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Evolution of the Late Cretaceous Whistler Au-(Cu) porphyry corridor and magmatic-hydrothermal system,… Hames, Benjamin P. 2014

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 Evolution of the Late Cretaceous Whistler Au-(Cu) Porphyry Corridor and Magmatic-Hydrothermal System, Kahiltna Terrane, Southwestern Alaska, USA  by Benjamin P. Hames B.Sc (Hons.), The University of Western Australia, 2009  A THESIS SUBMITTED IN PARTIAL FULFILMENT OF  THE REQUIREMENTS FOR THE DEGREE OF  MASTER OF SCIENCE in The Faculty of Graduate and Postdoctoral Studies (Geological Sciences)  THE UNIVERSITY OF BRITISH COLUMBIA (Vancouver)  August 2014   © Benjamin P. Hames, 2014 ii  Abstract The Whistler Corridor is located in the Alaskan Range 150 km northwest of Anchorage. Hosted by the regionally extensive Kahiltna flysch terrane, the Whistler Igneous Suite (WIS) volcano-magmatic sequence is calc-alkalic, metaluminous, and exhibits an arc related trace element signature. Extrusive rocks comprise andesite flows, volcaniclastic rocks, and hypabyssal dykes and sills. Intrusive rocks are dioritic with two major phases. An initial phase associated with porphyry mineralisation was dated by zircon U-Pb (CA-TIMS) at 76.4 ± 0.3 Ma. A later unmineralised phase had previously been determined by hornblende Ar-Ar at 75.5 ± 0.3 Ma. Mineralised diorite exhibits Nb/Y ratios >1.1 distinct from unmineralised diorite (Nb/Y<1.1). Of several porphyry occurrences the largest is the Whistler deposit hosting an indicated and inferred resource of 3.13 Moz Au and 769 Mlbs Cu. The main Au-Cu zone is characterised by feldspar-stable albite-magnetite (sodic-ferric) and K-feldspar-magnetite (potassic) alteration associated with magnetite (M-) and quartz (A-, B-) veins. High-temperature albitic alteration was characterised using energy dispersive spectroscopy (EDS) analyses of previously unidentified alteration. A peripheral zone of quartz-sericite-pyrite (phyllic) alteration is associated with quartz (D1-3) and pyrite (D4-5) veins. Sphalerite and galena in D3-veins define an overprinting Zn-Pb zone. An intermineral intrusive phase in the core of the deposit is associated with a magmatic-hydrothermal breccia hosting the highest-grade Cu-Au zone. Locally, shallow-level equivalent of D3-veins comprise colloform and crustiform textured intermediate-sulphidation Pb-Zn-Ag-Au veins.  Sulphide δ34S isotopes range from 0.4-7.7‰ (xˉ=3.8‰; σ=1.3‰). δ34S in M/A-veins is 1.7‰; B-veins 3.4‰; D1-3 veins 3.7‰; D4-5 veins 4.9‰; and E-veins 6.5‰. δ34S values increase temporally due to the preferential fractionation of 34S into increasingly acidic, reduced fluids.   iii  Chlorite and sericite overprint feldspar-stable alteration. Short-wave infrared spectroscopy and X-Ray diffraction demonstrate higher temperature, more crystalline sericite in phyllic than chlorite-sericite alteration. A lack of a negative Nb-Ta anomaly, consistently positive sulphide δ34S isotopes, and oxidised magnetite-series igneous rocks suggest a lack of crustal contamination. Thus, at ca. 76 Ma Whistler represents the earliest, least crustally contaminated, porphyry occurrences of the Late Cretaceous magmatic epoch in SW Alaska.     iv  Preface  This thesis is the original, unpublished, independent work of the author, B. P. Hames. Project progression was overseen by C. J. R. Hart and M. D. Roberts. All unreferenced analytical data, figures, photographs, discussion and interpretations are the original work of the author. Regional geologic history, figures and maps in Chapter 2 include significant contributions from the literature especially Nokleberg at al. (1994); Ridgway et al. (2002); Trop and Ridgway (2007); and Kalbas et al. (2007). Camp-scale maps and some geologic observations in Chapter 3 include contributions from Young (2005) and Roberts (2011); referenced as appropriate. Where copyrighted images are reproduced, explicit permission has been granted from the copyright owner.    Benjamin P Hames August 2014    v  Table of Contents  Abstract ............................................................................................................................................ ii Preface ............................................................................................................................................. iv Table of Contents ............................................................................................................................. v List of Tables.................................................................................................................................... x List of Figures ................................................................................................................................. xi Acknowledgments ......................................................................................................................... xiii 1 Introduction ................................................................................................................................. 1 1.1 Rationale for study ...................................................................................................... 2 1.2 Objectives and methods .............................................................................................. 2 1.3  Location of study ........................................................................................................ 4 1.4  Deposit discovery and subsequent exploration ........................................................... 4 1.5  Nomenclature .............................................................................................................. 6 1.5.1  Geologic features nomenclature ............................................................................ 6 1.5.2  Sample naming nomenclature ................................................................................ 7 1.6  Supplemental data ....................................................................................................... 7 1.7  Thesis structure ........................................................................................................... 8 2 Regional Geology ..................................................................................................................... 10 2.1  Introduction .............................................................................................................. 10 2.2  Neoproterozoic to Triassic summary of the North American Cordillera ................. 12 2.2.1  Neoproterozoic to Cambrian formation of the continental margin ...................... 12 2.2.2  Cambrian to Devonian passive margin evolution ................................................ 12 2.2.3  Devonian and Carboniferous arc magmatism ...................................................... 12 2.2.4  Permian to Jurassic subduction and arc accretion................................................ 13 2.3  Jurassic and Cretaceous accretion of the Wrangellia Composite Terrane ................ 