitat, Heidelberg(Germany).

66

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.Ia

-

c. AMSTUTZ et a].

1 crn c

ma 5

lcm H

-

---

llIb

Ie

icrn

H

*

1crn U

IIa

lIb

Fig.1. I , II. Congruent patterns (on bedding planes or disseminated).IlI, ZV. Non-congruentpatterns (crosscuttingwithin a certain layer). p v = plan view; qtz = quartz; s = section; I = solid; 2 = disseminated; 3 = calcite core.

DIAGENETIC BEHAVIOUR OF SULPHIDES

67

As a basis for any genetic interpretation, the observational material should be classified and studied in ample detail in a purely objective manner. For this purpose, the variety of forms can be conveniently classified into congruent and non-congruent features. There are, of course, many transitions and combinations as shown in Fig. 1 which will now be briefly described. The sequence of patterns from Zu-ZZg corresponds to the right side of the fabric triangle of the AGI data sheet 21. Patterns Zu-f are essentially linear or planar, marking a simple bedding plane (Zu),crossbedding (Zb), stylolites with (Zc) or without (Id) quartz accumulations; more massive or thin basin-shaped forms follow (Ze) and represent the transition to the isolated patterns, for example ZZu, ZZb, ZZc. Pattern I f shows typical transitions from patterns of type Z to those of type ZZ. Group ZZ patterns are found isolated or abundantly disseminated. Black represents a megascopically, more or less solid mass of iron sulphide, whereas dots signify finely scattered grains of pyrite or marcasite. Quartz is shown by small irregular squares (Zc, ZZg). The extent of ZZb is so much more horizontal than vertical that a section (s) is given together with a plan view (P.v.).The patterns ZZd, ZZe,and Zlfare often so faint that the term nebulitic fits this distribution best. Pattern ZZg consists of geodes with sulphides and. with or without quartz. The scale given for each pattern is 1 cm. Patterns ZZZu-ZVd display a marked vertical extent which dominates the horizontal dimension in detail but not always the overall grouping. Patterns ZZZu and ZZZc are bound to bedding planes, but their conspicuous features transgress the bedding plane s.str. and extend downward into the cracked “mud” layer (ZZZu) or dendritically or as veins upward into the next bed (ZZZc). Patterns ZZZb and ZVu-d cut across a certain bedding unit. In the case of ZZZb, most of the “cracks” or veinlets extend upwards to a bedding plane, as also seen in Fig.3. Fig.1, ZVu-d represents a set of rather typical vertical features which look like pipes, chimneys or hoses. They may consist of a ghost-like nebulite only (ZVu)with or without a solid sulphide core. ZVb and IVc are the most common “pipes” or channels. These contain continuous or interrupted parallel streaks of megascopicallymassive sulphides and are mostly surrounded by a faint nebulitic “ghost” of disseminated sulphides. ZVd is a special but quite abundant pattern where a fractured and busted calcite core is surrounded by dots, lenses, or sheets of massive and of nebulitic sulphides. The calcite veinlet was broken by the diagenetic compaction and serves as a relative measure of the amount of compaction after its formation. In order to understand the diagenetic history of these various patterns of sulphide occurence, thin, polished sections were made of various subtypes of all patterns. This study revealed four different microscopic patterns of sulphide distribution in regard to its relationship with the carbonate grains. Microscopic observations

Microscopically, the pyrite occurs in essentially four distribution types: (5 massive; (2) as a matrix or network including holes or Mg-calcite grains; (3) densely disseminat-

68

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al.

Fig.2. Stylolite with small amounts of sulphideshide the seam. Patterns Ilc, IId and geodes (I&) in the lower half. The “double lense” of pyrite in the lower left is more resistant to weatherkg than the dolomitic limestone.

Fig.3. Example of pattern IIIb below a shallow-water erosion surface. Also various discoidal aggregate varieties of pattern II present.

DIAGENETIC BEHAVIOUR OF SULPHIDES

69

ed in quantities comparable to those of the calcite; (4) as scarce inter- or intra-granular disseminations in or between the Mg-calcite grains. The pyrite is xenomorphic, subhedral and, more rarely, euhedral. Various features may serve as indications of the diagenetic crystallization sequence and of diagenetic recrystallization. The intra-granular pyrite grains must have formed early, at least before any recrystallization may have taken place. Clusters of distribution type 1-2 must have crystallized after the formation of the idiomorphic carbonate “phenocrysts” which they enclose, but may have accumulated at an early stage, or at least before the main consolidation of the carbonate rock. Large “porphyroblasts” of idiomorphic pyrite measuring from 0.1-2 mm formed occasionally from early massive or almost massive types during diagenetic recrystallization. Inwardly, they still grade into the early mosaic of small pyrite grains (30-50 p in diameter). In the vertical features of ZVu-d, the core corresponding approximately to the nebulitic sulphide haloes is, as a rule, densely cemented by late carbonate matter. This, together with the crosscutting nature, may serve as proof for late migration and deposition of the sulphide matter leading to the vertical features. Fossil shells, so far, have not been found around the geodes. But a process similar (1950) as a cause for geode formation may still have been to that described by CORRENS active, starting from a cluster of decaying organic matter and leading to the precipitation of quartz and pyrite. These two minerals occasionally occur as perfect crystals up to several millimeters in size in the geodes, quartz may also occur on stylolite surfaces. The microscopic observations, only briefly summarized here, together with the megascopic evidence suggests at least four diagenetic generations of pyrite formation: ( I ) The early homogeneously and scarcely disseminated intragranular pyrite (not represented in any megascopic pattern). ( 2 ) The major portion of the layered pyrite patterns, accumulating at early or intermediate stages but crystallizing at intermediate or late stages (probably most of the sulphides of patterns Zb, Ze, g,ZZu-f). (3) The sulphides of the crosscutting patterns, collecting at intermediate stages but crystallizing at intermediate to late stages. ( 4 ) The geode sulphides and perhaps also the sulphides of pattern ZZZc, probably forming at late stages. A most convenient help for dating a pattern is the feature ZVd. The early diagenetic calcite veinlet is congested and broken by compaction. The sulphide haloes and “sheets” surrounding these vertical fissures are only occasionally congested too. This suggests an intermediate to late age. Much additional “cross-evidence ”is available; it further substantiates the conclusions offered here and in the abstract.

Summary

A megascopic and microscopic study of sulphide distribution patterns in,Ordovician dolomite limestones of shallow marine origin has revealed various generations of iron sulphides in regard to the diagenetic crystallization of the main rock constituents. The

PLATE I

DIAGENETIC BEHAVIOUR OF SULPHIDES

71

later generations have occasionally migrated and filled diagenetic partings, veinlets or vugs, and sun-cracks. A textural classification is offered. It corresponds in part to subdivisions in diagenetic generationswhen combined with additional microscopic features. Sulphide patterns are shown to be a convenient clue to the diagenetic history of a sediment.

11. GALENA LOCALISATION IN LATE DIAGENETIC FISSURES IN ALGAL CARBONATE ROCK,

ELVINS MINE, MISSOURI (G.

c. AMSTUTZ)

Fig.4 represents a typical “ore specimen” of rich lead ore from Elvins Mine, Missouri. It belongs to the late Cambrian Bonne Terre Formation and contains distinct brownish dense algal fingers which rest on a shale layer rich in disseminated galena. The top-bottom features at the base of the algal “fingers” are genuine; usually a hollow has been pressed into the shales by the weight of the fingers and mud has formed salt-dome shaped, upwards-trendingdomelets as high as 5 cm above the top of the shale layer. In these inter-finger spaces, some of the galena has accumulated, whereas the buff dense bodies of the fingers contain practically no sulphides. A major portion of the galena is distributed homogeneously throughout the shale layer. In this shale, starshaped “phenocrysts” have formed in some cases and top-bottom features are quite common (although not as distinct as in the sandy shaley layers of Fredericktown, see section 111). Between the algal fingers, there are fissures which die out downwards and upwards and can be shown, by a simple analytical procedure of rock mechanics, to be of late diagenetic age. This mechanical analysis shows that the fingers must have been the stiff elements which did not allow homogeneous compaction and caused the intermediary material to break and to slip or to part. There must not always be movement to form these fissures since the dehydration of the lime ooze during diagenetic crystallization means a reduction of space. Most of this reduction is, of course, taken care of by the diagenetic compaction. However, in an inhomogeneous field of compaction-stress and at the latest stages of compaction, some of the lateral space reduction can not be accomodated by small differential adjustments between grains which leads to vertical “reduction fissures” (German: “Schwundrisse”; see, for example, HUMMEL, 1960). Galena has entered into these late diagenetic spaces and crystallized. The fact that it occurs as a supporting element in both the fissures and the matrix of diagenetic PLATE I

Various subtypes of pattern IV, as well as bedding plane disseminations of pattern q,Ila, Ilc, Ild and

ZZC Plate IA shows a sack-likevertical slump pattern which occasionallyaccompanies pattern I Vb, c, d, The upper portions of the “veins” in Plate IB and C show congestions as drawn in Fig.1, IVd. The “dip” of these sheet-like features is not always vertical; it may cross the bedding planes at almost any angle.

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DIAGENETIC BEHAVIOUR OF SULPHIDES

73

Fig.5. Movement of pore waters during diagenesis (Leduc Riffchain, Canada; after ILLING, 1959).

idiomorphic dolomite supports, together with other observations, the idea of a late diagenetic age of its crystallization. There is no evidence of replacement except for the type describedin section 1V;which appears to be of diagenetic age. A similar late diagenetic accumulation of galena appears to take place on a larger scale also. There is no space for a presentation of full details at this time. However, if we visualizethe diagenetic circulation paths of pore solutions in areef structure (FigS), as demonstrated in petroleum geology (cf. ILLING,1959), the high content of galena in the porous flanks and crests of reefs is perfectly well explained. Late diagenetic phases get moved around and PbS will be precipitated in areas of anaerobic conditions where the decay of organic matter produces NH,. III. GENERATIONS OF DIAGENETIC CRYSTALLIZATION IN THE Cu-Pb-Co-Ni-DEPOSIT

OF

FREDERICKTOWN, MISSOURI

(F. EL BAZ

and G.

c . AMSTUTZ)

The abundance of distinct top-bottom features in the Missouri Lead Belt has been described by the authors (Fig.6) and used as genetic criterium for a syngenetic origin (AMSTUTZ, 1958; AMSTUTZ et al., 1962). In various instances small fissures were observed in the concretionary accumulations or in individual clusters of sulphides. These were filled by the same mineral which was also last in the paragenetic sequence of the concretions; i.e., by galena, and more rarely by chalcopyrite. Fig.7 illustrates an example of large vertical grains of marcasite which are broken parallel to the diagenetic vertical stress which was exerted on sulphide “phenocrysts” or clusters during diagenesis. Some of these marcasite grains broke and the breaks were filled by galena. This is just one more criterion for a later diagenetic age of galena crystallization in the Lead Belt of Missouri and probably in most other carbonate provinces with PbS (cf. AMSTUTZ, 1962).

74 G.

c. AMSTUTZ et al.

9

U

DIAGENETIC BEHAVIOUR OF SULPHIDES

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G. C. AMSTUTZ et

76

d.

IV. SPHALERITE, FLUORITE! A M , GALENA AS DISTINCT DIAGENETIC CRYSTALLIZATION GENERATIONS OF AN OOLITIC PHASE OF THE FREDONIA FORMATION, SOUTHERN ILLINOIS FLUORSPAR DISTRICT (G. c . AMSTUTZ

and WON c. PARK)

In the studies on the genesis of the famous fluorspar district of southern Illinois, virtually only the rich and always quite unusual “ore textures” are described. It is true that these textures differ greatly from the “normal” country rock, and it is easy to see how the genetic theories deviated into speculations about unusual processes (cf. BRECKE,1962). The present study deals with low grade material, the content of which in “ore matter” is too low for the formation of textures differing from the “normal”. One should start here with an objective study in order to understand what factors may have been active in the genesis of ore deposits. The rock samples described here are oolitic portions of the Fredonia Limestone, Hardorff Mine. They only contain from &lo% Pb or Zn. As shown in Fig.8, the sphalerite occurs only in two loci: (I) in the bituminous rims of oolites, and (2) in the meandering stylolite seam traversing the thin section.

I

f‘diagenetic period PddiagenetIc period lshallow burial) (deDOSiffOna1) ~~

clear carbonate cores

1

3d diagenetic perioc (cementation)

----- I

SiO, (quartz. quartzine) bituminous oolitic rings Zn 5 clear corona calcite clear cement calcite stylollte formation

Fig.8. Diagenetic crystallization sequence.

In detail,the ooliticlimestone consists of the following distinct diageneticgenerations: (I) Clear insides of oolites (mosaic or monocrysts of calcite or of concentric “spherules” of chalcedonic quartz). (2) Brownish-layered rims of bituminous carbonates; grain size small to medium. (3) A rim of clear, dog-tooth shaped calcite of medium grain size around the oolites.

PLATE I1

Individual “ooids” with diagenetic sphalerite “idioblasts” within the bituminous portions. Note the four distinct generations pictured in Fig.8. Enlargement: A, B, x 100; C, D, x 50. A, B, C with plain light; D with slightly crossed nicols. Barely transparent idiomorphic patches in A and B, and black patches in C and D are sphalerite.

DIAGENETIC BEHAVIOUR OF SULPHIDES

PLATE I1

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78 G.

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c 0

4

DIAGENETIC BEHAVIOUR OF SULPHIDES

79

(4) Coarse grained matrix calcite, often consisting of only one grain, filling the interstices between the oolites rimmed by generation 3. Frequently a black tar-like, irregular rim follows between generation 3 and 4, or between grains of gneration 4. On the basis of the paragenetic sequence pictured on Fig.8 which corresponds to some 500 oolites with sphalerite, typical examples of which are shown in Fig.9 and Plate 11,we may conclude that the sphalerite crystallized during the second diagenetic stage (cf. DAPPLES, 1959, 1962, for the definition of the stages). This theory finds additional support in observations made on the stylolitic seam which crosses the slide. Here, the sphalerite has been accumulated as a residuum during the Riecke-solution of the oolites (cf. VONENGELHARDT, 1960). The stylolite nature is obvious from the many partially eliminated “ovoids” and the pressure cracked sphalerite which, as a matter of fact, has the same grain size and shape as in the ovoids. Pressure twinning in third generation calcite and the quartz accumulation, formation of autogenic quartz and, finally, the accumulation of hydmcarbon along the stylolitic rims is additional proof for the stylolite nature of the seam and its late diagenetic age. Fluorite and galena occur in a late diagenetic stage and will be described later.

V. THE DIFFERENTIAL LOCALIZATION OF SULPHIDES IN FOSSIL WOOD

(G.

c. AMSTUTZ)

In many fossil wood specimens in coal and in “common” sediments, sulphide fillings are observed. Occasionally more than one sulfide species or more than one type of pyrite is present. The most distinct occurence known to the author is material from Mitterberg, Austria (Fig.10, ll).l Five different types of sulphides are localized in distinctly different portions of the fossil wood, as shown diagrammaticallyin Fig. 11. On the basis of an area corresponding to several hundred wood cells, there is no doubt about the existence of some sort of a differential factor during the implacement of the different sulphides. The physical difference between pyrite I and I1 is reflected by the chagrined, somewhat darker surface of pyrite 11. Pyrite I is cleaner and brighter. It looks as if the chalcopyrite has penetrated and in part destroyed the cell walls (X).Tetrahedrite either destroyed the cell structure (? X)or never penetrated into it. I am grateful to Professor Friedrich for having brought this material to my attention. For a descrip(1954). tion of the complete deposit see KARL(1953), MATZ(1953) and STERK

Fig.10. Cell structure with four types of sulphides in four distinct geometric loci: ( I ) “clean” pyrite (white) within the cells (2) chagrined pyrite in cell walls and, with somewhat smoother,surface and brighter reflecticity,in the “channels” between cell walls (3) chalcopyrite (light grey, strong relief) between cells and cell walls, wherever these textures have been obliterated (4) tetrahedrite (grey) outside but near (5)arsenopyrite(white) idiomorphic grains away from the wood.

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DIAGENETIC BEHAVIOUR OF SULPHIDES

81

82

G.

I

cell interior

I

cell walls

c. AMSTUTZ et al.

I

immediate neighbourhood

I

I I

‘‘ distant “ neighbourhood

j

I

Fig.11. Differential localization of sulphides in fossil wood possibly during diagenetic crystallization. X sipiies possible destruction (diagenetic replacement).

Arsenopyrite never touched it, but occurred as idiomorphic grains in its neighbourhood. If one considers the known fact that pH-Eh relationships between the individual space units of Fig.11 (i.e., the cell center, the cell wall, the immediate and the more distant neighbourhood of the wood) are the more different the less diagenetically destroyed the decaying organic “agents” within these spaces are - then it becomes probable that the most likely factors leading to the observed differentiationin sulphide emplacement are probably those active during diagenetic decomposition. One may, of course, construct a post-diagenetic theory; however, it is easy to show that the number of assumptions necessary is at least twice as large as for a syn-diagenetic origin in a sapropelic environment. This, therefore, may probably be considered to be another typical example for a diagenetic behaviour of sulphides.

VI. CRITERIA FOR DIAGENETIC CRYSTALLIZATION AND DEFORMATIONS IN THE MOUNT ISA SULPHIDE BEDS

(P. RAMDOHR and G.

c. AMSTUTZ)

Introduction

Recent papers on the ore deposits of Mount Isa by FISHER (1960), WALPOLE (1960), LOVEand ZIMMERMANN (1961), and by others discussed many facets of the Mount Isa ore textures so well pictured by BLANCHARD and HALL(1942). All these later papers rejected, in principle, the pan-epigenetic origin proposed by Blanchard and Hall and suggested an essentially syngenetic mode of formation. Many interesting and valuable criteria were developed in the latest papers. One question remained open: the problem of the age of deformation of the sulfide beds. In the discussion of the genetic problem as a whole, one type of information was, to the knowledge of the present authors, left essentially untouched: the information on the age of crystallization of the sulphides,i.e., whether they are diagenetic or post-diagenetic. This is the question of primary crystallization versus re-crystallization in a stress-field

83

DIAGENETIC BEHAVIOUR OF SULPHIDES

foreign to the primary symmetry of the bedding. It is the limited aim of the present preliminary paper to shed some light on this question. The samples on which this study is based were in part collected by the senior author during a recent stay at Mt. Isa (1962) and in part on specimens sent to the junior author by Mr. R. La Ganza in 1958. The senior author wishes to acknowledge the visit to the deposit with Mr. Bennett, Chief Geologist, and to the discussion of genetic problems. On this occasion, he was pleased to note an almost complete agreement on subaqueous slumping as a main cause of the formation of the fabrics discussed below. Independently,the junior author had developed the same ideas during a study of the literature and of samples. Geometricfeatures as criteria for a diagenetic age

Synsedimentary structures, in this paper, are defined as geometric features which have been found in sedimentary primary rocks and bear no relationship to tectonic activity after diagenesis. Such features have been described and defined in numerous papers, for example by SHROCK (1948) and KUENEN(1953). The structures here described are predominantly formed by submarine slumping, where water was the lubricant; however, similar structures are also known to the authors from ‘‘nukes ardentes” or ignimbritic material, where a hot air cushion acted as the “lubricant”. Yet, the latter possibility does not have to be considered in this case. The textural analysis of polished sections of Mt. Isa ore allowed recognition of distinct age relationships in the crystallizationof the various sulphides. This is one part of the evidence. The criteria for age relationships are: ( I ) idiomorphism per se; (2) convex, “aggressive” intergrowth lines of a later mineral B on a semi-idiomorphic, presumably earlier mineral A; (3) filling of cracks in an earlier mineral A by a later mineral B; (4) inclusions of an earlier mineral A in a later mineral B; (5) coatings of a later mineral B on an earlier mineral A.

d

i

a

g

e

n

e

I deposition

i

c

p

e

r

i

o

d

s

I1 s.str:

(mechanical, colloidal. chemical) “gangue minerals” pyrite pyrrhotite sphalerite

t

pore space and

d e p

0

s i t i

0

n

c o m p a c t i o n compaction b (cementation b ) with i Rieckesolution

burial and compaction a (cementation a )

--.-----------.---- ----- -------------------------..--------------I

Fig.12. Tentative, generalized “paragenetic sequence”.

84

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c. AMSTUTZ et al.

Any of these criteria alone was not considered to be conclusive enough for establishing a clear relationship. Idiomorphism, for example, may be an expression of a difference of form e n e r e between two contemporaneously crystallizing phases or a product of later idioblastic growth. Two or more criteria were combined to lead to the tentative, generalized “paragenetic sequence”, as shown in Fig. 12. Except for some late carbonates and quartz, most of the gangue minerals appear to have cxystallized before or contemporaneously with pyrrhotite and pyrite I. In a few cases, however, gangue minerals filled diagenetic “fissuresyyand appear to have been later. Since the Mount Isa ores are often finely bedded and since each bed usually contains only two to five, and rarely less (thus one) or more (thus six or more) phases, the paragenetic sequence of Fig. 12 is a summary over various beds which are connected by cross-cutting “intraformational”, diagenetic features as now will be described. In Fig.13 a clear relationship is seen between two properties of the rock layers and their mechanical behaviour during deformation, (I) the mineralogical composition, and (2) the depth of burial below the (presumably,but quite obviously)free surface of the material on the bottom of the sea. The more gangue (gg) a layer has, the more brittle it behaved during mechanical deformation; the more sphalerite (sl)and, especially, the more galena (gn) it has, the more isotropic (amorphous) it behaved. There is also some pyrite, pyrrhotite, tetrahedrite, jamesonite, chalcopyrite, and cody substance, but all of these phases occur, in this specimen, in small quantities unessential to the mechanical strength. Layer I

Fig.13. Relationship between the mechanical behaviour during the formation on one hand and the mineralogical composition and the depth of burial below the free surface on the bottom of the sea on the other hand.gg = gangue;gn = galena; sl = sphalerite; x 5.

DIAGENETIC BEHAVIOUR OF SULPHIDES

85

is hardly bent. It is the thickest layer with high gangue content and apparently served as the stable base during the movement. Layer 2 consists actually of a series of about ten small beds; according to the terminology applied and defined by LOMBARD (1956), it is really a rhythmite, i.e., an alternation of five sandy-shaly layers with five galena layers. The younger the beds, the more they were affected by the lateral movement which broke layer 3 and caused a micro-overthrust of 2 mm on the left side of the figure. Layer 3 is also composite and consists of two galena layers surrounding a gangue layer. The latter shows minute folds near the overthrust. The following layer 5 shows some internal stratification too. It is to be noted that it did not break, but rather “neutralized” all the lateral movement by a large and several small ondulations and by internal rearrangements within the galena, as can be seen from the geometric distribution patterns of the galena. It thus reacted partly isotropic (amorphous) and partly anisotropic. Layer 6 is a somewhat coarser grained layer also consisting of two or three sublayers which are highly contorted in portions. Two small “injections” into a vertical fissure and a horizontal split in the next upper bed, number 7,are seen. Layer 7 was the last “solid” bed below the massive galena-sphalerite “mud”. It broke up into small fragments during the movement, and many of these fragments are now seen floating in the galena-sphalerite mass. It behaved much more brittle than layer 5 because of its higher gangue to sulfide ratio. Its fragments were not confined by an overlaying layer and floated upward in the sulfide mass, either because of gravitational buoyancy or because of fluid flow within layer 8. A number of geopetal or gravity features are readily seen. One of them was mentioned above and consists of the gradual decrease of mechanical confinement from bottom to top. The layers witH even numbers, 2, 4, 6, served as lubricating surfaces (similar to the listric surfaces of alpine tectonics). It is not difficult to show, by means of methods developed by rock mechanics, that the galena layers must have been in a mechanically amorphous, and thus fluid, state when the movement took place, especially in layers 6 and 8. The mathematical treatment will be published at a later date by the junior author. At this time, it may only be emphasized that an analysis of the stress pattern around the broken portions of layers rich in gangue revealed that it is not possible to establish solid phase transmission patterns of mechanical vectors. Each piece has its own independent symmetry field and the coherence of these fields can only be understood by fluid isotropic (amorphous) flow patterns and not by any deformation pattern in a solid phase, which must always be anisotropic. It is not possible, either, that a solid phase pattern was eliminated by recrystallization because broken grain fragments are still seen within the area of anisotropy, i.e., inside and alongside the fragments of gangue beds. The hypothesis that much or all of the latest generation minerals, galena and in part sphalerite, were still in a colloidal disperse or in another amorphous state is further supported by various primary crystallization phenomena, additional to, the ones mentioned in the text. Perhaps the major one is the fact that both pyrite phenocrysts as well as the gangue layers in unit 8 are overgrown by a layer of sphalerite. The

86

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et d.

Fig.14. Example with a coarse-grained layer of pyrite (brightest white) at the bottom of the sample. Galena from above (white) is filling a fissure between two ends of broken sandy-shaly layers which were pulled apart. Excellent convolute bedding is present within the complex layer following above; x 5.

Fig.15. Essentially the same as shown and analyzed in Fig.13. Note the thrust faults and the folds in subsequent layers in mechanically amorphous relationship with each other; x 5.

DIAGENETIC BEHAVIOUR OF SULPHIDES

87

layered gangue pieces show this corona of sphalerite even around the breaks vertical to the bedding. Most significant is the coincidence of point 3 of the list of criteria with the breakage features of micro- and megastratigraphic units, and also the clear relationship of the crystallization generations one or two, and in certain instances perhaps even more generations of rupture, or with a continuous movement of the strata (compare the “saddle-cracks” in Fig. 16). The younger generations heal or cement the diagenetic ruptures of earlier “phenocrysts” as well as the space between the diagenetically broken or bent and warped fragments of layers. The older the generation of sulphides, the more it is affected by the breakage and the less it takes part itself in the cementing, healing and filling process. Thus, pyrrhotite I and pyrite I are often broken and “healed” by later generations, and sphalerite I is often accumulated mechanically by the moving snow-shovel-shaped broken layers of gangue. The fact that the obviously not dissolved and reprecipitated sphalerite I1 and most frequently galena often enter into fractures and “interstrata veinlets” leads to the conclusion that these phases existed as “mud” when the movements took place which broke up early grains and stiff layers. In addition, the latest generations, especially galena, play still another role which suggests late diagenetic crystallization. In small diagenetic thrust-faults and folds and even in larger folds, disharmonicdifferential folding of shale and sand layers took

Fig.16. A portion of a medium size fold exhibitingfeatures of breakage of the gangue layers caused by isotropic (mechanically amorphous) flow of the galena. This “mineral” was squeezed, when in a fluid state before complete solidification, into the crest of the fold and tore the two gangue layers apart to accumulate them also in the crest. Note the cracks in the crest of the banded major gangue layer; these cracks are filled by galena; x 2.

88

G.

c. AMSTUTZ et al.

place in a matrix of obviously soft PbS-mud. The galena “mud”-layer has acted as a soft matrix which was squeezed into saddles of folds, out of the flanks of folds. This squeezing action is illustrated in Fig.16 and the ruptured shale layer on the sides of the fold is excellent proof for the squeezing movement. This action is similar to the formation of boudins, except that here the matrix must have been fluid. A distinct detail which may be noted at this time is the almost submicroscopic mixture of about s/4 galena with 1/4 gangue-“dust” which occurs, occasionally, either in coarser grained layers or, more often, in the neighbourhood of gangue layers. Again, would the material filling the spaces, which were created by the breakage or the folding, consists of epigeneticproducts of recrystallization, its grain size would naturally be much different from that of the layers from which the material came. Only in the “fissures” is t h i s the case, but not so much within folded areas. Also, Riecketype corrosion which, along stylolite faces, is excellent proof for the presence and interaction of two solid phases, is absent in general. The coincidence then of the paragenetic sequence with the behaviour in micromechanical diagenetic movements speaks a clear language for a diagenetic age of crystallization of the major phases. This does not exclude any later recrystallizations which may have been caused in tectonically stressed zones. However, such stresses should be evident through transsecting lineations or s-planes, and through Riecke-reduction of normal grains. In samples studied, the transverse pyrrhotite and micas may perhaps belong to a later stress period. Some of the persistent fractures and a part of the recrystallizations may also extend into, or belong to the post-diagenetic period. The extent and characteristics of these later features are presently being investigated. In its main traits, however, these ores afford a very excellent example for the diagenetic behaviour of sulphides.

