PETROLOGY OF LAMPROITES PETROLOGY OF LAMPROITES

Roger H. Mitchell Lakehead University Thunder Bay, Ontario Canada and Steven C. Bergman ARCO Oi! and Gas Company Plano, Texas

SPRINGER SCIENCE+BUSINESS MEDIA, UC Llbrary of Congress Cataloglng-ln-Publlcation Data

Mitchell, Roger H. Petrology of lamproites I Roger H. Mitehell and Steven C. Bergman. p. em. Ineludes bibliographieal referenees and index. ISBN 978-1-4613-6688-1 ISBN 978-1-4615-3788-5 (eBook) DOI 10.1007/978-1-4615-3788-5 1. Lamproite. 2. Petrology. 3. Geoehemistry. 4. Rocks, Igneous. I. Bergman, Steven C. 11. Tit18. QE462.L35M57 1991 552' .3--de20 90-25226 CIP

ISBN 978-1-4613-6688-1

© 1991 Springer Science+ Business Media New York Origioallypublished by Plenum Press, New York in 1991 Spftcover reprint of the hardcover 1st edition 1991 All rights reserved No part of this book may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, microfilming, recording, or otherwise, without written permission from the Publisher This work is dedicated to

REX T. PRIDER

Emeritus Professor of Geology University of Western Australia in recognition of his pioneering studies of the mineralogy and petrology of lamproites. Preface

In this book, the first dedicated entirely to the petrology of lamproites and their relationships to other potassium-rich rocks, the objective of the authors is to provide a comprehensive critical review of the occurrence, mineralogy, geochemistry, and petrogenesis of the clan. Although lamproites represent one of the rarest of all rock types, they are both economically and scientifically important and we believe the time is ripe for a review of the advances made in their petrology over the past two decades. Many of these advances stem from the recognition of diamond-bearing lamproites in Western Australia and the reclassification of several anomalous diamond-bearing kim• berlites as lamproites. Consequently lamproites, previously of interest only to a small number of mineralogists specializing in exotica outside the mainstream of igneous petrol• ogy, have become prime targets for diamond exploration on a worldwide basis. Contemporaneously with these developments, petrologists realized that lamproites possess isotopic signatures complementary to those of midoceanic ridge basalts, alkali basalts, kimberlites, and other mantle-derived melts. These isotopic studies provided new insights into the long-term development of the mantle by suggesting that the source regions of lamproites were metasomatically enriched in light rare earth and other incompatible elements up to 1-2 Ga prior to the melting events leading to generation of the magma. We believe that an understanding of the nature of lamproites is essential for geologists concerned with exploration for diamond, and petrologists and geochemists interested in continental alkaline magmatism and mantle evolution. In the book we present new inter• pretations of various aspects of lamproite petrology. Hence, the work is not simply a summary of existing information and accepted concepts; rather it proposes hypotheses that it is hoped, will serve to stimulate further studies of these unusual rocks. The book is the work of two authors, and although in overall agreement regarding the content and philosophy of the text, each assumes primary responsibility for any errors or omissions to be found in his particular contributions. In addition to the style and overall editing of the work, Roger Mitchell was responsible for Chapters 1, 2, 6-8, and 10 and Steven Bergman was responsible for Chapters 3-5 and 9. Alan Edgar and Henry Meyer are thanked for reviewing initial drafts of many of the chapters. Valerie Dennison is especially thanked for proofreading the entire work. Many people have contributed to the production of this book. We are particularly appreciative of preprints, thin sections, and rock samples provided by and discussions with

