UNDERSTANDING MINERAL DEPOSITS

Transcription

1 UNDERSTANDING MINERAL DEPOSITS

2 U nderstanding Mineral Deposits by Kula c. Misra Department of Geological Sciences, The University oftennessee, Knoxville, U.S.A. SPRINGER-SCIENCE+BUSINESS MEDIA, B.V.

3 A c.i.p. Catalogue record for this book is available from the Library of Congress. ISBN ISBN (ebook) DOI / Printed on acid-free paper AII Rights Reserved 2000 K.C. Misra Softcover reprint of the hardcover 1 st edition 2000 No part of the material protected by this copyright notice may be reproduced or utilized in any form or by any means, electronic or mechanical, incjuding photocopying, recording or by any information storage and retrieval system, without written permission from the copyright owner.

4 To my wife, Geeta, for her patience during the years ofpreoccupation with the book and the clutter it generated all around our home

5 TABLE OF CONTENTS PREFACE xiii CHAPTER 1. INTRODUCTION Mineral Deposit versus Orebody Styles of Mineralization and Morphology of Mineral Deposits Distribution of Mineral Deposits Understanding Mineral Deposits 4 CHAPTER 2. FORMATION OF MINERAL DEPOSITS Ore-forming Processes Orthomagmatic Processes Examples of Orthomagmatic Deposits Sedimentary Processes Metamorphic Proce c Examples of Metamorphic Deposits Hydrothermal Processes Examples of Hydrothermal Deposits Summary Recommended Reading 92 CHAPTER 3. INTERPRETATION OF MINERAL DEPOSITS - I Introduction Geologic Setting Ore Minerals Ore-Gangue Textures Stability Relations ofore Minerals and Assemblages Hydrothermal Alteration Zoning Fluid Inclusions Trace Element Distribution Recommended Reading 147 CHAPTER 4. INTERPRETATION OF MINERAL DEPOSITS - II Stable Isotopes Sulfur Isotopes 153 vii

6 Vlll CONTENTS 4.3. Carbon Isotopes Oxygen and Hydrogen Isotopes Lead Isotopes Strontium Isotopes Geothermometry and Geobarometry Metamorphism of Ore Assemblages Age of Mineralization A Comprehensive Example: The Creede District, Colorado, USA Summary Recommended Reading 237 CHAPTER 5. CHROMITE DEPOSITS Introduction Types of Deposits Distribution Stratiform Deposits Podiform Deposits Examples Chromite Composition Origin Metallogenesis Summary Recommended Reading 272 CHAPTER 6. NICKEL (-COPPER) SULFIDE DEPOSITS Introduction Distribution Types of Deposits Examples Ore Composition Hydrothermal Alteration and Metamorphism Origin of Kambalda-type Deposits Metallogenesis Summary Recommended Reading 318 CHAPTER 7. PLATINUM-GROUP ELEMENT (pge) DEPOSITS Introduction Types ofdeposits Examples Ore Composition Origin of Merenskky-type PGE Deposits 337

7 CONTENTS ix 7.6. Orgin ofpge-enriched Chromitites in Layered Intrusions Metallogenesis Summary Recommended Reading 352 CHAPTER 8. PORPHYRY DEPOSITS Introduction Porphyry Copper Deposits Porphyry Molybdenum Deposits Porphyry Tin Deposits Summary Recommended Reading 413 CHAPTER 9. SKARN DEPOSITS Introduction Skarns and Skarn Deposits Types ofskarns and Skarn Deposits Examples Origin Metallogenesis Summary Recommended Reading 449 CHAPTER 10. VOLCANIC-ASSOCIATED MASSIVE SULFIDE 450 (VMS) DEPOSITS Introduction Distinguishing Features Distribution Types ofdeposits Examples Ore Composition Hydrothermal Alteration Metamorphism and Deformation Origin Metallogenesis Summary Recommended Reading 496 CHAPTER II. SEDIMENT-HOSTED MASSIVE ZINC-LEAD 497 SULFIDE (SMS) DEPOSITS Introduction Distinguishing Features 498

8 x CONTENTS Distribution Types ofdeposits Examples Ore Composition Hydrothennal Alteration Origin Metallogenesis Summary Recommended Reading 538 CHAPTER 12. SEDIMENT-HOSTED STRATIFORM COPPER (SSC) 539 DEPOSITS Introduction Distinguishing Features Distribution Types ofdeposits Examples Ore Composition Origin Metallogenesis Summary Recommended Reading 572 CHAPTER 13. MISSISSIPPI VALLEY-TYPE (MVT) ZINC-LEAD 573 DEPOSITS Introduction Distinguishing Features Distribution Examples Ore Composition Alteration Brecciation Origin Metallogenesis Summary Comparison ofvms, SMS, SSC, and MVT Deposits Recommended Reading 612 CHAPTER 14. URANIUM DEPOSITS Introduction Types ofdeposits and Distribution Examples 627