13 2.3.1  The Yukon Tanana Terrane (YTT) ...................................................................... 14 2.3.2  The Wrangellia Composite Terrane (WCT) ........................................................ 14 2.3.3  The Alaska Range Suture Zone (ARSZ) ............................................................. 15 2.3.4  The Denali-Farewell fault system ........................................................................ 16 2.4  Stratigraphic and structural synthesis of ARSZ basinal terranes .............................. 16 2.4.1  Cantwell basin: structurally deformed autochthonous terrane ............................. 17 2.4.2  Macleren and Aurora Peak: metamorphic terranes .............................................. 18 2.4.3  The Windy and Pingston terranes: victims of Denali fault translation ................ 19 2.4.4  Nutzotin terrane: stratigraphic analysis ............................................................... 19 2.4.5  Kahiltna terrane: stratigraphy and provenance analysis ...................................... 22 2.5  Southwestern Alaska regional Cretaceous magmatism ............................................ 26 2.5.1  Mid-Cretaceous magmatism ................................................................................ 26 2.5.1.1  Nyac magmatism .................................................................................... 26 2.5.1.2  Kaskanak Batholith ................................................................................ 26 2.5.2  Late Cretaceous and Paleocene magmatism ........................................................ 27 2.5.2.1  Whistler Igneous Suite ........................................................................... 27 2.5.2.2  Composite plutons and Mt Estelle .......................................................... 28 2.5.2.3  Summit Lake/Kichatna plutons .............................................................. 28 2.5.2.4  McKinley Series Plutons ........................................................................ 29 2.5.2.4  Crystal Creek Sequence .......................................................................... 29 2.6  Summary of WCT collision and terrane accretion ................................................... 29 3 Whistler Property Geology ....................................................................................................... 35  vi  3.1  The Whistler Corridor............................................................................................... 35 3.2  Lithology .................................................................................................................. 38 3.2.1  Sedimentary rocks................................................................................................ 39 3.2.1.1  Lower, middle and upper greywacke units ............................................. 39 3.2.1.2  Lithic sandstone ...................................................................................... 40 3.2.2  Intermediate volcanic rocks of the WIS .............................................................. 41 3.2.2.1  Andesite .................................................................................................. 43 3.2.2.2  Pyroxene-phyric andesite ....................................................................... 43 3.2.2.3  Undivided intermediate volcanic rocks .................................................. 43 3.2.2.4  Intermediate volcanic breccia ................................................................. 44 3.2.2.5  Volcaniclastic tuff/sandstone/conglomerates ......................................... 45 3.2.3  Intrusive rocks of the WIS ................................................................................... 47 3.2.3.1  Unmineralised diorite ............................................................................. 48 3.2.3.2  Mineralised diorite ................................................................................. 49 3.2.3.3  Mineralised diorite: main-stage porphyry (MSP) ................................... 50 3.2.3.4  Mineralised diorite: inter-mineral porphyry (IMP) ................................ 51 3.2.3.5  Mineralised diorite: late-stage porphyry (LSP) ...................................... 51 3.2.3.6  Basaltic andesite dykes ........................................................................... 51 3.3  Alteration .................................................................................................................. 53 3.3.1  Potassic (magnetite-potassium feldspar±biotite) alteration ................................. 53 3.3.2  Sodic-ferric (albite-magnetite) alteration ............................................................. 54 3.3.3  Phyllic (sericite-pyrite±quartz) alteration ............................................................ 54 3.3.4  Chlorite-sericite alteration ................................................................................... 55 3.3.5  Propyllitic (chlorite-epidote-carbonate) alteration ............................................... 56 3.3.6  Iron carbonate (ankerite/siderite) alteration ......................................................... 56 3.4  Veins ......................................................................................................................... 57 3.4.1  Magnetite-dominant veins (M1, M2) ................................................................... 57 3.4.2  Quartz-dominant veins (A1, A2, A3, B1, B2, B3, D1, D2, D3) .......................... 58 3.4.3  Quartz-dominant A-veins (A1, A2, A3) .............................................................. 58 3.4.4  Quartz-dominant B-veins (B1, B2, B3) ............................................................... 59 3.4.5  Quartz-dominant D-veins (D1, D2, D3) .............................................................. 60 3.4.6  Pyrite-dominant D-veins (D4, D5) ...................................................................... 61 3.4.7  Sulphide-dominant epithermal-style E-veins (E) ................................................ 62 3.4.8  Chlorite-muscovite veinlets (SC) ......................................................................... 63 3.4.9  Iron carbonate-dominant veins (FeCarb) ............................................................. 64 3.4.10 Gypsum veins (G) ............................................................................................... 64 3.4.11 Calcite veins (C) ................................................................................................. 64 3.5  Hydrothermal breccias .............................................................................................. 64 3.5.1  Magnetite-chlorite-chalcopyrite intermineral hydrothermal breccia ................... 65 3.5.2  Quartz-sericite-pyrite intermineral magmatic-hydrothermal breccia .................. 65 3.5.3  Quartz-carbonate-pyrite-sphalerite-galena hydrothermal breccia ....................... 66 3.5.4  Tourmaline-pyrite breccia .................................................................................... 67 3.6  Structurally deformed rocks and tectonic breccia..................................................... 