Supergene and Surficial Ore Deposits. Textures and Fabrics PDF
Preview Supergene and Surficial Ore Deposits. Textures and Fabrics
HANDBOOK OF STRATA-BOUND A ND STRATIFORM ORE DEPOSITS Edited by K.H. WOLF I PRINCIPLES AND GENERAL STUDIES 1. Classifications and Historical Studies 2. Geochemical Studies 3. Supergene and Surficial Ore Deposits; Textures and Fabrics 4. Tectonics and Metamorphism II REGIONAL STUDIES AND SPECIFIC DEPOSITS 5. Regional Studies 6. Cu, Zn, Pb, and Ag Deposits 7. Au, U, Fe, Mn, Hg, Sb, W, and Ρ Deposits ELSEVIER SCIENTIFIC PUBLISHING COMPANY Amsterdam - Oxford - New York 1976 HANDBOOK OF STRATA-BOUND A ND STRATIFORM ORE DEPOSITS I. PRINCIPLES AND GENERAL STUDIES Edited by K.H. WOLF Volume 3 SUPERGENE A ND SURFICIAL ORE DEPOSITS; TEXTURES A ND FABRICS ELSEVIER SCIENTIFIC PUBLISHING COMPANY Amsterdam - Oxford - New York 1976 ELSEVIER SCIENTIFIC PUBLISHING COMPANY 335 Jan van Galenstraat P.O. Box 211, Amsterdam, The Netherlands Distributors for the United States and Canada: ELSEVIER/NORTH-HOLLAND INC. 52, Vanderbilt Avenue New York, N.Y. 10017 ISBN: 0-444-41403-7 Copyright © 1976 by Elsevier Scientific Publishing Company, Amsterdam All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior written permission of the publisher, Elsevier Scientific Publishing Company, Jan van Galenstraat 335, Amsterdam Printed in The Netherlands LIST OF CONTRIBUTORS TO THIS VOLUME Β. BOULANGE Office de la Recherche Scientifique et Technique, Outre Mer (ORSTOM), Boudy, France G. GRAND IN Office de la Recherche Scientifique et Technique, Outre Mer (ORSTOM), Boudy, France J.R. HAILS Department of Environmental Studies, The University of Adelaide, Adelaide, S.A., Australia F. LELONG Laboratoire de Geologie Appliquee et Institut de Recherches sur les Ressources et Materiaux Mineraux, Universite dOrleans, Orleans (CEDEX), France W. SCHOTT Bundesanstalt fur Geowissenschaften und Rohstoffe, Hannover, German Federal Republic O.SCHULZ Abteilung Geochemie und Lagerstattenlehre, Institut fur Mineralogie und Petrographie der Universitat Innsbruck, Innsbruck, Austria M. SCHWARZBACH Geologisches Institut der Universitat Koln, Koln, German Federal Republic Y. TARDY Centre de Sedimentologie et de Geochimie de Surface (C.N.R.S.), Strasbourg (CEDEX), France J.J. TRESCASES Office de la Recherche Scientifique et Technique, Outre Mer (ORSTOM), Boudy, France J. VEIZER Department of Geology, University of Ottawa, Ottawa, Ont., Canada VI LIST OF CONTRIBUTORS TO THIS VOLUME Η. WOPFNER Geologisches Institut der Universitat Koln, Koln, German Federal Republic R.A. ZIMMERMAN Mineralogisch-Petrographisches Institut der Universitat Heidelberg, Heidelberg, German Federal Republic P. ZUFFARDI Cattedra di Giacimenti Minerari, Universita de Milano, Milano, Italy Chapter 1 EVOLUTION OF ORES OF SEDIMENTARY AFFILIATION THROUGH GEOLOGIC HISTORY; RELATIONS TO THE GENERAL TENDENCIES IN EVOLUTION OF THE CRUST, HYDROSPHERE, ATMOSPHERE AND BIOSPHERE JAN VEIZER INTRODUCTION Economic geology, like any other field of the geosciences, is at present in a turbulent state of development. One obvious trend is evident in attempts to relate economic de posits, particularly of the endogenic type, to the "new global tectonics" with all its consequences. The second feature, currently very strongly emphasized, is the treatment of economic deposits not as a special entity, but as an integral part of their geological environment. Economic geology is becoming more and more a geology of rocks, with ores being only one example of them (Stanton, 1972, p. 34). This is a very important step, in particular for "ores of sedimentary affiliation", which may have a direct relationship to the surrounding "country rocks". Their actual genesis is treated in detail in various parts of this multi-volume publication and is not a subject of the present review. On the other hand, if such ores are intimately related to their sedimentary environment, and this en vironment evolved during geologic history, the apparent evolution should be reflected also by the "ores of sedimentary affiliation". An