Lecture Notes in Earth Sciences 56 Editors: s. Bhattacharji, Brooklyn G. M. Friedman, Brooklyn and Troy H. J. Neugebauer, Bonn A. Seilacher, Tuebingen and Yale Springer-Verlag Berlin Heidelberg GmbH Daniel MUller David I. Groves Potassic Igneous Rocks and Associated Gold-Copper Mineralization Springer Authors Dr. Daniel MUller Placer International Exploration Inc. Av. Gertrudis Echenique 30, Piso 3 Las Condes, Santiago, Chile Prof. Dr. David I. Groves Key Centre for Strategic Mineral Deposits Department of Geology and Geophysics The University of Western Australia Nedlands, WA 6009, Australia "For all Lecture Notes in Earth Sciences published till now please see final pages of the book" ISBN 978-3-540-59116-0 ISBN 978-3-662-00920-8 (eBook) DOI 10.1007/978-3-662-00920-8 CIP data applied for This work is subject to copyright. All rights are reserved, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, re-use of illustrations, recitation, broadcasting, reproduction on microfilms or in any other way, and storage in data banks. Duplication of this publication or parts thereof is permitted only under the provisions of the German Copyright Law of September 9, 1965, in its current version, and permission for use must always be obtained from Springer-Verlag. Violations are liable for prosecution under the German Copyright Law. © Springer-Verlag Berlin Heidelberg 1995 UrsprUnglich erschienen bei Springer-Verlag Berlin Heidelberg New York 1995 Typesetting: Camera ready by author SPIN: 10498051 36/3142-543210 -Printed on acid-free paper Preface In recent years, there has been increasing interest from geoscientists in potassic ig neous rocks. Academic geoscientists have been interested in their petrogenesis and their potential value in defining the tectonic setting of the terranes into which they were intruded, and exploration geoscientists have become increasingly interested in the association of these rocks with major epithermal gold and porphyry gold-copper deposits. Despite this current interest, there is no comprehensive textbook that deals with these aspects of potassic igneous rocks. This book redresses this situation by elucidating the characteristic features of potassic (high-K) igneous rocks, erecting a hierarchical scheme that allows interpre tation of their tectonic setting using whole-rock geochemistry, and investigating their associations with a variety of gold and copper-gold deposits, worldwide. About two thirds of the book is based on a PhD thesis by Dr Daniel Muller which was produced at the Key Centre for Strategic Mineral Deposits within the Department of Geology and Geophysics at The University of Western Australia under the supervision of Professor David Groves, the late Dr Nick Rock, Professor Eugen Stumpf!, Dr Wayne Taylor, and Dr Brendon Griffin. The remainder of the book has been compiled from the literature using the collective experience of the two authors. The book is dedi cated to the memory of Dr Rock who initiated the research project but died before its completion. Sincere thanks are due to our colleagues and friends at the Key Centre for provid ing a stimulating environment in which to do the research and to write the first drafts of the book. Gratitude is also expressed to colleagues at Placer International Explo ration Inc., Santiago, for encouraging the completion of the book following Dr Muller's appointment to the Company. Professor Eugen Stumpf! is also sincerely thanked for his hospitality and assistance in the early stages of the research recorded in the book. We are particularly indebted to Dr Susan Ho who assisted in the editing of the book, produced the camera-ready copy, and organised the subject index. Without her help the book would not have been completed on schedule, if