Minerals and Rocks. Editor in Chief P.J.Wyllie, Chicago, IL Editors A. El Goresy, Heidelberg W von Engelhardt, Tubingen. T.

Transcription

1 Minerals and Rocks 17 Editor in Chief P.J.Wyllie, Chicago, IL Editors A. El Goresy, Heidelberg W von Engelhardt, Tubingen. T. Hahn, Aachen

2 1. Sawkins Metal Deposits in Relation to Plate Tectonics With 173 Figures Springer-Verlag Berlin Heidelberg New York Tokyo 1984

3 Dr. FREDERICK J. SAWKINS Department of Geology and Geophysics University of Minnesota 108 Pillsbury Hall 310 Pillsbury Drive S.E. Minneapolis, MN 55455, USA Volumes I to 9 in this series appeared under the title Minerals, Rocks and Inorganic Materials ISBN-13: e-isbn-13: DOl: / Library of Congress Cataloging in Publication Data. Sawkins, Frederick J. Metal deposits in relation to plate tectonics. (Minerals and rocks; 17) Includes index. \. Ore-deposits. 2. Plate tectonics. 1. Title. II. Series. TN263.S This work is subject to copyright. All rights are reserved, whether the whole or part of the material is concerned, specifically those of translation, reprinting, re-use of illustrations, broadcasting, reproduction by photocopying machine or similar means, and storage in data banks. Under 54 of the German Copyright Law, where copies are made for other than private use, a fee is payable to 'Verwertungsgesellschaft Wort', Munich. by Springer-Verlag Berlin Heidelberg 1984 Softcover reprint of the hardcover 1st edition 1984 The use of registered names, trademarks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. Media conversion, printing and binding: Briihlsche Universitiitsdruckerei, Giessen 2131/

4 Preface I attempt this volume with no small degree of trepidation, for despite the near universal acceptance of plate tectonic theory, and the undeniable sweep and power of the concepts involved, points of controversy and uncertainty still abound. This is especially true with regard to the limited extent to which many ancient geologic terrains, however well studied, lend themselves to plate tectonic interpretation. There is also considerable controversy regarding the genesis of many metal deposits, and this impacts upon the degree to which such deposits can be meaningfully related to the tectonic settings in which they occur. It is relatively simple matter to point out that certain types of ore deposits exhibit impressive time-space associations with certain kinds of more recent plate boundary environments. It is also all too easy to possible plate tectonic-ore deposit relationships in ancient geologic terrains. What is more challenging is the recognition of the boundaries beyond which speculation is idle, but within which useful new insights regarding the relationship of certain ores to their lithologic and tectonic environments may emerge. My interest in plate tectonic-metal deposit relationships was initially motivated by a desire to find a suitable framework within which students could be introduced to the wide variety of distinctive metal deposit types. Somewhat later it was fostered by the desire to investigate the degree to which such concepts could be used in creative planning of exploration programs. However, I have encountered a certain degree of confusion about metal deposits and their divergent types amongst students, exploration geologists, and geochemists interested in ore genesis problems. We all have much to learn regarding these matters, but an attempt as synthesis seems warranted at this time, especially in view of our increasing dependence on earth resources. I make no claim that application of plate tectonic concepts can pinpoint new metal deposits. The main tool available to the exploration geologist is