attempt to formulate pertinent questions in this direction was hampered by the overwhelming influence of the magmatic theory of the origin of ores, and even more by the lack of knowledge of the Precambrian and its stratigraphy. These two defects have been rectified to a considerable degree during the last 10-15 years and as a result, first attempts at a comprehensive approach to the problem were formulated. Of particular importance were the publications of Strakhov (1964, 1969), Ronov (1964), Ronov and Migdisov (1971), Garrels and Mackenzie (1971) and Stanton (1972). These authors set the stage for the treatment of ore genesis and sedimentary rocks as a complementary system. A review of such a broad subject is extremely difficult and this chapter is no more than an attempt to indicate the general problem and to expose possible interrelations and mutual consistency of the evolution of the outer spheres of the earth. The author is deeply convinced that concentrated research into the questions tackled in the present review would be extremely rewarding and beneficial and may change to a considerable degree the picture presented below. 2 THE EVOLUTION OF SEDIMENTARY ORES IN GEOLOGIC HISTORY ORES OF SEDIMENTARY AFFILIATION AND THEIR TRENDS IN GEOLOGIC HISTORY limiting the ores of sedimentary affiliation to those described below, it is possible to discuss their major types and distribution during geologic history. The available data vary in detail and reliability and therefore discussion of the problem is rather uneven. Never theless, this description may serve as a basis for outlining general features and the direc tion of future research and interpretation. Residual deposits and weathering crusts1 Depending on the climate and bedrock composition, weathering may lead to forma tion of laterites of either iron- or alumina-rich type. These, in some cases, may serve as tOO 1000 my. Fig. 1. Histogram of the identified world resources of bauxites and the proportion of various fades during geologic history. (Based on the data of Valeton, 1972, and compilation of resources by Pater- son, 1967.) a = gibbsite bauxites on igneous and metamorphic rocks; b = gibbsite bauxites on clastic rocks; c = gibbsite bauxites on karst; d = boehmite bauxites on karst; e = diaspore bauxites on karst; / = corundum schists. The dotted line representes the slope for decrease in total world sedimentary mass with increasing age (cf. Fig. 7). 1 Editor's note: see also in this Volume, Chapter 3 by Lelong et al. TRENDS IN GEOLOGIC HISTORY OF SEDIMENTARY ORES 3 economic accumulations of iron, manganese and alumina (bauxites). Ferruginous laterites also contain a high proportion of known nickel resources (Cornwall in Brobst and Pratt, 1973). Their potential for extraction of other metals as byproducts is not yet fully realized (cf., Krauskopf, 1955), but the ferruginous laterites could be a potential source of Co, Ni, As, Be, Cr, Mo, Cu and possibly also Sc, Se, V, and the alumina-rich laterites of Be, Ga, Ti and possibly also Mo, Zn, Nb, Zr and others. The origin and classification of bauxites was discussed recently by Valeton (1972). From Fig. 1 it is evident that the total reserves as well as the facies of deposits were highly variable during geologic history. The mineralogical composition changes in the order gibbsite boehmite diaspore corundum with increasing age. This trend very likely represents diagenetic and/or metamorphic dehydratation (cf., Valeton, 1972 p. 179). The rapid decrease in total reserves of bauxites with increasing age, as well as the higher proportion of karst-type deposits in Mesozoic and Paleozoic sequences, will be discussed later in the text. woo 106t T06y ο ν Ο2 Μ Ο LU (Τ 700 J ο Ο ο ο IM ΓΜ Ο Ο</> oIM 0. α. ID Ο < UJ I Q_ ο 70 J <\ w WO 7000 my WO WOO m.y Fig. 2. Histogram of the identified world resources of sedimentary iron ores and the proportion of various facies during geologic history. (Based on the United Nations Survey of World Iron Ore Re sources, 1970.) a = laterites, gossans, placers, etc.; b = Minette type; c = Clinton type;d = Superior type; e = Algoma type. The dotted line as in Fig. 1. 