67 3.6.1  Fault gouge .......................................................................................................... 68 3.6.1  Sheared rocks ....................................................................................................... 68 3.6.2  Rock-flour breccia ............................................................................................... 68 3.7  Mineralisation ........................................................................................................... 86 3.7.1  Whistler deposit ................................................................................................... 86 3.7.1.1  Main-stage porphyry (MSP): geometry, alteration, mineralisation ........ 87  vii  3.7.1.2  Inter-mineral porphyry (IMP): geometry, alteration, mineralisation ..... 89 3.7.1.3  Late-stage porphyry (LSP): geometry, alteration, mineralisation .......... 89 3.7.2  Raintree North...................................................................................................... 90 3.7.3  Raintree West ....................................................................................................... 91 3.7.4  Other deposits ...................................................................................................... 92 3.7.5 Metal zonation ..................................................................................................... 93 3.7.6  Epithermal-style mineralisation and Au deportment ........................................... 93 3.7.7  Gold deportment at Whistler ................................................................................ 94 4 Whole-Rock Geochemistry ..................................................................................................... 103 4.1  Introduction ............................................................................................................ 103 4.2  Methods .................................................................................................................. 104 4.2.1  Sample collection and processing ...................................................................... 104 4.2.2  Analytical methods ............................................................................................ 105 4.3  Observations: overview .......................................................................................... 106 4.4 Major element primary igneous geochemistry ....................................................... 107 4.4.1 Observations ...................................................................................................... 107 4.4.1 Discussion .......................................................................................................... 116 4.5  Major element secondary metasomatic geochemistry ............................................ 118 4.5.1  Observations ...................................................................................................... 118 4.3.3.1  Silica (SiO2) .......................................................................................... 119 4.3.3.2  Alumina (Al2O3) ................................................................................... 119 4.3.3.3  Iron (total Fe2O3) .................................................................................. 119 4.3.3.4  Calcium (CaO) ..................................................................................... 120 4.3.3.5  Magnesium (MgO) ............................................................................... 120 4.3.3.6  Sodium (Na2O) ..................................................................................... 120 4.3.3.7  Potassium (K2O) ................................................................................... 120 4.3.3.8  Titanium (TiO2) .................................................................................... 121 4.3.3.9  Loss-on-ignition (LOI) ......................................................................... 121 4.3.3.10   Carbon (C) ............................................................................................ 121 4.3.3.11   Sulphur (S) ........................................................................................... 122 4.5.2  Discussion .......................................................................................................... 122 4.6 Trace element geochemistry ................................................................................... 127 4.6.1 Observations ....................................................................................................... 127 4.6.1.1 Multi-element trace and rare earth element diagrams .............................. 127 4.6.1.2 Trace element variation diagrams ......................................................... 132 4.6.2 Discussion .......................................................................................................... 136 4.7  Conclusion .............................................................................................................. 140 5 Feldspar-Stable Alteration Mineral Chemistry ....................................................................... 147 5.1  Introduction ............................................................................................................ 147 5.2  Methodology ........................................................................................................... 147 5.2.1  Sample selection and preparation ...................................................................... 147 5.2.1  Analytical methods ............................................................................................ 148 5.3  Results .................................................................................................................... 148 5.4  Interpretation .......................................................................................................... 154 5.5  Discussion ............................................................................................................... 156 5.6  Conclusion .............................................................................................................. 159 6 Sericite Crystallinity: XRD and SWIR Characteristics........................................................... 160 6.1  Introduction ............................................................................................................ 160 6.2  Methodology ........................................................................................................... 160  viii  6.2.1  Sample selection and preparation ...................................................................... 160 6.2.1  Analytical methods ............................................................................................ 161 6.3  Results .................................................................................................................... 161 6.4  Discussion and conclusion ...................................................................................... 