at all. Col Steel is also thanked for his excellent drafting of the more complex maps displayed in the book. Dr Wolfgang Engel of Springer-Verlag is also thanked for his encouragement of the project. VI Preface The following colleagues also provided support, contributed ideas, shared author ship on papers, and/or provided unpublished information: Eric Bloem, David Bowes, Mari Carrizo, Andi Chang, Megan Clark, Hilko Dalstra, Alan Edgar, Michael Farrand, Richard Forster, Michael Gareau, Sue Golding, Eliseo Gonzalez-Urien, Roland Gorbatschev, Lalu Gwalani, Greg Hall, Adolf Helke, Paul Heithersay, Bruce Hooper, Abraham Janse, Rod Jones, Rob Kerrich, Neal McNaughton, Claudio Milliotti, Aberra Mogessie, Brian Morris, Peter Neumayr, Juhani Ojala, Julian Pearce, Joe Piekenbrock, David Quick, Rob Ramsay, Steve Sheppard, Richard Sillitoe, Henning S~rensen, Heman Soza, Jon Standing, Joe Stolz, William Threlkeld, Spencer Titley, Linda Tompkins, Takeshi Uemoto, Ignacio Ugalde, Gianpiero Venturelli, Marcial Vergara, Richard Vielreicher, Mike Wheatley, Noel White, and Derek Wyman. Elsevier permitted the use of Figures 5.6, 6.2, 6.3, 6.4, 6.5, 6.6, and 6.15, and Tables 5.5 and 6.2. Daniel Miiller, Santiago David I. Groves, Perth Table of Contents 1 Introduction 1 1.1 Preamble: Potassic Igneous Rocks and Their Importance 1 1.2 Scope of Book. 2 2 Def'mitions and Nomenclature . 3 2.1 Historical Perspective of Potassic Igneous Rocks 3 2.2 Potassic Igneous Rocks as an Umbrella Term 4 2.3 Shoshonites 5 2.4 Shoshonitic and Alkaline Lamprophyres 5 2.5 Ultrapotassic Rocks 6 2.5.1 Introduction 6 2.5.2 Lamproites 7 2.5.3 Kamafugites 7 2.5.4 Orogenic Ultrapotassic Rocks 8 2.6 Group II Kimberlites . 8 2.7 Potassic Igneous Rocks as Considered in this Book 9 2.8 Field Recognition of Potassic Igneous Rocks 10 3 Tectonic Settings of Potassic Igneous Rocks 11 3.1 Introduction 11 3.2 Tectonic Settings of Potassic Igneous Rocks 11 3.2.1 Continental Arc 11 3.2.2 Postcollisional Arc 16 3.2.3 Oceanic (Island) Arc 16 3.2.4 Within-Plate 16 3.2.5 Problems with Tectonic Classifications 17 3.3 History of Discrimination of Tectonic Setting by Geochemical Means 17 3.4 Erection of Databases SHOSHI and SHOSH2 . 20 VIII Table of Contents 3.5 Discrimination of Tectonic Setting by Multivariate Statistical Methods 28 3.6 Discrimination via Simple Geochemical Diagrams. 31 3.7 Theoretical Basis for Discrimination between Potassic Igneous Rocks in Different Tectonic Settings 34 3.8 Conclusions. 37 4 Selected Type-Localities of Potassic Igneous Rocks from the Five Tectonic Settings 39 4.1 Roman Province (Italy): Example from a Continental Arc Setting 39 4.1.1 Introduction 39 4.1.2 Regional Geology . 41 4.1.3 Mineralogy and Petrography of the Potassic Igneous Rocks 41 4.1.4 Geochemistry of the Potassic Igneous Rocks 41 4.2 Kreuzeck Mountains, Eastern Alps (Austria): Example from a Postcollisional Arc Setting 42 4.2.1 Introduction 42 4.2.2 Regional Geology . 43 4.2.3 Mineralogy and Petrography of the Lamprophyres. 45 4.2.4 Geochemistry of the Lamprophyres . 46 4.3 Northern Mariana Arc (West Pacific): Example from an Initial Oceanic Arc Setting 53 4.3.1 Introduction 53 4.3.2 Regional Geology . 53 4.3.3 Mineralogy and Petrography of the Potassic Igneous Rocks 54 4.3.4 Geochemistry of the Potassic Igneous Rocks 55 4.4 Vanuatu (Southwest Pacific): Example from a Late OceanicArc Setting 55 4.4.1 Introduction 55 4.4.2 Regional Geology . 55 4.4.3 Mineralogy and Petrography of the Potassic Igneous Rocks 56 4.4.4 Geochemistry of the Potassic Igneous Rocks 57 4.5 African Rift Valley (Uganda, Rwanda, Zaire): Example from a Within-Plate Setting 59 4.5.1 Introduction 59 4.5.2 Regional Geology . 