5 VI Preface that of analogy with respect to other deposits and to their lithologic settings, i.e., certain types of metal deposits occur in association with certain types of rocks. The importance of plate tectonics is simply that plate interactions spawn various types of lithologic assemblages and, thus, such concepts can considerably sharpen our perceptions and interpretations of geologic terrains. As such, they can aid the exploration geologist in his(her) evaluation of various lithologic sequences and the types of metal deposits that might have been generated within them. The study of metal deposits has accelerated a great deal in the last two decades, in particular through geochemical study. The application of fluid inclusion, stable isotope, and various experimental techniques to the study of metal deposits has broadened our insights into the chemical and hydrodynamic aspects of ore formation. These advances have, in turn, allowed the formation of more realistic conceptual models for various types of ore generating systems. Such models are of considerable aid to the exploration and mining geologist in areas of known mineralization, but are of more limited utility in terms of the search for new mineral districts. The problem of the geographic distribution of metal deposits must be addressed initially in terms of geologic and tectonic environments rather than the nuances of ore solution geochemistry. Endeavors in this field, it seems, have not kept pace with those of a more geochemical nature (e.g. Barnes, 1979). In part, this is because geochemical research tends to be more 'tidy' and amenable to institutional funding and publication that the rather less rigorous and more empirical aspects of regional synthesis and compilation. The latter have to be based on some combination of personal experience and literature research. An important point in this regard is that metal deposits and the systems that generate them need to be viewed not as geochemical accidents, but rather as fortunate culminations of normal geologic and geochemical processes. No one has made this point with more eloquence than Wyllie (1981), who states that metal deposits are not "the illegitimate offspring from random couplings of rocks and fluids from intermediate sources," but "have respectable... family lineages, with ancestors deep within the continental crust, or below it." The extent to which ore generating systems can proceed to fruition and where they develop depends on a host of local factors, but the broad environmental controls in each case

6 Preface VII will be tectonic. It follows that if these tectonic controls result in the main from plate interactions, and if plate tectonics have operated throughout much of earth history, then a variety of environments favorable for ore generation must have repeated themselves through geologic time. A consequence of these observations, if correct, is that major irregularities in the time distribution of various metal deposit types require explanation. Ore deposits can be broadly divided into those generated by endogenetic processes and those generated by exogenic processes. The former are invariably associated with thermal processes and, in general, can be related more readily to magnetic and tectonic events instigated by plate activity. Deposits formed by surficial processes such as weathering or shallow marine sedimentation will have relationships to their tectonic environment that are more tenuous. This volume represents an attempt to provide a rational basis for the observed time-space distribution of metal deposits, at least those of endogenous type. Such deposits can form by a wide variety of mechanisms in a highly diverse spectrum of geologic environments, and it follows that their relationships to plate tectonics will vary from significant in some instances to more tenuous in others. In fact, it is important to realize that even in cases where an impressive association between plate tectonics and certain ore types is manifest, plate interactions merely provide the master control for the particular geologic environments within which such deposits tend to form. What I propose to do in the chapters that follow is deal with specific plate tectonic environments and cover the ore deposits that can be associated with each. Descriptions of individual type examples for which abundant data exist are provided to add substance to the volume. Additional examples are catalogued, where feasible, but any exhaustive compilation of world metal deposits is early beyond the scope of this book. Certain of my interpretations of distant ore deposits garnered from the literature will inevitably be in error, and possibly enrage some of those with first-hand local knowledge. To such people I can only offer an advance apology and an exhortation to publish and set the record straight. The line between creative synthesis and idle speculation is an extremely fuzzy one. I have included, wherever feasible, some thoughts on how the relationship between tectonics, geologic terrains, and metal deposits can be used

7 VIII Preface in the context of exploration planning. Inevitably, such thoughts will be of a speculative nature, but the literature on ore deposits is notably lacking in attempts to do this. A concerted attempt has been made to include up to date references and to avoid references pertaining to obscure sources or unpublished material, so that the interested reader with access to a good geological library can backtrack on any particular subject. It is hoped that this book will prove useful to students at the advanced undergraduate and graduate levels, and to mining and exploration geologists. lowe no small debt of gratitude to various company geologists around the world for their willingness to share freely of their time and local expertise with an itinerant academic. Without their enormous, and sometimes unheralded, contributions, the science of economic geology would be sad shape indeed, and in recognition of this, I dedicate this volume to them. I am also indebted to the front line troops such as Richard Sillitoe, who, not only have covered vast amounts of territory, but have written lucidly and imaginatively about their observations. Finally, it is hoped that we will be able eventually to use "fundamental ore deposit geology to elucidate plate tectonics, not (only) the reverse" (Guilbert, 1981). Acknowledgments. The initial typescript of this book was produced by Kathy Ohler, for whose competent, patient, and always cheerful help I am most grateful. The figures were draftet by Roxann Cioper and Jim Kiehne, and I thank them for their timely aid. lowe a special debt of gratitude to Richard Sillitoe who reviewed nearly all stages of the manuscript and corrected a number of my misconceptions. Discussions with my colleagues at the University of Minnesota were also most helpful. Finally, my thanks to Peter Wyllie for initially suggesting the project and for encouragement during its evolution. Frederick J. Sawkins