167 7 Sulphur Isotopic Characterisation ........................................................................................... 170 7.1  Introduction ............................................................................................................ 170 7.2  Methodology ........................................................................................................... 171 7.2.1  Sample preparation ............................................................................................ 171 7.2.2  Analytical methods ............................................................................................ 172 7.2.3  Analytical methods: geothermometry ................................................................ 174 7.3  Results .................................................................................................................... 178 7.3.1  Statistical correlation between intrusive phases ................................................ 178 7.3.2  Statistical analyses by mineral species .............................................................. 179 7.3.3  Correlation of δ34S values with vein paragenesis .............................................. 182 7.3.4  Geothermometry ................................................................................................ 182 7.4  Discussion ............................................................................................................... 183 7.4.1  Effects of fluid-rock interaction ......................................................................... 183 7.4.2  Validity and significance of temperature results ............................................... 185 7.4.3  Global comparisons of sulphur isotopic characterisation and analogues .......... 187 7.5  Conclusion and recommendations .......................................................................... 189 7.5.1  Summary of results ............................................................................................ 189 7.5.2  Exploration implications .................................................................................... 189 7.5.3  Recommendations for future work .................................................................... 190 8 Radiogenic Isotopic Geochronology ....................................................................................... 192 8.1  Introduction ............................................................................................................ 192 8.2  Methodology ........................................................................................................... 192 8.2.1  Sample preparation ............................................................................................ 192 8.2.1.1  WH11-33-692m .................................................................................... 193 8.2.1.2  WH10-21-576m, WH11-33-573m, WH11-34-221m, and 204 ............ 193 8.2.2  Analytical methods ............................................................................................ 195 8.2.2.1  U-Pb: LA-ICP-MS ............................................................................... 195 8.2.2.2  U-Pb: CA-TIMS ................................................................................... 196 8.2.2.3  Re-Os: ID-NTIMS ................................................................................ 196 8.3  Results .................................................................................................................... 197 8.3.1  Whistler deposit ................................................................................................. 197 8.3.2  Raintree West ..................................................................................................... 198 8.3.3  Raintree North.................................................................................................... 198 8.4  Interpretation and discussion .................................................................................. 207 8.5  Regional comparison .............................................................................................. 209 8.6  Conclusion .............................................................................................................. 211 9 Summary and Conclusions ...................................................................................................... 213 9.1  Syntheses of significant discoveries ....................................................................... 213 9.1.1  Igneous geochemistry ........................................................................................ 214 9.1.2  Whole-rock metasomatic geochemistry ............................................................. 214 9.1.3  Identification of two types of feldspar-stable alteration .................................... 215 9.1.4  Sericite crystallinity: multiphase feldspar-destructive alteration ....................... 216 9.1.5  Summary of sulphur isotopes and geothermometry .......................................... 217 9.1.6 Molybdenum in metal zonation ......................................................................... 218 9.1.7  Geochronology................................................................................................... 219  ix  9.2  Geologic history of the Whistler Corridor .............................................................. 220 9.2.1 Tectonic history ................................................................................................. 220 9.2.2  Paragenesis of magmatic-hydrothermal systems ............................................... 221 9.3  Discussion of objectives ......................................................................................... 227 9.4  Exploration implications ......................................................................................... 229 9.5  Recommendations for further work ........................................................................ 232 9.5.1 Mapping and drill-core logging ......................................................................... 232 9.5.2  Whole-rock geochemistry .................................................................................. 233 9.5.2  Mineral chemistry, spectroscopy, and crystallinity ........................................... 234 9.5.3 Stable isotope analyses ...................................................................................... 234 9.5.4 Geochronology................................................................................................... 235 9.6 Concluding statements ............................................................................................ 236 References .................................................................................................................................... 238 Appendix A: Summary of Samples .............................................................................................. 258 Appendix B: Petrography Study of Select Samples ..................................................................... 261 Appendix C: Raw Whole-Rock Geochemistry and data quality (QAQC) ................................... 