9 CONTENTS Xl Mineralogy and Textures Origin Metallogenesis Summary Recommended Reading CHAPTER 15. PRECAMBRIAN IRON-FORMATIONS Introduction Iron-formation Distribution Iron-formation Facies Types of Iron-formations Examples Ore Composition Metamorphism Secondary Enrichment Origin Time-bound Distribution ofiron-formations Summary Recommended Reading CHAPTER 16. GOLD DEPOSITS Introduction Distribution Types of Gold Deposits Examples Origin of Hydrothermal Gold Deposits Metallogenesis Summary Recommended Reading REFERENCES INDEX

10 PREFACE Mineral deposits have supplied useful or valuable material for human consumption long before they became objects of scientific curiosity or commercial exploitation. In fact, the earliest human interest in rocks was probably because of the easily accessible, useful (e.g., red pigment in the form of earthy hematite) or valuable (e.g., native gold and gemstones) materials they contained at places. In modern times, the study of mineral deposits has evolved into an applied science employing detailed field observations, sophisticated laboratory techniques for additional information, and computer modeling to build complex hypotheses. Understanding concepts that would someday help geologists to find new mineral deposits or exploit the known ones more efficiently have always been, and will continue to be, at the core of any course on mineral deposits, but it is a fascinating subject in its own right, even for students who do not intend to be professional economic geologists. I believe that a course on mineral deposits should be designed as a "capstone course" that illustrates a comprehensive application of concepts from many other disciplines in geology (mineralogy, stratigraphy and sedimentation, structure and tectonics, petrology, geochemistry, paleontology, geomorphology, etc.). This book is intended as a text for such an introductory course in economic geology, primarily for senior undergraduate and graduate students in colleges and universities. It should also serve as a useful information resource for professional economic geologists. The overall objective of the book is to provide the reader with a critical understanding of selected classes mineral deposits: how are they distributed in space and geologic time, what are their distinguishing and general characteristics, and what can be inferred about their genesis from the available data. The expectation is that the information and discussions in this text will provide students with an insight into the formulation of appropriate exploration strategies for various classes of mineral deposits and kindle their interest in further research on aspects of mineral deposits that are poorly understood or that remain unresolved. As an applied discipline, the study of economic geology requires a background in other disciplines of geology (particularly mineralogy, petrology, structural geology, and stratigraphy and sedimentation) as well as in allied sciences, such as physics and chemistry. It is assumed that the student has had one or more courses in these subjects and is in a position to appreciate the applications of various principles taught in those courses to issues related to mineral deposits. There is an emphasis on geochemistry throughout the book; this is necessary because the formation of almost all mineral Xlll

11 deposits ultimately involves the chemical precipitation of minerals from fluids of appropriate characteristics. Considering the vast spectrum of mineral deposits that are either of potential economic interest or are actually being exploited for our use, it is practically impossible to include a comprehensive treatment of mineral deposits in an introductory text of this kind constrained by page limitations. The selection included here is based on what I perceive as the more interesting (and usually controversial) classes of deposits, especially from the points of view of origin and crustal evolution in space and time. This does not imply that the classes of deposits excluded from consideration here are not interesting or that their origins are devoid of controversy, but I had to draw the line somewhere. A recurring problem I have had to deal with in writing this book is to keep it updated with the latest information, which is being produced at an ever increasing rate. In addition, space limitation has compelled me to a selection of the references I have used, a judgement, which I am afraid, is probably not totally devoid of personal bias. Kula C. Misra Knoxville, Tennessee August, 1999 XIV

12 ACKNOWLEDGMENTS The information contained in this book has come from a variety of sources: thousands of journal articles, scores of books, visits to many mines around the world, and a lifetime of endeavor to understand mineral deposits. I am thankful to all those authors who have shared their knowledge, the publishers who have been instrumental in disseminating the information, the mine geologists and mine managers who have made the mine visits a rewarding experience, and the teachers, such as Samar Sarkar, Asoke Mookherjee, Sisir Sen, and Michael Fleet, who taught me to think critically. A book of this length and effort does not happen without the sustained cooperation and help of a substantial number of individuals. In addition to the anonymous reviewers selected by the publisher, I am grateful to my colleagues Harry Y. McSween, Jr., Otto C. Kopp, Robert D. Hatcher, and Marvin Bennett for critically reviewing several of the chapters. I am particularly indebted to Hap McSween for his continued support throughout the writing of this book. I thank Marvin Bennett for all the help with the computer softwares I have used for this book, especially for graphics. The Office of Research, The University of Tennessee, Knoxville, is gratefully acknowledged for a generous grant toward the completion of this project. This book would not have been completed without the encouragement of my wife, Geeta, our children, Lolly and Anand, and our son-in law, Tom, or published without the patience of the publishers. xv