Potassic Igneous Rocks and Associated Gold-Copper Mineralization

Potassic igneous rocks have gained much attention among petrologists worldwide, mainly due to their distinct geochemistry, and many geoscientists still consider them as petrological curiosities with an obscure petrogenesis. In the past, a plethora of genetic hypotheses and of local names for potassic igneous rocks from different localities have been created. This has produced some confusion in the literature. This book reviews the geochemical and petrological characteristics of the potassic igneous rock complexes and investigates the different tectonic settings in which these rocks occur. The authors provide an overview and a classification of these rocks and attempt to elucidate the geochemical differences between barren and mineralized potassic igneous complexes. Many epithermal gold and porphyry copper-gold deposits are hosted by high-K rocks. Therefore, this book is not only relevant to academic petrologists working on alkaline rocks, but also to exploration geologists prospecting for epithermal gold and/or porphyry copper-gold deposits in modern and ancient terranes. This third, updated and enlarged edition contains several new sections, new geochemical data and additional references.

Contenu

1 Introduction.- 1.1 Preamble: Potassic Igneous Rocks and Their Importance.- 1.2 Scope of Book.- 2 Definitions and Nomenclature.- 2.1 Historical Perspective of Potassic Igneous Rocks.- 2.2 Potassic Igneous Rocks as an Umbrella Term.- 2.3 Shoshonites.- 2.4 Shoshonitic and Alkaline Lamprophyres.- 2.5 Ultrapotassic Rocks.- 2.5.1 Introduction.- 2.5.2 Lamproites.- 2.5.3 Kamafugites.- 2.5.4 Orogenic Ultrapotassic Rocks.- 2.6 Group II Kimberlites.- 2.7 Potassic Igneous Rocks as Considered in this Book.- 2.8 Field Recognition of Potassic Igneous Rocks.- 3 Tectonic Settings of Potassic Igneous Rocks.- 3.1 Introduction.- 3.2 Tectonic Settings of Potassic Igneous Rocks.- 3.2.1 Continental Arc.- 3.2.2 Postcollisional Arc.- 3.2.3 Oceanic (Island) Arc.- 3.2.4 Within-Plate.- 3.2.5 Problems with Tectonic Classification.- 3.3 History of Discrimination of Tectonic Setting by Geochemical Means.- 3.4 Erection of Databases SHOSH1 and SHOSH2.- 3.5 Discrimination of Tectonic Setting by Multivariate Statistical Methods.- 3.6 Discrimination via Simple Geochemical Diagrams.- 3.7 Theoretical Basis for Discrimination Between Potassic Igneous Rocks in Different Tectonic Settings.- 3.8 Conclusions.- 4 Selected Type-Localities of Potassic Igneous Rocks from the Five Tectonic Settings.- 4.1 Roman Province (Italy): Example from a Continental Arc Setting.- 4.1.1 Introduction.- 4.1.2 Regional Geology.- 4.1.3 Mineralogy and Petrography of the Potassic Igneous Rocks.- 4.1.4 Geochemistry of the Potassic Igneous Rocks.- 4.2 Kreuzeck Mountains, Eastern Alps (Austria): Example from a Postcollisional Arc Setting.- 4.2.1 Introduction S.- 4.2.2 Regional Geology.- 4.2.3 Mineralogy and Petrography of the Lamprophyres.- 4.2.4 Geochemistry of the Lamprophyres.- 4.3 Northern Mariana Arc (West Pacific): Example from an Initial Oceanic Arc Setting.- 4.3.1 Introduction.- 4.3.2 Regional Geology.- 4.3.3 Mineralogy and Petrography of the Potassic Igneous Rocks.- 4.3.4 Geochemistry of the Potassic Igneous Rocks.- 4.4 Vanuatu (Southwest Pacific): Example from a Late Oceanic Arc Setting.- 4.4.1 Introduction.- 4.4.2 Regional Geology.- 4.4.3 Mineralogy and Petrography of the Potassic Igneous Rocks.- 4.4.4 Geochemistry of the Potassic Igneous Rocks.- 4.5 African Rift Valley (Rwanda, Uganda, Zaire): Example from a Within-Plate Setting.- 4.5.1 Introduction.- 4.5.2 Regional Geology.- 4.5.3 Mineralogy and Petrography of the Potassic Igneous Rocks.- 4.5.4 Geochemistry of the Potassic Igneous Rocks.- 5 Primary Enrichment of Precious Metals in Potassic Igneous Rocks.- 5.1 Introduction.- 5.2 Theoretical Discussion.- 5.3 Case Study: Potassic Alkaline Lamprophyres with Elevated Gold Concentrations from the Karinya Syncline, South Australia.- 5.3.1 Introduction.