8 Contents Introduction: Plate Tectonics and Geology..... Part I Convergent Plate Boundary Environments Chapter 1 Principal Arcs and Their Associated Metal Deposits Porphyry-Type Deposits Associated Igneous Rocks Mineralization and Alteration Patterns Fluid Inclusions and Stable Isotopes The EI Salvador Porphyry Copper Deposit, Chile Genetic Models for Porphyry Copper Deposits Suggestions for Exploration Copper-Bearing Breccia Pipes Distribution and Associated Igneous Rocks Mineralization and Alteration Formation and Mineralization of Breccia Pipes The Cumobabi Breccia Pipe Deposits, Mexico Suggestions of Exploration Skarn Deposits Distribution and Associated Igneous Rocks Mineralization Genesis of Contact Metasomatic Skarn Deposits Discussion and Suggestions for Exploration Vein Deposits Distribution and Associated Igneous Rocks Mineralization and Alteration The Baguio, Philippines and Tayoltita, Mexico Vein Systems Discussion and Suggestions for Exploration.. 46

9 x Contents 1.5 Precious Metal Deposits of the Western United States Vein Deposits Carbonate-Replacement Gold Deposits Hot Spring-Type Gold Deposits Discussion Additional Deposits of Principal Arcs Massive Magnetite Deposits Manto-Type Copper Deposits 1. 7 Discussion Chapter 2 Metal Deposits on the Inner Sides of Principal Arcs Contact Metasomatic Deposits Mineralization The Providencia Ag-Pb-Zn-Cu Deposit, Zacatecas, Mexico Discussion and Suggestions for Exploration Polymetallic Vein Systems The Casapalca Ag-Pb-Zn-Cu Deposit, Peru Discussion and Suggestions for Exploration Tin-Tungsten Deposits Mineralization The Llallagua Tin Porphyry Deposits, Bolivia Discussion and Suggestions for Exploration 81 Chapter 3 Metal Deposits of Arc-Related Rifts Climax-Type Porphyry Molybdenum Deposits Mineralization and Alteration Patterns Discussion and Suggestions for Exploration Additional Lithophile Suite Deposits in Arc-Related Rifts Kuroko-Type Massive Sulfide Deposits Mineralization and Alteration Patterns Fluid Inclusion and Stable Isotope Data. 99

10 Contents XI Buchans Polymetallic Sulfide Deposit, Newfoundland Discussion and Suggestions for Exploration Base and Precious Metal Vein Deposits 106 Chapter 4 Additional Aspects of Arc-Related Metallogeny Metal Deposits Related to Fore-Arc Felsic Magmatism Paleozoic and Older Porphyry Copper Deposits Massive Sulfide Deposits of the Caledonides, Scandinavia Similar Massive Sulfide Deposits Elsewhere Massive Sulfide Deposits in Greenstone Belts The Kidd Creek Massive Sulfide Deposit, Ontario Discussion and Suggestions for Exploration Additional Aspects of Greenstone Belt Metallogeny Gold Deposits in Greenstone Belts The Homestake Gold Mine, South Dakota Discussion and Suggestions for Exploration Overview of Arc-Related Metallogeny Relation of Arc Metallogeny to Subduction Style 132 Part II Divergent Plate Boundary Environments Chapter 5 Metallogeny of Oceanic-Type Crust Generation of Oceanic-Type Crust Contemporary Mineralization at Oceanic Spreading Ridges The Salton Sea Geothermal System Massive Sulfide Deposits of the Troodos Ophiolite, Cyprus Additional Examples of Cyprus-Type Massive Sulfide Deposits 147