ACKNOWLEDGEMENT

In connection with section I1 we wish to express at this time our thanks to the St. Joseph Lead Company and especially to Dr. F. Snyder, Chief Geologist, for the many interesting discussions and field trips, as well as for the permission to work on specimens collected from their mines. SUMMARY

In the present world-wide discussion on epigenetic versus syngenetic theories on ore formation, there are two areas where not enough information and criteria have been developed yet towards a satisfactory answer: The paleogeographic loci and the possible diagenetic position of sulphides. The foregoing six short papers on the diagenetic behavior of sulphides represent progress reports on work done in the second area, the diagenetic position and role of sulphides. The first report comprises patterns of pyrite-marcasite formed at various stages

DIAGENEIlC BEHAVIOUR OF SULPHIDBS

89

during diagencsis. One of the main purposes was to show that sedimentation and diagenesis do produce cross-cutting features. It is, therefore, incorrect to use them as proofs of “hydrothermal” origin. Purposely, these patterns were first described for a non-commercialmineral and for non-commercialconcentrations. The comparison with commercial materials described in the later reports may convince the unaware of the validity of this approach. The second, third and fourth papers offer examples of diagenetic features of sulphides in three distinct districts and sediments of the MississippiValley Pb-Zn-CuCo-Ni-deposits. The fifth paper describes a differential pattern of sulphide formation within wood. The sixth paper considers fabric patterns in the Mount Isa layered sulphide deposits which are best understood as having formed during diagenetic compaction.

REFERENCES

AMSTUTZ, G. C., 1958. Syngenetic zoning in ore deposits. Proc. Geol. Assoc. Can., 11 :95-1 13. AMSTUTZ, G. C., 1963. Bemerkungen zur Genese von kongruenten Blei-Zink-Lagerstatten in Sedimenten. Ber. Glcol. Ges. Berlin, Sonderh., 1 : 3142. AMSTUTZ,G. C., UHLEY, R. P. and EL BAZ,F., 1961. Sedimentary features in the layered sulfide deposits of Fredericktown, Missouri. Geol. SOC.Am., Spec. Papers, 68 : 128 pp. BLANCHARD, R. and HALL,G., 1942. Rock formation and mineralization at Mount Isa. Proc. Am. Inst. Mining Met. Engrs., 125 :1-60. BRECKE, E. A., 1962. Ore genesis of the Cave-in-Rock fluorspar district, Hardin county, Illinois. Econ. Geol., 57 :499-535. C. W., 1950. Zur Geochemie der Diagenese. Geochim. Cosmochim.Acta, 1 :49-54. CORRENS, DAPPLES,E. C., 1959. The behavior of silica in diagenesis. In: Silica in Sediments - SOC.Econ. Paleontologists Mineralogists, Spec. Publ., 7 : 36-54. DAPPL~S, E . C., 1962. Stages of diagenesis in the development of sandstones. Bull. Geol. SOC.Am., 73 :913-934. FISHER, N. H., 1960. Review of evidence of genesis of Mt. Isa ore bodies. Rept. 21st Intern. Geol. Congr., Copenhagen, 16 : 99-111. GRAF,D. L. and LAMAR, J. E., 1950. Petrology of Fredonian oolite on southern Illinois. Bull. Am. Assoc. Petrol. Geologists, 34 : 2318-2336. HUMMEL, P., 1960. Petrographie, Gtiederung and Diagenese der Kalke im Oberen WeissenJuru der Schwubischen Alp. Thesis, Geol. Palaontol. Inst., Tech. Hochschule, Stuttgart, 87 pp. ILLING, V., 1959. Deposition and diagenesis of some Upper Paleozoic carbonate sediments in western Canada. World Petrol. Congr., Proc., 5th, N.Y., 1959,l (2) : 23-50. KARL,F., 1953. Anwendung gefiigeanalytischer Arbeitsmethodenam Beispiel eines Bergbaues (Kupferbergbau Mitterberg, Salzburg). Neues Jahrb. Mineral., Abhandl., 85 :203 pp. PH. H., 1953. Significant features of graded bedding. Butl. Am. Assoc. Petrol. Geologists, KUENEN, 37 : 1044-1066. LOMBARD,A., 1956. GPologie skdimentaire.Les SPries marines. Masson, Paris, 722 pp. LOVE,G. and ZIMMERMANN, D. O., 1961. Bedded pyrite and micro-organisms from the Mount Isa Shale. Econ. Geol., 56 : 875-896. MATZ,E., 1953. Die Kupfererzlagerstatte Mitterberg (Miihlbach am Hochkonig, Salzburg). Mitt. Abt. Mineral., Landesmuseum Joanneum, Sonderhef, 1953 : 7 pp. SHROCK, R. R., 1948. Sequence in Layered Rocks. McGraw-Hill, New York, 507 pp. STERK, G., 1954. Vererzte Manzenreste aus der Kupferkieslagerstatte Miihlbach/Hochkonig (Salzburg). Berg- Hiittenmann. Monatsh. Montan. Hochschule Leoben, 99 (3) :48-51. STRAKOV, N. M., 1953. Diagenese der Sedimente und ihre Bedeutung fur die Bildung ddimenttirer Erzlagerstatten.Zzv. Akad. Nuuk S.S.S.R., Ser. Geol., 5 : 12-49.

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VON ENGELHARDT, W., 1960. Der Porenraum der Sedimente. Springer, Berlin-Heidelberg-Wien, 207 pp. WALWLE,B. P., 1958, 1960. Discussions of the “source bed concept”. &on. Geol., 53 : 890-893; 55 : 615-617.

SUPERGENE SULFIDES AND SULFATES IN THE SUPERGENE ZONES OF SULFIDE ORE DEPOSITS P. ZUFFARDI and I. SALVADORI Istituto di GiacimentiMinerari, Universit2di Cagliari, Cagliari, Sardinia (Italy)

INTRODUCTORY REMARKS

In discussions on the possibilities of ore genesis in sedimentary environments, the question is often raised whether recoverable sulfides and sulfates can form under conditions existing on or near the surface of the crust of the earth. The oxidation zones of sulfide deposits offer perhaps one of the best examples exposed of mineral formation under surface conditions. Barites were described from various oxidation zones, for example by SWRNOW (1951-1954, p.61) and AMSTUTZ and WARD (1956, p.24). Supergene sulfides are abundant in cementation zones (“supergene enrichment zones”) of sulfide deposits. The present authors, therefore, believe that a discussion of problems of “sedimentology and ore genesis” should include a few examples of sulfides and sulfates which formed in deiinitely supergene conditions. Smirnow has offered an extensive summary on “the oxidation zone of sulfidic ore deposits.” R. M. Garrels was the first to summarize laboratory information on stability ranges in supergene solutions, whereas L. G. M. Baas Becking pioneered actual occurrences of present day sulfide deposition and their laboratory counterparts.

I. SUPERGENE BARITES FROM SARDINIA

(I. SALVADORI and P. ZUFFARDI)

The following is a brief report on some occurrences of probably supergene barites in Sardinia. Theoretically, two types of supergene deposition are possible: (a) mechanical (mainly residual) deposition; (b) crystallisation from solutions. In nature, these two types are intimately interwoven, and both may be present in a single deposit. ( I ) An excellent example of the coexistence of mechanical and chemical deposition of barite was found in an oolitic iron-barite orebody capping Cambrian limestones, intersected by massive barite veinlets. In this deposit, the following paragenetic assemblage was observed: A breccia of white opaque barite fragments cemented by oolitic iron ore minerals (Fig. l), and large

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Fig.1. Breccia of white opaque barite fragments cemented by oolitic iron ore; x p.5.

Fig.2. Large perfect crystal of yellow transparent barite embedded in the same oolitic iron ore as Fig.1; x 0.5.

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93

Fig.3. Barite crystal group occurring in a crevice of Monteponi oxidized ores: the limonitic wall of the crevice is visible: natural size.

perfect crystals of yellow transparent barite (Fig.2) embedded in similar oolitic iron ore. It is suggested that the two types of barite have a different origin: the first generation consists of a mechanical concentration of eroded primary barite veins; the second generation of a crystallisation from ground water solutions. (2) An outstanding example of supergene BaSO, is, in our opinion, the presence of BaSO, in anglesites. According to Ramdohr (as quoted by DANA,1960, p.424) some anglesites contain more than 7 % BaSO,. Anglesites from Montevecchio mines studied by us all contained some BaSO, (and SiO,); the lowest values are 0.09% BaSO, (0.018 SiO& the highest values are 3 % BaSO, (1.6 % SiO,). Montevecchio baritic anglesites appear perfectly homogeneous in thin sections and, consequently, one may assume that BaSO, and PbSO, form solid solutions. Undoubtedly, in these cases, BaSO, is syngenetic with PbS0, and, consequently, it has to be supergene, deposited by weathering processes. The same genesis is proposed for the barite crystal groups that occur in crevices of some oxidized ores; Fig.3 shows one of them, in which the limonitic wall of the crevice is clearly visible. Other instances of probably supergene barites are found in other portions of the same mine. Fig.4 shows perfectly formed, transparent, slender prisms of barite associated with calcite-aragonite coating the walls of a large fissure across a main lead-zific vein of the Montevecchio mine. In the same mine, perfect crystals of transparent, tabular

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Fig.4. Slender prisms of barite associated with-calcite-aragonite coating the walls of a large fissure across a main lead-zinc vein of Montevecchio mine; x 0.33.

barite in association with monheimite were found. No instances of this supergene barite have been encountered outside of the ore body. Other minerals occurring with this barite type are: gypsum, hemimorphite, marcasite, and pyrite. In all cases, barite and its allied minerals are deposited along the side walls of fault fractures that cut across and displace the ore-body. Faulting is alpine in age, whereas the ore is older. In some cases, barite crystals were found which formed a bridge between the two sides of minor fractures. This observation suggests that barite deposition was not only later than fracturing and faulting, but also later than any movement along those fractures and faults. In the opposite case, if the deposition was earlier, one would expect that barite and its allied minerals would be broken. If one considers that probably some movement took place in Quaternary and perhaps even in the most recent times, one may conclude that the barite in the fissures is very recent; at least post-alpine. On the other hand, the association barite-gypsum-carbonates-marcasite-pyrite points to a supergene deposition by descending ground waters that percolated the fractures along the ore-body and collected the material from it. The main unresolved problem is the source of barium. Present investigators are attempting to find criteria for these sources. More details on local geology and mineralogy are given in the papers of the present authors listed in the bibliography.

SUPERGENE SULFIDES AND SULFATES 11. SOME EXAMPLES OF SULFIDES OF Cd,

95

Hg, Fey Pb, AND Zn, REGENERATED BY OXIDATION-

REDUCTION PROCESSES IN SARDINIA (P. ZUFFARDI)

Summary

Attention is called to some examples of possible regeneration of sulfides of Cd, Hg, FeyPb, and Zn by supergene processes in the oxidation-cementation zones of sulfide deposits in Sardinia. Example 1: Deposition of greenockite on galena

A thin film of microgranular greenockite is spread on galena along cleavage surfaces, grain boundaries and minor fractures. The sample was collected in a cadmiferous sphalerite-galena vein (Sos Emattos), just below the water table. This example may be considered to be a good illustration of the “Schiirmannseries” of reactivity. Example 2: Deposition of cinnabar in association with lead oxides on galena

A red crust of cinnabar associated with lead oxides (whitish yellow) is deposited on corroded galena. The order of deposition is: galena-lead oxides (mainly cerussite)-cinnabar. The sample was collected above the water table in a lead-zinc ore-body in dolomite wall rock (at Monteponi). Mercury may derive from weathering of mercuriferous sphalerjtes. Here again, another example of the validity of the Schiirmann series is seen; just a very small amount of H,S - so small as to leave cerussite unaffected and that can be available even in oxidizing conditions - is able to precipitate Hg, the element with the highest affinity for sulfur of all metals of the Schiirmann series. Example 3 and 4: Deposition of marcasite andpyrite

Example 3 shows drop-like deposition of marcasite-pyrite along a late crevice in quartz. Example 4 shows stalactitic deposition of marcasite; internal holes are visible in some cases. The original length of the stalactites reached 15 cm (Fig.5). Both these types of deposition call for crystallisation from solutions with reducing environments during or after the oxidation state of the deposits. Examples 5-10: Deposition of colloidal sphalerite and galena in the oxidatjon zone

These samples have been collected at various depths along the Montevecchio lead-

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Fig.5. Stalactiticmarcassite from a crevice in Montevecchio mine; x 0.66.

zinc ore-body from about 10 m below the outcrops on the surface to about 500 m below the surface (200 m below sea level). Example 5 shows nodules of botryoidal sphalerite deposited on top of partially dissolved ankerite (Fig.6). Example 6 consists of gypsum (platy white crystals) in association with the same type of sphalerite. Examples 7 and 8 show reniform to botryoidal sphaleriteupon which some embryonal crystals of galena grew (Fig.7). Examples 9 and 10 represent the same situation in polished section. Galena crystals are arranged along the boundaries of the sphalerite “shells” and/or in contraction fissures in the external portions of the sphalerite nodules. On the basis of examples 5-10 a paragenetic order of deposition may be established: galena was deposited during or after sphalerite. This fact would be in contrast with the Schurmann series if one assumes that zinc and lead have circulated in true solution. Perhaps, in this case, zinc sulfide was formed from a colloidal suspension, while lead was circulated in ionic solution.

Examples 11-13: Deposition of galena andlor marcasite onlor with barite The samples in this case originated from deep levels of the Montevecchio lead-zinc mine.

SUPERGENE SULFIDES AND SULFATES

Fig.6. Botryoidal sphalerite on top of partially dissolved ankerite; x 0.5.

Fig.7. Botryoidal sphalerite upon which two embryonal crystals of galena are visible; x 8.

97

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Fig.8. Massive galena coating tabular, probably supergene, barite crystals; natural size.

Examples 11 and 12 consist of massive galena coating tabular transparent crystals of barite (Fig.8). As discussed in the previous paper, this barite has a supergene origin. If this is the case, the galena would also have formed by supergene solutions. (No reference is made at this time to the major galena masses of the Montevecchio mine.) Example 13 shows marcasite nodules covered by and/or covering the barite of examples I 1 and 12: one may apply the same interpretation for its genesis as to the galena. Example 14: Deposition of suyur into pockets of the oxidation zone

The sample has been collected in the outcrops of Montevecchio. Small spots of granular sulfur (yellow) are distributed into a limonite pocket, in association with hemimorphite (acicular vitreous crystals in the pocket) and cerussite (short vitreous crystals outside of the pocket). This is to demonstrate the possibility of local reducing conditions in generally oxidative environments.

SUMMARY

Some examples of barite and of various sulfides deposited in late supergene fissures

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99

and in the oxidation-cementation zone of sulfide deposits in Sardinia are described. Paragenetic evidence supports the view that supergene waters may be considered to be “ore solutions” capable of fonning sulfate and sulfide depositions.

REFERENCES

Ahlsmz, G. C. and WARD, H. J., 1956. Geologia y mineralizaci6n del deposit0 de plomo de Matagente, Cerro de Pasco, Peru. Bol. Soc. Geol.Peru, 30 : 13-31. DANA, J. D., 1960. m e System of Mineralogy,7 ed. Wiley, New York, 2 : 1124 pp. SALVADORI, I., 1951. Su alcune particolari mineralizzazioni del Sulcis (Sardegna Sud-Occidentale). Rend. Assoc. Mineraria Sarah, 65 (8) : 58-71. SUIRNOW, S. S., 1954. Die Oxyahtionszone surjidischer Lqgerstatten. Akademie Verlag, Berlin, 312 pp. (Russian edition 1951). ZUPPARDI, P., 1960. Segnalazione della presenza di Monheimite fra i minerali del giacimento di Montevecchio. Rend. Assoc. Mineraria Sarah, 64 (8) : 5-9. ZUPPARDI, P., 1962. Fenomeni di ricircolazione nel giacimento di Montevecchio e I’evoluzione in profonditil della sua mineralizzazione. Rend. Assoc. Mineraria Sarah, 66 (1,2) : 17-73. ZUPPARDI, P.,1963. Fenomeni di ricircolazione nel giacimenti sardi a solfuri. Rend. Assoc. Mineraria Sarda, 67 (7) :5-28.

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DISCUSSION OF PAPERS IN PART A

A . Bernard (France):

A propos de la communication de L. Love: Pyrite des Malines et du Soulier (Gaid). Elles montrent frequemment une evolution esquisske dans Fig. 1.

r6lique de texture en frarnboise

pyrite

Fig. 1.

D . H . Welte (Germany): With reference to the paper by L. Love: If one dissolves the little pyrite globules with HNO,, one can find a kind of a network of organic matter. D. di Colbertaldo (Italie): A propos de la structure microframboidale illustree par L. Love, de pyrite, je veux remarquer d’avoir observe plusieur fois dans les calcaires Ladinique et dans les dolomites anisiques des Alpes Meridionales, des veins microscopiques avec spherulites framboidales de pyrite. P. Zufsardi (Italy): Referring to L. Love’s paper on the possibility of low temperature sulfide deposition, I wish to present two examples which, in my opinion, can be taken as a proof that some sphalerite and some galena may be deposited at a low temperature; namely, the temperature of weathering. The first example refers to mammillary sphalerite on corroded ankerite. The sample was collected on outcrops of the Montevecchio lead-zinc mine (Sardinia). I think that the corrosion of ankerite and the deposition of sphalerite are linked, and both depend on local variations of oxidation-reduction conditions. The second example refers to embryonal galena growing on mammillary sphalerite. The sample was collected on a lower level in the same mine, where reducing conditions were prevalent. If more time was available, I should like to present more instances of sulphide deposition at low temperatures by weathering processes; namely: (I) pyrite-marcasite, in drop-like little masses and in stalactites; (2) greenockite on galena; (3) cinnabar on I lead-oxides. Of course I wish to emphasize that the samples presented by me are, in my opinion,

102

DISCUSSION OF PAPERS IN PART A

connected only to weathering processes and they do not involve any implication on the general genesis of the main ore-bodies from which they come. H. J. MacGiIlavry (The Netherlands): Does Mr. Bernard consider his haut-fonds hypothesis as an alternative to the hypothesis of late volcanic exhalations? Some writers would consider it necessary to have depressions, rather, of the sea-floor. However, both would then consider the configuration of the sea-floor as the main cause of metal-concentration. This however does not necessarily mean that these hypotheses are alternative to the hypothesis of submarine volcanic exhalations. That hypothesis would also presumably need some conditions of sea-floor configuration in order to cause the ore to be formed. Isn’t it necessary to consider the entire geologic context? A. Bernard (France): L’hypothtse purement skdimentaire s’oppose 21 l’hypothtse exhalative-skdimentaire, dans la mesure oa cette dernitre se veut unique. La nature de l’apport exceptionnel de mktaux lourds dans un site skdimentologique pitge doit &re recherchke dans l’histoire gkologique de l’environnement du gite: (1) Skries transgressives sur un socle longtemps kmerg6 (milieux kpicontinentaux), absence de manifestations effusives, par exemple, province sous-cdvenole; il semble ici I’apport le plus probable soit terrigtne. (2) Skries gkosynclinales (mio-gkosyclinales) a volcanisme sous-marin pr6orogknique, visiblement en liaison spatiale et temporelle avec les minkralisations: la, et si j’en crois H.-J. Schneider et A. Maucher, il semble que l’apport le plus probable soit volcanique-exhalatif. Ma communication n’a donc d’autre but que de donner droit de citk 21 l’apport terrigtne sans exclure pour autant l’apport exhalatif. Ph. Launey (France): A propos de la communication d’ A. Bernard: L‘analyse gkochimique en roche, portant sur 5.000 kchantillons du gite de zinc de Figeac et de sa pkiphkrie, montre que ce gite est ceinturk d’une anomalie negative en zinc: le fond gkochimique qui entoure le haut-fond a une valeur Cgale au tiers de celle trouvke rkgionalement. La combe de variation du fond gkochimique dans le sens bassin haut-fond ainsi &re schkmatiske comme en Fig.2. Cette anomalie nkgative n’est pas l’dquivalent de signe E

coupe schematique

N

Fig.2.

DISCUSSION OF PAPERS IN PART A

103

inverse de l’“anoma1ie positive” que constitue le gisement. Elle lui est nettement infkrieure. P . Routhier (France): Observe que le raisonnement d’A. Bernard suppose que la composition de la lame d’eau varie peu suivant le “sibe”, la position au-dessus du haut-fond ou non; qu’il n’y aurait pas d’effet de “barribre chimique”. A . Bernard (France): Le schkma que j’ai proposk se place dans les conditions les plus dkfavorables: la dissymktrie de rkpartition des teneurs par effet de barribre lors du d6pBt ne peut qu’augmenter le taux de concentration du versant p l a d “sous le courant”. P . Routhier (France): Je demande a H.-J. Schneider des prkcisions sur le lien spatial entre produits volcaniques et minkrais dans les Apes orientales. H.-J. Schneider (Germany): The minerals derived from volcanic ashes do not always occur within the same stratigraphic horizon as the ore beds. But this is not necessary in order to support a common origin since, in active volcanic areas, the exhalation products do not always coincide exactly with either the horizons of ash beds or the lavas. R. W. van Bemmelen (The Netherlands): During my field studies of the Gail-Alps with students of the Geological Institute of the State University, Utrecht (The Netherlands), I also arrived at the conclusion that the occurrences of lead-zinc ores in this belt (to which belong the ore deposits of Bleiberg-Kreuth at their eastern end, near Villach) are syngenetic Ladinian deposits which have been remobilized during the Tertiary alpine orogenesis. These views have been stated in my papers on the Gail-Alps (“Beitrage zur Geologie der Gailtaler Alpen”, I and II) published in the Juhrbuch der Geologischen Bundesunstult, 1957, 100 and 1961, 103. Therefore, I fully agree with the views expressed by H.-J. Schneider in his paper presented to the Symposium on sedimentology and ore genesis at Delft. Ph. Launey (France): A propos de la communication de G. C. Amstutz: J’ajouterai que l’on peut trouver des relations non plus qualitatives m a i s bien quuntitutives entre certaines figures saimentaires et la concentration des m6taux lourds: Par example, dans les gisements stratoides de zinc du Lias infkrieur de Figeac (France). Les couches minBralis6es de

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DISCUSSION OF PAPERS IN PART A *

Fig.4.

ces gisements se prksentent en lentilles allongks nord-sud, de 700 m A 1 km de long, penttes ver l’ouest et adossCes A des hautfonds. Ces minCralisations sont associies A des slumping. La concentration du zinc, le gradient isopaque dans le sens haut-fond -+ bassin pkriphkrique, l’intensitk des slumping varient du nord au sud qu’en Fig.3. Quelques mbtres au dessus du gisement un lit de 10 cm de shale dolomitique noir contient des terriers. La longueur de ces terriers, leur frkquence varient du Nord au sud ii l’inverse de la relation prtcedente (Fig.4). G. Miiller (Germany): With reference to the paper by P. Zuffardi: Determinations of solubility of BaSO, in different solutions (H,O, H,O-NaCl, seawater etc.) are at present being carried out by H. Puchelt in Tiibingen. P. Zufardi (Italy): In reply to the question of H.-J. Schneider: The solubility of BaSO, is thought to be very low. This statement is doubtful as there may be some environment (special atmosphere enriched in C1 by sea-wind, for instance) in which BaSO, can be taken in solution. When I find anglesite containing BaSO,, syngeneticwith it, I am compelled to think that BaSO, has a very similar story to that of PbSO,! H. Harder (Germany): With reference to the paper by P. Zuffardi: Perhaps the solutions forming the baryte are not only weathering solutions; the solubility of BaSO, in different types of solvents is very low. Perhaps the solutions are formed below the surface by wells.

PART B

O X I D A T E D E P O S IT S

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KOHLENSAUERLMGE ALS EINE EISENQUELLE DER SEDIMENTAKEN EISENERZE HERMANN HARDER

Mineralogisches Institut, Wesrfiilische WiIheIms-Universitat, Miinster (Deutschland)

EINLEITUNG

Die Anreicherung des Eisens in marinen, sedimentaren Lagerstatten kann ( I ) durch reine Verwitterungsvorgange erfolgen (z. B., bei den Minette-Eisenerzen) oder (2) das Eisen kann durch vulkanologische Prozesse zugefuhrt worden sein (z. B., bei den Eisenerzen vom Lahn-Dill-Typ). Genetisch verschiedeneEisenerze konnen durch den Spurenelementgehalt der reinen Proben (frei von Tuff bzw. Ton) unterschieden werden. Die Eisenerze des MinetteTyps, die ihr Eisen aus Verwitterungslosungen erhalten haben, zeichnen sich durch einen hohen Gehalt an Ti, Cr, V, P und vor allem an Aluminium aus. Die Eisenerze des Lahn-Dill-Typs zeigen geringe Gehalte an diesen Elementen. In dieser Arbeit soll nur uber die Entstehung der Eisenerze vom Lahn-Dill-Typ gesprochen werden. Ein umfangreiches Literaturverzeichnis iiber die Lahn-Dill-Erze enthalt HENTSCHEL (1960).

Die hamatitischen Eisenerze, die an der Grenze des Mitteldevon zum Oberdevon in Deutschland zur Ablagerung gelangten (Lahn-Dill-Eisenerze), werden seit langem mit dem geosynklinalen Vulkanismus dieser Zeit in genetische Verbindung gebracht. Nach HARBOT (1903) nahm man an, dass untermeerische Exhalationen von FeC1, die Erze gebildet haben. In dem Meereswasser reagierte das FeCl, unter Bildung von Hamatit: 2 FeCl,

+ 3 H 2 0 = Fe20, + 6 HCl

Ebenso soll die Kieselsaure als fluchtiges Chlorid zugefuhrt worden sein. Naturbeobachtungen an einigen aktiven Vulkanen, wo nach Ausbriichen Eisenoxydkrusten (die wahrscheinlich aus FeCl, entstanden sind) beobachtet werden, scheinen diese Annahme zu bestatigen. Gleichzeitig findet man aber an diesen Vulkanen Sulfide, vor aliem von Blei, Zink, Kupfer, Molybdan, etc. Diese Verhaltnisse wurden zur Erklarung der Lahn-Dill-Erze herangezogen. SCHNEIDERH~HN (194 1) war es, der dieser Theorie allgemeine Anerkennung verschaffte. Gegen die Annahme der exhalativen Zufuhr des Eisens und der Kieselsaure in chloridischer Form sprechen aber eine Reihe von geologischen und geochemischen Fakten: ( I ) Die fur die Sublimation der Chloride erforderlichen hohen Temperaturen von

108

H. HARDER

mehreren 100°C konnen auch in einem Nebenmeer nicht wahrend geologischer Zeiten vorgelegen haben; denn die Eisenerzbildung ist kein sporadischer, kurzfristiger Vorgang, sondern vielmehr finden wir in dem Grenzlager in den unteren Schichten (MATERN, 1931) eine Fauna, die fur das obere Mitteldevon spricht, wahrend in den oberen Horizonten oberdevonische Fossile vorkommen. (2) Die bei der Hydrolyse der Chloride freigewordene Salzsaure hatte das pH im Meerwasser wesentlich verandern mussen. Die Fauna beweist aber, dass normale pH, sowie auch normale Temperaturbedingungenvorgelegen haben. (3) Die Erze sind zum allergrossten Teil in Zeiten vulkanischer Ruhe zur Ablagerung gelangt. Nimmt man aber eine Zufuhr von Eisen in chloridischer Form an, wie sie bei aktiven Vulkanen wahrend der Eruption und unmittelbar danach vorkommt, so musste man auch in den Eisenniederschlagen die vulkanischen Produkte beobachten konnen. (4) Der Spurenelementgehalt der Lahn-Dill-Erze spricht aber vor allem gegen eine exhalative Zufuhr der Metalle als Chloride. Es ist zu erwarten, dass nicht nur das Eisen und die Kieselsaure angereichert werden, sondern auch die anderen fluchtigen Metallchlorideentsprechend ihrem Dampfdruck und der Haufigkeit in den Gesteinen. Die Chloride von P, Sn, As, Ti, Al, Sb, Mo, Hg haben hohere Dampfdrucke als das FeCl,. Diese Elemente sind aber nur in geringer Menge in den Erzen enthalten. Ausserdem weiss man von der technischen Anreicherung der Schwermetalle mittels Chlorgas, dass Eisen aus den Oxyden erst zwischen 800-900°C in die Chloride ubergeht, das Si02erst bei ca 1500°C.Es ist so auch aus diesem Grunde unwahrscheinlich, dass Eisen und Kieselsaure als Chloride angereichert werden.