60 4.5.3 Mineralogy and Petrography of the Potassic Igneous Rocks 60 4.5.4 Geochemistry of the Potassic Igneous Rocks 60 5 Primary Enrichment of Precious Metals in Potassic Igneous Rocks 63 5.1 Introduction 63 5.2 Theoretical Discussion 63 Table of Contents IX 5.3 Case Study: Potassic Alkaline Lamprophyres with Elevated Gold Concentrations from the Karinya Syncline, South Australia 67 5.3.1 Introduction 67 5.3.2 Regional Geology and Tectonic Setting . 67 5.3.3 Mineralization in the Vicinity of the Lamprophyres 68 5.3.4 Nature of the Lamprophyres . 69 5.3.5 Petrology and Geochemistry of the Lamprophyres . 71 5.3.6 Precious Metal Abundance and Significance 77 5.4 Comparison of Precious Metal Abundances for Lamprophyres from the Karinya Syncline and Kreuzeck Mountains. 79 6 Direct Associations between Potassic Igneous Rocks and Gold-Copper Deposits . 83 6.1 Direct Associations in Specific Tectonic Settings: Introduction 83 6.2 Erection of Database GOLD 1 87 6.3 Late Oceanic Arc Associations . 89 6.3.1 Ladolam Gold Deposit, Lihir Island, Papua New Guinea 90 6.3.2 Emperor Gold Deposit, Viti Levu, Fiji . 93 6.3.3 Goonumbla Copper-Gold Deposit, New South Wales, Australia 97 6.4 Continental Arc Associations. .102 6.4.1 Bingham Copper Deposit, Utah, USA . .104 6.4.2 Twin Buttes Copper Deposit, Arizona, USA .106 6.4.3 Chilean Andes . .109 6.5 Postcollisional Arc Associations . · 111 6.5.1 Grasberg Copper-Gold Deposit, Indonesia · 111 6.5.2 Porgera Gold Deposit, Papua New Guinea .115 6.6 Synthesis of Direct Genetic Associations · 119 7 Indirect Associations between Lamprophyres and Gold-Copper Deposits . 121 7.1 Introduction . 121 7.2 Shoshonitic Lamprophyres with Elevated Gold Concentrations from the Goodall Gold Deposit, Northern Territory, Australia (Proterozoic) . . 121 7.2.1 Introduction .121 7.2.2 Regional Geology. . 122 7.2.3 Nature of Mesothermal Gold Mineralization .125 7.2.4 Mineralogy of the Lamprophyres . 125 7.2.5 Geochemistry of the Lamprophyres . . 125 7.2.6 Direct or Indirect Link between Potassic Lamprophyres and Mineralization . 129 X Table of Contents 7.3 Shoshonitic Lamprophyres from the Tom's Gully Gold Deposit, Northern Territory, Australia (Proterozoic) .130 7.3.1 Introduction .130 7.3.2 Regional Geology . .130 7.3.3 Nature of Mesothermal Gold Mineralization .130 7.3.4 Petrology of the Lamprophyres .131 7.3.5 Indirect Link between Lamprophyres and Gold Mineralization .131 7.4 Shoshonitic Lamprophyres from the Eastern Goldfields, Yilgarn Block, Western Australia (Archaean) · 132 7.4.1 Introduction .132 7.4.2 Regional Geology . .133 7.4.3 Nature of Mesothermal Gold Mineralization · 133 7.4.4 Lamprophyres and Their Association with Mineralization .135 7.4.5 Petrology and Geochemistry of the Lamprophyres . · 135 7.5 Shoshonitic Lamprophyres from the Superior Province, Canada (Archaean) .138 7.5.1 Introduction .138 7.5.2 Nature of Mesothermal Gold Mineralization .139 7.5.3 Lamprophyres and Their Association with Mineralization .139 7.5.4 Petrology and Geochemistry of the Lamprophyres . · 141 7.6 Indirect Link between Lamprophyres and Archaean Gold Mineralization .143 7.7 Synthesis of Indirect Associations · 143 8 Halogen Contents of Mineralized versus Unmineralized Potassic Igneous Rocks . .145 8.1 Introduction .145 8.2 Erection of Database MICAI · 147 8.3 Discussion . · 147 8.3.1 Behaviour of Halogens in Magmatic Hydrothermal Systems .147 8.3.2 Halogen Contents of Mica in Potassic Igneous Rocks .149 8.3.3 Significance of Halogen Contents .157 9 Implications for Mineral Exploration · 159 9.1 Introduction .159 9.2 Area Selection . .159 9.2.1 Composition of Host Rocks .159 9.2.2 Tectonic Setting .160 9.3 Prospect Evaluation .160 9.3.1 Favourable Tectonic Elements on the Prospect Scale .160 9.3.2 High Oxidation State of the Magmas .160 9.3.3 Elevated Halogen Contents of the Magmas . · 161