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The Southwest Zone Breccia-Centered Silica

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The Southwest Zone Breccia-Centered Silica The Southwest Zone breccia-centered silica-undersaturated alkalic porphyry Cu-Au deposit, Galore Creek, B.C: Magmatic-hydrothermal evolution and zonation, and a hydrothermal biotite perspective by Kevin Byrne BA. (Hons.) Mod Geology, Trinity College, Dublin, 2004 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE in THE FACULTY OF GRADUATE STUDIES (Geological Sciences) THE UNIVERSITY OF BRITISH COLUMBIA (Vancouver) April, 2009 © Kevin Byrne 2009 ABSTRACT Situated in northwest B.C Canada, the Southwest Zone Cu-Au breccia-centered deposit is one of twelve mineralized centers in the Galore Creek alkalic porphyry district. Formed in an island arc-setting outboard of ancestral North America in the lateTriassic, deposits in the Galore Creek district have a combined measured and indicated resource of 785.7 Mt at 0.52 per cent Cu, 0.29 g/t Au and 4.87g/t Ag. Mineralisation in the Southwest Zone is centered in narrow hydrothermally cemented breccias. Composite dikes of megacrystic orthoclase-phyric syenite and megacrystic orthoclase and plagioclase-phyric monzonite are cut by polylithic, poorly sorted pebble- cobble clast size matrix-rich breccias. Hydrothermally cemented breccias, characterised by the cement (infill) assemblage phlogopite ± K-feldspar ± magnetite ± anhydrite ± diopside ± suiphide, overprint the western contact between matrix-bearing breccias and megacrystic porphyries. Coeval with cemented breccia formation, intrusions of biotite phyric monzodiorite occur at the matrix-bearing breccia-wall rock contact and in the matrix-bearing breccias. Biotite-phyric monzodiorite and the principal cemented breccia domains are co-spatial and syn-Cu-Au. Drilling has outlined a zone of >0.3% hypogene Cu approximately 20-lOOm thick, 500m wide and 400m in length that strikes l0O, dips 45-60°S, and has a semi- ellipsoidal morphology. This mineralisation is coincident with potassic (stage D) alteration and infill. Cu-poor, diopside-dominated (calc-[potassic]) alteration formed contemporaneously with, and locally flanks, potassic-D infill. Sulphide minerals are zoned from a core of chalcopyrite-bomite, to chalcopyrite>pyrite, to pyrite>chalcopyrite out to pyrite only. Garnet-bearing peripheral propylitic alteration overlaps with a pyrite and Au-halo and locally overprints potassic and calc-Q,otassic) assemblages. Based on electron microprobe analysis, systematic spatial variations in Ti-content 2 overlap and Fe3/Fe2 of infill biotite are evident. Increases in Ti-contents and Fe317Fe with positive gradients in Cu concentration, taken with interpreted alteration reactions, this suggest Cu-deposition is caused by decreasing102 coupled with an increase in pH at 2O/JHF), determined from infill biotite, distinguish 420-475°C. Low logQH potassic fluids in the Southwest Zone, and other alkalic porphyry deposits, from fluids in calc alkalic systems and reflects the contrasting magmatic composition. 11 TABLE OF CONTENTS. ABSTRACT I TABLE OF CONTENTS iii LIST OF TABLES vi LIST OF FIGURES vii ACKNOWLEDGMENTS xi CHAPTER 1: OVERVIEW I 1.1 Rationale for Study I 1.2 Thesis organization 2 1.3 Regional Geological Setting 3 1.4 Galore Creek District 5 1.4.1 Geography 5 1.4.2 Exploration History 5 1.4.3 Supracrustal Rocks 5 1.4.4 Igneous Rocks 8 1.4.5 Hydrothermally Altered and Mineralized Centers 11 1.4.6 Structural History 11 1.4.7 Southwest Zone 12 1.5 Breccias 15 1.5.1 Approach and Nomenclature 15 1.5.2 Fragmentation Mechanisms and Breccia Classification 15 1.5.3 Principal Breccia Fades Characteristics 17 1.6 Biotite 22 1.6.1 Crystal-chemistry 22 1.6.2 Normalization Schemes for Microprobe Data 24 1.6.3 Mechanisms of Ti Al and Fe3+ Incorporation 25 1.7 Biotite in the Porphyry Environment 27 1.7.1 Example Studies 27 1.7.2 Geothermometry 29 1.7.3 Oxygen Fugacity Estimates 31 1.7.4 Halogen and Water Fugacity Estimates 31 1.8 Research Objectives 32 1.9 Study Methodology 33 1.10 References 35 111 CHAPTER 2: MAGMATIC-HYDROTHERMAL EVOLUTION AND ZONATION OF A BRECCIA CENTERED CU-AU ALKALIC PORPHYRY: SOUTHWEST ZONE, GALORE CREEK 43 2.1 Introduction 43 2.2 Exploration History 46 2.3 Regional Geological Setting 46 2.4 District Geology 47 2.5 Rock types of the Southwest Zone 51 2.5.1 Coherent rocks 52 2.5.2 Clastic rocks 60 2.5.3 Rock paragenesis 67 2.6 Structural controls on rock distribution 68 2.7 Alteration 69 2.7.1 K-feldspar ± biotite ± hematite dusting (potassic-A and-B)-Stage-1 70 2.7.2 Phlogopite ± chlorite ± magnetite (potassic-C)-Stage-1 70 2.7.3 Phlogopite ± magnetite ± K-feldspar (potassic-D)-Stage-2 70 2.7.4 Diopside ± magnetite ± phiogopite (calcic-fpotassicD-Stage-2 72 2.7.5 