UNTERSUCHUNGEN AN REZENTEN KOHLENSAUERLINGEN

Urn eine plausible Vorstellung uber die Entstehung der Lahn-Dill-Erze zu geben, erschien es notwendig, ‘die rezenten Eisenausscheidungen einer Untersuchung zu unterziehen. Die hamatitischen Lahn-Dill-Eisenerze zeigen in ihrem Chemismusviele Parallelen zu den Niederschlagen der Eisensauerlinge, vor allem durch einen hohen $30,-Gehalt und geringe Gehalte an Al, P, Ti, Cu, Pb, etc. Es wurden so verschiedene Eisensauerlinge einer genaueren Untersuchung unterzogen (Tafel I): Kohlensauerlinge in der Umgebung von zeitweise tatigen Vulkanen (Xtna, ltalien; Santorin, Griechenland); verschiedene Kohlensauerlinge als postvulkanische Nachwirkung in der Eifel; Kohlensauerlinge in der Dachla-Oase (Agypten), die nicht im unmittelbaren Zusammenhang mit vulkanischen Gesteinen stehen. Bei allen Quellen handelt es sich urn niederthermale (bis 30°C) Kohlensauerlinge. Als Quellgas kommt neben Kohlensaure auch Stickstoff vor. Das pH liegt um 6 und wird durch die Kohlensaure-Ionen erzeugt. Neben Kieselsaure sind in den Quellwassern Fe2+-, Mn2+-, Mg2+-, Na+-, K+- und Ca2+-Ionen vorhanden. Der Chloridgehalt ist da, wo keine anderweitigen Zufliisse vorliegen, sehr gering. Kommen die Wasser in den Bereich der sauerstoff-

109

KOHLENSAUERLINGE ALS EISENQUELLE

haltigen Oberflache, so bleibt das Fe2+nicht mehr stabil und wird zu Fe3+oxydiert. In diesem pH-Bereich ist das Fe3+aber praktisch unloslich und es flockt als rontgenamorphes Eisenhydroxyd aus. Diese positiv geladenen Eisenhydroxyd-Sole flocken die negativ geladene Kieselsaure aus und nehmen so grossere Mengen Kieselsaure auf. Die zunachst ausgeflockten Niederschlage sind arm an Calcium und Mangan und reicher an Eisen und Kieselsaure. Calcium und Mangan werden bei Iangerem Stehen der Losung und vor allem bei erhohten Temperaturen (was mit einer C0,-Abgabe verbunden ist) in grosserer Menge ausgeschieden. Der Eisengehalt in den Kohlensaurewassern ist nicht gross (bis 50 mg/l H,O). Diese Mengen konnen aber, wie die rezenten Beispiele zeigen, Eisenlagerstatten in geologischen Zeiten bilden. Es ist moglich, dass es Obergange von den kalten, etwa neutralen Kohlensaurequellen zu heissen, sauren Quellen gibt, die vor allem unmittelbar nach einer aktiven vulkanischen Tatigkeit auftreten. Die heissen Quellen konnen neben Eisen auch sehr grosse Gehalte an Aluminium aufweisen und an anderen Schwermetallen, wie Zink, Kupfer, Arsen etc. Durch das Ausfallen der Eisenniederschlage aus den Kohlensauerlingen wird so das chemische Ausgangsprodukt fur die Bildung der beiden Erztypen geschaffen: hamatitische Erze mit Kieselsaure oder mit Kalk als Gangart. TAFEL I ZUSAMMENSETZUNG VON EISENNIEDERSCHL~~GENAUS MINERALQUELLEN

Fundort

Kameni-Inseln, Santorin, Griechenland Paterno, Atna, Italien Wehrer Kessel, Eifel, Deutschland, verschiedene Quellen Welschwiese, Wehrer Kessel, Eifel, festes Eisenerz Dachla-Oase, Agypten

SiO, %

Fe,O, %

18

58

21 7-20

22

16,8 15

40-65 54,2 41,5

Die aus den Kohlensauerlingen ausgeflockten Hydroxyde sind rontgenamorph. Diagenetische und metamorphe Vorgange werden im Laufe der geologischen Vergangenheit diese Hydroxyde in mehr oder weniger gut kristallisierten Hamatit und Quarz umgewandelt haben. Feine Verwachsungen von Quarz und Hamatit sind auch heute in den Erzen noch zu beobachten. Finden die zugefuhrten karbonathaltigen Wasser keine oxydierenden Bedingungen im Fallungsraum vor, so kann das Eisen in anderer Form ausgeschieden werden: Eisenkarbonat kann ausfallen in einem Meeresbecken, dessen Wasser frei an Sauerstoff und Schwefelwasserstoff ist; Eisensulfid wird sich bilden, wenn das Wasser H,S enthalt. Bei diesen verschiedenen Arten der Fallung des Eisens werden andere Spurenelemente angereichert. Bei primar ausgeschiedenem Eisenkarbonat wird der Gehalt an Mangan und Calcium hoher sein, bei der sulfidischen Fallung der Gehalt I an Schwermetallsulfiden. Wahrscheinlich ist das Eisen durch die Kohlensauerlinge aus dem Nebengestein

110

H. HARDER

TAFEL I1 CHEMISCHE ZUSAMMENSETZUNG DES QUELLWASSERSUND DES DARAUS AUSGEFLOCKTEN EISENNIEDERSCHLAGESIM WEHRER KESSEL

Im Eisenniederschlag % (in Oxyden angegeben, H 2 0frei berechnet)

Si02 Fez+ Mn2+ M3+

Ti4+

Ba2+ Ca2+ Mg2+ Sr2+

Na+ K+ Li+ Rb

HC0,-

c1-

so42-

HP042-

60,8 18,8

4,1 0,3 0,005 0,Ol 64 404 0,37 100

52 ca.0,l positiv 765 13,6 4,6 0,27

0,02 0,24(P20.5)

ausgelaugt worden. Es gibt keinen sicheren Hinweis dafur, dass es sich um rein vulkanisch zugefuhrtes Eisen handelt. Die an den rezenten Kohlensauerlingen zu beobachtenden physikalisch-chemischen Bedingungen erklaren die Verhaltnisse, die auf Grund geologischer Beobachtungen bei der Ablagerung der Lahn-Dill-Erze geherrscht haben mussen: normale pH- und Temperaturbedingungen wahrend der Ablagerung. Die Forderung von Kohlensauerlingen kann bei vulkanischer Ruhe geologische Zeiten uberdauern und die Elemente anreichern, die wir in den besprochenen Erzen finden.

ZUSAMMENFASSUNG

Fur die hamatitischen Eisenerze vom Lahn-Dill-Typ wurde bisher eine hochtemperierte exhalative Zufuhr des Eisens und der Kieselsaure als FeCl, bzw als SiCl, angenommen. Es wird eine Entstehung dieser sedimentaren Eisenerze durch Zufuhr des Eisens aus niederthermalen Eisensauerlingen diskutiert. Rezente Eisensauerlinge wurden chemisch untersucht. Sie enthalten: Fe2+-, Mn2+-, Ca-, Mg-, Na-, Si0,-, HC0,-, CL- und SO,-Ionen. An der Oberflache sind die Fe2+-Ionennicht stabil, das Eisen wird oxydiert und flockt als rontgenamorphes Hydroxyd aus. Diese Hydroxyde adsorbieren grossere Mengen an Kieselsaure. Durch diagenetische Vorgange konnen die Hydroxyde umkristallisieren und grobkristallinen Hamatit und Quarz bilden, die die Hauptbestandteile der Erze vom Lahn-Dill-Typ sind. Chemisch sind die rezenten

KOHLENSAUERLINGE ALS ELSENQUELLE

111

Eisenniederschlage ahnlich zusammengesetzt wie die Erze vom Lahn-Dill-Typ, so dass es als wahrscheinlich angesehen wird, dass die Erze eine ahnliche Genese haben. SUMMARY

Two different sources of the iron in the marine-sedimentary iron-ores are possible: (I)iron solution from weathering (Minette iron ores), (2) iron solution from volcanic processes (Lahn-Dill-type). Genetically different iron ores can be distinguished by using the trace element content of pure samples (free of clay or tuff). Iron ores derived from weathering solutions are geochemically characterized by high contents in Ti, Cr, P and especially Al. Iron ores derived from volcanic processes have a low content of these trace elements. This paper deals with sedimentary iron ores the Fe-content of which is attributed to volcanic processes (Lahn-Dill-type). Other investigationshave suggested that volcanic FeC1,-exhalations at high temperature are the source of iron for the Lahn-Dill ores. According to these views, hematite was formed by reaction of FeCI, with water: 2 FeCl,

+ H 2 0 + Fe203+ 6 HC1

Similar processes are postulated for the deposition of silica. Fumaroles connected with recent volcanism contain, besides water vapour, gases rich in various elements: As, Cu, Pb, Zn, Fe, Al, P etc. Hot springs in volcanic environments are strongly acid and sometimescontain the same trace elements, as well as Fe and much Al. Submarine exhalations of these gases were suggested as the iron source for the Lahn-Dill ores. These views, however, prove wrong in the light of recent evidence, which is (a) geochemical: elements with high vapour pressur of their halogen compounds (Hg, As, Sn, Ti, Al. etc.) are very rare in the ores; (b) geological: FeCI, is exhaled only at high temperatures during a time of eruption. But the iron ores were deposited during a period of repose. Fossils - which are found in the ores are made up of CaCO, cannot exist at higher temperatures nor in HC1-solutions. To understand the origin of the Lahn-Dill ores, it seemed necessary to analyze recent iron-rich emanations. Some acid, iron-rich springs were investigated accordingly. Carbonate springs in the vicinity of temporarily active volcanoes (Etna, Italy; Santorin, Greece); several postvolcanic carbonate springs in the Eifel mountains; carbonate springs in the Dachla Oasis (Egypt) which are not directly related to volcanic rocks. AN these are low-temperature (10-30°C) carbonate springs. The pH ranges about 6 and is produced by the carbonate acid ions. Beside silicic acid, Fe2+-, Mn2+-,Na+-, K+- and Ca2+-ionsare of special interest. (See Table 11.) If the waters get to the oxygenated surface, the Fe2+does not remain stable and is oxydized to Fe3+.In this range of pH Fe3+is practically insoluble and it flocculates as non-crystalline iron hydroxyde. This iron hydroxyde flocculates greater quantities of silicic acid1. The precipitates flocculated in the beginning contain little cqkium and See the composition of the iron precipitationin Table I.

112

H. HARDER

manganese and much iron and silicic acid. During a longer settling period of the solution and at higher temperatures C02is released and calcium and manganese are eliminated in greater quantities. From the precipitate of the carbonate springs the chemical product for the origin of the two types of ores is produced: hematitic ores with silicic acid or with lime. The Fe content in the spring waters is not great (40 mg/l H20). These quantities of iron can, however, form iron deposits in geological times. Among the low thermal iron mobilisation by carbonate springs it is possible that there are transitions to the acid iron springs with high temperature. The acid hot springs have a higher content of Al, Cu, Zn etc. The hydroxydes flocculated from carbonate springs are non-crystalline. In the course of geologicdevelopment diagenetic and metamorphic processes may have transformed these hydroxydes into more or less crystallized hematite, quartz and calcite. Fine intergrowths of quartz and hematite are still observed in the ores. If the added carboniferous waters do not find any oxydizing conditions in the area of precipitation, the iron may be eliminated in a different way: iron carbonate can precipitate in a seabasin the water of which is without any oxygen and H,S. Iron sulfide will be formed, if the water contains H,S. In these different kinds of iron precipitate, more productive trace elements are rendered provided they exist in the emitted solutions. In primarily eliminated iron carbonate the manganese and calcium content will be higher, whereas in the sulphide precipitate the content of metal-sulphides is higher. The iron is possibly leached out by the carbonate springs from the country rock. There is no evidence that the iron has been added by magmatic processes. The physical and chemical conditions to be observed in the carbonate springs explain the processes which must have taken place during the sedimentation of the Lahn-Dill ores: normal conditions of pH and temperature. On the assumption that iron is added as FeCl,, high temperatures and acid pH are to be expected. The emission of carbonate springs can outlast geological times and make the elements to be found in the ores in question richer.

LITERATUR

HARBOT, E., 1903. Zur Frage nach der Entstehung gewisser devonischer Roteisenerzlagerstten. Neues Jahrb. Mineral., Geol. Palaontol., 1 : 179-192. HARDER, H., 1954. Beitrag zur Petrographie und Genese der Hamatiterze des Lahn-Dill-Gebietes. Heidelberger Beitr. Mineral. Petrog., 4 : 54-66. HARDER, H., 1963. K6nnen die Eisensauerlinge die Genese der Lahn-Dill Erze erklilren? Beitr. Mineral. Petrog., 9 ( 5 ) : 379-422. HARDER, H., 1964. The use of trace elements in distinguishingdifferent genetic types of marine sedimentary iron ores. Intern. Geol. Congr., 22nd, New Delhi, 1964, in preparation. HENTSCHEL, H., 1960. Zur Frage der Bildung der Eisenene vom Lahn-Dill-Typ. Freiberger Forschungsh., C, 79 : 82-105. MATERN, H., 1931. Das Oberdevon der Dillmulde. Abhandl. Preuss. Geol. Landesanstalt, 134, 51-139. SCHNEIDERH~HN, H., 1941.Lehrbuch der Erzlagerstattenkunde.Fischer, Jena, 784 pp.

J?TUDE Sl?DIMENTOLOGIQUE DU MINERAI DE FER OOLITHIQUE DE LORRAINE L. B U B E N I C E K

Institut de Recherches de la Sidirurgie, Maizisres-les-Metz (France)

P~TROGRAPHIEDES ROCHES ET DES MINERAIS DE LA FORMATION FERRIF~~RE

Les minerais

La premiere observation que l'on peut faire sur les minerais de Lorraine, est la grande diversitt des aspects et l'htttrogtntitt 21 I'tchelle des blocs (BICHELONNE et ANGOT, 1939; CAILLBEE et KRAUT, 1954; C A ~1922). , Dans une analyse plus dttaillk, il apparait que tous les minerais appartiennent toujours de par l e u structure primaire B l'une des deux grandes catdgories suivantes (BUBENICEK,1961a): les minerais en stratification entrecroiste et les minerais B structure contournte; les minerais du pre-

Fig.1. Structure en Stratification entrecroisk d'une d n i t e oxydke. La calcite at distribde en lits concr6tionn6sgrossikrementparallkles a m feuillets. Concession de Tressange, couche grise, largeur = 80 cm.

114

L. BUBEMCEK

mier type sont de loin les plus frdquents, reprtsentant environ 90% de l’extraction actuelle.

Les minerais h structure en stratijication entrecroisie DistribuCes en paquets de 10-30 cm d’tpaisseur, les laminae de la stratification entrecroisde des minerais de Lorraine (Fig.1) ont gCnCralement entre 10 et 30 m de longueur. Les pentes moyennes varient de 10”-25”et ceci surtout en fonction de la dimension des particules dttritiques. Parfois cette structure est soulignCepar des rides de courant, au contact des sCries de laminae. L’Ctat initial, parfois observable, est un sable dont les constituants sont les oolithes ferrifhres, les grains de quartz et les debris de coquilles: parfaitement calibrtes, ces particules ont une dimension mCdiane de 200-250 p pour les oolithes et les grains de quartz (Fig.2), et de 500-1,OOO p pour les d6bris de coquilles. Des proportions relatives de ces constituants dBrive la qualit6 calcaire ou siliceuse, pauvre ou riche d’un minerai donn6. Le constituant original et dCterminant est l’oolithe ferrifire: cette oolithe est formCe d’enveloppes de limonite autour d’un noyau d’origine quelconque, gtnkrale-

1 * ;;,

50-

Q

-

s

c

10-

cg

C

3020-

30-

-

$

20-

10-

O - - K

a

10-

-

0 -

- 7

-

P t

Fig.2. Histogrammes des distributions granulomttriques des phases quartz et oolithes ferrifkres d’arhites en stratification entrecroide. A. Oolithes. Boulange, couche grise. B. Oolithes, Hussigny, calcaire pauvre. C. Quartz. Tressange, couche grise. D. Quartz. Tressange, couche jaune sauvage.

SBDIMENTOLOGIE DU MINERAI D E FER OOLITHIQUE DE LORRAINE

115

TABLEAU I ANALYSE DE LA LIMONITE

&kment, composk

.__

Pourcentage

ment non ferrifkre. La limonite est un produit de composition moyenne relativement constante od predomine la goethite et qui repond A I'analyse de Tableau I. La structure et la texture de ces minerais nous conduisent A les considtrer comme le resultat du d6pp6t de particules detritiques dans un courant. Parmi ces particules les oolithes femfires apportent le fer sous la forme d'hydroxydes ferriques impurs. Immtdiatement aprks le dtpat, la diagenbse a pour effet prtcoce de permettre A la calcite de se rassembler en concrttions ou lits calcaires concrttionnts (Fig.1, 3); ce sont ces figures structurales secondaires qui contribuent A donner au minerai sa physionomie

Fig.3. Concrktions calcaires. I1 y a continuit6 entre la concrktion et le minerai internodulaire. L'inflexion des feuillets au contact des deux zones indique un tassement du minerai internoNaire et une augmentation de volume de la concrktion. Concession de La Mouritre, couche grise, hauteur environ 30 cm.

Fig.4. Arenite de paragenkse chloriteuse. Zone interconcretion. Les oolithes de limonite sont ciment&s par de la chlorite en texture pelliculaire. Les figures de contact entre limonite et chlorite indiquent le sens des reactions qui sont apparues au cows de la diagenkse: la chlorite derive de la limonite. Concession de Landres, couche grise, dimension moyenne des oolithes 250 p.

Fig.5. Corrosion d‘un grain de quartz par la siderose. Les deux plages residuelles de quartz presentent des contours dentelts, arrondis, et conservent la mgme orientation optique. Concession d’hgevillers, couche grise, dimension moyenne du grain corrode 250 p.

S~DIMENTOLOGIEDU MINERAI DE FER OOLITHIQUEDE LORRAINE

117

actuelle et en particulier l’hkttrogknkitt macroscopique. A la diagenbse doit Ctre tgalement rattachk le moment ou apparaissent des conditions rkductrices dans le milieu, probablement sous l’influence de la matikre organique emprisonnke au moment du dkpdt. On assiste alors a une rkorganisation des kltments chimiques en nouveaux minkraux plus stables, oh le fer intervient sous sa forme Fez+: ce sont surtout la chlorite, la sidkrose et la pyrite (dans certaines conditions rkalistes localement peuvent apparaitre des associations hkmatite-magnktite-sidkrose) (Fig.4, 5). Cette transformation au cours de laquelle la limonite et le quartz sont corrodks au profit de mintraux ferrifkres plus rtduits, s’effectue en conservant invariks les kltments majeurs FeySi02, A1,0,, P, mais s’accompagned’un apport sensible de MgO et COz (BUBENICEK, 1961a). Les paragenbses actuelles reflbtent les degrks divers de rtduction; ainsi s’expliquent les teintes des minerais variant du rouge au noir en passant par le jaune, le vert et le bleu. Les minerais h structure contournke D’apparence homogkne en grandes masses, les minerais se montrent formks, A petite kchelle, de masses mintraliskes arrondies, isoltes par des lames plus fonckes contourntes: il s’agit la d’une lutite litke indurte, ou mieux d’un shale argileux. Le contournement peut &re causk par deux phtnomknes: compaction avec glissements pknkcontemporains, ou brassage par des animaux fouisseurs. En fait les passages lattraux avec le minerai en stratification entrecroiske, nous permettent de mieux comprendre l’origine de ces roches mixtes: en effet, lorsque Yon suit latkralement le niveau oa ktait apparu un joint argileux soulignant une ride, on observe le dtveloppement progressif de celui-ci avec amincissement des paquets de laminae de la stratification entrecroiske; A partir d’une certaine abondance relative de shales argileux apparait le contournement. Dans ces roches, des phknomtnes analogues de rkduction du fer avec formation de chlorite et sidkrose doivent Ctre attribuks B la diagenbse. Les roches encaissantes

Les principales roches assocites au minerai dans la formation ferrifbre de Lorraine sont des calcaires coquilliers grossiers, des microarknites, des argilites et des silts.

Les calcaires coquilliers Dknommkes “crassins”, ces roches sont des artnites coquillibres grossibres dont la structure caractkristique de dkpat est la stratification oblique. Les constituants essentiels des crassins sont des coquilles, restes d’une faune ntritique, de plusieurs mm de dimension mtdiane, et des granules ferrifbres, qui sont des morceaux de minerais remaniks. Les microarknitks FrBquemment calciques ou quartzeuses, les microarknites prksentent une structure contournke caracttristique; dans ce contournement, le rale jouk par Ids animaux fouisseurs est essentiel, A tel point qu’on peut souvent parler de structure grumeleuse

118

L. BUBENICEK

(STRAKHOV, 1957). Les particules constitutives, en dehors du mattriel argileux distribut en lits contournts, sont des petits grains de quartz et des petits fragments de coquilles, avec parfois ef en faible quantitk des fragments d’oolithes. Les mCdianes des distributions granulometriques sont toujours inftrieures B 150 p, et plus gtntralement voisines de 80-100 p. h s argilites et les aleurites Ces roches, toujours intimement assocites, reprksentent les termes granulomttriques les plus fins de la strie. Gtntralement peu tpais, ils peuvent parfois exister en bancs de plusieurs mttres de puissance. Le litage horizontal caracteristique de l’argilite, est perturb6 par la prksence des lits qui se distribuent en petits paquets finement contournts en figures d’aleurites, ressemblant a des “flow-casts”.

SUCCESSION LITHOLOGIQUE

L‘examen pttrographique des diffkrents termes lithologiques montre sans kquivoque

que la quasi-totalitt des sediments aaltniens est d’origine dttritique: arhites mintralis k s ou non, microartnites, silts et shales argileux. Comme dans toute strie dttritique, c’est sur le facteur granulomttrique que doit reposer la dtfinition de la strie virtuelle locale (LOMBARD, 1956). I1 ressort par ailleurs de ces ttudes que dans l’ensemble de la formation, les distributions des diffkrents tltments dktritiques prtsentent des coefficients de dispersion propres: ainsi le champ des dttritiques calcaires est trts Ctendu: de 80 p B quelques centimttres, tandis que celui des grains de quartz varie de 20-800 w. Les oolithes ferriftres, quant B elles, n’existent qu’entre 60 et 500 p. Sur ces bases, tant dans le bassin ferriftre lorrain que luxembourgeois, une seule et mEme succession lithologique apparait A l’kchelle macroscopique comme unit6 de la formation, et qui se rtptte 12-15 fois pendant la ptriode envisagke. Ces unites ou sequences dtbutent h la base par des dtpdts fins, argileux, qui passent progressivement par l’intermtdiaire des microarknites, B l’arknite minkraliske. Ce minerai est souvent recouvert par une arenite coquillitre grossitre, puis parfois par des conglomkrats argileux caracttristiques des bourrelets de plage. La stquence est limitte au toit par une surface de stratification. La nature dttritique des skdiments et la polarisation de la skquence permet de la caracttriser comme negative (Fig.6). Des variations lattrales introduisent une certaine diversitt dans son aspect lithologique: certains termes peuvent Etre rtduits ou disparaitre: paralltlement des variations

Fig.6. Sequence nkgative, unit6 ddimentologique de la drie ferrifere de Lorraine. A = Arenite coquillibre grossiere. E = Arknite en stratification entrecroih. C = Arknite i’i joints de shales argileux. D = Arknite fine i’i p a s h s i’i shales contournes. E = Arknite i’i shales contournks. F = Micro-arknite B shales contournks. G = Argilite et aleurite. a = Stratification entrecroik. b = Joints de shales argileux. c = Structure contournix. d = Structure finement contournix. e = Shales argileux et aleurite en structure finement contournix et 1itk.f = Coquilles.g = Surface de stratification avec galets.

S~DIMENTOLOGIEDU MINERAI DE FER OOLITHIQUE DE LORRAINE

MURVILLE

SONDAGE

NO1

SEQUENCE DE LA COUCHE ROUGE PRINCIPALE

T E N E U R EN F E R

LITHOLOGIE

D E

5

10 15 20 25 30

NATURE

MI N I ~ R E INTER-

I I

I I I

I

I I I I I I I I I I

CALAIRE COUCHE ROUGE 'RINCIPALE BASE DE COUCHE

I I I I

INTERCALAIRE

I I I

I I I I I IUCHE JAUNE 'RINCIPALE

COUCHE GRISE

Fig.6. Lkgende A p. 11 8.

119

120

L. BUBEMCEK

de puissance notables interviennent (de quelques dkimbtres A plusieurs dizaines de mktres). L’AalBnien comporte au total une quinzaine de sequences sur une mbme verticale. La skrie sddimentaire apparait ainsi rythmique et montre une derive sensible de la base plus marneuse au sommet plus calcaire; cette sCrie peut btre considerbe comme n6gative sur le plan granulombtrique, et comme positive sur le plan chimique (LOMBARD, 1956). Sur ces donndes, il semble bien que les diffdrenciations shdimentaires mdcaniques et chimiques soient relativement indkpendantes.

CONDITIONS PAL~~OGEOGRAPHIQUES DE FORMATION

Que ce soit dans les formations actuelles ou dans les d6ppbts anciens, les sables marins presentant une structure en stratification entrecroide, peuvent etre rapport& aux dBp6ts littoraux ou nkritiques dans la zone d’agitation de l’eau par les vagues. De tels dBp8ts ont BtB signalts A plus grande profondeur, mais il s’agit toujours de formations de trbs faible extension; elles ne constituent que des anomalies locales (GUILCHER, 1954; TWENHOFEL, 1950). Les faits precedemment Bnoncks permettent de penser que la minette lorraine s’est depose6 dans des conditions analogues. Ceci est confirm6 par l’ttude du passage latttal du minerai aux roches stdriles. Vers les zones topographiquement plus Blevtes, et surtout le long du littoral suppos6, les arenites mintralisees passent A des artnites plus grossikres, coquillibres, qui marquent l’extrbme limite des dkpdts. Ceux-ci sont ensuite tronquts par une surface de stratification prtsentant des figures indubitables d’exondation, tout au moins temporaire. Localement, cette surface n’apparait que sur des roches riches en galets, argileuses et constitudes essentiellement de minerai remanid. Vers les zones marines plus profondes, l’arknite mineralisee passe lattralement et progressivement A des roches contenant des argiles; plus on s’6loigne vers le large d’autrefois, plus la dimension des grains enrobts dans le ciment argileux diminue, et plus la proportion de ce ciment augmente. Les figures structurales qui apparaissent sont celles de dkppbts en milieu progressivement moins agites par l’eau, et en particulier, des litages horizontaux ultkrieurement dtformks par le brassage d’animaux fouisseurs: ces traces confirment la nature oxydante de l’eau sur le fond, ainsi qu’une grande abondance de mati2re organique (STRAKHOV, 1957). Les artnites, par contre, ne montrent pas de telles figures: leur zone de dtp6t cofncide en fait avec la bande oh ont dO s’kraser violemment les vagues. Ces difftrents termes qu’on observe en passage lateral A partir du minerai, et qui se rapportent A ce qu’on sait des dippbts littoraux actuels (PETTIJOHN, 1956; TWENHOFEL, 1950) sont Bgalement distribues de manibre remarquable en sequences verticales. La formation de telles sequences ne peut s’expliquer que par des regressions qui ambnent en un point donne, des dkppbts plus grossiers et donc plus littoraux sur des sediments plus fins anterieurement d6posCs. Les transgressions intermidiaires n’ont apportt que peu de dtppbts, A l’exception de remaniements A la base des skquences, et

S~~DIMENTOLOGIE DU MINERAI DE FER OOLITHIQUE DE LORRAINE

121

quelques successions locales positives, dans les zones d’extrCme transgression ou rkgression (BUBENICEK,1961b). Ce mode de formation de la minette pose A nouveau le problbme des isochrones: en effet, B un moment donnt, les divers facits se sont klaborks sur un fond marin. La distribution en couches n’est que le rtsultat d’une variation du niveau de ce fond marin. Aucun critbre lithologique ne peut donc, dans ces formations littorales, Ctre considtrt comme repbre-temps. Quant B l’origine du fer, tout laisse B penser qu’il provient d’un lessivage du continent dtjB arask, et qui bordait ti l’est cette mer tpicontinentale ? l’emplacement i du Bassin parisien. Ce continent, form6 par la pkntplaine cristalline, et par les stdiments du Trias et du Lias fraichement dkposts et kmergts au cours de la rCgression aalknienne, subit une krosion importante sous climat probablement chaud, ainsi que le laisseraient supposer les ttudes sur les debris vtgttaux. La charge solide amente li la mer par les eaux douces est essentiellement constituke d’argiles du Lias, et de grains de quartz du Trias; seules ces dernibres particules se seraient dtposkes dans les formations littorales: ainsi par deux cycles successifs skdimentaires s’expliquerait le bon arrondi de ces particules (STRAKHOV, 1957). Les produits argileux auraient ktk entraints vers le large et.se seraient dkposts dans les parties les plus profondes du bassin. Le fer, trhs frkquent dans les formations du Lias sous forme de concrttions sidtritiques associks A des concrktions phosphatkes, ktait entrain6 vers la mer sous une forme dissoute et prtkipitait en oolithes sur le littoral. Cependant, certains fragments de ces concrttions primitives sont parvenus dans l’aire de dtpdt: malgrt l’oxydation du fer, on les reconnait dans les granules ferrifbres, phase toujours plus riche en phosphore que les oolithes ferrifbres.