370 Appendix D: MicroProbe Data .................................................................................................... 379 Appendix E: Summary of XRD Samples ..................................................................................... 385         x  List of Tables Table 4.1  Whole-rock geochemical data for all samples. .......................................................... 110 Table 5.1  Statistical summary of the three populations based on sodium content .................... 150 Table 5.2  Summary of individual microprobe rim-core analyses .............................................. 155 Table 6.1  Summary of mineralogy determined by XRD from 30 samples ............................... 163 Table 7.1  Results of δ34S analyses ............................................................................................. 173 Table 7.2  Coefficients for sulphur isotope fractionation ........................................................... 175 Table 7.3  Sulphur isotopic thermometers .................................................................................. 175 Table 7.4  Calculated formation temperatures from sulphur-bearing mineral pairs ................... 175 Table 8.1  Results of LA-ICP-MS analyses of zircons from sample 204 ................................... 199 Table 8.2  Results of CA-TIMS analyses on zircons. ................................................................. 200 Table 8.3  Results of Re-Os analysis of molybdenite from sample 1133602 ............................. 201 Table 8.4  Summary of age dates calculated by CA-TIMS ........................................................ 201 Table 8.5  Southern Alaskan metallogeneic epochs. .................................................................. 202 Table 9.1  Summary of the mineralogy and geometry of alteration and veins ........................... 222    xi  List of Figures  Figure 1.1  Whistler property location. ........................................................................................... 4 Figure 2.1 Regional geology maps. .............................................................................................. 11 Figure 2.2  Nutzotin basin stratigraphic and structural development. .......................................... 21 Figure 2.3  Alaska Range and Talkeetna Mountains provenance study. ...................................... 23 Figure 2.4  Kahiltna basin evolution and accretion. ..................................................................... 25 Figure 2.5  Temporal evolution of the ARSZ. .............................................................................. 31 Figure 3.1  Geology map of Whistler and surrounding areas. ...................................................... 36 Figure 3.2  Geology map of the Whistler Corridor. ..................................................................... 37 Figure 3.3  Sedimentary rocks of the Whistler Corridor. ............................................................. 42 Figure 3.4  Volcanic rocks of the WIS. ........................................................................................ 47 Figure 3.5  Unmineralised diorite of the WIS. ............................................................................. 49 Figure 3.6  Mineralised diorite phases of the WIS. ...................................................................... 52 Figure 3.7  Potassic and sodic-ferric alteration. ........................................................................... 70 Figure 3.8  Phyllic and chlorite-sericite alteration........................................................................ 72 Figure 3.9  Iron carbonate and propyllitic alteration. ................................................................... 73 Figure 3.10  M-veins. ................................................................................................................... 74 Figure 3.11  A-veins. .................................................................................................................... 75 Figure 3.12  B-veins. .................................................................................................................... 76 Figure 3.13  D-veins: Quartz dominant. ....................................................................................... 77 Figure 3.14  D-veins: Pyrite dominant. ........................................................................................ 78 Figure 3.15  E-veins...................................................................................................................... 79 Figure 3.16  Late veins. ................................................................................................................ 80 Figure 3.17  Magmatic-hydrothermal breccia. ............................................................................. 81 Figure 3.18  Magnetite-chlorite-chalcopyrite hydrothermal breccia. ........................................... 82 Figure 3.19  Quartz-carbonate-pyrite-base metal hydrothermal breccia. ..................................... 83 Figure 3.20  Tourmaline-pyrite hydrothermal breccia. ................................................................ 84 Figure 3.21  Faults and structurally disrupted rocks. ................................................................... 85 Figure 3.22  Aeromagnetic 3-D inversion model of the Whistler Corridor. ................................ 87 Figure 3.23  Lithologic map of the Whistler deposit at 1:8000. ................................................... 95 Figure 3.24  Alteration map of the Whistler deposit at 1:8000. ................................................... 96 Figure 3.25  Lithologic cross-section A-B of the Whistler deposit.. ............................................ 97 Figure 3.26  Alteration cross-section A-B of the Whistler deposit. ............................................. 98 Figure 3.27  Metal zonation cross-section A-B of the Whistler deposit. ..................................... 99 Figure 3.28  Lithologic cross-section of the Raintree North deposit. ......................................... 100 Figure 3.29  Alteration cross-section of the Raintree North deposit. ......................................... 101 Figure 3.30  Gold deportment in porphyry-style mineralisation of the Whistler deposit. .......... 102 Figure 4.1  Tukey diagram displaying major element compositional for all samples . .............. 107 Figure 4.2  Harker (1965) diagrams for all samples. .................................................................. 114 Figure 4.3  Total alkalis and silica diagram. ............................................................................... 114 Figure 4.4  AFM diagram ........................................................................................................... 115 Figure 4.5  Petrographic images of selected geochemistry samples. ......................................... 117 Figure 4.6  Molar Na/Al versus K/Al alteration discrimination plot .......................................... 