ORE DEPOSITS AND MANTLE PLUMES Ore Deposits and Mantle Plumes by Franeo Pirajno Geological Survey ofWestern Australia, Perth, Australia SPRINGER-SCIENCE+BUSINESS MEDIA, B.V. Library of Congress Cataloging-in-Publication Data ISBN 978-90-481-4026-8 ISBN 978-94-017-2502-6 (eBook) DOI 10.1007/978-94-017-2502-6 Cover illustration: The image on the cover is a modified version of that shown in Figure 5.7B in the text and represents a computer simulation of mantie processes; hot regions are red and cold regions are blue and green. The hot mantie material rises and uplifts the surface of the planet. The rising hot mantie simulates a mantie plume. This convection simulation model was created by Walter Kiefer Lunar and Planetary Institute, Houston, USA) and Louise Kellogg (University of California, Davis, USA) for the planet Mars, but is not specific to Mars, and is applicable to mantie plumes that occur on Earth. The element symbols represent those that may be directiy or indirectly linked to mantie plume activities on Earth, resulting in anomalous concentrations of these elements in the crust where they form ore deposits. The image is used by permission of the authors. Printed on acid-free paper Ali Rights Reserved © 2000 F. Pirajno Originally published by Kluwer Academic Publishers in 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, including photocopying, recording or by any information storage and retrieval system, without written permission from the copyright owner. To Mariateresa, my wife CONTENTS PREFACE XI ACKNOWLEDGEMENTS XIII INTRODUCTION XVII PARTONE CHAPTER 1 The Earth's Interna! Structure and Convection in the Mantle 1 1.1 Introduction 1 1.2 Early planetary evolution 2 1.3 The Earth's interna1 structure 5 1.3.1. The crust 7 1.3.2. The mantle 11 1.3.3. The core-mantle boundary (CMB) and D" 1ayer 20 1.3.4. The core 25 1.4 Convection in the mantle; theories and models 27 1.4.1. Theories and dynamics of convection 29 1.4.2. Physical parameters ofmantle convection 31 1.4.3. Whole mantle and two-layers mantle convection models 32 1.5 Mantle geochemistry 41 1.6 Mantle evolution through time and implications for Earth's h~~cy % 1. 7 Concluding remarks 53 1.8 References CHAPTER 2 Mantle Plumes and Superplumes; Contineotal Breakups, Supercontinent Cycles and Ore Deposits 59 2.1 Introduction 59 2.2 Hotspots: distribution and relationship to rifting 61 2.3 Labaratory modelling, structure and dynamics of mantle plumes 65 2.4 Doming ofthe crust (hotspot swells) and associated topographic and drainage features 71 VIII Contents 2.5 Mantle plume-lithosphere interactions and plume-generated melts 77 2.5.1. Crustal stress regimes in response to mantle plumes 85 2.6 Superplumes and continental breakup 86 2.6.1. Gondwana and Rodinia breakups, mantle plumes or plate forces? 90 2.6.2. Supercontinent cycles and ore deposits 94 2.7 The "other side" ofthe mantle plume theory 100 2.8 Concluding remarks 104 2.9 References 105 CHAPTER 3 Oceanic Islands, Large lgneous Provinces, Mafic Dyke Swarms, and Intracontinental Alkaline Magmatism 111 3.1 Introduction 111 3.2 Oceanic volcanic islands 112 3.2.1. The Hawaiian-Emperor seamounts chain 116 3.2.2. Marquesas Islands 119 3.2.3. Walvis Ridge and Tristan da Cunha 119 3.2.4. leeland 124 3.2.5. Reunion Island 127 3.2.6. Geochemical and isotopic characteristics of oceanic volcanic island basalts 128 3.3 Large igneous provinces (LIP): oceanic p1ateaux and continenta1 flood basalts (CFB) 135 3.3.1. lntroduction 135 3.3.2. Isotope systematics 139 3.3.3. Oceanic plateaux 140 3.3.4. Volcanic-rifted continental margins 149 3.3.5. Continental flood basalts (CFB) 151 3.4 Mafic dyke swarms 183 3.4.1. Mafic dyke swarms in the Kaapvaal Craton, South Africa 189 3.4.2. The Mackenzie dyke swarm, Canada 190 3.4.3. Parami-Etendeka dykes 192 3.5 Intracontinental alkaline magmatism 193 3.5.1. Teetonic settings, ages and controls of intracontinental alkaline magmatism in Africa 194 3.5.2. The Damaraland alkaline province, Namibia 198 3.5.3. Carbonatites 199 3.5.4. Kimberlites and lamproites 200 3.6 Concluding remarks 201 3.7 References 202 CHAPTER 4 Rifting Proeesses, Volcano-Sedimentary Basins and the Role ofMantle Plumes 215 4.1 Introduetion 215 4.2 Rifting dynamies: passive and aetive 220 4.2.1. Passive rifting 221 4.2.2. Aetive rifting 222 4.3 Rifting and basie formation related to eompression in thiekened erust 223 4.4 Geophysieal signatures of rifts 227 4.5 Stratigraphie sueeessions as reeords ofbasin evolution 230 4.5.1. The Stratigraphie reeord ofintraeontinental basins and aulaeogens 230 4.6 The East Afriean Rift System and the Afar Triangle: examples of modern eontinental rifting where mantle plume aetivity is reeognised 239 4.6.1. Introduetion 239 4.6.2. The East Afriean Rift System (EARS) 240 4. 