L‘analyse pktrographique dttaillke des minerais de fer oolithiques de Lorraine permet de faire la part des phtnombnes postkrieurs au dkpdt, d’ordre diagknktique, qui ont contribut a donner B la minette sa physionomie actuelle. Ces phknomtnes consistent essentiellement en un concrktionnementde la calcite constitutive des debris de coquilles et en la rtduction du fer, qui apparait dans de nouveaux mintraux: chloritesidtrose-pyrite. Par delB ces transformations, le stade initial qu’on peut parfois observer, toujours reconstituer, est un sable indurt constitut d’oolithes, de grains de quartz et de dtbris de coquilles: il s’agit d’arknites. La structure primaire de ces artnites est de manibre caracthristique, la stratification entrecroiske. Ces faits permettent de penser que la minette s’est dkposte dans des zones d’agitation de l’eau par les vagues sur le littoral. L’examen pttrographique des diffkrents termes lithologiques montre sans Cquivoque que, commeles minerais,la quasi-totalitt des sedimentsaaltniens est d’originedktritique. L’ktude de la distribution des couches de minerai dans la formation ferrifbre fait apparaitre des sequences granulombtriques oh la dimension moyenne des grains dktritiques croit de la base vers le sommet; ce sont des sequences nkgatives.

122

L. BUBENICEK

La formation de telles skquences ne peut s’expliquer que par des rkgressions qui ambnent, en un point donnk, des dtpbts plus grossiers et donc plus littoraux sur des skdiments plus fins antkrieurement dkposks. Les transgressions intermkdiaires n’ont apportk que peu de dkpbts et des facibs de remaniement. SUMMARY

Detailed petrographic analysis of the oolitic iron minerals of Lorraine make it possible to recognize the part played by diagenetic processes which have contributed in giving the minette ore its present appearance. These processes consisted mainly in the concentration, leading to the formation of concretions, of the calcite material of shells, and in the reduction of the iron, which resulted in the formation of new minerals: chlorite, siderite, pyrite. In their original state, which is sometimes preserved, and in the remaining cases can always be reconstructed, these sediments were indurated sands composed of oolites, quartz grains and shell fragments, i.e., arenaceous material. Their original structure was cross bedded (or -laminated). These facts render it likely that the minette ore was deposited in littoral environment under the influence of waves. The petrography of the various lithological units shows unequivocally that not only the ore minerals, but almost the whole mass of the aalemian deposits is of detrital origin. In studying the distribution of the ore layers in the whole formation, granulometrical sequences have become apparent, in which the mean diameter of the detrital grains increases from the base to the top: they are “negative sequences”. The formation of such sequences can only be explained as the result of regressions which led, at a given point, to the deposition of coarser and more littoral material on older sediments of finer grain. The intervening transgressions have resulted in little sedimentation, the material having a reworked character. BIBLIOGRAPHlE

BICHELONNE, J. et ANOOT,P., 1939. Le Bassin ferrifpre lorrain. Berger-Levrault, Nancy-Strasbourg, 464 pp. BUBENICEK, L., 1961a. Recherches sur la constitution et la repartition du minerai de fer dans 1’AalBnien de Lorraine. Sci. Terre, 8 (1) : 5-204. BUBENICEK, L., 1961b. Conditions paleogbgraphiques de formation de la minette lorraine. Compt. Rend,, 253 : 1468-1469. CAILL~RE, S. et KRAUT, F., 1954. Les gisements de fer du bassin lorrain. MPm. MusPum Natl. Hist. Nut., SPr. C (Paris), 4 (1) : 175 pp. CAYEUX, L., 1922. Les Minerais de Fer oolithiques de France, Minerais de Fer secondaires II. hprimerie Nationale, Paris, 1051 pp. GUILCHER, A., 1954. Morphologie littorale et sous-marine. Presses universitaires de France, Paris, 210 pp. LOMBARD, A., 1956. GPoIogie skdimentaire. Les SPries marines. Masson, Paris, 722 pp. F. J., 1956. Sedimentary Rocks, 2nd ed. Harper, New York,718 pp. PEITIJOHN, N. M., 1957. MPthodes d’gtudes des Roches skdimentaires. I. Traduction du Bur. Rech. STRAKHOV, GBol. Minikres, Paris, 542 pp. TWENHOFEL, W. H., 1950. Principles of Sedimentation,2 ed. Mac Graw-Hill, New York,675 pp.

FACIES PROBLEMS OF BOEHMITIC AND DIASPORITIC BAUXITES I D A VALETON

Geologisches Staatsinstitut, Hamburg (Germany)

The bauxites in southern France are derived from fine clastic sediments. They are deposited in layers on an ancient karst relief, on the southern slope of the “Massif Central”, the “Isthme durancien”, and the “Massif des Maures”. Petrographically they may be divided into three different facies: ( I ) Bauxite with gibbsite. (2) Bauxite with boehmite. (3) Bauxite with diaspore. (VALETON and KLINT,1962.) The experimental representation of the system Al,O,-H,O (Fig.1) by ERVINand OSBORN(1951) gave the incorrect idea that natural diaspore can only be built under high temperature and pressure conditions, and thus that it is always metamorphic.

TEMPERATURE

O C

Fig.1. Equilibriumdiagram for the system Al,Os-HzO. Heavy lines delineate regions of stability of the crystalline phases. Light line is the vaporisation curve for water; and, in view of the low solubility of alumina in water, this curve approximates the vaporisation curve for solutions in this system. (After ERVIN and OSBORN, 1951.)

124 m

O’”

I. VALETON Sno.

0

10

20

KAOLlNlTE

39

40

0

to

20 30 BOEHMITE

40

50

60

70

10 20 M 40 Weight,% HEMATITE + GOETHITE

0

-+ ANATASE

Fig.2. Quantitative mineral distribution of section 3, Mazaugues (Var).

Here the boehmitic and the diasporitic facies may be compared: A. The boehmitic facies -in Mazaugues (Var) - consists of three zones in a vertical succession: 111. Bright bauxite, with few pisolites. 11. Red bauxite, with many pisolites and “fluidal” textures. I. Bright bauxite, with few pisolites. The following minerals appear: Kaolinite in the zones I and I11 in the matrix, boehmite and a little gibbsite in all zones in the matrix as well as in the pisolites. The content of anatase rises with that of boehmite. Hematite and sometimes goethite are found in zone 11in the matrix and in the pisolites (Fig.2). The chemical investigation shows that the A1,03 content increases only a little towards the top. SiO, has a maximum in zones I and 111 corresponding to the content of kaolinite. The content of Fe,03 increases in zone I1 from bottom to top and vanishes almost completely in zone III. TiOz and ZrO, contents behave like Al,03. NiO, however, is proportional to SiO, and is included in the kaolinite. The content of trace elements in the minerals of iron changes abruptly between zones I1 and 111. In that section there is no FeO (Fig. 3).

BOEHMITIC AND DIASPORITIC BAUXITES

125

d

n

-

lI

-

I

' i O- I -

1 0 .

10

20 30 KAOLlNlTE

40

1

20 BOEHMITE 10

f

30 40 DIASPORE

50

-

60

70 0 10 20 GOETHITE t HE MAT I T E

Fig.4. Quantitative mineral distribution of section 9, Pkreille (Arikge),

Weight,%

BOEHMITIC AND DIASPORITIC BAUXITES

I

I

I

I

1 I

I

127

128

I. VALETON

B. One section of the diasporiticfacies follows: Section 9, Ptreille (Aritge). There are also three zones in a vertical succession: (I) Bauxite clay, with few pisolites. (2) Pisolitic bauxite, bright, with “fluidal” textures. (3) Gray clay (on the top). The mineralogical composition (Fig.4) differs from that of the bauxite of the Var. Kaolinite is more plentiful, goethite and hematite more scarce and compounds of Fe2+, such as siderite, traces of pyrite and iron silicates, are present. Among the minerals of A1,0,, boehmite disappears and is replaced by diaspore. All the minerals may be present in the matrix as well as in the pisolites. The chemical composition (Fig.5) here also shows regular variation corresponding to the level within the section. It differs from that of the bauxite with boehmite by a feeble content of Fe,O, and by the presence of FeO, C02, S and C. The content of TiO, rises with that of A1203. NICHOLLS (1963) studied the relation between iron compounds, pH and redox potential and has given the diagram of Fig.6.

0.2

0.1

0.0 0.1 0.2

0.3 0.4 0.5

0.6 0.7

0.8

I

0

1

2

3

4

5

6

7

0

9

1011

12

13

i

PH

Fig.6. Eh-pH stability fields for hematite (Fe,O,), magnetite (Fe,O,), siderite (FeCO,) and pyrite (FeS,) at 20°C and 1 atmosphere under the following conditions: (Z dissolved sulphur ionic species) = 1 0 9 moles/l. (X dissolved carbonate ionic species) = 10-l molesll. The dotted lines mark the field boundaries of FeCO,, Fe(OH), and Fe(OH), under the following conditions: (Z dissolved sulphur ionic species) = 1o-S moles/l. (Z dissolved carbonate ionic species) = lWmoles/l. (After NICHOLLS, 1963.)

BOEHMITIC AND DIASPORITIC BAUXITES

129

If the iron compounds of our bauxite are placed in this scheme, than the diaspore bauxite appears as the result of natural diagenesis without metamorphism and with a lower redox potential than that of the bauxite with boehmite. On the other hand, BARDOSSY(1958) has shown that bauxite with gibbsite is formed at a higher redox potential than boehmite.

SUMMARY

According to the predominant aluminium minerals, the bauxite deposits in southern France can be subdivided into two facies ranges. By means of the iron minerals it was possible to determine the oxidation potential during diagenesis and to establish that this increased in the order: diaspore-boehmite-gibbsite.

REFERENCES

BARDOSSY, G . J., 1958. The geochemistry of Hungarian bauxites. 11. Acta Geol. Acad. Sci. Hung., 5 : 103-155. . ERVIN, G . and OSBORN, E. F., 1951. The system AI,O,-H,O. J . Geol., 59 : 381-394. NICHOLLS, G. D., 1963. Environmental studies in sedimentary geochemistry. Sci. Progr. (London), 51 (201) : 12-31. VALETON, I. and KLINT,W., 1962. Petrographie der Bauxite von Mazaugues, Siidfrankreich. Geol. Rundschau, 52 :475492. VALETON, I., 1963. Petrographie und Geochemie siidfranziisischer Bauxitlagerstatten. Beitr. Mineral. Petrog. - Festband Prof. Correns, in press.

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DISCUSSION OF PAPERS IN PART B H. J. MacGillavry (The Netherlands): H. Harder has compared ore-bodies of Lahn-Dill type with springs of continental position and found them similar geochemically. What would be the explanation that ores of Lahn-Dill type occur almost exclusivelyin marine sediments? H. Harder (Germany): Iron ores -with the same chemical composition -can be found in marine (LahnDill ores) or in continental position. Iron precipitation was also tested in the sea (see the publication on Santorin Island). The conditions for deposition of the iron ores are more favourable under marine deposition near the shore line. J. H. Taylor (Great Britain): I would like to ask H. Harder whether, in his experience, the deposits in which iron had been derived by weathering contained iron alumino-silicates of the chamosite type, while those deposits in which the iron came from volcanic sources had iron silicates such as greenalite. In commenting upon the diagenetic changes of the Lorraine ores described by L. Bubenicek,the speaker said he had seen examples of replacement relationships between almost all the minerals that occured in sedimentary ironstones. It was easy to see evidence for replacement but more difficult to define criteria for primary deposition. In certain ironstones, for example in parts of the English Middle Lias, oolitic and crystalline chamosite were almost wholly free of traces of limonite and there seemed no necessity to assume a diagenetic origin. The stability field of charnosite was not fully understood but, if it lay between the siderite and hematite fields, there seemed no reason to doubt the possibility of its forming as a primary precipitate. H. Harder (Germany): Iron ores derived from weathering solutions are geochemically characterized by high contents of aluminium. Chamosite (Fe Al silicate) forms from this precipitate by diagenetic reaction. Iron ores derived from volcanic processes are usually characterized by low contents of aluminium. Mostly greenalite (Fe silicate with low Al content) is formed in the ores of this type. A paper about this matter is in preparation. P . Routhier (France): Je demande A L. Bubenicek combien de sBquences peuvent se superposer sur une meme verticale, comment expliquer cette rdgression pulsatile; peut-on faire intervenir des rythmes bio-rbistasiques ? Apr2s la rdponse de L. Bubenicek, P. Routhier remercie l'auteur de ses belles Btudes sur un bassin qui demeurait ma1 connu, comme d'ailleurs tant de grand; gisements mondiaux !

132

DISCUSSION OF PAPERS IN PART B

A. Bernard (France): L. Bubenicek pourrait-il nous donner, en parallhle, son opinion sur l’origin terrigene du fer? L. Bubenicek (France): Pour expliquer une telle concentration du fer dans I’Aalenien de Lorraine, plusieurs auteurs ont 6th aments a imaginer une ttape anttrieure de concentration, cette fois ptdologique; en particulier les sols ferralitiques ou lattritiques. En fait il semble qu’une solution plus simple, et surtout exigeant des conditions moins extraordinaires, puisse Ctre envisagte: En effet, la fin du Toarcien (ex-Aalenien)co’incideen Lorraine avec une vaste regression faisant suite une ptriode assez longue durant laquelle se sont dtposks des assises extrCmement tpaisses de skdiments argileux marins. Ces stdiments se sont trouvds exondts et soumis l’trosion sur d’immenses surfaces en avant des massifs primaires. Or une premiere concentration du fer (et du phosphore) est apparue au stade diagknttique dans ces produits argileux sous forme de concretions sidtritiques ou phosphattes. L’action de l’trosion de cet ensemble liasique s’est traduit par un transport de l’ensemble vers la mer. Le long du littoral les conditions physiques et physicochimiques du milieu ont effectut une stparation des produits: (a) par dimensions et donc entre divers dttritiques apportts ou meme d’origine littorale (en particulier les oolithes et les dtbris de coquilles) et les produits argileux fins; (b) par nature chimique: prtcipitation littorale du fer avec formation d’oolithes, ce qui lui permet d’etre ensuite trit par dimension. Le cycle du fer est apparemment indtpendant du cycle gtntral d’tvolution du bassin marin: lorsque du fer est apportt dans le bassin, il est stdimentt le long du littoral sous forme d’oolithes limonitiques. Pour qu’il y ait gisement, il est nkessaire alors que les apports d’autre nature soient faibles. En Lorraine, la pauvrett en grains de quartz des sBries ferrifhres s’expliquerait par la nature essentiellement argileuse des assises dont les produits de l’trosion alimentent le bassin a la fin du Toarcien. Ainsi, dans le minerai, la dilution des oolithes dans l’ensemble des grains dttritiques est faible, et ne s’ophre surtout que par la calcite des dtbris de coquilles. Par ailleurs les quantitks de fer mises en jeu par cette trosion, sont largement supkrieures a celles de l’ensemble du gisement. La position des divers minerais de fer oolithiques du monde au cours des Bges gtologiques montre par ailleurs que cette hypothtse, Cmise anttrieurement par M. Kolbe pour expliquer la gtntse du gisement de Salzgitter, peut &re largement appliquke. J. Senstius (USA.): In connection with Mrs. I. Valeton’s paper mentioning kaolin, I should like to ask whether she has used modern methods of kaolin determination and, if so, whether she has not found montmorillonite, which would be of great importance in the consideration of the origin of bauxite.

DISCUSSION OF PAPERS IN PART B

133

P. Routhier (France): Je demande A Mme I. Valeton si elle peut s'expliquer la rtpartition (paleo) gtographique de l'hydrargillite, de la boehmite, du diaspore, etc., et fait observer que la rtgion A diaspore semblerait tout de mbme se trouver dans la region la plus d6formke. I. Valeton (Deutschland): Als Antwort auf die Frage von P. Routhier, Ursachen der Faziesunterschiede Boehmit-Diasperbauxite: Boehmit-Bauxit mit Haematit und Goethit; Diasporbauxit mit wenig Haematit und Siderit, Pyrit, etc. als primare Bildungen. Die tektonische Beanspruchung am Col de Btzon ist so gering, dass keine Metamorphose durch tektonische Einwirkung aufgetreten sein kann. Die Bildungszeit war sehr kurz, Liegendes Baremien, Hangendes Aptien in der gleichen karbonatischen Riffazies. Frage ob authochton oder allochton: Alle untersuchten Profile zeigen eine sicher authochtone Abfolge. In den untersuchten Profilen treten keine Umlagerungsprodukte auf und sind keine Erosions-erscheinungen zu beobachten. Frage von J. Senstius nach Tonmineralgehalt: Im Var nur Kaolinit mit blattchenformiger Gestalt, pseudohexagonal, und d = 7.2 A, in Aritge und Ande wurden in der tonigen Fazies auch ein geringer Gehalt an Montmorillonit beobachtet.

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PART C

S U L P H A T E A N D PHOSPHATE D E P O S I T S

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SfiDIMENTOLOGIE ET RECHERCHE DES GISEMENTS SfiDIMENTAIRES MARINS DE PHOSPHATE MAURICE SLANSKY

Bureau de Recherches Gkologiques et MiniPres, Paris (France)

INTRODUCTION

Les roches phosphaths sont relativement frdquentes dans les formations sedimentaires, mais la plupart du temps elle ne prdsentent aucun intCrQtkonomique et n’indiquent mQmepas la proximite d’un niveau A mindralisation plus abondante. Seuls les indices trbs importants, s’ils sont visibles, peuvent mener directement au gisement. Aussi, si Yon. veut dhouvrir une accumulation economiquement intdressante sans trop faire appel au hasard, l’dtude des indices doit Ctre compldtde par des methodes gdologiques dont cette note essaie d’dvoquer l’importance.

RELATIONS ENTRE LA MIN~RALISATIONPHOSPHAT~EET LA S~DIMENTATION

L’analyse sdquentielle prdconisde par LOMBARD (1956), au cours de cette dernibre dkade a remis l’accent sur l’interddpendance des diffdrents facibs se succedant dans les series sddimentaires. L‘existence de cette interddpendance parait Cvidemment sdduisante lorsque l’on recherche des gisements sedimentaires de phosphate, d’autant plus que dans la “sdrie virtuelle gdndrale”, le phosphate i n c h dans les “mdtagendtiques”, suit les argiles et prdctde les calcaires. Or l’dtude de diffdrents niveaux phosphatds montre d’une part, que Yon ne peut gdndraliser cette position, d’autre part que les argiles lides aux ddpdts phosphates sont souvent du type montmorillonite-attapulgite et, par ce fait, ne peuvent Qtretoujours assimul&s aux colloides de la sdrie virtuelle gdndralel. En fait, lorsque l’on y regard0 de plus prbs, on s’aper~oitque les phosphates ne peuvent Ctre groupds avec les termes habituels des sdquences lithologiques; ils s’en distinguent par divers aspects.

Les argiles magnksiennes telles que la montmorillonite, l’attapulgite et la dpiolite f o m n t , dam cet ordre, une dquence positive comparable h la dquence calcaire, calcaire dolomitique, dolomie. Je pew que ces Sequences sont parall&leset ne peuvent etre condensks en une seule.

138

M. SLANSKY

Opposition d’origine

I1 semble, que l’on puisse admettre que la plupart des d$&s rencontrbs dans les series sedimentaires habituelles sont la constquence directe de l’erosion des continents. En suivant les idBes de ERHART (1956), on peut distinguer trois modes d’drosion: ( I ) Celle qui entraine essentiellement vers le bassin les solutions chimiques de la “phase migratrice” des sols, en periode biostasique. (2) Celle qui entraine vers le bassin les particules de la “phase rbsiduelle” des sols, en pkriode rhexistasique. (3) Celle qui entraine vers le bassin des debris plus ou moins gros des roches mBres du continent en periode post-rhexistasique. Ces trois modes d’krosion expliquent bien la formation concomitante, dans le bassin, des roches sedimentaires habituelles: roches detritiques diverses likes A la rhexistasie ou la post-rhexistasie, roches d’origine chimique tels que les calcaires, dolomies, cherts, argiles magnesiennes neoformies likes A la biostasie. En dehors de cas exceptionnels d’krosion directe de roches riches en phosphates, seule la phase migratrice des sols de la pkriode biostasique semble pouvoir constituer pour le bassin un approvisionnement rkgulier en solutions phosphatkes. Cependant, la proportion de phosphate de la phase migratrice des sols du continent parait bien faible par rapport aux autres produits en solution apportes au bassin et il est difficile d’imaginer que cette seule source, utilisee directement, permette la formation d’un niveau phosphate important prenant le pas sur toute autre sbdimentation. Par contre, si ce phosphate n’est pas utilise immidiatement, s’il est m i s en reserve dans la mer, on conCoit beaucoup mieux qu’il puisse intervenir ensuite, dans certaines conditions, de facon beaucoup plus massive. L‘etude des dBp6ts chimiques effectues au cours d’une pkriode biostasique permet de remarquer que de grandes series argilo-marneuses magnbsiennes ne contiennent que trBs peu de phosphate et souvent pas du tout; cela semble aussi le cas des grandes series cherteuses. La phase migratrice correspondante, cependant vraisemblablement phosphatk, a donc, pendant tout ce temps contribue A renforcer la reserve phosphatee de la mer. Au bout d’une longue periode de sedimentation chimique pauvre en phosphate, cette contribution peut devenir importante. La rkserve phosphatee de la mer apparait ainsi comme la meilleure source susceptible de contribuer A la formation d’un dBp6t important de phosphate. Cette idee n’est bvidemment pas nouvelle; elle a 6t6 notamment utilisee de f q o n particulikrement fkconde par KAZAKOV (1937) pour expliquer la formation des dkp6ts phosphates par l’existence de courants marins ascendants venant des profondeurs marines oil le phosphate est plus soluble qu’A faible profondeur; elle permet ici de mettre l’accent sur l’opposition originelle existant entre une couche de phosphate et les niveaux s6dimentaires stbriles plus habituels. Ceux ci se constituent en general A partir de matkriaux provenant directement du continent, celle-lA ne trouve une matike premihre abondante que dans les solutions mises en reserve dans la mer au cours de longues periodes anterieures.

GISEMENTS ~BDIMENTAIRES MARINS DE PHOSPHATE

139

Opposition quantitative Plusieurs auteurs ont dCja remarquk que les zones les plus riches en phosphate d’une formation gkologique, correspondent a des zones de moindre kpaisseur de cette formation. SALVAN(1959) a notamment constatk ce phknombne au Maroc et j’ai eu l’occasion de le remarquer en Afrique occidentale. Par exemple au Togo, la formation phosphatke a une dizaine de mbtres d’tpaisseur et appartient a la partie suptrieure du Lutttien; la minkralisation devient diffuse et disparait vers le sudest en mCme temps que cette mCme formation atteint rapidement une Cpaisseur de plus de 100 m. Au Sknkgal, la diffkrence d’kpaisseur entre le Lutktien supkrieur phosphate et son kquivalent latkral stkrile est du mCme ordre et mdme plus important. Ces diffkrences d’kpaisseur montrent que l’apport phosphate est beaucoup plus faible que l’apport responsable des dip& skdimentaires plus habituels.

Opposition de conditions de dkp8t Lorsque l’on s’kloigne d’un gisement de phosphate en direction des Cpaisseurs croissantes de la formation stratigraphique correspondante, la minkralisation disparait, soit brutalement, soit par l’intermkdiaire d’une zone plus ou moins importante A minkralisation diffuse. Mais il ne semblejamais y avoir rtellement dilution de la minkralisation par la sedimentation abondante des zones kpaisses, il y a en quelque sorte inhibition plus ou moins rapide. Les conditions de dkp6t favorables a l‘abondance de la skdimentation stkrile ou de la sedimentation phosphatke semblent s’opposer.

FILS CONDUCTEURS DE LA RECHERCHE D U PHOSPHATE

La recherche du phosphate est ktroitement like A cette opposition existant entre cette roche et les formations stkriles habituelles. En effet, du fait de l’origine gknkralement diffkrente de ces deux sortes de dkp6ts, l’un lib aux solutions en rkserve dans la mer, l’autre aux matkriaux provenant directement du continent, un bassin marin peut &re au mCme moment aliment6 concurremment de ces deux facons. Mais dans ce cas, la skdimentation stkrile, par son abondance et ses propri6tes inhibitrices possibles, a de fortes chances de l’emporter. Aussi, pour qu’un gisement de phosphate se :oit formk, il faut qu’aient exist6 A la fois dans le bassin une pkriode favorable a la phosphatogknbse une rkgion favorable aux accumulations de phosphate a bonne teneur, une pkriode ou une rkgion dkfavorables A la sedimentation stkrile abondante.