123 Figure 4.7  Tukey diagram of diorite samples grouped by alteraiton. ........................................ 124 Figure 4.8  Petrographic images of altered samples analysed for whole-rock geochemistry. .... 125 Figure 4.9  Trace element multielement diagrams of WIS rocks. .............................................. 131 Figure 4.10  REE multielement diagram. ................................................................................... 131  xii  Figure 4.11  TiO2-Zr and Nb-Zr variance diagrams. ................................................................. 134 Figure 4.12  Y-Nb, Lu-Nb, Y-La, Lu-La variance diagrams. .................................................... 135 Figure 4.13  Comparison of Yttrium and the HREEs. ................................................................ 141 Figure 4.14  La/Y-La/Lu and Nb/Y-Nb/Lu discrimination diagrams. ....................................... 142 Figure 5.1  Ternary diagram demonstrating relative abundance of Na2O, K2O and CaO. ....... 149 Figure 5.2  Comparison of phenocryst and groundmass Na2O, CaO and K2O values. ............. 151 Figure 5.3  Comparison of feldspar compositions. ..................................................................... 153 Figure 5.4  Feldspar/sericite phase diagram. .............................................................................. 158 Figure 6.1  Select samples demonstrating position of AlOH 2200 nm feature .......................... 164 Figure 6.2  Down-hole plot for drill-hole WH11-34 at Raintree North. .................................... 165 Figure 6.3  Down-hole plot for drill-hole WH10-21 at Whistler. .............................................. 166 Figure 6.4  Sericite crystallinity diagram. .................................................................................. 168 Figure 7.1  A selection of samples taken for sulphur isotopes. .................................................. 176 Figure 7.2  Samples of sulphur isotope pairs for geothermometry. ............................................ 177 Figure 7.3  Graphical representation of δ34S analyses as histograms. ........................................ 180 Figure 7.4  Spatial distribution of δ34S values ............................................................................ 181 Figure 7.5  Fractionation potential of sulphide and sulphates relative to H2S. .......................... 186 Figure 7.6  Comparison of δ34S values globally. ...................................................................... 188 Figure 8.1  Images of geochronology samples. .......................................................................... 203 Figure 8.2  Results of LA-ICP-MS analyses on zircons from Whistler discovery outcrop ....... 204 Figure 8.3  Concordia diagram of all included point CA-TIMS analyses. ................................. 205 Figure 8.4  Comparative weighted mean average (WMA) ages from Whistler ......................... 206 Figure 8.5  Summary of intrusive duration for select porphyry systems .................................... 208 Figure 8.6  Paleo positions of major intrusive bodies and metallogenic .................................... 210 Figure 9.1  A model for the formation of the Whistler Corridor. ............................................... 223 Figure 9.2  The paragenesis of the Whistler magmatic-hydrothermal system ........................... 224       xiii  Acknowledgments  I would like to firstly thank both my academic supervisor Dr. Craig J. R. Hart and corporate supervisor Dr. Michael D. Roberts. Craig has provided me with this fantastic opportunity and years of guidance. Mike has been an invaluable provider of advice, support, and patience. I would also like to thank Kiska Metals Corporation for supporting this project financially as well as facilitating the necessary logistics in accessing field areas and old drill-core around southwest Alaska. The following acknowledgments are in no particular order.  I would like to thank Professor Mati Raudsepp, Edith Czech and Jenny Lai at at the UBC-EOS Electron Microbeam/X-ray Diffraction Facility. Mati helped with all stages of microprobe and XRD analysis. Edith provided invaluable assistance with microprobe operation and Jenny help with carbon coating and XRD sample preparation Thanks to Dr Richard Friedman and Hai Lin at the PCIGR for help with geochronology. Hai Lin instructed me in the art of zircon sample processing and Rich conducted U/Pb analyses. I would like to thank Dr Rob Creaser at the University of Alberta for Re/Os age determinations, Kristen Feige at Queen’s University for sulphur isotope analyses, and Peter LeCouteur for help with some early petrography. AT UBC I would like to thank Dr. Farhad Bouzari at the MDRU for help with SWIR analyses. I would also like to thank Arne Toma at MDRU for providing excellent logistical and IT support. Discussion on SW Alaskan geology and metallogeny with Melissa Gregory and Witold Ciolkiewicz also deserve mention. At Kiska Metals I would like to thank, Mark Baknes, John Lamborn, Jake Wozow, Dan Lui, Tracy Roach, David Caulfield, Brian Miller, Ron Prasad, Matt Carter, Curtis Wilkey, Emma Owen, Brett Marsh, Chris Kerr and Candice Ridyard.  At the USGS I would like to thank Garth Graham, his ongoing research into regional magmatism and metallogeny of SW Alaska provided me with a lot of background information. A special mention goes to Lorne Young for providing informative and entertaining stories in the field about the original discovery of Whistler. In the course of the past few years, I have had countless conversations with some fellow students that provided me with ideas and insights. I would like to thank Leif Bailey, Brendan Scorrar, Greg Mckenzie, Lindsay McClenaghan, Alfonso Rodriguez, Irene Del Real, Abdul Razique, Santiago Vaca, Esther Bordet, Jess Norris, Mike Tucker, Tim Wrighton, Brian McNulty, Dave Cox and Peter MacDonald. To those I have not mentioned, it is an oversight and I thank you too! In my personal life I would like to thank some of my Vancouver friends, Tobias Ryan, Dalyce Amelia, David Tull, Jarrad Hill, Jeff Meyler, Jenn Morris, and Carla Poggioli.  My parents and family, thank you for your support from distant Australia. An extra special thanks to Emily Carlaw for everything.    1  1 Introduction The search for base and precious metals in Alaska is one that reflects the changing economic and technological status of the United States’ “final frontier”. The modern history of the State of Alaska parallels its history of mining and exploration. It begins prior to US acquisition of Alaska, when Russian explorers found the first mineral occurrence, a cinnabar-stibnite deposit in the Aniak district in 1838 (Bundtzen and Miller, 1997). Significant placer gold was discovered in the Kenai Peninsula by Russians in 1848 (Koschmann and Bergendahl, 1968). After US acquisition in 1867 significant placer and lode gold mining near Juneau led to it becoming the State capital in 1900 (Miller, 1997). By this time the Klondike gold rush brought significant numbers of prospectors to all parts of Alaska and during the 1900’s prospectors found gold near Fairbanks, the Talkeetna Mountains, Brooks Range, Yukon River, Kuskokwim River, Tanana River and the beaches of Nome (Menzi, 2014). Throughout the 1910’s and 1920’s major mining operators modernised the mining of placer and lode gold deposits. Diversification of metal extraction included the opening of the giant Kennett copper mine in 1911.  