vii viii PREFACE

Lynton Jaques, Barbara Scott Smith, Alan Edgar, Danielle Velde, Henry Meyer, Bram Janse, Leendert Krol, Peter Berendsen, John Lewis, Steve Foley, Gino Venturelli, Mike Roden, Peter Nixon, Carter Hearn, Ted Scamboz, Howard Coopersmith, Hugh O'Brien, Tony Irving, Ken Collerson, Tony Erlank, Nick Rock, and Dave Nelson. Special thanks go to Henry Meyer for providing many hours of microprobe time at Purdue University, Barbara Scott Smith for photographic work, and Ken Foland for geochronological data. 1. Toney, D. 1. Henry, and L. Liang assisted with some of the microprobe analyses in Dallas. We thank P. A. Sheahan, K. Weissman, P. A. Carper, L. Batzle, and 1. M. Prokesh for literature searches and the acquisition of citations. Technical assistance at ARCO in Dallas was provided by 1. Talbot, V. Mount, S. R. Yang, F. Stiff, and E. Kinsel, and at Lakehead University by A. MacKenzie, M. Downey, A. Hammond, R. Viitala, W. Bons, and S. Millar. Sam Spivak drafted all of the original diagrams. Mitchell's work on lamproites is supported by the Natural Sciences and Engineering Research Council of Canada and Lakehead University. Much of Bergman's contribution was supported by the Anaconda Minerals Company (Industrial Minerals Group) and the ARCO Oil and Gas Company Exploration and Production Research Laboratory, in conjunction with their (presently expired) diamond exploration and minerals research programs. Roger Mitchell wishes to thank Valerie Dennison for her continued encouragement of his studies of lamproites and maintenance of an environment favorable to the preparation of this book. Steve Bergman acknowledges the support and consideration provided by Mary, Allison, Everett, Louise, and Maggie Bergman.

Roger Mitchell Thunder Bay Steven Bergman Dallas Contents

Chapter 1. The Lamproite Clan-Etymology and Historical Perspective 1 1. 1. Introduction 1 1.2. Initial Discoveries-1870-1906 1 1.3. Etymology of Lamproite 2 1.4. Western Australian Discoveries-The Legitimization of Lamproites 3 1.5. Johannsen and Modal Classifications of Rocks 4 1.6. Further Developments, New Occurrences, and Diamond- Bearing Lamproites 5 1.7. Reclassification of Anomalous Kimberlites 6 1. 8 . Recent Developments 7

Chapter 2. Potassic Rocks and the Lamproite Clan 9 2.1. Alkalinity, Sodic, Potassic, and Ultrapotassic Rocks 9 2.2. Alkali-Alumina Relationships 10 2.3. Potassic Rocks-General Petrographic Characteristics and Terminology 11 2.3.1. Lamproites 11 2.3.2. Roman Province Leucitites 12 2.3.3. Ultrapotassic Leucitites 13 2.3.4. Kalsilite-Bearing Lavas (Kamafugitic Rocks) 14 2.3.5. Potassic Lamprophyres 15 2.3.6. Kimberlite and Micaceous Kimberlites 15 2.3.7. The Shoshonite Association 16 2.3.8. Potassic Intrusive Rocks 17 2.4. Petrochemical Classifications of Potassic Rocks 17 2.4.1. Niggli Parameters 18 2.4.2. K20-Na20 Diagrams 19 2.4.3. Total Alkali-Silica Classifications 19 2.4.4. Sahama (1974) 21 2.4.5. Barton (1979) 23

ix x CONTENTS

2.4.6. Bogatikov et al. (1985) 26 2.4.7. Foley et al. (1987) 29 2.5. Petrographic and Mineralogical Classifications 31 2.5.1. Petrographic Classifications 31 2.5.2. Mineralogical Classifications 32 2.6. The Lamproite Clan 35 2.6.1. Geochemical Criteria for Lamproite Recognition 37 2.6.2. Mineralogical Criteria for Lamproite Recognition 37