Pkriodesfavorables h. la phosphatogknke La recherche de ces pkriodes peut Ctrz abordke de deux facons diffkrentes qui, d’ailleurs, se complbtent. ;

140

M. SLANSKY

Crittrespalko-odanographiques Determiner directement le moment oh ont exist6 des courants amenant vers la surface les solutions plus riches en phosphate des profondeurs marines, est un problbme pal6o-ockanographique difficile & resoudre. Cette determination peut &re faite cependant indirectement par l’bge des indices de phosphate que l’on connait dans la strie stratigraphique locale ou dans les bassins voisins. Critires skdimentologiques Du fait de la permanente de la reserve phosphatk de la mer, on peut s’attendre B ce que les courants phosphatogbnes puissent concrktiser leur effet dans un bassin & n’importe quel moment du cycle sedimentaire. Certains exemples viennent & l’appui de cette id&. Toutefois, les dt5pBts phosphates importants ont une position beaucoup moins variee par rapport & la skdimentation. VISE (1953) avait dkjh remarque que ces dkpBts importants se produisaient en fin de cycle sedimentaire. A la lumibre de ce que j’ai pu voir en Afrique occidentale, plus rapidement en Afrique du nord, et tout rkcemment en Colombie, on peut ajouter que les dkpdts phosphates importants interviennent vers la fin d’une sedimentation chimique pauvre en phosphate. C‘est ainsi qu’au Togo et au Sknkgal, les dt5pBts exploites de l’fiocbne moyen se superposent a une importante serie argileuse B attapulgite pauvre en phosphate, qui dkbute dbs la fin du PalBocbne. En Colombie, les niveau COMUS les plus importants interviennent & la fin de dBpBts chimiques 2i montmorillonite - attapulgite dans lesquels les cherts sont particulibrement dkvelopp6s. On peut alors se demander si ces dkpBts, au lieu #&re liks simplement A la reserve phosphatte gBnQale du fond des mers, ne sont pas lies au contraire 6troitement & la rkserve phosphatke particulibre qui s’est constituke dans le bassin ou & proximitk, a partir de la phase migratrice des sols, pendant tout le temps de dCpBt des formations argileuses magnksiennes ou cherteuses peu phosphatks. I1 semble ainsi qu’on ait des chances notables de rencontrer une periode favorable & la phosphatogknbe abondante, vers l’issue d’une longue periode & sedimentation chimique peu phosphatee. On voit alors que, dans ce premier aspect de la recherche du phosphate, & c6tB de la recherche habituelle des indices, l’ktude skdimentologique des formations stkriles prend un rBle important. Rkgionsfavorables 6 la phosphatogkntse

Ces regions du bassin doivent avoir eu facilement accbs, au moment de la sedimentation, a u rkserves phosphatkes des profondeurs marines et sont, en principe, des zones peu profondes du bassin. I1 s’agit 121 d’un problbme pal6ogCographique, mais aussi skdimentologique dans lequel 1’6cologie des faunes a notamment un rBle interessant. Pkriodes dkfavorables 6 la skdimentation stkrile

Lorsque Ies reliefs sont vigoureux sur le continent, l’krosion est vive, les d$Bts sont dktritiques et abondants. Les reliefs ensuite s’attknuent, l’6rosion est moins Bnergique,

GISEMENTS SfiDIMENTAIREs MARINS DE PHOSPHATE

141

la skdimentation s’affine et, si les conditions climatiques sont favorables, la vkgdtation se dkveloppe, multipliant les obstacles A l’krosion directe des sols ou des roches mkres. La skdimentation du bassin se transforme et l’apport dktritique trks ralenti commence a &re relay6 par les solutions de la phase migratrice des sols. Cette transformation peut &re marquee par une pkriode incertaine au cours de laquelle le remplissage du bassin peut se trouver considkrablement ralenti. Ce ralentissement est d’ailleurs confirm6 par l’existence de niveaux phosphatks, A ce moment du cycle, au Sknkgal et au Dahomey. Dans la suite du cycle, la skdimentation chimique prend le dessus mais, gknkralement moins abondante que la skdimentation dktritique et beaucoup plus dkpendante des conditions physico-chimiques du bassin, elle peut comporter des ralentissements notables. Enfin, aprks une longue pkriode biostasique continue, on peut imaginer deux cas. Ou bien l’attaque chimique des roches m&resdevient de moins en moins aiske A cause de l’kpaisseur trks importante des sols, ou bien le climat se modifie, les apports chimiques diminuent alors que, A cause de l’abondance de la vkgktation qui persiste encore et des reliefs attknuks, les apports dktritiques restent faibles. Les deux cas semblent concourir a situer vers la fin d’une longue pkriode biostasique le moment le plus favorable au ralentissement maximal de la &dimentation sterile dans le bassin. RPgions dbfavorables ci la skdimentation stkrile La rkpartition de la skdimentation issue des apports continentaux est notamment conditionnke par son poids. LOMBARD (1956) a nommk celA le “controle par le fond”. Les sediments sont ainsi plus abondants dans les creux du fond marin, les zones subsidentes. Inversement, la skdimentation la plus rkduite sera situke, kventuellement en bordure de bassin, en bordure du talus continental et surtout sur les hauts fonds kloignks des cdtes. La dktermination des zones a skdimentation rkduite est un problbme de palkogkographie qui a besoin, pour Ctre rksolu, de donnkes prkcises de stratigraphie, de skdimentologie et de structure. Les cartes isopaques et de variation de faciks constituent dans ce cas un instrument de travail particulibrement prkcieux.

CONCLUSION

Cette courte note ne peut prktendre traiter tout le problkme de la recherche du phosphate. Elle essaie simplement de montrer que ce problkme peut Ctre abordk de plusieurs manikes qu’il faut d’ailleurs associer. Au stade de la recherche des zones favorables aux accumulations phosphatkes, la recherche des indices minkralisks, si elle est importante, n’a cependant qu’un r61e relativement secondaire. L‘ktude skdimentologique des formations stkriles, des dkp6ts d’origine chimique notammeht, joue au contraire un r6le de premier plan.

142

M. SLANSKY

Lorsqu’il s’agit de vkrifier la prksence du phosphate puis d‘essayer de dklimiter un gisement exploitable, l’ktude des niveaux minkralisks reprend kvidemment la premiere place. Mais 18 aussi l’ernploie des raisonnements skdimentologiques garde toute son importance car il existe des relations ktroites entre la rkpartition du phosphate et les courants marins, entre les teneurs en P,O, et celles en carbonates par exemple.

RESUMB Les phosphates de chaux skdimentaires s’opposent aux termes plus habituels des skquences lithologiques par l’origine distincte des matkriaux qui leur ont donnk naissance, la diffkrence quantitative existant entre les apports phosphatks et les apports stkriles contemporains, les conditions de dkp6t. Ces oppositions servent de fils conducteurs a la recherche du phosphate qui consiste 51 localiser a la fois des pkriodes et des rkgions favorables a la phosphatogknbse et des pkriodes et rkgions dkfavorables a une skdimentation stkrile abondante. Au stade de la recherche des zones favorables aux accumulations phosphatkes, l’ktude skdimentologique des formations stkriles joue un r61e essentiel.

SUMMARY

The sedimentary calcium phosphates are opposed to the more usual lithological sequences by the distinct origin of the materials that have given them birth, by the quantitative difference existing between the influx of phosphates and the influx of contemporaneous barren materiel, and by the conditions of sedimentation. These oppositions serve as a guide to the research for phosphates which consists in localizing, at the same time, the periods and regions favourable for the genesis of phosphates and those unfavourable for an abundant sedimentation of barren material. The sedimentological study of the barren formations is essential during the phase of research of zones fwourable for the accumulation of phosphates.

BIBLIOGRAPHIE

ERHART, H., 1956. La Gendse des Sols en tant gue Phdnomdnegdologigue.Masson, Paris, 90 pp. A. V., 1937. Les facibs phosphatks et la genkse des phosphates. Tr. Nauchn. Inst. PO Udobr. KAZAKOV, i Insektofug., 139 : 3-73. LOMBARD, A., 1956. Gdologie sddimentaire. Les Sdries marines. Masson, Paris, 722 pp. H., 1959. Le problbme de la phosphatogknbse et son kvolution. Mines Gdol. (Morocco), SALVAN, 6 : 3141. SLANSKY, M., 1962. Contribution it l’ktude gkologique du bassin sidimentairecotier du Dahomey et du Togo. Mdm. Bur. Rech. Minidres, 11 : 270 pp. VISSE,L., 1953. Les facibphosphates. Rev. Znst. Franc. Pdtrole Ann. Combust. Liguides, I : 87-99.

MINERALOGTSCH-GEOCHEMISCHE UNTERSUCHUNGEN AN COELESTOBARYTMIT SEDIMENTAREM GEFUGE (Bohrung Hohes Moor Z 1, Nordwest-Deutschland) HARALD PUCHELT

und

GERMAN MULLER

Mineralogisch-PetrographischesInstitut der Universitat, Tiibingen (Deutschland)

EINLEITUNG; BISHERIGE UNTERSUCHUNGEN

1959 wurde in der Gemarkung Diidinghausen, west-siidwest von NienburglWeser (Messtischblatt 3419), die Aufschlussbohrung Hohes Moor Z 1 vom Konsortium Mobil Oil A. G.-Gewerkschaft Elwerath niedergebracht. Die geologische Bearbeitung erfolgte durck die Mobil Oil A.G. In ihrem unteren Abschnitt traf die Bohrung laut Schichtenverzeichnis folgendes (hier gekiirzt wiedergegebenes) Profil an: Unterer Buntsandstein Zechstein 4-2, z.T. verfaltet und uberkippt Zechstein 2, Basal-Anhydrit Storung Zechstein 2, Hauptdolomit mit 0,75 m Barytlage unterhalb der Storung Zechstein 1

- 2820,5 m

- 3560,O m - 3568,7 m - 3580,O m

- 3896,2 m

Der Bereich der angenommenen Storung wurde durch die Kernstrecke 3568,8(1959) in die vier fol3578,4 m (Gewinn 9,0 m) erfasst und lasst sich nach QUESTER genden Abschnitte gliedern (von oben nach unten): Anhydrit (a) ca. 0,lO m Baryt mit schlierigen Fetzen und Brocken von Karbonatgesteinl (b) 0,75 m Kalkstein und Dolomit mit brekziosem Habitus und zahlreichen calcit6,OO m verheilten Kliiften (c) Kalkstein, schwach dolomitisch, relativ wenig calcitverheilte Klufte (d) 2,15 m Der Baryt (b)stellt nach QUESTER(1959) eine das primar hier vorhandene Karbonatgestein verdrangende Einschaltung dar, unterhalb der eine 6 m machtige, stark zerbrochene und zerriittete Kalk- und Dolomitserie (c) folgt. Einzelne Gesteipsteile sind Die fur diese Untersuchung zur Verfugung gestellten Kernabschnitte ergaben eine Machtigkeit der Barytlage von 0,79m.

Abb.1. Legenda siehe S.145.

COELESTOBARYT MIT SEDIMENThEM GEFUGE

145

zerbrochen und gegeneinander versetzt (zum Ted mit calcitverheilten Kliiften, die Fluorit enthalten), der urspriingliche Gesteinsverband ist jedoch stets noch erkennbar. QUESTER (1959) folgert hieraus, dass der obere Teil des in der Bohrung Hohes Moor Z 1 auftretenden Hauptdolomits im Bereich einer St6rungszone liegt, die auch die im Vergleich zu den benachbarten Bohrungen Deblinghausen Z 1 und Buchhorst Z 1 angetroffene geringe Machtigkeit des Hauptdolomits deuten wiirde. Die vorliegenden Untersuchungen beschranken sich auf die eigentliche Barytzone sowie auf die Gesteinsbereiche im unmittelbaren Hangenden und Liegenden.

MEGASKOPISCHE BESCHREIBUNG

(Abb. 1A-D)

Auffalligste Merkmale sind: (I) Die v6llig scharfen Grenzen des Baryts sowohl gegen den hangenden Anhydrit wie auch gegen das liegende Karbonatgestein. (2) Der in Bezug auf den Anhydrit schichtparallele Verlauf der Anhydrit-BarytGrenze. Die liegende Grenze Baryt-Karbonatgestein ist durch auf- und absteigende, dunkelgefarbte Stylolithen gekennzeichnet. (3) Die im Baryt vorherrschenden, deutlich ausgepragten, mit evaporitischen Anhydrit-Gesteinen vergleichbaren (RICHTER-BERNBURG, 1955) sedimentaren Gefiige, die jedoch stellenweise (Abb. 1C) von senkrecht oder spitzwinklig hierzu verlaufenden, unscharf begrenzten gang- oder keilahnlichen Gefiigeeinheiten (heller Baryt mit Schwefel) durchsetzt werden. Zerbrechungen sind deutlich erkennbar (Abb. 1D). Der Baryt ist grobkristallin ausgebildet. Seine Farbe ist in reinen Partien weiss bis grauweiss. Durch die haufig vorhandenen dunklen Schlieren erscheint das Gestein jedoch im ganzen hell- bis mittelgrau. In Analogie zu den von RICHTER-BERNBURG (1955) an sedimentaren Anhydriten beobachteten Gefiigemerkmalen, die bestimmten Faziestypen und palaogeographischen Anordnungen entsprechen, kann die Barytzone der Bohrung Hohes Moor Z 1 rein phanomenologisch nach der zunehmenden Erkennbarkeit einer schichtigen Ausbildung im Bereiche von Schwaden-, Wolken- und Flaser-Baryt untergliedert werden, wobei Lagen mit wolkigem Gefiige am haufigsten sind. MIKROSKOPISCHE BESCHREIBUNG

Der hangende Anhydrit (Abb.2)

Farblose, meist hypidiomorphe bis idiomorphe isometrische Anhydritkristalle mit

Abb.1. AnscM-Bilder der Coelestobarytzone; x 1. A. Obere Grenze Coelestobaryt (unten)Anhydrit (oben). B. Coelestobaryt mit Schwaden- und Flaser-Textur. C. Coelestobarytvt?rheilteKluft (mit Schwefel) in flaserigem Coelestobaryt. D. Untere Grenze Coelestobaryt-Karbonatgestein (Stylolithen) Zerbrechungenim Coelestobaryt.

146

H. PUCHELT UND G . MULLER

Abb.2. Der Grenzbereich Coelestobaryt(untentAnhydrit (oben); x 20.

rechteckigem Querschnitt und einer mittleren Grosse von 0,1o-O,25mm bilden ein unregelmassig-korniges Gefuge, gelegentlich wird die fur primare Anhydritabscheidung typische “pile of brick-structure” beobachtet.

I47

COELESTOBARYT MIT SEDIMENTAREN GEFUGE

Stellenweise treten einzelne grosse (bis 2 mm) Anhydritkristalle auf, die auf Kosten kleinerer Kristalle gewachsen sind. Untergeordnet sind feinstkorniger Calcit und Tonmineralien (Illit und Kaolinit) am Gesteinsaufbau beteiligt.

Die Barytzone Die im Diinnschliff erfasste Grenze Anhydrit-Baryt (Abb.2) ist scharf. Folgende Mineralien treten in dieser Zone auf: (a) Baryt (im folgenden wegen des hohen isomorph eingebauten Strontiumgehaltes als “Coelestobaryt” bezeichnet), (b) Karbonate, (c) Quarz, (d) Anhydrit, (e) Schwefel,(f) Fluorit, (g) Pyrit und (h) Tonminerale, wobei die Minerale c-h insgesamt im Durchschnitt weniger als 1 % des Gesteins ausmachen. Die Verteilung der Hauptkomponenten Coelestobaryt und Karbonate ist in Abb.4 dargestellt. Coelestobaryt Der Coelestobaryt tritt fast niemals in definierten Einzelkristallen sondern meist in facherformigen und rosettenartigen Aggregaten auf. Die im Durchschnitt 3-6 mm langen, haufig gekriimmten und sich ineinander verzahnenden, nach der a-Achse gestreckten, xenomorphen bis hypidiomorphen Kristalle, die undulos ausloschen und haufig aufeinander senkrecht stehencie Spaltrichtungen (nach 001 und 0 10) erkennen lassen, sind durch feinstverteilten Pyrit schwach dunkel gefarbt (Abb.3). Vom strahligen, grobspatigen Typus abweichend sind hypidiomorphe bis idiomorphe Kristalle von 0,1-0,3 mm Lange, die nicht gekriimmt sind und keine undulose Ausloschung zeigen. Sie treten stets in karbonatreichen Partien der Coelestobarytzone auf und ahneln in Ausbildung und Gesteinsverband den von MULLER (1962) beschriebenen evaporitischen Coelestin-Karbonat-Mischgesteinen. Karbonate Calcit und Dolomit mit einem Einzelkorndurchmesservon ca. 0,Ol mm bilden unregelmassig begrenzte wolkig-schlierige Haufwerke. Daneben tritt klarer Calcit als Zwickelfiillung (bis 6 mm Durchmesser) im Coelestobaryt auf. Idiomorpher Dolomit (Rhomboeder) ist haufig auf Coelestobaryt-Korngrenzen sowie auf Kliiften zu beobachten. Quarz Quarz tritt vereinzelt als EinschluB in Coelestobaryt oder (hier zum Teil stark angereichert) auf Stylolithenflachen auf. Er ist stets idiomorph, haufig enthalt er Einschlusse von feinverteiltem Karbonat. ;

Anhydrit Anhydrit tritt in bis 2 mm grossen, langprismatischen, in Bezug auf den sie ein-

148

H. PUCHELT UND G . MULLER

Abn.3. Coelestobaryt in typischer Ausbildung; x 20.

COELESTOBARYT MIT SEDIMENTAREM GEFUGE

149

schliessenden Coelestobaryt keine Orientierung zeigenden Kristallen auf. Sehr haufig sind die idiomorphen Kristallezum Teil durch Coelestobarytverdrangt, die so erzeugten Strukturen sind denen von korrodiertem Quarz in Eruptivgesteinen nicht unahnlich. Schwefel Geringe Mengen von Schwefel sind feinverteilt uber das ganze Profil vorhanden. Lediglich im Bereich von barytverheilten Kluften finden sich bis zu 1 cm grosse Kristalle.

Fluorit Fluorit wurde nur im untersten Teil der Coelestobarytzone als Seltenheit beobachtet. Er tritt als Zwickelfullung (max. 1,5 mm) zwischen Coelestobaryt auf. Pyrit und Tonmineralien Sie bilden in feinstverteilter Form das dunkle Pigment der Coelestobarytlage. Tonmineralien (Illit und Kaolinit) sind in den dunklen Schlieren angereichert.

Das liegende Karbonatgestein Das unmittelbar Liegende der Coelestobarytzone bilden strukturlose mikrokristalline kalkige Dolomite, die von oolithischen Karbonatgesteinen mit Algenstrukturen unterlagert werden. Coelestobaryt fehlt vollig, jedoch ist nach den Untersuchungen von QUESTER (1959) Fluorit stellenweise sehr haufig.

CHEMISCHE UNTERSUCHUNGEN (Tabelle I,

Abb.4)

Die chemische Untersuchung des Profils wurde derart ausgefuhrt, dass die gesamte Machtigkeit des Coelestobaryts in 40 Abschnitte zerlegt wurde. Der hangende Anhydrit wurde in einer, der liegende Kalk mit sechs Proben erfasst. Bestimmt und in Tabelle I angegeben wurden die Werte Dichte, Sr, CaO, MgO, Schwefel, COz und Fluor. Ausserdem wurden an einer Anzahl von Proben die Porositat und der Kaliumgehalt bestimmt. Qualitativ konnte im Kalk Mangan nachgewiesen werden. Strontium, Calcium und Kalium wurden flammenphotometrisch bestimmt (cf. PUCHELT, 1963). Mg sowie Calcium (als Kontrolluntersuchungen) wurden mit AeDTE titriert. Die ubrigen Werte wurden nach gangigen Methoden erhalten (siehe HILLEBRAND et al., 1953). Die Porositat betragt bei allen Proben unter 6%, in vielen Fallen war uberhaupt kein Porenraum mehr feststellbar. Der Kaliumgehalt aller untersuchten Proben (12) ist unter 0,02 % K,O. Das Karbonat der Proben ist in Calcit und Dolomit enthalten. Durch Vergleich der Analysenwerte fur Kohlendioxyd und MgO sowie CaO geht hervor, dass nur geringste Mengen des CaO (stets < 0,1%) in den Baryt eingebaut sein konnen. Unter Beriicksichtigung der Grbsse der untersuchten Profilabschnitte errechnet

TABELLE I ERGEBNISSE DER CHEMISCHENUNTERSUCHUNGEN

1

2

Laufende Abstand von Nr. der Grenze BarytProbe Anhydrit: cm

1 2 3 4 5

6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26

- 4,O- 0,o 0,O- l,o 1,O- 3,O 3 , s 5,O 5,O- 7,O 7,O- 8,5 8,5-10,O lO,O-11,5 11,5-13,O 13,o-14,O 14,0-15,5 153-17,0 17,O-19,0 19,0-21,0 21,O-23,0 23,O-25,5 25,5-27,0 27,0-30,0 30,O-33,0 33,O-35,0 35,0-37,0 37,O-39,0 39,0-42,0 42,M,O

44,0453 45,5473

urn DER DICHTEBESTIMMUNGEN~

3

4

5

6

7

Dichte 20"/4"

CO,

CaO

MgO

CaIcit2

DolomitS

%

%

%

%

%

2,973 4,320 4,280 4,324 4,309 3,974 3,906 4,288 4,333 4,347 4,250 4,333 4,040 4,155 4.185 4,08 1 4,300 4,351 4,417 4,315 4,261 3,724 4,078 3,750 4,195 4,362

0.66 0,97 1,Ol 1,25 1,23 8,09 8,41 0,92 0,51 0,67 1,50 1,68 6,02 4,22 4,07 6,14 0,76

n.b. 1,22 1,26 1,55 1,54 10,13 10,28 1,14 0,62 0,81 2,02 2,24 6,95 4,93 4,79 6,68 0,92

0:05 0,05

0,06

1,19 1,48 12,73 5,15 14,62 3,36 1,54

1,12 1\90 15,83 6,12 18,02 4,17 1,79

404

n.b.

< 0,Ol < 0,Ol < 0,Ol < 0,Ol 0,20 0,38 < 0,Ol < 0,Ol 0,02 < 0,Ol 0,02 0,56 0,24 0,14 0,68 0,08

< 0,Ol < 0,Ol 0,14 0,04

0,37 0,31 0,50

0,12 < 0,Ol

n.b. 2,18 2,25 2,77 2,75 17,58 179 1,11 1,39 3,61 3.94 10,99 8,21 8,21 10,23 1,45 0,ll 0,07 1,66 3,28 27,33 10,14 30,92 7,14 3,20

8

n.b.

< 0,05 < 0,05 < 0,05 < 0,05 0,91 1,74

< 0,05 < 0,05

0.10

< 0,05

0,lO 2,56 1,14 O,@

3,11 0,37

< 0,05 < 0,05 O,@

0,18 1,69 1,42 2,29 0,55 < 0,05

9 Sr

0,23 3,76 4,67 3,99 3,02 3,08 3,21 4,63 4,65 3,76 4,85 4,42 3,84 4,3 1 4,49 3,74 4,67 5,15 4,78 4,85 4,47 3,11 3,75 2944 4,07 4,22

10

I1

SrSO, SrSO, Gewichts- Molekular prozent4 Prozent4

8,06 10,02 8,60 6,48 7,92 8,32 9,90 9,87 8,00 10,55 9,65 9,32 9,96 10,33 9,05 9,97 10,79 10,02 10,41 9,71 9,18 8,89 7,65 9,24 9,14

10,02 12,40 10,68 8,09 9,85 10,34 12,25 12,22 9,95 13,03 11,95 11,55 12,32 12,77 11,23 12,34 13,32 12,40 12,87 12,02 11,54 11,13 9,52 11,45 11,46

I2

13

F

5

< 0,002 < 0,002 n.b. n.b. 0,007 n.b. n.b. < 0,002 < 0,002 n.b. < 0,002 n.b. n.b. < 0,002 < 0,002 n.b. < 0,002 n.b. < 0,002 n.b. < 0,002 n.b. 0,004 0,013 n.b. 0,004

' 0,27

0,09 0,10 0,30 0,47 0,19 0,14 0,45 0,11 0,26 0;39 0,22 0,08 0,06 0,16 0,10 < 0,02 0,04 0,06

0,08 0,07 0,W 0,08

0,03 0,05

0,08

TABELLE I (Fortsetzung)

1 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43

44 45 46 47

2

3

4

5

47,5-49,5 49,5-52,O 52,0-54,5 54,5-56,5 56,5-58,5

4,163 4,192 3,857 3,772 3,550 3,435 3,974 4,317 2,928 3,999 3,852 3,945 4,073 4,129 4,207 2,941 2,755 2,752 2,850 2,721 2,720

2,90 3,36 9,88 11,72 16,89 19,09 10,25 1,30 40,26 5,42 11,67 7,68 5,lO 4,81 3,58 46,20 44,25 43,71 44,23 43,33 44,13

3,76 4,03 12,15 14,30 21,19 23,63 12,46 1,51 32,80 6,67 14,00 9,30 6,42

58,5-60,0

60,0-61,5 61,5433 63,5-66,O 66,0-68,0 68,0-70,0 70,&72,5 72,5-74,5 74,5-77,0 77,O-79,0 79,O-8 1,O 81,&83,0 83,O-85,O 85,0-87,0 87,&89,0 89,0-91,5

5,80

4,423 37,60 48,06 50,55 45,50 48,80 51,34

6

< 0,Ol 0,18 0,13 0,42 0,26 0.55

0,37 0,lO 3,40 0,21 0,58

0,28 0,09 0,14 0,09 15,32 606 3,74 7,43 4,93 3,42 -

Vergleiche Abb.4. Berechnet aus Spalten 4 und 5 . BerThnet aus Spalten 5 und 6. Berechnetfur SrSO, BaSO, = 100%.

+

7

8

9

10

I1

6,71 6,75 21,37 24,49 37,18 40,81 11,94 2,45 25,28 9,34 19,39 13,Ol 8,87 8,25 6,16 29,06 70,76 80,95 62,76 74,88 83,15

< 0,05

4,75 4,36 3,28 3,08 2,26 2,16 3,65 4,66 0,83 3,lO 3,18 3,23 3,36 3,30 3,91 0,015 0,023 0,034 0,028 0,030 0,027

10,34 9,89 8,81 7,72 7,68 7,98 8,85 10,05 12,96 7,24 8,56 7,90 7,77 739 8,76

12,78 12,24 10,93 9 61 9,56 9,93 10,98 12,43 15,91 9,02 10,63 9,83 9,67 9,52 10,97

0,82 0,59 1,92 1,19 2,52 1,69 0,46 61,30 0,96 2,66 1,28 0,41 0964

0,41 70,09 27,72 17,ll 33,99 22,53 15,64

12

13

n.b.

0,09 0,13 0,11 0,10 0,38 0,24 < 0,02 0,04 0,05 0,09 0,25 0,07 0,22 0,15 0,17 0,94 0,12 0,06 0,33

< 0,002 n.b.

< 0,002 n.b.

< 0,002 n.b.

< 0,002 < 0,002 0,049

< 0,002 n.b. 0,006 0,004

< 0,002 n.b. n.b. n.b. n.b. n.b. n.b.

0,05

0,06

152

H. PUCHELT UND G. M a L E R Robe

cm 0

4

10

r

20

40

50

70

80

90 0 M 40 €0 80 1 W Gew% Boryr. Calcit, Dolornit

o m m

Dichte fg/cm’J

I

Gew% SrSOl bezogen ouf IBaSO++ SrSO,,: 100%

1

Gew 7 . Schwefei

Abb.4. Graphische Darstellung der Untersuchungsergebnisse

sich fur die Proben 2-41 (Coelestobarytmachtigkeit)ein mittlerer Strontiumgehaltvon 3,60 %. Wird dieser lediglich auf die nicht verunreinigten Sulfate bezogen, so liegt der mittlere SrS0,-Gehalt bei 8,62 %. Rontgenographische Bestimmungen zeigten, dass der SrS0,-Gehalt nicht als Coelestin vorliegt, sondern isomorph im Baryt eingebaut ist. Es liegt daher ein Coelestobaryt vor. Die von STARKE und RUHLICKE (1961) angegebene rontgenographische Methode zur Bestimmung des SrS0,-Einbaus auf Grund der Lage des (410)-Reflexes fiihrte in unserem Falle zu keinen befriedigenden Ergebnissen. Die rontgenographisch ermittelten Werte lagen mehr als doppelt so hoch wie die chemisch gefundenen. Die

COELESTOBARYT MIT SEDIMENT-M

GEFUGE

153

Diskrepanz zwischen den beiden Methoden lasst sich nicht durch die Anwesenheit von Ca oder Pb im Gitter erklaren, da beide Elemente nur in Spuren im Coelestobaryt nachgewiesen werden konnten. Der Coelestobaryt der Bohrung Hohes Moor Z 1 zeigt in chemischer Hinsicht zwei Besonderheiten: (1) einen sehr hohen und in Bezug auf das Verhaltnis SrSO,/BaSO, verhaltnismassig konstanten Strontiumgehalt, (2) das Auftreten deutlicher Mengen von elementarem Schwefel. Der Strontiumgehalt im Coelestobaryt zeigt uber die gesamte Coelestobarytzone keine gesetzmassigen Schwankungen.