During these early days, exploration was conducted primarily by boots-on-the-ground prospectors. Discoveries were made by gold panning and outcropping supergene mineralisation. Mined deposits, particularly for gold, were dominantly placer deposits. Today placer mining is still dominant and nearly all the large placer gold mines in the US are in Alaska (George, 2014). However, lode-gold deposits have become attractive targets due to their large footprint and significant quantity of contained metal. Exploration methods have diversified to reflect this changing target model. In addition to the traditional methods employed by prospectors, exploration now employs; geophysical surveys; geochemical surveys; and geologic mapping. In order to predict the location of an ore deposit, modern explorers should have a good technical understanding of ore deposit genesis.  2  1.1 Rationale for study Porphyry deposits currently supply the global market approximately three quarters of our Cu; half our Mo; most of our Re; and one fifth of our Au (Sillitoe, 2010). Furthermore, the largest minable reserves of Cu (Los Broncos-Río Blanco); Mo (El Teniente); and second largest Au (Grasburg) reserves are contained in porphyry deposits. Accordingly, porphyry deposits have been studied in great detail and summarised succinctly by Seedorff et al. (2005) Sillitoe (2010) and Hedenquist et al. (2012). However, the subset of porphyry deposits that are gold-rich and relatively copper-poor have distinct characteristics that are not comprehensively covered in these major contributions. Thus, the goal of this thesis is to evaluate what features control or contribute to gold enrichment in porphyry systems.  In this thesis specific objectives are employed in order to characterise a gold-rich porphyry case-study. The Whistler deposit is a gold-copper rich porphyry-style magmatic-hydrothermal system in the Alaskan Range of SW Alaska. Characteristics will be evaluated in the context of understanding the controls on gold enrichment. 1.2 Objectives and methods A number of specific objectives are prepared in order to establish what features control or contribute to gold enrichment at Whistler. These objectives include;  Summarising the regional geology and tectonic history;  Characterising the various lithologies, alteration, and mineralisation styles;  Evaluating the chemistry of causative intrusive rocks;  Evaluating the metasomatism of hydrothermal alteration associated with gold mineralisation;  Synthesising the temporal evolution of the magmatic and mineralising systems;  Examining the role of sulphur in the deposition and remobilisation of gold;  Comparing these features to other mineralised occurrences regionally and gold-rich porphyries globally; and  Applying new understanding of gold deposition to exploration and targeting.  3    It is important to understand the regional geologic setting and history when examining any particular mineral deposit. The summary provided in Chapter 2 is sourced primarily from over 75 scientific papers. A detailed summary of the Whistler deposit and associated magmatic-hydrothermal system is provided in Chapter 3. This includes detailed descriptions, with petrography, of the lithology, alteration, veins, breccias and other geologic features. The geometry of Whistler and nearby porphyry occurrences is described. This was accomplished by the author over two field seasons using; mapping; drill-core logging, rock descriptions and petrography. The chemical characteristics of magmatic rocks associated with porphyry mineralisation may be related to gold enrichment. Dioritic calc-alkalic rocks without significant potassium feldspar have been considered most prospective for gold-rich porphyries (Hollister, 1975; Kesler et al., 1977) although not crucial (Sillitoe, 1979). In Chapter 4 the whole-rock geochemistry of mineralised and unmineralised intrusive phases at Whistler are characterised to evaluate how this might contribute to gold enrichment. Metasomatism associated with hydrothermal alteration is also evaluated to determine what bulk chemical changes are associated with gold. The temporal evolution of the magmatic and mineralising system is synthesised in Chapter 9. Several methods were employed in this compilation. Early feldspar-stable alteration is characterised using microprobe mineral chemistry to determine whether there are alteration assemblages specific to this gold-rich porphyry. Feldspar-destructive sericitic alteration is characterised using a compilation of short-wave infrared spectroscopy and X-Ray diffraction crystallography. Sulphur-bearing minerals occur throughout the temporal evolution of the system. The sulphur isotopic composition of these minerals are analysed in Chapter 7. The role of sulphur in the deposition and remobilisation of gold is examined in Chapter 9.  In order to compare the features determined through these objectives and procedures with regional metallogeny, a regional temporal correlation must be established. This is done through radiometric geochronology, specifically evaluating the U-Pb systematics of igneous zircon and Re-Os systematics of hydrothermal molybdenite.   4  1.3  Location of study  The Whistler corridor and the project are located in the Alaskan Range, SW Alaska, USA. The property is approximately 150 km northwest of Anchorage. The centre of the property has the location 152.57° longitude west and 61.98° latitude north. The location of the property with proposed access routes is shown in Figure 1.1.   Figure 1.1  Whistler property location.  (© 2011 Kiska Metals Corp., by permission). Proposed ground access routes are included. Current access is by air only. Modified from Roberts (2011).    1.4  Deposit discovery and subsequent exploration  The earliest exploration in the region comprised single-pass reconnaissance surveys conducted by the U.S. Geological Survey in 1898 (Spurr and Hinckley, 1900), 1902 (Brooks and Prindle, 1911) and 1926 (Capps, 1929). Due to a lack of placer gold potential and logistical issues  5  these early naturalist surveys did not result in any mineral deposit discoveries in the Whistler region.  Early prospecting in the region was conducted in the 1960’s through 1980’s and  reconnaissance mapping and rock/stream sampling by Reed and Elliott (1970) demonstrated the “presence of base and precious metal anomalies over a very large area of the southern Alaska Range that overlapped the southern portion of the Whistler region” (Young, 2006).  