Chapter 3. Description of Lamproite Occurrences-Distribution, Age, Characteristics, and Geological Framework 39 3.1. Introduction 39 3.2. North American and Greenland Lamproites 40 3.2.1. Group Name: Prairie Creek 43 3.2.2. Group Name: Leucite Hills 46 3.2.3. Group Name: Smoky Butte 50 3.2.4. Group Name: Francis 52 3.2.5. Group Name: Hills Pond 55 3.2.6. Group Name: Sisimiut 57 3.2.7. Group Name: Yellow Water Butte 59 3.2.8. Group Name: Froze-to-Death Butte 61 3.3. European Lamproites 63 3.3.1. Group Name: Murcia-Almeria 65 3.3.2. Group Name: Sisco 69 3.3.3. Group Name: Sesia-Lanzo and Combin 70 3.4. African Lamproites 72 3.4.1. Group Name: Kapamba 73 3.4.2. Group Name: Pneil, Postmasburg, Swartruggens 75 3.4.3. Group Name: Bobi 76 3.5. Australian Lamproites 79 3.5.1. Group Name: Argyle 80 3.5.2. Group Name: West Kimberley 83 3.6. Antarctic Lamproites 86 3.6.1. Group Name: Gaussberg 86 3.6.2. Group Names: Mount Bayliss and Priestley Peak 87 3.7. Asian Lamproites 89 3.7.1. Group Name: Chelima 90 3.7.2. Group Name: Majhgawan 93 3.7.3. Group Name: Barakar 96 3.7.4. Group Name: Murun 97 3.8. South American Lamproites 98 3.8.1. Group Name: Coromandel 98 3.9. Conclusions 101 CONTENTS xi

Chapter 4. Tectonic Framework of Lamproite Genesis 103 4.1. Age and Temporal Relations of Lamproite Magmatism 104 4.2. Regional Geological and Tectonic Setting Generalizations 107 4.2.1. Lamproites and Plate Tectonics 108 4.2.2. Lamproites and Contemporaneous Subduction Zones 108 4.2.3. Fracture Zones, Transform Faults, and Continental Lineaments 110 4.2.4. Mantle Plumes, Hot Spots, and Hot Regions 111 4.2.5. Continental Rift Zones and Aulacogens 114 4.2.6. Orogeny and Postorogenic Relaxation 115 4.3. Lithospheric History of Lamproite Settings 116 4.3.1. Regional Structure 116 4.3.2. Basement Age, Composition, and Evolution 117 4.3.3. Contemporaneous, Previous, and Subsequent Magmatism 117 4.3.4. Importance of Paleosubduction and Fossil Benioff Zones 119 4.3.5. Mantle Metasomatism-Another Necessary Condition 120 4.3.6. Comparison with Kimberlites, Alkali Basalts, Lamprophyres, and Potassium-Rich Rocks 121 4.4. Tectonic Framework of Four Mesozoic-to-Cenozoic Lamproite Type-Locality Magmatic Fields 122 4.4.1. Leucite Hills 122 4.4.2. West Kimberley 122 4.4.3. Murcia-Almeria 123 4.4.4. Prairie Creek 123 4.5. Conclusions and Preferred Model 123

Chapter 5. Petrological Facies and Igneous Forms of the Lamproite Clan 125 5.1. Introduction 125 5.1.1. Historical Development 126 5.1.2. Lamproite Igneous Forms 126 5.1. 3. Lamproite Facies Classification 127 5.2. Lava Flow Facies 128 5.2.1. Examples of Lava Flow Facies Lamproites 130 5.2.2. Comparisons with Other Mafic and Intermediate Lavas 136 5.2.3. Summary 137 5.3. Crater and Pyroclastic Facies 137 5.3.1. Vent Morphology 138 5.3.2. Pyroclastic Fall Deposits 139 5.3.3. Base Surge and Pyroclastic Flow Deposits 142 5.3.4. Epiclastic Deposits 146 5.3.5. Examples of Crater and Pyroclastic Facies Lamproites 147 xii CONTENTS

5.4. Hypabyssal Facies 157 5.4.1. Examples of Hypabyssal Facies Lamproites 158 5.5. Plutonic Facies 161 5.6. Generalized Model of Eruptive Sequences 162 5.7. Comparison with Kimberlite Diatremes 165 5.8. Summary 166