- 5.3.2 Regional Geology and Tectonic Setting.- 5.3.3 Mineralization in the Vicinity of the Lamprophyres.- 5.3.4 Nature of the Lamprophyres.- 5.3.5 Petrology and Geochemistry of the Lamprophyres.- 5.3.6 Precious Metal Abundance and Significance.- 5.4 Comparison of Precious Metal Abundances for Lamprophyres from the Karinya Syncline and Kreuzeck Mountains.- 6 Direct Associations Between Potassic Igneous Rocks and Gold-Copper Deposits.- 6.1 Direct Associations in Specific Tectonic Settings: Introduction.- 6.2 Erection of Database GOLD 1.- 6.3 Late Oceanic Arc Associations.- 6.3.1 Ladolam Gold Deposit, Lihir Island, Papua New Guinea.- 6.3.2 Emperor Gold Deposit, Viti Levu, Fiji.- 6.3.3 Dinkidi Copper-Gold Deposit, Didipio, Phillipines.- 6.3.4 Goonumbla Copper-Gold Deposit, New South Wales, Australia.- 6.4 Continental Arc Associations.- 6.4.1 Bajo de la Alumbrera Copper-Gold Deposit, Catamarca Province, Argentina.- 6.4.2 Bingham Copper Deposit, Utah, USA.- 6.4.3 El Indio Gold Deposit, Chile.- 6.4.4 Twin Buttes Copper Deposit, Arizona, USA.- 6.5 Postcollisional Arc Associations.- 6.5.1 Grasberg Copper-Gold Deposit, Indonesia.- 6.5.2 Misima Gold Deposit, Misima Island, Papua New Guinea.- 6.5.3 Porgera Gold Deposit, Papua New Guinea.- 6.6 Synthesis of Direct Genetic Associations.- 7 Indirect Associations Between Lamprophyres and Gold-Copper Deposits.- 7.1 Introduction.- 7.2 Shoshonitic Lamprophyres with Elevated Gold Concentrations from the Goodall Gold Deposit, Northern Territory, Australia (Proterozoic).- 7.2.1 Introduction.- 7.2.2 Regional Geology.- 7.2.3 Nature of Mesothermal Gold Mineralization.- 7.2.4 Mineralogy of the Lamprophyres.- 7.2.5 Geochemistry of the Lamprophyres.- 7.2.6 Direct or Indirect Link Between Potassic Lamprophyres and Mineralization.- 7.3 Shoshonitic Lamprophyres from the Tom's Gully Gold Deposit, Northern Territory, Australia (Proterozoic).- 7.3.1 Introduction.- 7.3.2 Regional Geology.- 7.3.3 Nature of Mesothermal Gold Mineralization.- 7.3.4 Petrology and Geochemistry of the Lamprophyres.- 7.3.5 Indirect Link Between Lamprophyres and Gold Mineralization.- 7.4 Shoshonitic Lamprophyres from the Eastern Goldfields, Yilgarn Block, Western Australia (Archaean).- 7.4.1 Introduction.- 7.4.2 Regional Geology.- 7.4.3 Nature of Mesothermal Gold Mineralization.- 7.4.4 Lamprophyres and Their Association with Mineralization.- 7.4.5 Petrology and Geochemistry of the Lamprophyres.- 7.5 Shoshonitic Lamprophyres from the Superior Province, Canada (Archaean).- 7.5.1 Introduction.- 7.5.2 Nature of Mesothermal Gold Mineralization.- 7.5.3 Lamprophyres and Their Association with Mineralization.- 7.5.4 Petrology and Geochemistry of the Lamprophyres.- 7.6 Indirect Link Between Lamprophyres and Archaean Gold Mineralization.- 7.7 Synthesis of Indirect Associations.- 8 Halogen Contents of Mineralized Versus Unmineralized Potassic Igneous Rocks.- 8.1 Introduction.- 8.2 Erection of Database MICA1.- 8.3 Discussion.- 8.3.1 Behaviour of Halogens in Magmatic Hydrothermal Systems.- 8.3.2 Halogen Contents of Mica in Potassic Igneous Rocks.- 8.3.3 Significance of Halogen Data.- 9 Implications for Mineral Exploration.- 9.1 Introduction.- 9.2 Area Selection.- 9.2.1 Composition of Host Rocks.- 9.2.2 Tectonic Setting.- 9.3 Prospect Evaluation.- 9.3.1 Favourable Tectonic Elements on the Prospect Scale.- 9.3.2 High Oxidation State of the Magmas.- 9.3.3 Elevated Halogen Contents of the Magmas.- 10 Characteristics of Some Gold-Copper Deposits Associated with Potassic Igneous Rocks.- 10.1 Abbreviations.- 10.2 Tables of Deposit Characteristics.- 10.2.1 Andacollo, Chile.- 10.2.2 Bajo de la Alumbrera, Catamarca Province, Argentina.- 10.2.3 Bingham, Utah, USA.- 10.2.4 Cadia, New South Wales, Australia.- 10.2.5 Choquelimpie, Chile.- 10.2.6 Cripple Creek, Colorado, USA.- 10.2.7 Dinkidi, Didipio, Philippines.- 10.2.8 El Indio, Chile.- 10.2.9 Emperor, Viti Levu, Fiji.- 10.2.10 Goonumbla, New South Wales, Australia.- 10.2.11 Grasberg, Indonesia.- 10.2.12 Kirkland Lake, Superior Province, C…