11 XII Contents 5.5 Discussion Chromite Deposits in Ophiolite Complexes The Chromite Deposits of the Vourinos Complex, Greece The Chromite Deposits of Selukwe, Zimbabwe Additional Minor Mineralization in Ophiolite Complexes Chapter 6 Intracontinental Hotspots, Anorogenic Magmatism, and Associated Metal Deposits Tin Deposits Associated with Anorogenic Granites Iron-Titanium Deposits Associated with Anorthosites Hotspot-Related Layered Mafic Complexes and Associated Ores The Geology and Ores of the Bushve1d Igneous Complex, South Africa The Platinum Deposits of the Stillwater Complex, Montana The Copper-Nickel Ores of the Sudbury Irruptive, Ontario, Canada Discussion Metal Deposits Related to Carbonatites Afterword Chapter 7 Metal Deposits Associated with the Early Stages of Continental Rifting General Considerations Hydrothermal Copper Deposits The Messina Copper Deposits, South Africa Discussion Rift-Related Molybdenum Deposits Rift-Related Stratiform Copper Deposits Lithologic Setting Mineralization

12 Contents XIII Ores of the Zambian Copper Belt Discussion and Suggestions for Exploration Rift-Related Magmatic Copper-Nickel Deposits Copper-Nickel Deposits of the Noril'sk-Talnakh Region, U.S.S.R Discussion Carbonate-Hosted Lead-Zinc Deposits in Relation to Rifting Mississippi Valley-Type Deposits Alpine-Type Lead-Zinc Deposits Irish-Type Lead-Zinc Deposits Discussion and Suggestions for Exploration. 211 Chapter 8 Metal Deposits Related to Advanced Stages of Rifting GeneralObservations Metalliferous Deposits of the Red Sea Metalliferous Deposits of the Atlantis II Deep Discussion Sediment-Hosted Massive Sulfide Deposits Settings of Sediment-Hosted Massive Sulfide Deposits Mineralization The Sullivan Massive Sulfide Deposit Discussion and Suggestions for Exploration Volcanic-Hosted Massive Sulfide Deposits Massive Sulfide Deposits of the Bathurst- Newcastle District, New Brunswick, Canada Discussion Massive Sulfide Deposits in High-Grade Metamorphic Terrains Additional Facets of Rift-Related Metallogeny Early Proterozoic Uraniferous Conglomerates and Rifting Major Occurrences of Banded Iron Formation in Relation to Rifting Events

13 XIV 8.7 Metallogenesis and Rifting - Some Final Thoughts.... Contents 243 Part ill Collisional Environments and Other Matters Chapter 9 Metal Deposits in Relation to Collision Events Ophiolite-Hosted Metal Deposits Tin-Tungsten Deposits Associated with Collisional Granites Mineralization The Panasquiera Tin-Tungsten Deposits, Northern Portugal Discussion and Suggestions for Exploration Uranium Deposits Associated with Collision Granites The Rossing Uranium Deposit, Namibia Discussion and Suggestions for Exploration Additional Examples of Collision-Related Terrains and Metallogenic Implications Metallogenesis and Collision Events - Some Final Thoughts Chapter 10 Metal Deposits and Plate Tectonicsan Attempt at Perspective Lineaments and Metal Deposits to.2 Transform Faults and Metal Deposits Plate Tectonics and Metal Deposits of Surficial Origin loa An Enigmatic Class of Uranium Deposits to.5 Metal Deposits and Plate Tectonics: Time-Space Perspectives Metal Deposits and Plate Tectonics: Exploration Perspectives 280 Afterword 281 References 282 Subject Index 317