GENETISCHE BETRACHTUNGEN

Die Art der konkordanten Lagerung bei scharfen Grenzen gegen das Hangende und Liegende, das Fehlen eines Salbandes und eines Zonenbaus sowie das deutliche sedimentare Gefuge sprechen gegen eine hydrothermale Gangfullung. Ein Vergleich mit Strontiumgehalten von Baryten aus Gangen zeigt, dass nur einige wenige Vorkammen ahnlich hohe Strontiumgehalte aufweisen: GUNDLACH (1959) untersuchte 186 Baryte aus verschiedenen Vorkommen des Harzes, aus dem Ruhrcarbon, dem Schwarzwald sowie weitere Einzelstucke und fand bei nur drei Proben einen Strontiumgehalt > 4 %. BUSCHENDORF und PUCHELT (1962) stellten die Strontiumgehalte von 174 Baryten des Ruhrcarbons fest und fanden nur eine Probe mit einem Strontiumgehalt > 2 % Sr. An 136 Schwerspaten aus verschiedenen Gangen des Schwarzwaldes bestimmten BUSCHENDORF et al. (1962) Strontiumgehalte bis max. 3,54% Sr (24 Proben > 2%, davon 4 Proben > 3 % Sr). WERNER (1958) bearbeitete unter anderem die Baryte des Schmalkaldener Reviers geochemisch. Er erhielt bei insgesamt 659 Proben einen Maximalwert fur Sr von 2,58 %, wahrend die Mittelwerte fur die verschiedenen Gange von 0,98 bis 2,24 % schwanken.Eine Unterscheidungsmoglichkeitvon Gangen saxonischerund variscischer Genese liegt nach WERNER (1958) in den Strontiumgehalten, die fur die erstgenannten zwischen 0,48 und 1,67% und fur die letzteren zwischen 1,91 und 4,78% liegen. STARKE (1962) bestimmte im Owospat von Freiberg/Sa. den Strontiumgehalt zu maximal 2,9 %. BAUMANN (1958) fand fur den Zentralteil der Freiberger Gange Strontiumgehalte bis zu 2,4 %. Die bekannten deutschen sedimentaren Lagerstatten Meggen/Lenne und Rammelsberg/Harz wurden von BUSCHENDORFund PUCHELT (1963a, 1963b) bearbeitet. Fur Meggen (239 Proben) wurde ein hochster Strontiumgehalt von 1,14 % gefunden, wahrend fur die beiden Lagerteile Mittelwerte von 0,30 und 0,79 % erhalten wurden. Der Baryt des Rammelsberges ergab maximal 1,08 % Sr. Aus diesen Vergleichen ist die Sonderstellung des Coelestobaryts dei Bohrung Hohes Moor Z 1 aufgrund seines hohen Strontiumgehaltesersichtlich.

154

H. PUCHELT UN'D G. MULLER

Aus hydrothermalen Gangen sind uns keine Paragenesen bekannt, die Baryt und elementaren Schwefel enthalten. Zur Erklarung der Entstehung solcher Mineralvergesellschaftungen mochten wir auf Beobachtungen von BUTLIN(1953) hinweisen, der eine Tatigkeit von sulfatreduzierenden Bakterien bis zu einer Tiefe von 1.200 m und bis zu einer Temperatur von 63°C in artesischen Wassern in der Nahe von Tripoli feststellte. Weitere Angaben fur die Entstehung elementaren Schwefelsdurch Bakterien finden sich unter anderem bei DESSAU et al. (1962), die mit Hilfe von Schwefelisotopenuntersuchungen Beweise fur die bakterielle Entstehung sizilianischer Schwefellagerstatten erbrachten. Fur die Deutung der Genese miissen unseres Erachtens die deutlich vorhandenen sedimentaren Gefugemerkmale besonders herausgestellt werden. Bei metasomatischen Prozessen in Sedimenten wird das primare Gefuge haufig ebenfalls erhalten, desgleichen konnten im vorliegenden Falle die im Coelestobarytkorper noch vorhandenen feinkornigen Karbonate als Relikte der primaren Karbonatgesteine aufgefasst werden. Zahlreiche Beobachtungen weisen jedoch darauf hin, dass eine syngenetischsedimentare Bildung des Coelestobaryts in einem Evaporitzyklus nicht auszuschliessen ist. Sedimentare Barytabscheidungen sind in Salinarfolgen des Perms und Neogens aus der U.d.S.S.R. bekannt (DRAGUNOV und KATSCHENKOV, 1953; KATSCHENKOV, 1961; KOSSOVSKAJA und SCHUTOV,1954). Fur die Bildung wird Ausfallung in ufernahen Regionen des Meeres sowie in lagunaren Bereichen angegeben. Aus rezenten pelagischen Sedimenten des Pazifiks beschreibt ARRHENIUS (1962) das Auftreten von authigenem Coelestobaryt mit einem SrS0,-Gehalt von 5,4 mol. %. Das konkordante Auftreten des Coelestobaryts zwischen Hauptdolomit und Basalanhydrit bei verringeiter (bisher tektonisch gedeuteter) Schichtmachtigkeit des Hauptdolomits ist palaogeographisch zu begrunden, wenn man annimmt, dass die Abscheidung des Coelesto6aryts ahnlich wie bei den Coelestinvorkommen von HemmelteWest und am Ostrand des Rheinischen Schiefergebirgesauf einer submarinen Schwelle erfolgt ist, auf der in Bezug auf den Gesamtozean wegen der hier hoheren Verdunstung eine Vorkonzentration des Meerwassers stattfand. Wahrend der hohe Sr-Gehalt des Baryts sich ohne weiteres aus den primar im Meerwasser vorhandenen Sr-Gehalten ableiten lasst, trifft dies auf das Barium nur bedingt zu (vergleichehierzu die Diskussion um die Herkunft des Ba in den bekannten Lagerstatten Meggen und Rammelsberg). Das Auftreten von Fluorit widerspricht nicht einer synsedimentaren Entstehung, da erst kiirzlich (KRUGER,1962) im Plattendolomit des Geraer Beckens syngenetischsedimentarer Fluorit nachgewiesen worden ist. Bereits fruher war Fluorit aus dem Haupt- und Plattendolomit des Emslandes beschrieben worden (FUCHTBAUER, 1958), dessen Auftreten an Algen oder Algenlagen benachbarte Zonen gebunden war. Den Firmen Mobil Oil A.G. in Deutschland, Celle, sowie Gewerkschaft Elwerath, Hannover, danken wir fur die Zurverfugungstellung des Untersuchungsmaterials sowie fur die Genehmigung zur Veroffentlichung dieser Ergebnisse.

COELESTOBARYT MIT SEDIMENTAREM GEFUGE

155

ZUSAMMENFASSUNG

In der AufschlussbohrungHohes Moor Z 1 (Zechstein 2) bei Dudinghausen/Nienburg an der Weser wurde eine 75 cm dicke Lage von Coelestobaryt mit einem durchschnittlichen SrS0,-Gehalt von 8,6 Gewichtsprozent gefunden. Die sedimentaren Strukturen, die deutlichen Grenzen sowohl gegen das Hangende als auch das Liegende, der hohe Sr-Gehalt und das Vorkommen von elementarem Schwefel sprechen gegen eine hydrothermale Entstehung. Es wird vielmehr eine synsedimentare Abscheidung im Zechstein-Salinar angenommen, da der Coelestobaryt in gewisser Hinsicht I Lagerungsform, Ausbildung, palaogeographische Verhaltnisse) mit der Coelestin-Lagerstatte von Hemmelte-West verglichen werden kann.

SUMMARY

A 75 cni thick layer of celestobarite with an average SrS0,-content of 8.6 weight percent has been found in the upper Permian (Zechstein 2) of the Hohes Moor Z 1 wildcat in northwestern Germany. Owing to its sedimentary structures, its distinct boundaries with both the hanging and the foot wall, its high Sr-content and the occurrence of native sulphur, the authors deny a hydrothermal origin. They suppose a syngenetic intraformational deposition in the Zechstein-salinare since the celestobarite corresponds in some respects (bedding, fabric, paleogeographicalconditions) with the Hemmelte-West celestite deposit.

LITERATUR

ARRHENIUS, G., 1962. Pelagic sediments. In: M. N. HILL,E. D. GOLDBERG, C. O’D. ISELIN and W. H. MUNK(Editors), The Sea, Ideas and Observations on Progress in the Study of rhe Seas. 3. Interscience, New York (N.Y.), in press. L., 1958. Tektonik und Genese der Erzlagerstatte von Freiberg (Zentralteil). Freiberger BAUMANN, Forschungsh., C, 46 : 106. BUSCHENDORF, F. und PUCHELT, H., 1962. Untersuchungen an Baryten des Ruhrcarbons (Zur Geochernie des Baryts, 111). TechnischeHochschule, Hannover (unveroffentlichtesManuskript). F. und PUCHELT, H., 1963a. Untersuchungen am Schwerspat des Meggener Lagers BUSCHENDORF, (Zur Geochemie des Baryts, I). Geof.Jahrb., 82, im Druck. BUSCHENDORF, F. und PUCHELT, H., 1963b. Untersuchungen am Schwerspat der Rammelsberger Lager (Zur Geochemie des Baryts, 11). Geof.Jahrb., 82, im Druck. BUSCHENDORF, F., PUCHELT, H. und SCHURENBERG, H., 1962. Untersuchungen an Schwerspaten des Schwarzwafdes (Zur Geochernie des Baryts, ZV) . Technische Hochschule, Hannover (unveroffentlichtes Manuskript). BUTLIN.K. R., 1953. The bacterial sulphur cycle. Research (London), 6 : 184. DESSAU,G., JENSEN, M.L. und NAKAI,N., 1962. Geology and isotopic studies of Sicilian sulfur deposits. Econ. Geol., 57 :410-438. DRAGUNOV, V. I. und KATSCHENKOV, S. M., 1953. Uber Coelestin und Schwerspat aus den Neogenablagerungenam siidlichen Mangyschlak. Dokl. Akad. Nauk S.S.S.R., 93, (2) 315-318 (in russischer I Sprache). FUCHTBAUER, H., 1958. Die petrographische unterscheidung der Zechsteindolomite im Emsland durch ihren Saureriickstand. Erdol Kohle, 11 : 689-693.

156

H. PUCHELT UND G. MULLER

GWNDLACH, H., 1959. Untersuchungen zur Geochemie des Strontiums auf hydrothermalen Lagerstatten. Geol. Jahrb., 76 : 637-712. HILLEBRAND, W. F.. LUNDELL, G. E. F., BRIGHT,H. A. und HOFFMAN, J. I., 1953. Applied Inorganic Analysis, 2 ed. Wiley, London, 1034 pp. KATSCHENKOV, S. M., 1961. Characteristics of conditions of sediment accumulation from dispersed chemical elements. Tr. Vses. Neft. Nauchn. Issled. Geologorazved. Inst., 174 : 109. KOWVSKAJA, A. G. und SCHUTOV, V. D., 1954. Uber die Bildungsbedingungen der produktiven Schichtenfolgeder Republik Azerbajdshan. Dokl. Akad. Nauk. S.S.S.R.,97 : 141-144. KRUGER, P., 1962. uber ein Vorkommen von syngenetisch-sedimentaremFluorit im Plattendolomit des Geraer Beckens. Bergakademie, 11 : 742-750. MULLER, G., 1962. Zur Geochemie des Strontiums in ozeanen Evaporiten unter besonderer Berucksichtigung der sedimentaren Coelestinlagerstattevon Hemmelte-West (Sud-Oldenburg). Geologie (Berlin), Beih., 35 : 90 pp. PUCHELT, H., 1963. Eine Methode zur Bestimmung flammenphotometrischerfassbarer Elemente in schwerloslichen Sulfaten. Erzmetall, 1964, im Druck. H., 1959. Hohes Moor Z 1. Petrographische Untersuchungen an Kemproben des HauptQUESTER, dolornit. Mobil Oil A.G., Petrog. Ber., 213 : 28 pp. RICHTER-BERNBURG, G., 1955. uber salinare Sedimentation. Z. Deut. Geol. Ges., 105 : 593. STARKE, R., 1962. Die Strontiumgehalte der fba-Baryte des Freiberger Lagerstattenbezirks. Bergakademie, 14 : 282-286. STARKE, R. und RUHLICKE, D., 1961. Eine Methode zur flammenphotometrischenund rontgenographischen Bestimmung von Strontium und Kalzium im Baryt. Bergakademie, 7-8 : 505-51 1 . WERNER, C.-D., 1958. Geochemie und Paragenese der saxonischen Schwerspat-Flussspat-Gange im Schmalkaldener Revier. Freiberger Forschungsh., C, 47 : 1-120.

SMALL SCALE SEDIMENTARY FEATURES IN THE ARKANSAS BARITE DISTRICT R . A. ZIMMERMANN

and

G.

c.

AMSTUTZ

University of Missouri, School of Mines and Metallurgy, Rolla, Mo. (U.S.A.)

The following is a presentation of small scale details on sedimentary features only. These have not previously been described from the Arkansas barite belt. They appear to be of distinct genetic value and support a sedimentary origin, i.e., theory Ia or Ib on Fig.1. The observations reported here are a result of field work in the Arkansas barite belt during the summers of 1960, 1961 and 1962. The three basic small-scale geometric patterns pertaining to the barite in the Mississippian Stanley Shale of Arkansas are ( I ) continuous beds of variable thickness and grade, (2) lenticular and worm-like bodies and (3) nodules of pure barite. Between these patterns, there are gradational transitions. Also, all three patterns may be closely associated locally.

Syngenetic

At=o

la Sedimentation of material originating from erosion only; Ba, S, 0 endogenous to the rivers and to the ocean waters of the Mississipian sea.

I b Volcanic-exhalative Ba and/or S mixed andprecipitated with normal sediments; thus,exogenous source for Ba and/or S.

Ep ig e n e tic

&=n

I a BaSO, endogenous to the sediments, but concentrated by circulating groundwater:

Ub Bas04 exogenous to the sediments,intmduced from the Cretac.Magnet Cove ring dike.

Fig.1. The four basic theories on the genesis of the Arkansas barite belt. S.S. = sandstone.

158

R. A. ZIMMERMAN A N D G. C. AMSTUTZ

Fig.2. The bedded occurrence of barite nodules.

tFig.3. Thin section with spherical barite nodules; x 4.

SMALL SCALE SEDIMENTARY FEATURES

159

Fig.2 illustrates the bedded occurrrence of the barite nodules, which, on a millimeter scale, show the depositional patterns which we consider to be the most critical genetic features. The larger nodules generally occur within well-defined beds of silty shale which very often overlie silt or shale beds barren of barite. A simple rhythmic relationship exists between individual beds of shale or silt, shale with lenses and nodules, and beds consisting mainly of dense barite. Generally, a shale or silt bed is overlain by a similar bed consisting essentially of nodular or lenticular barite, which in turn is overlain by a dense barite bed. If the dense barite bed is absent, then the nodular or lenticular bed will be overlain by barren shale. Fig.2 illustrates these relationships with five distinct pairs of rhythms on top and eight indistinct pairs towards the bottom. This outcrop occurs in the barite section at the southeast end of the Chamberlain Creek syncline. Fig.3-7 are enlarged 1 : 1 photographs of thin sections. The present scale varies from 3 : 1 to 6.5 : 1 as indicated. Also, top and bottom in the picture always corresponds to top and bottom in the sedimentary bed. The barite nodules lie in distinct shale or silt layers. Their shape varies from perfectly spherical, as shown in Fig.3, to oval (Fig.4, 5) or even sausage- or worm-shaped (Fig.5, 6, 7). .

Fig.4. Thin section with oval barite nodules; x 3.5.

160

R. A. ZIMMERMAN A N D G . C. AMSTUTZ

Fig.5. Thin section with a combination of worm-shaped bodies, “drops”, lenses and spherical barite nodules; x 3.5.

Many barite nodules and the local bedding show geometric patterns typical of depositional sedimentary features. These patterns are clear evidence for the primary depositional origin of the barite. SANDER(1936) has used the term geopetal for these geometric patterns which are standard criteria for top-bottom distinction in sedimentary petrology. In Fig.3, one of the nodules rests on a lower nodule which is broken, with the broken part moved slightly to the left. The trend of the sediments around the nodules are typical depositional and diagenetic gravity or geopetal features. The breakage must have occurred during diagenesis because the layers surrounding it are adjusted. This then may be considered a case of diagenetic brecciation. At the bottom of this figure, micro-cross-bedding is seen. Fig.3-6 illustrate the polar depositional nature of the bedding in the vicinit! of the nodules. On the right side of the large unbroken nodule of Fig.3, there rests a wedge of indistinctly bedded sediment. This wedge is a polar or geopetal feature because it has always the same top-bottom orientation. The size and shape of these wedges, as well as the depth of burial in itself, are functions of the viscosity, the time of formation, the difference in specific gravity and a few other minor factors. Local bedding around the nodules often contains fine baritic laminae, or worm-tosausage shaped bodies, often with a core of pyrite. In such cases, another distinct geopetal feature is often found: if one of these baritic “sausages” overlies two neighboring nodules, the upper surface is essentially horizontal, whereas at the bottom it

SMALL SCALE SEDIMENTARY FEATURES

161

fills the V-shaped space between the two nodules (two examples in Fig.6). This is just another of the numerous small geopetal features observed on a microscopic scale. A combination of worm-shaped bodies, “drops”, lenses and spherical nodules is shown in Fig.5. The sedimentation featuresjust described could be called “static depositional features” because, essentially, they display only a vertical polar vector. A second type of feature displays patterns which cannot be visualized without assuming some horizontal movement in the unconsolidated state. In addition to the vertical gravity vector, a horizontal vector of movement must have played a role in the formation of the patterns observed and shown in Fig.7. This figure illustrates microfolding within one of the baritic shale beds. The axial planes of the intraformational drag-folds of baritic shale are roughly parallel to the overlying and underlying beds. Fig.7 also illustrates sedimentary or diagenetic flowage of a baritic layer. Other features suggesting horizontal movement before and during consolidation are the abundant step-like or en-echelon patterns of baritic beds with or without associated folds and corrugations of the associated shale layers (cf. Fig.5). In addition, in shaley barite layers which exhibit flowage patterns, the barite lenses are often flat oval, suggesting flattening during the diagenetic microtectonic lateral movement. These flattish lenses of granular barite may be called micro-pressure lenses. These observations are good evidence for assuming that the barite has played an integral part in the formation of this second class of depositional and diagenetic patterns with two vectors. Therefore, these patterns afford a second class of criteria for a sedimentary origin of the barite. A third class of small scale features and criteria for a syngenetic depositional origin

Fig.6. Thin section with several barite nodules; X 3.

162

R. A. ZIMMERMAN A N D G . C. AMSTUTZ

Fig.7. Thin section with oval and sausage-shapedbarite nodules, illustratingmicro-folding within one of the baritic shale beds and sedimentaryof diagenetic flowage of a baritic layer; x 6.5.

of the barite consist of the crystal growth features of the nodules themselves. The internal texture of the barite nodules is also of detective value. In the sediments which often do not show any horizontal vector of depositional movement, the nodules often display a radiating pattern. The individual barite rods either radiate from a common center as illustrated in Fig.4 or from a mass of varying size of fine-grained barite occupying the central portion of the nodule (upper portion of Fig.5). This central portion often shows a concentric ring-type pattern with the finest material in the center. Occassionally one of the concentric spheres consists of pyrite. A barite nodule in detail often shows a corrugated surface. Each individual bend corresponds to one individual barite crystal. These radiating crystal-growth textures are rarely found in the sediments showing horizontal movement during or before diagenesis. This fact may, therefore, be considered .to be additional proof of the depositional age of the growth of the barite nodules. Based on the observations presented here, the authors believe that the genetic hypothesis requiring the least number of assumptions is the one which assumes a sedimentaryformation of the Arkansas barite. The question of the possible source of the Ba and S is presently being investigated with chemical and isotope analyses.

SUMMARY

Small-scale features of the Mississippian barite beds of Arkansas are described. Their

SMALL SCALE SEDIMENTARY FEATURES

163

top-bottom or geopetal nature shows that they must have originated during sedimentation and diagenesis. These hitherto unknown features of primary sedimentation and the wide-spread regional distribution at distinct stratigraphic and paleogeographic loci rule out the conventional epigenetic theory.

ACKNOWLEDGEMENT

The interest and financial help of the Arkansas Geological Survey is gratefully acknowledged.

REFERENCES

AMSTUTZ, G. C., 1962. L'origine des gites minkraux concordants dans les roches skdimentaires. Chronique Mines Rech. MiniPre, 308 : 115-126. HAM, W. E. and MERRIT, C. A., 1944. Barite in Oklahoma. Oklahoma, Geol. Surv., Circ., 23 :42 pp. JONES,T. A., 1948. Barite depositsin the Ouachita Mountains, Montgomery, Polk and Pike Counties, Ark. U.S., Buy. Mines, Rep'. Invest., 4348 : 1-15. MISER,H. D. and PURDUE, A. H., 1929. Geology of the De Queen and Caddo Gap quadrangles, Ark. US.Geol. Surv., Bull., 808 : 1-195. SANDER, B., 1936 (Translation by E. B. Knopf, 1951). Contribution to the Study of Depositional Fabrics. Am. Assoc. Petrol. Geologists, Tulsa, 160 pp. SCULL,B. J., 1958. Origin and occurence of barite in Arkansas. Arkansas Geol. Conserv. Comm., Inform. Circ., 18 :101 pp. SHROCK, R. R., 1948. Sequence in Luyered Rocks. McGraw-Hill, New York, 507 pp. ZIMMERMANN, R. A. and AMSTUTZ, G. C., 1961. Sedimentary features in the Arkansas barite belt. Ann. Meeting Geol. SOC.Am., Cincinnati, 1961. Abstracts -Bull. Geol. SOC.Am., 68 : 306-301. ZIMMERMANN, R. A., 1963. Sedimentary Petrology of the Barite Deposits of Arkansas. Ph. D. Thesis, University of Missouri, Rolla, Missouri, in preparation. ZIMMERMANN, R. A. and AMSTUTZ, G. C., 1964. Die Arkansas-Schwerspatzone(neue sedimentpetrographische Beobachtungenund genetischeUmdeutung). Erzmetall, in press.

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DISCUSSION OF PAPERS IN PART C

M. Brongersma-Sanders (The Netherlands): Upwelling causes a high concentration of phosphates in the surface water. Plankton and fish concentrate the phosphate many thousand times. Phosphate concentration probably may reach very high values within a mass of plankton and/or dead fish lying on the bottom of the area of upwelling. Upwelling causes an extreme aridity of the hinterland. As a result, runoff is almost completely absent and the supply with terrigenous material is unusually low. This might explain the fact emphasised by M. Slansky and others that the quantity of terrigenous material usually is very scanty in phosphatic deposits. M. A. Condon (Australia): With reference to the paper by R. A. Zimmermann and G. C. Amstutz: In the Lower Cretaceous shale of the Carnawan Basin of Western Australia, a few beds of baryte, up to 1 ft. thick, are very widespread. The baryte occurs as small crystals, up to 1 mm in diameter, in loose granular arrangement. The shale is a dark marine shale with many pelagic Foraminifera and Radiolaria.

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RAPPORT DE SYNTH~SE PIERRE R O U T H I E R

Laboratoire de Gkologie appliquke, Universitk de Paris, Paris (France)

INTRODUCTION

Ce Symposium a eu lieu dans le cadre du sixitme Congrts stdimentologique international, qui s’est tenu aux Pays-Bas et en Belgique en m i 1963. L’initiative, due a G. C. Amstutz, a t t t t r b bien accueillie par le Comitk d‘organisation du Congrh. Le Symposium a r e p l’hospitalitt de l’Universit6 technique de Delft, reprksentte par F. J. Faber. Si les 75 participants annoncts n’ktaient pas tous prksents, les khanges de vues, quoique brefs (communications et discussions ne durerent pas plus de quatre heures !), y furent particuli6rementvivants et fructueux. Avant m&med’en rtsumer et d’en ordonner les lignes directrices on peut en dtgager un enseignement. Dans la mesure - et celle-ci est large - oa, par la force des faits, la gitologielest de plus en plus conduite A s’inttresser aux phtnomgnes de stdimentation, elle devra chercher des enseignements dans la skdimentologie et auprts des stdimentologistes. Cette idte a ktk le motif des promoteurs du Symposium, et elle s’est exprimte, A la fin de celui-ci, sous la forme de rtsolutions dont on trouvera le texte ci-aprts. Au lieu de se borner a publier, B la suite les unes des autres, les communications prtsenttes au Symposium, il a paru utile d’en rechercher les tendances les plus marquantes. Ces tendances peuvent s’exprimer par le vocable “points de vue”, ou mieux “mtthodes d‘approche”, dtpendant surtout de l’tchelle a laquelle on consid6re les phtnomtnes. En rtalitk ce Symposium fut remarquable en ce sens qu’il a apportt des faits sans sombrer dans les discussionsgtnktiques; il rappelle B cet tgard le remarquable “Symposium sur les gisements de cuivre stratiformes en Afrique” (21e Congrts gtologique international, Copenhague, 1960). Si le terme diagenPse y revient souvent, c’est dans une perspective tout A fait historique, et non pas dam le cadre d’une sempiternelle discussion ou option syngentse-tpigenbe. I1 semble donc bien qu’un nombre de plus en plus grand de chercheurs ressente le besoin d’accumuler des faits, pendant longtemps inobservts et nkgligts, avant de reconstruire, par ktapes, une thtorie gknktique digne de ce nom. Encore les faits ne sont-ils rapidement utilisables, et assimilables, que si on les rapQue Yon nous autorise les neologismes, rnsme ma1 construits, “gitologie” et “gitologu6”! Chacun sait ce qu’il faut entendre par la; ils sont dtja pass& dans l’usage oral de divers spkialistes et le premier est encore le rneilleur tquivalent de l’allemand “Erzlagerstattenkunde”.

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proche dans des ensembles logiques. C’est ce que nous tenterons ici, en rtservant pour la fin l’tvocation des interprktations gtnttiques. Dans ce rassemblement apparait, tout naturellement, une petite difficultt: divers auteurs ne se limitent Bvidemment pas a une mtthode d’approche et a une tchelle. Leurs communications seront alors cities sous plusieurs rubriques. En effectuant ce travail, dont il a rapidement brosst l’tbauche a la fin de la journte du Symposium, le rapporteur a pu se rendre coupable de quelques schtmatisations ou omissions. I1 espbre cependant faciliter la tiiche des tr6s nombreux gitologues qui n’ont pu assister au Symposium, et s’il avait en partie “trahi” la penste de certains auteurs, les textes dtposts par ceux-ci demeurent, auxquels on peut se rtftrer. Les rtftrences non suivies d’annte, de publication ont trait aux communications contenues dans le prtsent ouvrage.