Chapter 6. Mineralogy of Lamproites 169 6.1. Phlogopite 169 6.1.1. Paragenesis 169 6.1.2. Leucite Hills, Wyoming 172 6.1.3. West Kimberley, West Australia 179 6.1.4. Argyle, West Australia 190 6.1.5. Prairie Creek, Arkansas 191 6.1.6. Murcia-Almeria, Spain 192 6.1.7. Smoky Butte, Montana 195 6.1.8. Kapamba, Zambia 195 6.1.9. Sisimiut, Greenland 197 6.1.10. Hills Pond-Rose Dome, Kansas 198 6.1.11. Bobi, Ivory Coast 198 6.1.12. Francis, Utah 199 6.1.13. Yellow Water Butte, Montana 200 6.1.14. Sisco, Corsica 201 6.1.15. Majhgawan, India 201 6.1.16. Gaussberg, Antarctica 203 6.1.17. Probable Lamproites-Murun, Presidente Oligario, and Chelima 203 6.1.18. Minor and 'frace Elements 205 6.1.19. Summary of Mica Compositional Variations 206 6.1.20. Solid Solutions in Lamproite Mica 207 6.1.21. Comparisons with Mica in Other Potassic Rocks 211 6.1.22. Conditions of Crystallization 215 6.2. Amphibole 217 6.2.1. Classification 217 6.2.2. Paragenesis 218 6.2.3. Composition 219 6.2.4. Minor and 'frace Elements 229 6.2.5. Comparisons with Amphiboles in Other Potassic Rocks 230 6.2.6. Conditions of Crystallization 232 6.3. Clinopyroxene 233 6.3.1. Paragenesis 233 6.3.2. Composition of Phenocrystal and Groundmass Pryoxenes 234 6.3.3. Compositions of Pyroxenes from Parageneses 2 and 3 239 CONTENTS xiii

6.3.4. Comparison with Pyroxenes in Other Potassic Rocks 240 6.4. Orthopyroxene 242 6.4.1. Paragenesis 242 6.4.2. Composition 242 6.5. Olivine 244 6.5.1. Paragenesis 244 6.5.2. Composition 245 6.5.3. Summary 249 6.6. Leucite 249 6.6.1. Paragenesis 249 6.6.2. Composition 251 6.7. Analcite 253 6.8. Sanidine 254 6.8.1. Paragenesis 254 6.8.2. Composition 255 6.9. Spinel 257 6.9.1. Paragenesis-Primary Spinels 257 6.9.2. Composition-Primary Spinels 258 6.9.3. Comparison with Primary Spinels from Kimberlite and Lamprophyre 264 6.9.4. Secondary Aluminous Spinels 266 6.10. Priderite 268 6.10.1. Paragenesis 268 6.10.2. Composition 268 6.10.3. Ba-Titanates Related to Priderite 272 6.10.4. Comparison with Hollandites in Other Potassic Rocks 272 6.11. Jeppeite 273 6.12. Iron Titanium Oxides 274 6.12.1. Arma1colite 274 6.12.2. Ilmenite 276 6.12.3. Titanium Dioxides 278 6.13. Potassium Zirconium Silicates 279 6.13 . 1. Wadeite 279 6.13.2. Dalyite 281 6.14. Apatite 282 6.14.1. Paragenesis 282 6.14.2. Composition 283 6.15. Perovskite 286 6.15.1. Paragenesis 286 6.15.2. Composition 286 6.16. Titanosilicates 287 6.16.1. Shcherbakovite 287 6.16.2. Davanite 289 6.16.3. Unnamed K-Ba-Titanosilicate 290 6.17. Minor Accessory and Secondary Minerals 290 xiv CONTENTS

6.l7.1. Zeolites 291 6.17.2. Carbonates 291 6. 17.3. Roedderitelike Phases 291 6.17.4. Cerium-Bearing Minerals 292 6.17.5. Silicon Dioxide 293 6.17.6. Barite 294 6. 17.7. Other Minerals 294 6. 17.8. Secondary Phases 294