7 Examples of aneient eontinental rifts where mantle plume aetivity is assumed: Thuli-Sabi-Lebombo hotspotjunetion; Damara and Irumide hotspot junetions 244 4.7.1. Tuli-Sabi-Lebombo hotspotjunetion 244 4. 7.2. Damara and Irumide hotspot junetions, southwestern Afriea 248 4.8 Sequenee stratigraphy, eustasy and mantle plumes 252 4.9 Concluding remarks 254 4.10 Referenees 256 CHAPTER 5 The P1anetary and Meteorite Impact Context of Mantle P1umes 261 5.1 Introduction 261 5.2 Moon 263 5.3 Mercury 265 5.4 Venus 265 5.5 Mars 269 5.6 Large meteorite impaets and possible eorrelations with mantle plumes 274 5.6.1. Ore deposits and impaet structures 277 5.6.2. Can meteorite mega-impaets trigger eontinental breakup and the ascent of mantle plumes? 279 5.7 Concluding remarks 285 5.8 Referenees 286 X Contents PARTTWO CHAPTER 6 Intracontinental Magmatism, Anorogenic Metamorphism, Ore Systems and Mantle Plumes 291 6.1 Introduction 291 6.2 Intracontinenta1layered igneous intrusions 291 6.3 Anorogenic prograde metamorphism and hydrothermal convention in hotspot-related rift systems 299 6.3.1. Anorogenic metamorphism in the Central Zone ofthe Damara Orogen, Namibia 301 6.3.2. Anorogenic metamorphism in the eastern Pyrenees 302 6.3.3. Anorogenic metamorphism and intraplate magmatism around the Vredefort Dome, South Africa 303 6.3.4. Metamorphism and fluid generation; metamorphogenic hydrothermal systems 306 6.4 Concluding remarks 317 6. 5 References 317 CHAPTER 7 Direct Links; Magmatic Ore Deposits- Fundamental Features and Concepts 323 7.1 Introduction 323 7.1.1. Definitions and terminology 323 7.1.2. Geometry of layered intrusions and magmatic processes 331 7.2 Magmatic oxide ores 342 7.2.1. Crystallisation of spine1s from mafic-ultramafic magmas 344 7.3 Magmatic sulphides and platinum group elements (PGE) ores 347 7.3.1. The formation ofNi sulphide ores 347 7.3.2. Platinum group elements (PGE) 355 7.4 Concluding remarks 378 7.5 References 380 CHAPTER 8 Magmatic Ore Deposits 387 8.1 lntroduction 387 8.2 Large layered igneous complexes 388 8.2.1. The Great Dyke, Zimbabwe 389 8.2.2. The Bushveld lgneous Complex, South Africa 401 8.2.3. Molopo Farms Complex, South Africa and Botswana 425 8.3 Magmatic ore deposits in igneous complexes associated with continental flood basalts 426 8.3.1. Duluth Complex, Mid-continent Rift System, USA 426 8.3.2. Noril'sk-Talnakh, Siberian Traps, Russia 428 8.3.3. The Insizwa Complex, Karoo lgneous Province 433 8.3.4. Skaergaard and Kap Edvard Holm, East Greenland 438 8.4 magmatic ores in Proterozoic troctolite-anorthosite complexes 441 8.4.1. Voisey's Bay Ni-Cu-Co 442 8.5 Komatiite-related magmatic ore deposits 445 8.5.1. Komatiite volcanology 446 8.5.2. Komatiite mineralogy and whole rock geochemistry 447 8.5.3. Komatiite-hosted Fe-Ni-Cu sulphide ores 449 8.6 Hydrothermal Ni-cu and PGE mineralisation in ultra- ultramafic rocks 453 8. 7 Concluding remarks 458 8.8 References 459 CHAPTER 9 Indirect Links: Hydrothermal Mineral Deposits 469 9.1 Introduction 469 9.2.1. Ring complexes and carbonatites 471 9.2.2. Proterozoic Cu-Au-U-REE-Fe deposits 473 9.2.3. Mesothermal ore deposits 480 9.2.4. Carlin-type epithermal ore deposits 483 9.2 Ore deposits associated with intracontinental anorogenic magmatism 471 9.3 Metallogeny ofthe Damara and Irumide orogens, Soutb- western Africa, and the Mid Continent Rift System, USA 491 9.3.1. Metallogeny ofthe Damara and Irumide orogens 491 9.3.2. Metallogeny ofthe Mid-continent Rift System, N orth America 497 9.4 Archaean 1ode Au deposits 498 9.5 Concluding remarks 502 9.6 References 504 CHAPTER 10 Indirect Links: Sedimentary Rock-Hosted Ore Deposits. Epilogue 509 10.1 Introduction 509 10.2 Metallogeny in modern rift settings 511 10.2.1. The East African Rift System 511 10.2.2. The Red Sea brine pools 516 10.3 Sedimentary-hydrothermal ore deposits 520 10.3.1. Mississippi Valley-type sulphide deposits 520 10.3.2. Sedimentary exhalative (SEDEX) massive sulphide deposits 523 10.3.3. Stratabound Cu-Ag and Cu-Co ore deposits 528 10.4 Metalliferous black shales 531 XII Contents 10.4.1. Mo-Ni-V-PGE-Au in black shales, southern China 533 10.5 Iron-formations and manganese deposits 534 10.6 Concluding remarks and epilogue 539 10.7 References 540 APPENDIX 547 INDEX 549 PREFACE PERTH Western Australia March 2000 Increasingly explorationists are seeking to find new ore deposits in poorly prospected areas, be they geographically remote, such as in the Arctic, or geologically remote, such as those under sedimentary cover.