LES ENSEMBLES DE FAITS,

ENVISAGBS

S U I V A N T LES

MBTHODES

D’APPROCHE

ET LES J ~ C H E L L E S

Nour irons dans I’ordre des Cchelles de plus en plus grandes. Point de vue palkogkographique; site, milieu (environnement)

La plupart des communications, et c’est la marque de l’effort essentiel des gitologues d’avant-garde durant les dernitxes anndes, s’efforcent de prtciser les caractbres du milieu oh s’est formte l‘enveloppe stdimentaire du gisement (pour ne pas dire: du milieu oh s’est form6 le gisement!). Minkralisations et aires de skdimentation ralentie Ces aires de stdimentation ralentie (expression due a BERNARD), situtes a la ptriphtrie de masses continentales importantes ou de hauts-fonds, se marquent par des signes particuliers. Biseaux stratigraphiquespar “condensation”, lacunes etc. Les biseaux par condensation se distinguent des biseaux par rtduction ou de lignes de rivage. Suljures. Sur la bordure triasique et liasique des Ctvennes du Sud (France) tous les gisements sulfurts stratoides de cette couverture de socle stable colncident avec des aires de stdimentation ralentie dont la meilleure image est celle des biseaux stratigraphiques par condensation marquant la ptriphtrie de hauts-fonds contemporains de la stdimentation. Ces hauts-fonds sont des lieux d’tlection pour l’accumulation du soufre (cf. Sicile), mais aussi des argilites et des ultra-dttritiques, beaucoup plus aptes B fixer par adsorption les mttaux lourds en solution que les stdiments moins fins et plus Bpais du bassin environnant (BERNARD;voir aussi et surtout la thbe de cet auteur, 1958). Remarquons que ces travaux, ainsi que d’autres effectuts en d’autres rtgions de France (LAUNEY et LEENHARDT, 1959; ESPOURTEILLE, 1960; ZISERMAN, 1964; ROGEL,

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1961 ;etc.) ont finalement tous abouti au m8me schtma paltobathymttrique favorable aux concentrations sulfurtes: protubtrance et talus du fond sous-marin. Phosphates d’origine marine. Les zones les plus riches en phosphate d‘une formation gtologique correspondent a des zones de moindre tpaisseur de cette formation (exemples: Maroc, Togo, Stntgal); la recherche de phosphates devra donc envisager la dttermination des zones A stdimentation rtduite (SLANSKY). Barytine (et ctlestite). La ctlestobarytine d‘un sondage dans le Zechstein du Nordouest de l’Allemagne, comme la ctlestite d’autres regions allemandes, et par exemple de la bordure orientale du Massif schisteux rhtnan, coincide avec une ride sous-marine (PUCHELT et MULLER). Remarquons que cet exemple en rappelle d’autres, oh la barytine semble s’8tre dCposCe plus prts des sommets de hauts-fonds que les sulfures (galtne). Appareils rbcijaux. Dans le Ladinien des Alpes orientales, oh se trouvent de nombreux dtp6ts de Pb-Zn (Gorno, Raibl, Mezica, Bleiberg-Kreuth, etc.), le milieu stdimentaire oh eut lieu la concentration mttallique est caractkist par des conditions ltgtrement euxiniques, et localist du c8tt de l’arritre-rkif ou lagon (communication H.-J. Schneider). Dans le schtma synthttique donnt par cet auteur on remarque que la plupart des.minCralisations se situent stratigraphiquement audessus de la phase de croissance principale de la barritre rtcifale ou bioherme. Dans le Lias inftrieur et moyen du Haut Atlas du Maroc, les mintralisations stratiformes peuvent se trouver en dessous du signe majeur de la dtformation, ttmoignte par l’installation du rtcif, ou au-dessus (communication de D. Bazin, M. Leblanc et P. Routhier). Dans tous les cas leur position rtpond au schtma paltobathymttrique indiqut plus haut et l’appareil rtcifal n’en est qu’une manifestation. A propos de cette dernitre communication, Ph. Launey rekve sur la bordure sud du Massif Central franGais, la quasi-contemporantitt (avec le Maroc) des rtductions de zones a Ammonites du Carixien et la prtsence simultante de petites occurences de zinc. DbpBts de j e r oolithiques du Palkozoique prbcoce (et du Mtsozo’ique).Les caracttres gCneraux de ces dep6ts de fer, par exemple leur zonalitt pttrographique et chimique, I’absence de litage fin et bien marqut, les oolithes bristes traduisant des remaniements, etc., les rapprochent des dCp8ts similaires plus rtcents, comme par exemple ceux de 1’Aaltnien de Lorraine (BUBENICEK). Comme eux ils se sont formts en eaux peu profondes, non loin des rivages, dam des dtpressions stpartes par des tltvations sousmarines ou des iles, ou m8me dans un milieu de plage ou de delta. Par divers caracttres les dCp6ts du Paltozoique prtcoce difftrent des dtp6ts prtcambriens, qui semblent s’gtre stdimentts dans des eaux beaucoup plus profondes. Aux ptriodes prdcambriennes la haute teneur en CO, de I’atmosphtre, d’oh le faible pH des eaux continentales, aurait en effet entrain6 une plus grande mobilitt du fer qu’aux ptriodes plus rtcentes (communication de J. Petranek). Ecorce d’altbration mbtborique. Les phtnomtnes qui s’y dtroulent n’ont Ctt que peu BvoquCs au cours de ce Symposium. La formation de barytine et de galtne supergtnes est explicitte par de belles photographies (ZUFFARDI). Une Ctude mintralogique fine de certaines bauxites du Midi de la France est preI

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sentee; les bauxites seraient autochthones et les bauxites B diaspore ne seraient pas likes au metamorphisme mais B la diagen6se normale VALETO ON)^. Minkralisations et kmissions volcaniques sous-aqueuses. Dans le cadre des reconstitutions palkogeographiques sont nottes, B plusieurs reprises, les relations Bvidentes ou possibles des minkralisations avec le volcanisme sous-marin. Dans le gkosynclinal ladinien des Alpes orientales les dep6ts minkralisks ne se placent jamais au contact direct des produits volcaniques, mais toujours A proxkitk. Il est possible que les eaux thermales likes B ce volcanisme soient responsables du dkp6t des petits corps minkralisks dans les parties profondes des appareils recifaux (SCHNEZDER). Pour le district de Raibl en particulier la supposition est avancee, avec plus d’insistance, d’un apport hydrothermal sous-marin (Scmz). La source et le mode de transport du fer des gisements hkmatitiques du type LahnDill, dont on conndt le lien avec le volcanisme sous-marin, sont rkexaminks, par comparaison avec les dBp6ts ferrugineux de certaines sources thermales actuelles qui succ6dent assez largement au volcanisme (Etna, Santorin etc.). Ces dernitres, caract6riskes par leur basse tempkrature (30”), leur haute teneur en silice, adsorbke par Fe3+- qui se forme en surface B partir de Fe2+- et leur richesse en CO,, donnent une meilleure image du mode de dkp6t pour les gisements du type Lah-Dill que la thkorie classique de I’apport exhalatif sous forme de chlorures. Au demeurant celle-ci semble controuvke par la presence de fossiles - qui exclut celle de HCI - par l’absence de produits volcaniques au mi3me niveau que les minerais, etc. (HARDER). Point de vue chronologique. Position des minkralisations dans les sequences

A c6tk de leur rtpartition horizontale (palkogkographique), la rkpartition verticale des minkralisations dans les sequences lithologiques mobilise l’attention des gitologues depuis quelques annkes (domaine ouvert par A. LOMBARD, 1956; puis explore notamment par NICOLINI, 1961, 1962). Mintralisations su!furkes Les premiers travaux dans cette voie ont d’abord portk sur les minkralisationsstratiformes de cuivre. A Delft, des donnees nouvelles sont apporttes sur le plomb et comparees B celles du cuivre (exemples empruntks aux Causses du Sud de la France, au Gabon, au Missouri, au Maroc, A Mansfeld). Retenons en particulier: (a) que, si les horizons cuprif6res se placent dans des sequences oscillantes positives surmontant une skquence en “I”, les sequences B plomb sont brutalement positives et la sequence en I sous-jacente n’est pas necessairement prksente (elle l’est B Mansfeld et dans le Missouri); (b) que les minkralisations plombifhres peuvent se trouver soit dans des phases rhexistasiques, soit dans des phases biostasiques (au sens d‘ ERHART,1956), c’est-a-dire Ces sujets trbs controvers6s n’ont pu Ctre discutCs en dktail, car la communicationn’a Ct6 pr6sent-k qu’en dance, sans &re prh5d-k d‘un “pre-print”.

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171

correspondant respectivement a la disparition ou a l’existence d’un couvert vtgttal sur le continent proche. Les mintralisations plombiftres stratgormes vraies correspondent A des phases biostasiques (Mansfeld, Mount Isa), tandis que les mintralisations pknkconcordantes correspondent a des phases rhexistasiques (Trias de la Loztre, France). Cette dernitre rtgle semble valable aussi bien pour le cuivre que pour le plomb. En utilisant simultantment les courbes lithologiques, les courbes de “cycles de stdimentation”, de couleurs, de milieu de stdimentation (marin ou continental), de cycles biorhexistasiques, on disposerait d’un ensemble de courbes prkvisionnelles (NICOLINI). Fer oxydk Les gisements deferpalkozoiques, ceux par exemple qui sont si rtpandus a l’Ordovicien, ont gtntralement Ctt m i s en liaison avec des transgressions ttendues ou mCme mondiales. En fait ils peuvent aussi s’Ctre formts durant des mouvements rkgressifs, par exemple les gisements de Boheme et de Thuringe, phtnomtne normal si 1,011 songe que, l’oscillation rtgressive s’accompagnant d’une m o n t e correlativt du continent, les produits ferrugineux de l’alttration mtttorique seront transportts en plus grandes quantitts a la mer (PETRANEK, 1964). Panni les gisements de minerais oolithiques mksozoiques, l’ttude de ceux de Lorraine permet d’aboutir A des conclusions analogues. Tous les stdiments aaltniens &ant dttritiques, la succession virtuelle locale est fondte sur la granulomttrie. Une seule et mCme succession lithologique se rtptte douze a quinze fois: dtpets fins argileux a la base, puis artnites fines, puis artnites plus grossitres mineralistes (ferri-artnites) et parfois conglomtrats argileux (“bourrelets de plage”). Du point de vue granulomktrique il s’agit d’une skquence negative. La formation de telles stquences ne peut s’expliquer que par une rkgression qui amtne, en un point donnt, des dtp8ts plus grossiers, et donc plus littoraux, sur des sediments plus fins anttrieurement dtposts (BUBENICEK) . Phosphates Les dtp6ts phosphatts importants interviennent vers la fin d’une stdimentation chimique pauvre en phosphates; par exemple argiles montmorillonite-attapulgite, au Togo, au Sinkgal, en Colombie (SLANSKY). Barytine Un lit de ctlestobarytine (5 8 % de SrSO,), tpais de 75 cm, du Zechstein de 1’Allemagne du Nordouest se place entre calcaires dolomitiques au mur et anhydrite au toit, donc dans une stquence positive tvoluant vers les tvaporites (PUCHELT et MULLER). Textures et structures des minerais et des roches encaissantes (“small scale sedimentary features”)

Celles-ci sont Ctudites a l’tchelle mtgascopique comme A l’tchelle micioscopique. Elles apportent de prtcieux enseignements sur l’histoire diagtnttique.

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Inclusions trhfines de pyrite dans I’intimitk du sediment Dans les skdiments rtcents, superficiels, non consolidts, des cdtes du Sud de 1’Angleterre ou de Long Island (U.S.A.) ont pu 6tre observks de nombreux cristaux de pyrite, le plus souvent agrkgks en sphbres A “texture en framboise”, dont le diametre mesure le plus frkquemment 4-10 p. De telles sphbres ont ktk observies tgalement dans des shales noirs et d’autres roches sapropkliques d’figes gkologiques variks: dans le Carbonifbre et le Lias d’Angleterre, dans les Kupferschiefer du Permien allemand, dans le minerai dkvonien de Rammelsberg, dans les shales prkcambriens de Mount Isa. Cette pyrite peut occuper les vides de micro-organismes, d’algues unicellulaires et de tissus vegetaux; une trame de matibre organique demeure entre les grains constitutifs des sphbres, aussi bien dans les exemples anciens (Kupferschiefer, Mount Isa) que dans les exemples rkcents! Dans les Kupferschiefer, a Rammelsberg, a Mount Isa, ont ktk reconnus, au sein des corps minkralisks et dans les roches adjacentes, des sphtres de pyrite ou leurs reliques. “Elles ktablissent un lien entre l’ensemble des sulfures et les caractkristiques des roches hdtesses”. Rappelons que, dans ces trois rtgions, ont ktk dtcrits de nets remplacements de la pyrite - d’ailleurs reproduits expkrimentalement - par des sulfures de Cu, Pb et Zn (SCHOUTEN, 1946). I1 reste dkfinir l’intervalle de temps entre la cristallisation de la pyrite primaire et son remplacement. Quant au caractbre diagknttique prkoce de la pyrite primaire, on n’en peut douter lorsqu’on l’observe a 2 ou 3 cm de la surface de stdiments rkcents. Tels sont les rksultats essentiels de ces ktudes micrographiques fines (LOVE). Gknkrations diagknktiques successsives de pyrite Une ktude mkgascopique et microscopique des formes de distribution de la pyrite dans des calcaires dolomitiques ordoviciens du Missouri aboutit a la distinction de plusieurs genkrations de pyrite, depuis la pyrite prkcoce intra-granulaire et disskmink jusqu’a la pyrite tardive, disposke en petites veinules ou “cheminkes’’ de diambtre centimttrique, recoupant la stratification (“non-congruentes”) et enfin B la pyrite des gtodes. On note que certaines veinules de calcite, tordues et briskes par la compacttion du skdiment, sont entourtes de lentilles ou de feuillets de pyrite non dkformts, donc cristallisksplus tardivement. Ces formes de distribution de sulfures apparaissent donc comme une clef pour ktablir I’histoire diagtnttique d’un skdiment (AMSTUTZ). Textures et structures’ skdimentaires de minerais variks Divers auteurs ayant participk A ce Symposium dkcrivent des structures typiquement skdimentaires, non seulement dans les lits associks aux minerais, mais encore au sein de ces derniers. Minerais sulfuks. Dans Ie Ladinien des Alpes orientales: granoclassement (graded

Nous ne distinguerons pas ici textures et structures, faute de pouvoir adopter une signification universellernent admise. Le terme allemand: “Gefuge” les rkunit.

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bedding), stratification entrecroiste, structures “gk~pttales”~ telles que figures de charge (“load casts”), craquelures de boue; des lits contournts avec schalenblende attestent de petits glissements sous-marins de stdiments encore plastiques, et montrent des transitions vers des brtches calcarto-dolomitiques, des calcirudites et des brkhes de calcaire et minerai (SCHNEIDER). Le rapporteur rappelle que des phtnomtnes de “restdimentation” de ce genre ont dtja Ctt plusieurs fois dtcrits, par exemple a Figeac (LAUNEY et LEENHARDT, 1959). I1 est alors impossible d’tchapper a la conclusion qu’une part au moins de la concentration des sulfures eut lieu avant la fragmentation des stdiments et la restdimentation de leurs fragments! Dans le district a barytine de l’Arkansas, d’iige mississipien, on observe de vtritables rythmes skdimentaires, de bas en haut: shale, shale avec lentilles et nodules, enfin lits de barytine - des structures gkopttales: “saucisses” de barytine plates en haut, bosseltes en bas - des fracturations de nodules barytiques durant la diagentse enfin des microplis d’koulement stdimentaire-diagknttique dans les lits de barytine (ZIMMERMANN et AMSTUTZ). La localisation de la galtne dans les roches carbonattes algaires, d’iige cambrien, a la mine Elvins (Missouri) montre aussi des structures gtopttales, ainsi que des concentrations dans des fissures diagtnktiques tardives, de la meme manitre que la pyrite signalte plus haut. Des observations analogues sont faites sur la galtne de Fredericktown (Missouri). Dans les calcaires oolithiques de la formation Fredonia (Illinois), de la sphalkite entre dans la constitution des oolithes, etc. (AMSTUTZ, EL BAZet PARK). Enfin l’ttude micrographique du minerai plombo-zinciftre de Mount Isa montre une coi’ncidencefrappante entre la succession des mintraux - ttablie d’aprts l‘ensemble des crittres habituels - et leur comportement au cours des petits mouvements diagtnttiques. A savoir: plus ancien est le sulfure, plus il est affect6 par la fracturation et moins il prend part a la chentation, au remplissageet a la cicatrisation. Notons que les structures Ctudikes dans ce gisement semblent avoir pour cause principale, elles aussi, des glissements sous-marins (RAMDOHR et AMSTUTZ).Ces donnks confirment, soulignons le en passant, la nouvelle interprttation syngtnttique de Mount Isa, due divers auteurs. Le rapporteur saisit ici l’occasion de nuancer une opinion qu’il a exprimte dans son ouvrage rtcent (ROUTHIER, 1963). Dans cet ouvrage il remarque que la prkoccupation des successions paragtnktiques a quelque peu oblitkrk la vue en gitologie. En fait constatons que, plus gtntralement, la science des textures et structures (“Gefiige” !) appliquke, non seulement aux minerais au sens tconomique, mais aussi leur enveloppe, et dans le cadre d’une reconstitution de leurs mutuelles histoires, apporte A cette reconstitution de trts prtcieuses donntes. I1 n’est pas non plus indiffkrent de souligner que l’tminent micrographiste RAMDOHR a su, mieux que tant d’autres, jeter un pont entre l’kchelle du microscope et les Cchelles plus usuelles du gkologue.

-

I

Ce terme dtsigne les structures orienths, dont on p u t reconnaitre la base et le sommet; ces structures servent donc de “crithres de polarite”.

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Analyse minkralogiquej n e

Sous cette rubrique noas mentionnerons en particulier l’ttude sur les bauxites du Midi de la France (VALETON). Les interpretations gkdtiques

Nous avons dit plus haut que le souci implicite des participants ce Symposium fut de ne pas sombrer dans les “thtories” gtnttiques au sens habitue1 du mot. I1 est cependant tvident qu’il n’est pas possible de collecter des faits, puis de les confronter, sans apporter quelques suggestions en vue d’une future thtorie. Nous regrouperons rapidement ces suggestions sous quelques rubriques. Source des mktaux Source continentale. Exemple: fer de Lorraine. I1 a t t t aliment6 par une masse continentale formde par la ptnkplaine cristalline vosgienne, les stdiments du Trias et du Lias fraichement dtposts et tmergts au cours de la regression aaltnienne. Notons que le fer est abondant dans le Lias, sous la forme de concrttions sidtritiques assocites a des concrttions phosphaties, et de pyrite dans les shales toarciens (BERNARD; BUBENICEK). Source marine. Exemple: phosphates. Pour ceux-ci, l’origine premike continentale ne fait pas de doute, mais le probltme est plus complexe. Seule la phase migratrice des sols de la ptriode biostasique semble pouvoir constituer pour le bassin un approvisionnement rtgulier en solutions phosphattes. Mais la proportion de phosphate ainsi apportte parait bien faible pour permettre la formation d’un niveau phosphate important. En revanche, si ce phosphate n’est pas utilist immtdiatement, s’il est mis en rtserve dans la mer, on congoit qu’il puisse intervenir de fagon massive; d’oh l’idte d‘une reservephosphatke marine dans les eaux profondes, reserve qui peut, en certains sites et a certains moments favorables, Ctre remontte vers la surface (SLANSKY). Source hydrothermale sous-marine lite a un volcanisme. Exemple: Pb-Zn des Alpes orientales (SCHNEIDER; SCHULZ); voir plus haut p.170. R61e des sources thermales C 0 2 ,application au fer du type Lahn-Dill (HARDER): voir plus haut p. 170. Transport des mktaux (et phases intermkdiaires) Transport sous forme de sels solubles; exemples: Pb, Zn, Cu (BERNARD). Passage au travers d’organismes: phosphate concentrt par le plankton (intervention de Mme Brongersma-Sanders). Mode de dkpGt Chimique (prtcipitation). Exemple: fer de Lorraine (en partie) - oolithisation de goethite. MBcanique. Exemple: fer de Lorraine (en partie). Rassemblement de particules

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htrittes: oolithes ferrifbres, quartz, dtbris de coquilles, d’ou formation d‘ “artnites” d’oolithes ferrifbres (BUBENICEK). Adsorption des mttaux lourds sur ultra-dttritiques, puis dtsorption par H,S de ces mttaux lourds. La concentration mttallifbre apparait alors comme syngtnttique et l’expression sous forme mintralogique de sulfures comme diagtnttique (BERNARD). DiagenBse (ses phases) La remarque prtctdente met l’accent sur l’importance de l’tvolution diagtnttique des stdiments dans la genbse des minerais. Plusieurs autres communications insistent sur ce point. Par exemple, dans les minerais de fer de Lorraine, la diagenbse se marque par le concrttionnement de la calcite, et la rtduction du fer, qui passe en partie sous la forme de chlorite, sidtrite, pyrite. Les conditions rtductrices ntcessaires sont probablement dues a l’influence de la matibre organique emprisonnte au moment du dtp6t. Les teintes varites des minerais s’expliquent par les degrts divers de rtduction (BUBENICEK). Le rapporteur observe qu’aprbs les travaux bien connus de L. Cayeux, qui accordaient une large part a ce que cet auteur appelait les transformations “Cpigtnttiques” (en fait diagtnttiques), puis la conception du dtp6t quasi-synchrone de tous les mintraux, due a CAILLBRE et KRAUT (1954), on tend A accorder de nouveau un r61e important aux transformations diagtnttiques. D’autres auteurs concentrent leurs efforts sur la distinction de diverses phases de la diagenbse en analysant les textures et structures des minerais (notes de AMSTUTZ et al.; voir plus haut p. 172).

CONCLUSIONS

Les conclusions que l’on peut tirer de ce Symposium, modeste par le nombre de ses contributions mais attachant par leur qualitt et leur “&at d’esprit”, ne peuvent Cvidemmentpas Ctre les m&mespour tous les lecteurs. Le rapporteur se contentera d’en souligner trois. (I) Tout d’abord il n’y a pas de contradiction entre les mtthodes d’approche et les Cchelles. De l’unitt paleogtographique (talus sous-marin, haut-fond) aux “framboises” de pyrite, tous les auteurs, des gtologues miniers aux microscopistes, tendent aujourd’hui a raccorder leurs observations au lieu de les opposer en en faisant des domaines Csoteriques sans communication entre eux. Un progrbs considtrable est ainsi largement amorct. (2) Le bien fondt de cette attitude est demontrt par une remarquable convergence des conclusions, sinon toujours exprimtes, du moins sous-jacentes. A savoir: la durte d’tlaboration des mintralisations stratiformes se resserre de plus en plus entre le dipat syngtnttique et les phases tardives de la diagenbse. L’histoire du minerai va de pair avec l’histoire du stdiment, depuis la boue gorgte d’eau jusqu’a la cdmpaction dtfinitive. Ainsi le r61e de l“‘tpigenbse”, pour les mintralisations tvoqutes ici, se rtduit de plus en plus.

176

P. ROUTHIER

(3) La plupart des contributions a ce Symposium utilisent assez peu de donntes gtochimiques. Ce constat, qui n’est pas une critique, indique seulement la ntcessitt d‘ttudes gtochimiques quuntitutives plus pousstes. Celles-ci sont Bvoqutes dans deux interventions trts inttressantes de Ph. Launey: l’une a trait aux relations quantitatives entre concentration du zinc, gradient isopaque, intensitt des glissements de stdiments, longueur des terriers; l’autre a trait aux tonnages compards de l’anomalie positive “gisement” (Figeac) et de l’anomalie ntgative qui l’entoure. Ainsi l’on aborde le domaine des vtritables lois gtochimiques, qui restent a fixer, et dont se prdoccupent d’ailleurs beaucoup de gitologues.

BIBLIOGRAPHIE

BERNARD, A., 1958. Contribution

A l’etude de la province metalliftre sous-dvenole. Sci. Terre

7 ( 3 4 ) : 125-403.

CAILL~RE, S. et KRAUT,F., 1954. Les gisements de fer du bassin lorrain. Mim. MusCum Natl. Hist. Nat., Sir. C (Paris), 4 (1) : 192 pp. ERHART, H., 1956. La GenPse des Sols en tant que PhinomPne giologique. Esquisse d’une Thiorie gkologique etgiochimique. Biostasie et Rhexistasie. Masson, Paris, 88 pp. ESPOURTEILLE, F., 1960. L h d e giologique et mhalloginique de la RPgion de Nant-St-Jean-du-BrueI (Aveyron)et de TrPves (Gard). Thtse, Fac. Sci., Paris, 147 pp. (inkdit). LAUNEY, PH. et LEENHARDT, R., 1959. Les brkhes ddimentaires zinciftres du Sinemurien du Lot. Bull. SOC.GCol. France, 1 (5) :467484. LOMBARD, A., 1956. GCologie sidimentaire. Les Shies marines. Masson, Paris, 722 pp. NICOLINI,P., 1961. Conclusions d’observations sur la localisation des mineralisations cupriftres stratiformes dans les dries sedimentaires. Compt. Rend., 255 (16) : 1717-1718. Aussi en Symposium sur les Gisements straiiformes de Cuivre en Afrique. Lithologie-Sidimentologie. Assoc. Serv. Gkol. Africains, Paris. J., 1964. Shallow-water origin of Early Paleozoic oolitic iron ores. In: L. M. J. U. VAN PETRANEK, STRAATEN (Editor), Deltaic and Shallow Marine Deposits. Elsevier, Amsterdam, pp. 319-322. ROGEL,P., 1961. Le Gisement de plomb de la Plagne (Savoie). b u d e giologique et mitalloginique. Thtse 3e cycle, Fac. Sci., Paris, 64 pp. (inedit). ROUTHIER, P., 1963. Les Gisements mitallif2res. Giologie et Principes de Recherche. Masson, Paris, 2 tomes, 1273 pp. SCHOUTEN, C., 1946. Synthetic replacements as an aid to ore-genetic studies. Econ. Geol., 42 (6) : 659-667.

ZISERMAN, A., 1964. .!?tudegblogique et mt3alloginique de la Rigion d’dlzoonle Vigam (Gard). Thtse, Fac. Sci., Paris (inedit).

INDEX

Absorption (see adsorption) Adsorption skdimentaire -, r81e metallogenique, 19-25 Algenstrukturen in oolithischen Karbonatgesteinen, 149 Alps, 5,29-45,47-52 -, rhodochrosite and siderite deposits, 5 -, Lechtal, 29 -, Limestone (Kalkalpen), 29 -, Mesozoic calcareous complex of the eastern, 31 AMSTUTZ, G. C., 1,15,16,165,172,173,175

-(1956), 24,99 -(1958), 21,26, 30,44, -(1959), 3, 7, 30, 74

Bauxites (continued) -, comparison of the facies, 124 -, Mazaugues (Var), 124, 125 -, PCreille (Arikge), 126, 127 -,bright, 124, 128 -, “fluidal” textures, 124, 128 -, goethite, 124, 126,128 -,hematite, 124, 126, 128 -, kaolinite, 124 -, red, with pisolites, 124 BAZIN,D., 169 B E R N A R D , A . ,102,103,132,168,174,175 ~~,

- (1958),

73, 89

- (1960), 2, 7, 89 - (1961), 25,26, 30, 163 - (1962), 44,73, 163 - (1963), 89 -(1964), 1,15,16,65,71,73,76,79,82,157,163 Anglesites, baritic, Monteveckhio, 93 ANGOT,P. (1939), 122 Anhydrite, Hohes Moor, 143,145, 146,147 Ankerite, 96,97 Archetypal patterns, 3 ArCnites minerai de fer de Lorraine, 113, 114, 115,116,119 Arkansas barite belt, 157-163, 173 ARRHENIUS, G. (1962), 154,155 ARNOULD, M. (1962), 56,64

“Banded’, Rammelsberg, 13, 14, 15, 172 BARDOSSY, G. J. (1958), 129 Barites (see also “Coelestobaryt”), 91-99, 104, 143,157-163,145,169,173

-, Arkansas district, 157-163, 173 -, associated with calcite-aragonite, 93, 94

-, baritic anglesits, 93 -, beds in the Cretaceous shale, West Austra-

22, 176 - (1960), 20, 26 - (1962), 23,26 - (1963), 61, 64 - (1964), 19 BICHELONNE, J. (1939), 113, 122 Bitumen, 47 -, bituminous laminae, in dolomite rocks, 48 BLANCHARD, R. (1942), 82,89 Bleiberg (Austria), 29, 31, 47-52 Blind River, Canada, 5 BOULADON, J. (1960), 56,64 BRADLEY, J. S. (1953), 45 Bravoite, 75 BRECKE, E. A. (1962), 76,89 BRIGHT,H. A. (1953), 156 Broken Hill, Australia, 5 BRONGERSMA-SANDERS, M., 165,174 BUBENICEK, L., 131, 169, 171, 174, 175 - (1960), 20,26 - (1961), 20,26 -(1961a), 113, 117, 122 - (1961b), 122 - (1964), 113 BUSCHENDORF, F. (1962), 153,155 - (1963a), 153, 155 - (1963b), 153,155 BUTLIN,K. R. (1953), 154, 155

lia, 165

-, celestobaryt, northwestern Germany,

143-

156

-, iron-,91 - of marine origin, 169 -, opaque, 92 -, solubility, 104 -, supergene, from Sardinia, 91-99 -, yellow transparent, 92 BAUMANN, L. (1958), 153,155 Bauxites, 123-129, 169, 170 -, boehmitic and diasporitic, facies problems, 123-129

CAILL~RE, S. (1954), 113, 122, 175, 176 Calcareous Alps, 3 1 -, lead-zinc deposits, 47 Carbonate acid springs and sedimentation of iron ores, 107-112,170 CARRIE,J. (1962), 56, 64 CAYEUX, L., 175 - (1922), 113 CHOW,T. J. (1962), 22,26 Chromite deposits, 5 CISSARZ, A. (1930), 43,44