K-feldspar-anhydrite (waning potassic)-Stage-2 76 2.7.6 Sericite ± anhydrite (phyllic)-Stage-3 76 2.7.7 Garnet ± chlorite (calcic)-Stage-3 77 2.7.8 Chlorite ± epidote ± calcite ± pyrite (propyiltic)-Stage-4 79 2.7.9 K-feldspar ± Fe-carbonate (carbonate-potassic)-Stage-4 80 2.7.10 Quartz (quartz veins)-Stage-4 81 2.8 Sulphide minerals 82 2.8.1 Potassic-D and calcic-fpotassicJ-Stage-2 82 2.8.2 Late-stage K-feldspar ± Fe-carbonate-Stage-4 84 2.9 Structural controls on alteration and mineralisation 84 2.9.1 Pre to syn Stage 2 and 3 84 2.9.2 Post-Stage 2 and 3 85 2.10 Oxygen and hydrogen isotope data 86 2.11 Metals Zoning 88 2.11.1 Copper, Gold and Silver 88 2.11.2 Lead and Zinc 90 2.11.3 Molybdenum 91 2.12 Discussion and Genetic Interpretation 92 2.12.1 Clastic rocks 92 2.12.2 Isotopic composition of hydrothermal fluids 95 2.12.3 Alteration zoning (Stages 2 and 3) 98 2.12.4 Metal transport, deposition and zoning 103 2.12.5 Palaeo-geometry and deposit model 111 2.13 Conclusions 116 iv 2.14 References .118 CHAPTER 3: COMPOSITION OF BIOTITE FROM THE SOUTHWEST ZONE ALKALIC PORPHYRY CU-AU DEPOSIT, GALORE CREEK, BC, CANADA: EVALUATION OF HYDROTHERMAL FLUID CHEMISTRY 124 3.1 Introduction 124 3.2 Geological framework 126 Regional: 126 District: 127 Deposit: 129 3.3 Biotite types classification 131 3.4 Analytical procedures and sample methodology 137 3.5 Normalization of microprobe data and estimation of Fe3 139 3.6 Biotite composition by type 142 3.7 Spatial variation in Ti and Fe3 145 3.8 Biotite halogen chemistry 150 3.9 Hydrothermal fluid halogen fugacity ratio estimates 153 3.10 Comparison of fugacity ratios with other porphyry systems 155 3.11 Discussion 158 3.11.1 Significance of gradients in infil biotite chemistry 158 3.11.2 Halogen chemistry 160 3.12 Conclusions 161 3.13 References 162 CHAPTER 4: CONCLUSIONS 167 4.1 Recommendations for future work (and other conjectures) 168 4.2 References 170 APPENDICIES A-D on disc I in sleeve and is also available at http:llwww.mdru.ubc.ca V LIST OF TABLES TABLE 1.1 Summary of Galore Creek intrusive rocks (Enns, et. al., 1995) 10 TABLE 1.2 Average conserved element ratios from Galore Creek intrusive rocks (Enns, et. al., 1995) 10 TABLE 1.3 Genetic classes and associated fragmentation processes, adapted from Sillitoe (1985), Davies (2002) and Davies et al (2008b) 20 TABLE 1.4 Common porphyry-system breccia facies and their descriptive criteria adapted from Seedorif et al. 2005, Sillitoe (1985), and Davies (2002) 21 TABLE 1.5 Substitution mechanisms for Ti4, Al3 and Fe3 in biotite 26 TABLE 2.1 List of abbreviations used in figures and tables 45 TABLE 2.2 Summary of Southwest Zone coherent rocks 53 TABLE 2.3 Summary of Southwest Zone clastic rocks 61 TABLE 2.4 Paragenetic stages of coherent and clastic rocks in the Southwest Zone 67 TABLE 2.5 Stable isotope results for Stage 2 infill phlogopite and phyllic stage sericite 86 TABLE 3.1 Hydrothermal apatite compositions from vein samples in the Southwest Zone 137 TABLE 3.2 Southwest Zone biotite data distribution 138 , Al3 and Fe3 in biotite 140 TABLE 3.3 Substitution mechanisms for Ti4 TABLE 3.4 Biotite Thomson-space components 141 TABLE 3.5 Representative biotite compositions from the Southwest Zone by textural type 143 3/ Fe2 values for infill biotite TABLE 3.6 Titanium, Fe3 and Fe 146 vi LIST OF FIGURES FIG. 1.1 Map of British Columbia showing the location of the accreted Quesnellia and Stikinia ocean arc terranes, major alkalic Cu-Au porphyry deposits and alkalic intrusive centers, morphogeological belts and Galore Creek 4 FIG. 1.2 A. Major tectono-stratigraphic elements and the location of the Galore Creek district, Eskay Creek, Red Chris, Schaft Creek and Copper Canyon in the Stikinia terrane 6 FIG. 1.3 Simplified geological and alteration-mineralisation map of the Galore Creek district 14 FIG. 1.4 Ferromagnesian biotite with labeled structural sites 23 FIG. 1.5 Biotite composition trends in an idealized porphyry alteration model 29 FIG. 2.1 Map of British Columbia showing the location of the accreted Quesnellia and Stikinia ocean arc terranes, major alkalic Cu-Au porphyry deposits and alkalic intrusive centers, morphogeological belts and Galore Creek 44 FIG. 2.2 A. Major tectono-stratigraphic elements and the location of the Galore Creek district, Eskay Creek, Red Chris, Schaft Creek and Copper Canyon in the Stikinia terrane 47 FIG. 2.3 Simplified geological, and alteration and mineralisation map of the Galore Creek district illustrating the location of mineralized centers and major structural features 49 FIG. 2.4 Photographs of the Galore Creek valley, looking A south, and B north with labeled mineralized centers 50 FIG. 2.5 Simplified bedrock geology plan map and Cu-grade distribution in the Southwest Zone.
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