4 THE EVOLUTION OF SEDIMENTARY ORES IN GEOLOGIC HISTORY to\ 1 Fig. 3. Histogram of the identified world resources of sedimentary manganese ores and the proportion of various facies during geologic history. (Based on the summary of Varentsov, 1964.) a = residual deposits; b = orthoquartzite-glauconite-clay association; c = carbonate association; d = orthoquartzite-siliceous shale-manganese carbonate association; e = volcano-sedimentary type; / = "jaspilitic" type. The dotted line as in Fig. 1. The rapid decrease in iron- (and manganese)-rich laterites in sequences older than Cenozoic is evident from Figs. 2 and 3. This decrease is more evident for iron than manganese. However, this is due mainly to the enormous tonnage of the Mn deposits of the orthoquartzite—glauconite—clay association (cf., Fig. 3). In fact the absolute eco nomic manganese reserves of lateritic type in Cenozoic formations are almost equal to the total Paleozoic reserves. Deposits associated with fluviatile to deltaic clastic sediments (1) According to United States Mineral Resources (Brobst and Pratt, 1973), placer and palaeoplacer deposits, whether of elluvial, alluvial or beach type, are at present the world's major source of Nb, Ta, Sn, W, Ti, Th, Zr and Hf. They are, or were, the source of TRENDS IN GEOLOGIC HISTORY OF SEDIMENTARY ORES 5 TABLE I Summary of characteristic features of the ores of fluviatile-deltaic association (in part a modification of Roscoe's, 1969, table XI) Placers and Conglomerate—gold— Sandstone -uranium - vanadium - 3 palaeoplacers1 uranium-pyrite type2 copper type Host rocks mostly oligomictic oligomictic conglome sandstones, arkoses, siltstones, sandstones and sands, rates; greenish argilla mud stones of variegated, pre less conglomerates ceous sandstones, dominantly red, colours (red beds), and pebbles arkoses, shales conglomerates, lignites and organic debris, carbonates Sedimentary continental-marine: continental: continental: mostly fluviatile environment elluvial, alluvial, fluviatile-deltaic beach placers Tectonic setting platform cover platform cover and rigid sialic blocs Age mostly Quaternary mostly Early Late Paleozoic to Quaternary and Tertiary Proterozoic Shape of deposits lenses and blankets stratiform, concordant peneconcordant tabular bodies, (concordant with in detail with sedimen elongate irregular bodies; sedimentary features) tary features discordant C-shaped bodies (rolls) Controls of primary features favourable for concentra facies variation, large-scale sedi localization tion of detrital heavy minerals; mentary features and tectonic palaeo topography structures affecting permeability (often dissemination and distribution of organic in arkosic matrix) material Minerals "heavy minerals": uraninite, uranotho- uraninite, coffinite, secondary U monazite, chromite, rite, brannerite, minerals; roscoelite, montroseite, zircon, columbite, thucholite, pyrite, V-clay; chalcocite, covellite, tantalite, native Au, gold, "heavy chalcopyrite, bornite, malachite, Pt, cassiterite, minerals" azurite; pyrite, marcasite, galena, wolframite, scheelite, sphalerite magnetite, hematite Ore mineral discrete grains small discrete sub- very fine-grained impregnations textures rounded to rounded and replacements grains Metals recovered Nb,Ta, Sn, W, Ti,Th, Au, U, Th, Y, REE, U, V, Cu, Mo, Ag (Se, As, Ni, Co) or concen Zr, Hf, Au, Pt-group, Pt-group (Pb, Ti, Zr, trated Sc, Y, Cr, REE Co, Ni, Cu, Zn, Ag) Sulphur little isotopic extreme isotopic fractionation fractionation Examples tin belt of SE Asia; Witwatersrand (S.A.); Colorado Plateau (U.S.A.); Florida beach sand Blind River-Elliot Ferghana (?) (U.S.S.R.); for Ti (U.S.A.) Lake area (Canada); Hamr (Czechosl.) Serra de Jacobina (Brazil); Tarkwa (?) (Ghana); Aldan Shield (U.S.S.R.) l>2,3 Editor's notes: 1 see Chapter 5 by Hails; 2 Chapters 1 and 2, in Vol. 7, by Pretorius, describe the Witwatersrand deposits; see, in Vol. 7, Chapter 3 by Rackley.
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