178

INDEX

CLAR,E. (1953), 29, 44 Clay minerals, 47 Climax molybdenum deposit, 5 Coelestobaryt, 143-156 -, Algenstrukturen, 149 -, Anhydrit, 143, 145,147,149 -, Baryt, 143, 145 -, Bohrung Hohes Moor, northwestern Germany, 143-156 -, chemische Untersuchungen, 149 -, Fluorit, 145 -, Hauptdolomit, 145 -, oolithische Karbonatgesteine, 149 -, Quarz, 147 -, Schwaden-, Wolkenbaryt, 145 -, Schwefel, 145, 149 -, Styolithen, 145 -, Zechstein, 143 Colorado Plateau, 5 CONDON, M. A., 165 Congenerationists, 2 Contact deposits, 5 Copper, 5 , 5 3 4 -, stratiform deposits, compared with strati-’ form lead concentrations, 5 3 4 , 1 7 1 - in marine or lagunal milieu, 53-64 Copper-lead-zinc deposits, 5 -, disseminated and massive, 5 CORNELIUS, H. P. (1941), 32,44 CORRENS, C. W. (1939), 20,26 - (1950), 69,89 Dahomey, Africa, phosphate deposits, 141 DANA, J. D. (1960), 99,424 DAPPLES, E. C. (1959), 79, 89 -(1962), 79, 89 Deardorff Mine, southern Illinois, 76 DEEVEY, E. S. (1963), 13,16 G. (1962), 23,26, 154, 155 DESSAU, Diagenesis, 11,22,47,65-90,91-99,167,175 -, differentation of the single phases, 175 -, early diagenetic pyrite, 11 -, genese des gisements stratoides de sulfures, 22 -, paragenetic charts, 76,82,83 -, sediment, diagenetically hardened, 47 -, supergene barites, 91-99 Diagenetic age, galena, 73 - behaviour of sulphides, 65-90 - crystallization, Fredonia Formation, 76 _ - ,sulphide beds, Mount Isa, 82-88 -evolution, 175 -periods, Mount Isa, 83 - sphaleritt: “idioblasts”, 77 DI COLBERTALDO, D., 101 - (1948), 29, 44

Dr COLBERTALDO, D. (continued)

- (1956), 30,44

- (1957), 30,44 - (1958), 30,44 DIOURI,M. (1962), 56,64 Dolomite-pelite, 47, 48,49 V. I. (1953), 154, 155 DRAGUNOV, Ducktown, Tennessee, 5

EL BAZ,F. (1961), 89, 173

- (1964), 65,73

Elvins Mine (Missouri), 71, 173 EMBERGER, A. (1962), 56,64 EMERY, K. 0. (1963), 16 Endogenous, historical, psychological and philosophical role, 1-7 Epigenesis, historical, psychological and philosophical role, 1-7 ERHART,H. (1956), 63,64,138,142, 170,176 - (1961), 21,26 ERVIN,G. (1951), 123,129 F. (1960), 168,176 ESPOURTEILLE, Evolution, identity with present day development or ore genetic theories, 1-7 Exogenous, historical, psychological and philosophical role, 1-7 Facies, copper, Mansfeld, 62 - development of ore-bearing units, eastern Alps, 33 - differentiation, lead-zinc concentration, eastern Alps, 2 9 4 5 -problems of bauxites, 123-129 -, “Sonderfazies”, Wetterstein limestone, 39 Falun deposit, Sweden, 5 FELENC, R. (1962), 56, 57,64 Figeac, France, gite de zinc, 102,103 A. G. (1953), 45 FISCHER, FISCHER, R. P. (1961), 60,64 FISHER, N. H. (1960), 82, 89 Fluorite, Hohes Moor, 145 -, dolomite, 48 Fluorspar district, southern Illinois, 76 FOGLIERINI, F. (1963), 61, 64 Foraminifera in dark marine shale, 165 Framboidal texture, 12 Fredericktown, Missouri, 73 Fredonia Formation, southern Illinois fluorspar district, 76 FRIEDRICH,0. M. (1937), 29,44 - (1953), 29,44 FUCHTBAUER, H. (1958), 154,155 Galena, crystallization, diagenetic age, 73

179

INDEX

Galena (continued) - in carbonate rock, Elvins Mine, 71-73,173 -, Mount Isa, 83-85,86,87,88, 173 -, northern Limestone Alps, 30 GARRELS,R. (1 952), 25 Geochemical cycles, 6, 7 Geopetal features, 2945, 47-52, 65-90, 157163, 173

GOETHE, J. W., 5 Goethite, Lorraine, 115 -,bauxite, 124, 126, 128, 133 GOLDSCHMIDT, V. M. (1937), 22,26 GOLFBERG, E. D., 155 GRABAU, A. W. (1906), 22,26 GRAF,D. L. (1950), 89 Granite Mt., Utah, 5 Greenockite, 95 GUILCHER, A. (1954), 120,122 GUNDLACH, H. (1959), 153,156 HALL,G. (19421, 82,89 HARBOT, E. (1903), 112 - (1960), 107 HARDER,H.,104,107,131,170,174 -(1954), 112 -(1963), 112 - (1964), 112 HAM,W. E. (1944), 163 HEGEMANN, F. (1948), 52,47 - (1949), 29,44 - (1957), 30,44 - (1960), 30,31,45,47, 52 Hematite, 124, 126, 128, 133 HENTSCHEL, H. (1960), 107, 112 HICKOX,J. E. (1953), 45 HILL,M. N., 155 HILLEBRAND, W. F. (1953), 149, 156 History of ore genesis, 1-7, 167-176 HJULSTROM,P. (1935), 14, 16 HOFFMANN, J. I. (1953), 156 HUMMEL, P. (1960), 71,89

Hydrothermalists in opposition to the sedimentary genesis of sulphides, 20-21 Hydrothermal supply, connection with sedimentary enrichment of Pb-Zn ores, 33, 49, 50

ILLING,V. (1959). 73, 89 Illinois, southern Illinois fluorspar district (see also Mississippi Valley type' mineral deposits), 5, 76 INMAN, D. L. (1949), 14, 16 ISELIN, C. O'D., 155 Iron, bisulphide, Pb-Zn deposits, 48 - deposits formed from thermal springs, 107

Iron (continued)

-, oolitic deposits of the Paleozoic era, 169 -, oolitic ore minerals, 92, 113-122 - oxyde, Paleozoic and Mesozoic era, 171 - sulphides, Jefferson City formation, 65-71 - deposits from thermal springs, 109, 110 Iron ores, carbonate acid springs as source, 107-112 -, contents of aluminium, 131 -, gisement de Salzgitter, gedse, 132 -in marine (Lahn-Dill type) and in continental position, 131 -, Lahn-Dill-type, 107-1 12 - of Lorraine, 113-122, 174 -, oolithic, 113-121 -, terrigenous origin, 132

Jefferson City Formation (Missouri), 65 JENSEN, M. L. (1962), 16,26, 155 - (1963), 17 JICHA,H. L. (1951), 29,45 JONES, T. A. (1948), 163 JUNG,C.G., 7,s KAPLAN, I. R. (1963), 13,16 Kaolinit, 124, 126, 127, 128, 133 Karbonatgesteine, oolithische mit Algenstrukturen, 149 KARL,F. (1953), 79, 89 KATSCHENKOV, S. M. (1953), 154,155 - (1961), 154, 156 KAZAKOV, A. V. (1937), 138,142 KEPLER, J., 7 KLINT,W. (1962), 123, 129 KNUP,J. (1962), 64 Kohlensauerlinge als Eisenquelle, 107-1 12 -, Atna, Italien, 108 -, Dachla-Oase, Agypten, 108 -, Lahn-Dillgebiet, 107-1 12 -, Santorin, Griechenland, 108 -, Wehrer Kessel, Eifel, 108 KOSSOVSKAJA, A. G. (1954), 154, 156 KRAUT,F. (1954), 113, 122, 175, 176 KRUGER, P. (1962), 154, 156 KRUMBEIN, W. C. (1951), 21,26 - (1952), 25,27 KRYNINE, P. D. (1949), 21,27 KUENEN, PH. H. (1950). 22,27 - (1953), 83,89 Kupferschiefer, 5, 14, 15, 172 Kuroko type ores, 5 ; Ladinian plateau reef type, evolution, 39, 41, 169

180

INDEX

Lahn-Dill-Eisenerz, 107-1 13, 170

-, iihnliche chemische Zusammensetzung der rezenten Eisenniederschlitge machen eine ahnliche Genese wahrscheinlich, 109-1 10 -, bisherige Annahme der Fntstehung aus hochtemperierter exhalati! er Zufuhr des Eisens und der Kieselsaure, 107 -, Moglichkeit der Entstehung durch Zufuhr des Eisens aus niederthermalen Eisensauerlingen, 108 -, Untersuchung rezenter Eisensauerlingeverschiedener Fundorte, 108-1 10 Lake Superior iron deposits, 5 LAMAR, J. E. (1950), 89 LAUNEY, PH., 102, 103, 176 - (1959), 24, 27, 168, 173, 176 - (I 962), 24 Lead, 53-64,71 -, Elvins Mine, Missouri, 71 -, Florac-Meyruis, France, 53 -, Mansfeld, Germany, 58 -, Morocco, 56 -, stratiform deposits, 53-64 -,-,compared with stratiform copper deposits, 53-64 Lead-zinc concentration, eastern Alps, 29 -, deposits in the Calcareous Alps, 47 -, deposits in the southern Limestone Alps, 29 Lead-zinc concentrations, depositional, in the eastern Alps, 29-45 -, deposits of the different areas, 32 -, discussion of the genesis, 41 -, evaporitic facies, 32 -, evolution of the Ladinian reefs, 39 -, facies development, 33 -, ore bearing units, 32 -, ore paragenesis, 30, 31 -, sedimentary fabrics of ore-bearing units, 33 -, structure of the ore bodies, 33 -, volcanism, 32 Lead-zinc deposits in the Calcareous Alps, example of submarine-hydrothermal formation, 47-52 -, discussion on the genesis, 47 -, Raibl Beds, 47-52 _ ,- ,bitumen, 47,48 -_ , ,carbonate pelite, 51 -, -,clay minerals, 47 _ ,_ ,dolomite-pelite, 47, 50 -,-,FeS2,47 -, -,fluorite, 47, 51 -,-,galena, 47 -, -, iron bisulphide, 47 -, -, macroscopic and microscopic fabric analysis, 47-52 -,-,quartz, 47,48 -,-,Schalenblende, 47, 5 1

Lead-zinc deposits in the Calcareous Alps (continued) -,-,sphalerite, 47, 48 -, -, tectonic analysis, 47-52 -, -,wurtzite, 51 LEBLANC, M., 169 LEENHARDT, R. (1959), 24,27,168,173,176 Leduc Riff-chain, Canada, 73 LEVORSEN, A. 1. ( I 959, 22,27 Limestone Alps, 29 Limestone, Wetterstein, Bavaria, 34-39 -, Fredonia, Illinois, 76 Limonite, minerai de fer lorraine, analyse, 115 LOMBARD, A., 170 -((1956), 17, 23, 27, 63, 64, 85, 89, 118, 120, 122,137,141,142,176 LOVE,L. G., 15, 16, 172 - (1961), 15, 17, 82, 89 - (1962a), 16 - (1962b), 14, 16 - (1963), 12, 13, 14, 17 -(1964), 11, 16 G. E. F. (1953), 156 LUNDELL, H. J., 102,103 MACGILLAVRY, Magnetite deposits, 5 MAGNUS, ALBERTUS, 1,2 Marcasite, grains of, 67, 73 -, “idioblasts”, 75 -, occuring with barite, 94 Maroc (Morocco), phosphate deposits, 139 MATERN, H. (1931), 108,112 MATZ,E. (1953), 79,89 MAUCHER, A. (1954), 30,45, 47, 52 - (1957), 30,45 MERRIT,C. A. (1944), 163 Metal-concentrations, 102, 103 -, hypotheses of sedimentary, 53-64 Metal sources, 174 MILLOT,G. (1952), 25,27 Mina Ragra, 5 Minette Lorraine, 19, 20 MISER,H. D. (1929), 163 Mississippi Valley deposits (Tri-State, Missouri, southern Illinois, Tennessee, etc.), 5, 24, 26, 30, 44, 56-63, 65-79, 89, 156-163, 170, 172, 173 Missouri (see Mississippi Valley) Mitterberg, Austria, 79 Montevecchio Mine, Sardinia, 93,94 Mount Isa, age of crystallization of the sulphides, 82-88 -shale, 14, 15, 17, 172 G., 104,169, 171 MULLER, - (1962), 147, 156 - (1964), 143

INDEX

MUNK,W. H., 155

181

Phosphates (continued)

-, genesis, periods and regions, 139-141, NAKAI,N. (1962),26, 155 - (1963), 13, 16 NAUMANN, E. (1919), 13, 17 NEEB,I. G. H. (1943), 12, 17 Neo-congenerationists, 2 Neoepigeneticists, 2 NEWELL, N. D. (1953), 40,45 - (19571, 39,45 G. D. (1963), 128, 129 NICHOLLS, NICOLINI, P. (1961), 170, 171, 176 - (1962), 53, 55, 56,62, 64 - (1964), 53 NIGGLI, P., 2 OGNIBEN, L. (1957), 23,27 Oolithes ferfifitres, minerais de Lorraine, 113-122 Oolitic iron ores of Lorraine, 113-122 Ore genesis theories, 2-6, 107 -, changing patterns of thought, 2-6 -, geochemical cycles, 6 -, Lahn-Dill-type, 107-1 12 -, schematic representation of, 4, 5 OSBORN, E. F. (1951), 123, 129 Outukumpu, Finland, 5 Oxidate deposits, 6, 105-133 Paragenesis, lead-zinc deposits, 30, 31 Patterns, sulphide, Jefferson City Formation, 65-71 PARK,W. C.,173 - (1964), 65,76 Patterns of thought, 1-7 -, in ore genesis, 1-7 -, the conventional and the new, 5 PATTERSON, C. C. (1 962), 22,26 PAULI,w. (r952), i , 7 Pegrnatites, 5 Perimagmatic vein deposits, 5 PETRANEK, J., 169 - (1964), 171, 176 W. E. (1932), 29,45 PETRASCHECK, - (1945), 29,45 -(1957), 30,45 - (1960), 30,45 F. J. (19.55), 122 PETTIJOHN, Phenomenon of man, 5 Phosphates, au Dahomey, 141 -, au Maroc, 139 -, au Sentgal, 141 -, au Togo, 139 -, causes for concentration, 165

171 gisements sedimentaires marins de, 137-142 -, mineralisationet skdirnentation, 137-139 -, fils conducteurs de la recherche, 139 guide to the research, 139-141 high concentration in the surface water, 165 -, plankton and fish as causes, 165 marine origin, 169 Pipe deposits, 5 Plankton as cause for phosphate concentration, 165 Plomb, courbes pour le cuivre, similitudes et differences, 59 -, gisements stratiformes, courbes previsionelles, 53-64 -, -, de Mansfeld, Allemagne, 58 -, -, de Missouri, 56 -, -, du Gabon, 55 --,-, du Maroc, 56 -, gites de Florac-Meyrueis, France, 53 -, sedimentation, 60,61 -, zinc du Maroc, 56 POUSTOVALOV, L. V. (1940),25,27 H., 169,171 PUCHELT, - (1962), 153, 155 - (1963), 149, 156 -(1963a), 153, 155 - (1963b), 153, 155 - (1964), 143 PURDUE, A. H. (1929), 163 Prkipitation stdimentaire rBle mttallog6nique, 19-27 Propylitic rocks and mineral deposits, 5 Pyrite, chalcopyrite, 73,79 -des Malines et du Soulier, tvolution esquisst, 101 -, diagenetic, early, 11 -, early diagenetic, in fine sediments, 11, 172 -, four types, microscopic observation, 67-69 - in ancient shales and mudstones, 13 - in ore shales, 14 -, network of organic matter, 101 -, recent sediments, 11 -, spheres, 11, 12, 172 -, spherulites framboidales de pyrite en veins, 101 -, sulphides in fossil wood, 79-81, 82 - with barite, 94

-, -, -, -, -, -, -,

Quarz, als Einschluss in Coelestobaryt, 147 - in dolomite rocks, 48 I Queechy Pond, pyrite spheres, 13 H. (1959), 149, 156 QUESTER,

182

INDEX

Radiolaria in dark marine shale, 165 Raibl Beds, in the Wetterstein Limestone, 47 RAMDOHR, P., 173 -(1 964), 65, 82 Rammelsberg deposit, 5, 14, 172 Rapport de synthkse des communications prksentks au Symposium, 167-1 76 -, les tendences les plus marquantes, 167 -, perspective du terme “diagenkse”, 167 -, point de vue paleogeographique, 168-170 -, -, mineralisation et aires de sedimentation ralentie, 168 -, -, biseaux stratigraphiques par condensation, lacunes, etc., 168 -, -, -, sulfures (BERNARD), 168 -, -, -, phosphates d’origine marine (SLANSKY),169 -, -, -, barytine et celestite (PUCHELTet MULLER), 169 -, -, -, appareils rkifaux, 169 -, -, -, dep6ts de fer oolithiques (BUBENICEK),169 -_ , ,-, formation de barytine et de galkne supergene, photographies (ZUFFARDI), 169 -, -, -, ktude minkralogique de certaines 169,170 bauxites (VALETON), -, -, -, mineralisation et emissions volcaniques, dkpbts dans les A l p orientales (SCHULZ,SCHNEIDER) et dans les gisements hkmatiques du type Lahn-Dill (HARDER), 170 -, point de vue chronologique; position des mineralisations dans les sequences, 170-171 -,-, minkralisations sulfur&, 170 -,-,-,min6ralisations stratiformes de cuivre, 170 -, -, -, min6ralisations plombifkres, 170 -, -, -, courbes prkvisionelles (NICOLINI), 171 -, -, fer oxyde, 171 -, -, -, gisements de fer palkozoiques (PETRANEK), 171 -, -, -, gisements de minkrais oolithiques mtsozoiques, 171 -, -, phosphates (SLANSKY), 171 -, -, barytine (cklestobarytine) (PUCHELTet MULLER),171 -, textures et structurcs des minerais et des rochesencaissantes (‘‘small scale sedimentary -. features”), 17 1-1 73 -, -, inclusions trts fines de pyrite dans l’intimit6 du sediment, 172 - ,_ _ , ,vides de micro-orpanismes, 172 -_ , -, ,etudes micrographiques de LOVE, 172 -, -, generations diagkdtiques successives de pyrite,

Rapport de synthese des communications presentks au Symposium, textures et structures des minerais et des roches encaissantes, textures et structures ddimentaires de minerais varies (continued) -,_. , -,formes de distribution de pyrite comme clef de I’histoire diaghktique (AMSTUTZ), 172 -, -, textures et structures stdimentaires de minerais varies, 172 -, -, -, minerais sulfures, dans les Alps orientales (SCHNEIDER), A Figeac (LAUNEY et LEENHARDT), dans Ie district de I’Arkansas (ZIMMERMANN et AMSTUTZ), observations de la galhe; dans les calcaires oolithiques de Fredonia (AMSTUTZ,EL BAZ et PARK); 1’6tude du minerai plombo-zincifkre de 173 Mount Isa (RAMDOHR et AMSTUTZ), _ ,- _ , ,remarque dc ROUTHIER, 173 -, les interpretations genetiques, 174 _ ,- ,sources des metaux, 174 -,-,__, source continentale, exemple: fer de Lorraine (BERNHARD; BUBENICEK), 174 -,-,-,source marin, exemple: phosphates (SLANSKY), 174 _ , _ , _,source hydrothemale sousmarine, exemple: Pb-Zn des Alpes orientales (SCHNEIDER, SCHULZ),174 _ ,_ ,mode de depdt, 174 - ,_ _ , ,chimique; mkanique (BUBENICEK); adsorption des metaux lourds (BERNARD), 174,175 - ,_ , diagenkse (ses phases), 175 _ , _,_,I’importance de I’tvolution diagdnktique des sediments dans la gknkse des minerais, 175 -,-,-,observations de BUBENICEK,de CAILLERE et KRAUT,175 Red Bed deposits, 5 Reduzate deposits, 6, 9-104 Reef, algal, deposits in, 29-45,73,149, 169-174 REGNELL, U. (1961), 12,17 RICHTER, G. (1947), 43,45 RICHTER-BERNBURG, G. (1955), 145,156 RIGBY,J. K. (1953), 45 - (1957), 39,45 RITTENBERG, S . C. (1963), 16 ROGEL,P. (1961), 169, 176 ROSHROVA, E. V. (1956), 23,24,27 ROUTHIER, P., 103, 131, 133, 169 - (1963), 173, 176 - (1964), 167 RUHLICKE, D, (196l), 152, 156 SALVAN, H. (1959), 139,142 SALVADORI, I. (1951), 99

183

INDEX

SALVADORI, I. (continued) - (1964), 91 Salzgitter, gisement de, genkse, 132 SANDER, B. (1936), 160, 163 Sardinia, supp,rge\e barites, 91-94 Schalenblende, northern Limestone Alps, 30 -, Wettersteir. Dolomite, 50, 51 SCULL,B. J. (1958), 163 SCHNEIDER, H.-J., 103,169,170,173,174 - (1953), 30,36,45 - (1954), 30,31,32,42,45,47,52 - (1957), 30,45 - (1963), 39,41 - (1964), 29 SCHNEDERHOHN, H. (1941), 21,27,29,45,107 - (1958), 30,44 SCHOUTEN, C. (1946), 172,176 - (1946a) 15, 17 - (1946b) 14,17 SCHROLL, E. (1953), 31,45 - (1945) 31,45 SCHTSCHERBAK, 0. V. (1956), 23,24,27 SCHURENBERG, H. (1962), 155 Schurmann series, 95,96 SCHULZ, O., 170,174 - (1955), 30,45 - (1959), 30,45 -(1 960), 30,45 - (1960a), 47,52 - (1960b), 47,52 - (1964), 47 SCHUTOV, V. D. (19541,154,156 SCHWINNER, R. (1942), 29,45 - (1946), 29,45 - (1949), 29, 32,45 Sedimentary cycles, (position of ore deposits within), 6, 19-27, 29-45, 53-64, 137-142, 167-1 76 Sedimentary features, small scale, Arkansas Barite District, 157-163 -,-,barite nodules, 158,159-162 -,-,geometric patterns, 157-163 -,-,pyrite, 162 -, -, sedimentary origin, theories, 157 -, shale beds, 159,161,162 -, -, detective value of the barite nodules, 162 -, -, conventional epigenetic theory, 163 -, -, assumption of sedimentary formation, 162 -, geopetal features, 29-45, 47-52, 65-90, 157-163 -, in diagenetic pyrite, 65-90 Senegal, phosphate deposits, 141 SENSTIUS, J., 132,133 Shale beds, 47-52,173 Shale dolomitique noir, Figeac, 104 Shales, ore, 14

SHROCK, R. R. (1948), 83,89,163 SIEGL, W. (1956), 30,45 SLANSKY, M., 137,169,171, 174 - (1962), 142 SLOSS, L. L. (1951), 21,26 SMIRNOW, S, S, (1951-1954), 91 - (I 954), 99 Sphalerite, botryoidal, 96, 97 -, dolomite rocks, 48 -, Fredonia Formation, Illinois, 76-79 -, Mount Isa, 83, 84, 85, 87 -, northern Limestone Alps, 30 Spilitic rocks, 5 STARKE, R. (1961), 152, 156 - (1962), 153, 156 STERK, G. (1954), 79,89 STEWARD, J. M. (1961), 60,64 STRAKOV, N. M. (1953), 89 - (1957), 118, 121, 122 Strontium gehalt, Coelestobaryt, Hohes Moor, 153,154 Structures and textures (“Gefiige”, fabric), geopetal fabrics, 2945,47-52,65-90, 167-163 -, remark of ROUTHIER, 173 Submarine-hydrothermal formation of mineral deposits (see also exhalative hydrothermal deposits), 1-7,29-45,47-52,65-90,157-163 Sulfures, g e n h sedimentah, 1-7, 11-1 6, 19-27,29-45,47-52,65-90 --,de mktaux, 19-27 Sulphates, deposits, 137-142 -in the supergene zones of sulfide ore deposits, 91-99 Sulphides, as reduzate deposits, 6 -, diagenetic behaviour of, 65-90 _ ,- ,iron sulphide distribution in the Jefferson City Formation, 65-71 -,-,-,distribution patterns, 66,67 -,-,-,-,congruent and non-congruent features, 67 -,-,-,-,quartz,67 - -, _, - , ,marcasite, 67 -,-,-, microscopic observations, 67, 69 _ ,- _ , _ , ,four distribution types, 67,69 _ ,_ ,- _, ,various generations of iron sulvhides, 69 -, -, galena localisation in late diagenetic fissures in algal carbonate rock. Elvins Mine. 71 -, generations of diagenetic crystallization in the Cu-Pb; CO-Ni-deposit of Fredericktown, Missouri, 73 -, diagenetic crystallization generations of an oolite phase, Fredonia Formation, 76 -, differential localization of sulphides in fossil wood, 79 -, criteria for diagenetic crystallization in the Mount Isa sulphide beds, 82-88 Y

184

INDEX

Sulphides (continued) - from the Mount Isa, 14, 82 -, genesis of ores, 11-17 - in ancient shales and mudstones, 13-14 -in the Kupferschiefer, 13-14 -in ore shales, 14-15 - in the Rammelsberg Bandeiz, 13-14 - in sulphide ore deposits, Sardinia, 91-99 -, iron, 65-71 -, localization in fossil wood, 79-82 -, low temperature sulfide deposition, exanples, 101 -, marine origin, 168, 169 -, ores, mineralization, 170 -, sedimentary genesis, 19-27 -, supergene, 91-99 Summary of the reports of the Symposium (see Rapport de Synthkse), 167-1 76 -, meanirig of the term “diagenesis”, 167 -, method and main features, 167 Supercene suiphides and sulphates in the Hugrgene zones of sulphidd ore deposits, 91-99 -, supergene barites, Sardinia, 91-94 -, -, mechanical and chemical deposition, 91 -, -, in anglesites, 93 -, -, with gypsum, hemimorphite, marcasi!e, and pyrite, 94 -, examples of sulfides, regenerated by oxydation-reduction processes in Sardinia, 95 -, -, deposition of greenockite on galena, 95 -, -, deposition of cinnabar, 95 -, -, deposition of marcasite and pyrite, 95 -, -, deposition of sphalerite and galena, 95 -, -, deposition of galena and/or marcasite on/or with barite, 96 -, -, deposition of sulphur, 98 Syngenesis. historical, psychological and philosophical role, 1-7 -, modes or ore formation: reduzates, 9-104, 167-1 16 - ,_ oxidate deposits, 105-133,167-176 -, -, sulphate and phosphates deposits, 135-165, 167kl76 Synthkse, rapport de synthese des communications presentkes, 167-176

.

TAMAYO, E. (1955), 62, M TAUPITZ, K. C. ( I 954). 30,45,47, 52 TAYLOR, J. H., 131 TEILHARD DE CHARDIN, P. (1955), 3, 5, 7

Textures of minerals science, remark of ROUTHIER, 173 Theories, scientific, and coniiection to the general cultural pattern, 3 Togo (Togoland), Africa, phosphate deposits, 139 TORNQUIST, A. (1929), 29,45 TWENHOFEL, W. H. (1939), 21,27 - (1950), 120, 122 UHLEY,R. P. (1961), 89 Uranium deposits, 5 VALETON, I., 132,133, 170, 174 - (1962), 123, 139 - (1963), 129 VALLENTYNE, J. R. (1961), 13,17 - (1963), 14, 17 VANBEMMELEN, R. W., 103 VIDAL,H. (1953), 32,45 VISE, L. (1953), 140, 142 VON COTTA, B., 2 VON ENGELHARDT, w. (1 960), 79,90 WALPOLE, B. P. (1958), 90 - (1960), 82, 90 WARD,H. J. (1956), 91,99 WATERS, F., 8 WELTE,D. H., 101 WERNER, C. D., 2 , 5 - (1958), 153, 156 Wetterstein Limestone, 34-39,47-52 WHITEMAN, A. J. (1953), 45 Witwatersrand, 5 Wurtzite in lead-zinc deposits, 51 Zinc, gite de Figeac, 102, 103 ZIMMERMANN, A. R., 165, 173 -(1961), 15, 17,82, 89, 163 - (1963), 17, 163 - (1964), 157, 163 ZIMMERMANN, D. 0. (1961), 15 ZISERMAN, A. (1964), 168, 176 ZUFFARDI, P., 101, 104, 169 -(1960), 99 - (I 962), 99 - (1963), 99 -(1964), 91, 95 ZVEREFF, R. (1953). 21.27

ERRATA

p. p. p. p.

V Contents; Diagenetic behaviour of sulphides: add author F. EL BAZ(Rolla, Mo., U.S.A.) 15 line 28: for variable, read visible 21 line 16: for nicellaire, read micellaire 65 adresses of authors, third line: for Department of Geology, read School of Mines and Metallurgy p. 76 line 15: for HardorlT Mine, read Deardorff Mine p.170 running headline: read P. ROUTHIER p.171 running headline: read RAPPORT DE SYNTHESE