Chapter 7. The Geochemistry of Lamproites 295 7.1. Major Element Geochemistry 295 7.1.1. General Characteristics 295 7. 1.2. Compositional Relationships to Other Potassic Lavas 298 7. 1.3. Intraprovincial Characteristics 301 7.2. Compatible Trace Elements 314 7.2.1. First Period Transition Elements 314 7.2.2. Platinum Group Elements 318 7.3. Incompatible Trace Elements-I: Ba-Sr, Zr-Hf, Nb-Ta, Th-U 319 7.3.1. Barium and Strontium 319 7.3.2. Zirconium and Hafnium 323 7.3.3. Niobium and Tantalum 325 7.3.4. Thorium and Uranium 326 7.4. Incompatible Trace Elements-2: Rare Earth Elements and Yttrium 327 7.4.1. Rare Earth Elements 327 7.4.2. Yttrium 337 7.5. Incompatible Trace Elements-3: Alkali Elements 337 7.5.1. Lithium 337 7.5.2. Rubidium 338 7.5.3. Cesium 240 7.6. Volatile Trace Elements: Fluorine, Sulfur, and Chlorine 341 7.7. Other Trace Elements 341 7.8. Interelement Relationships 342 7.9. Isotopic Composition 343 7.9.1. Strontium and Neodymium 343 7.9.2. Lead 348 7.9.3. Oxygen 350 7.10. Summary 351

Chapter 8. Experimental Studies Relevant to the Formation and Crystallization of Lamproites 353 8.1. Low-Pressure Studies of Lamproites 353 8.1. 1. Anhydrous Melting Relationships 353 CONTENTS xv

8.1.2. Water-Saturated Melting Relationships 354 8.2. High-Pressure Phase Relationships of Natural Lamproites 356 8.2.1. Phlogopite Lamproites 357 8.2.2. Olivine and Madupitic Lamproites 360 8.3. Synthetic Systems 362 8.4. The Oxidation State of Lamproite Magmas 367 8.5. Summary 370

Chapter 9. Diamonds, Xenoliths, and Exploration Techniques 371 9.1. Diamonds and Xenoliths: Alien, Yet Beneficial, Companions of Lamproites 371 9.2. Diamonds 371 9.2.1. Type, Morphology, Color, and Size 372 9.2.2. Mineral Inclusion Suite 372 9.2.3. Isotopic Composition 374 9.2.4. Comparison with Kimberlite Diamonds 374 9.2.5. Discussion 374 9.3. Xenoliths and Xenocrysts 375 9.3.1. Xenoliths in Olivine Lamproites 375 9.3.2. Xenoliths in Leucite and Phlogopite Lamproites 377 9.3.3. Discussion 377 9.4. Exploration Techniques for Diamondiferous Lamproite 378 9.4.1. Remote Sensing Techniques 379 9.4.2. Geophysical Techniques 380 9.4.3. Geochemical Surveys 382 9.4.4. Indicator/Heavy Mineral Sampling 383 9.4.5. Summary 384

Chapter 10. Petrogenesis of Lamproites 385 10.1. Introduction 385 10.2. Previous Petrogenetic Models 385 10.2.1. Fractionation of Peridotite and Kimberlite 385 10.2.2. Contamination of Kimberlite 387 10.2.3. Partial Melting of Garnet Lherzolite 387 10.2.4. Incongruent Melting of Phlogopite 389 10.2.5. Fractional Fusion and Diapiric Uprise 390 10.2.6. Partial Melting of Enriched Mantle 392 10.2.7. Partial Melting of Harzburgitic Sources 393 10.2.8. Subduction-Related Models 395 10.3. Genesis of the Lamproite Clan 396 10.3.1. Character of the Source 396 10.3.2. Melting of the Source 398 10.3.3. Relationships between Olivine and Phlogopite Lamproites and the Origins of the Isotopic Signatures of the West Kimberley Lamproites 399 xvi CONTENTS

10.3.4. Relationship of Madupitic Lamproites to Phlogopite Lamproites and the Origins of Isotopic Signatures of the Leucite Hills Lamproites 400 10.3.5. The Anomalous Murcia-Almeria Lamproites 401 10.4. Relationships to Kimberlites 401 10.5. Relationships to MARID-Suite Xenoliths 403 10.6. Relationships to Other Potassic Rocks and Lamprophyres 404 10.7. Summary 406

Postscript 407

References 409

Index 443