The Whistler deposit was discovered by Cominco Alaska Inc. in 1984 (Roberts, 2011), coincidentally coinciding with the author of this thesis’ birth. Continued work by Teck Cominco through the mid to late 1980’s included mapping, sampling and drilling and facilitated the discovery of the Island Mountain deposit, and mineralisation at Mount Estelle, Mount Stoney, One-Thirty, Terra Cotta, Portage Pass, Distin, McDoel, Canyon, South Canyon Kohlsaat and others (Young, 2006). With copper as the primary commodity of interest, the Whistler prospect failed to meet corporate objectives and exploration claims were allowed to lapse by the 1990’s (Young, 2006; Roberts, 2011) and all drill cores were donated to the State of Alaska.  In 1999 Kent Turner, a prospector, staked 25 State of Alaska claims and these were optioned to Kennecott Exploration Company in the early 2000’s. Kennecott conducted an aeromagnetic survey in 2003 and conducted extensive drilling, mapping, soil, stream and rock sampling, and ran induced polarisation (IP) lines in 2004 and 2005 (Franklin et al., 2006). By 2006 Kennecott had drilled 35 holes (12,449 m) on the Whistler project before the property was acquired by Geoinformatics Exploration Inc. in June 2007 as part of a strategic alliance with Kennecott (Roberts, 2011).  Geoinformatics drilled 18 holes from 2007 to 2008 including 12 (5,784 m) on the Whistler deposit and 6 (1,841 m) on other targets within the Whistler area. Geoinformatics also conducted 8.8 line-km of 2D IP in six lines, leading to the discovery of the Raintree West deposit in the Whistler Corridor. In 2008, Geoinformatics commissioned SRK Consulting to conduct a National Instrument 43-101 resource estimation for the Whistler deposit (Wahl et al., 2008).  In 2009  6  Geoinformatics acquired Rimfire Minerals Corporation and changed its name to Kiska Metals Corporation (Kiska). In 2009 Kiska commissioned Aurora Geoscience to conduct a 224 line-km offset pole-dipole 3D IP survey. These data were used in the construction of a 3D inversion model. Kiska also conducted 40 diamond drill-holes (18,144 m) in 2009-2010 and 147 diamond drill-holes (30,304 m) in 2011 including a grid-based shallow drill-hole program of 56 holes (Roberts, 2011). In addition, Kiska conducted extensive surface mapping and sampling of targets in the Whistler area including Island Mountain. In 2010 Kennecott Exploration informed Kiska that it would not exercise its right to a pre-existing ‘back-in agreement’, retaining a 2% Net Smelter Royalty and giving Kiska 100% ownership of the property (Weber, 2010). In 2011 Kiska commissioned Moose Mountain Technical Services to prepare an updated National Instrument 43-101 resource estimation (Morris, 2011) for the Whistler deposit. At the time of print (2013) exploration was halted on the property. 1.5  Nomenclature  Several terms are used consistently throughout this research. In order to alleviate confusion, a definition of these terms is given here. 1.5.1  Geologic features nomenclature The Whistler Corridor is a structurally bounded geologic feature which incorporates all the intermediate volcanic and hypabyssal rocks, intermediate intrusive rocks, and the associated hydrothermal activity with alteration and mineralisation. A complete description of the Whistler Corridor is given in Chapter 3. The Whistler Igneous Suite (WIS) includes all the intrusive and coeval extrusive phases of igneous activity within the Whistler Corridor The Whistler magmatic-hydrothermal system refers to the rocks and implied processes of magmatism and hydrothermal activity which intruded the extrusive phases of the WIS and surrounding sandstone.   7  The Whistler deposit is a gold-copper rich porphyry deposit associated with a dioritic cupola of the WIS intruding sandstone on the western margin of the Whistler Corridor. It is the most significantly well-endowed mineralising occurrence of the Whistler magmatic-hydrothermal system yet found. The Raintree West (deep and shallow), Raintree North, Raintree South, Rainmaker, Dagwood, and Snow Ridge deposits/prospects are a series of other porphyry deposits or prospects exhibiting porphyry-style characteristics. All but Snow Ridge are associated with WIS intrusive activity within the WIS extrusive rocks. Snow Ridge is an undeveloped prospect but is hosted within sandstone just to the north of, and similar to, the Whistler deposit. Raintree West and Raintree North are amongst the most comprehensively explored porphyry deposits of the Whistler Corridor and are partially characterised in this project.  1.5.2  Sample naming nomenclature Samples included in this project are named according to one of two conventions. The first method of drill-hole sample naming begins with the first two letter of the project being drilled, eg. WH is Whistler. The next two numbers indicate the year of drilling, eg. 07 would be 2007. The following two numbers indicate the drill-hole number, eg. 02 would be the second hole. The final three numbers indicate the depth the sample was taken down the drill-hole described, eg. 150 would be 150 metres down-hole. Therefore, sample WH10-19-348 would have been taken 348 m down drill-hole 19 at the Whistler deposit in 2010. During the progression of drilling between 2007 and 2012, drill-hole naming procedures changed such that the prefix WH could be from anywhere in the Whistler Corridor. As a result, sample naming in this project has, in some cases, been simplified to exclude the initial letters and numbers. For example, WH07-03-215 may become 73215 or WH11-34-567 may become 1134567. 1.6  Supplemental data  Appendix A is a summary of all rock samples used in this thesis. These include those collected in the field and from drill-core. A sample description is accompanied by a tally of which analytical methods were applied to which samples.   8  Appendix B is a collection of petrographic reports written by the author about select samples. Many of these reports are referred to in the text. Many are not referred to in-text but are included as a reference and as related information that may be useful for future studies researching this deposit or looking for analogues for other deposits. Appendix C includes the raw whole-rock geochemistry data. Values in this table differ from the in-text presentation which have been recalculated as a % without loss-on-ignition, in order to preserve true whole-rock values. Appendix C also includes an outline on the quality control (QAQC). Appendix D is the raw electron-probe data of feldspar compositions and sample descriptions. Appendix E is the sample descriptions, XRD data, and SWIR spectra of all samples used to determine sericite crystallinity. 1.7  Thesis structure  This thesis is divided into nine chapters.  Chapter 1 summarises the location of the study area, history of exploration in the study area, describes some nomenclature and acronyms used throughout the thesis, outlines the methods used in the assembly of the thesis, describes supplemental data compiled as Appendices, and outlines the structure of the thesis. Chapter 2 describes the regional geology and geologic history relevant to the study area. This includes a Mesozoic history of the North American Cordillera with detail on basinal strata and magmatism associated with the accretion and collision of the Wrangellia Composite Terrane and the North American margin. It also includes a summary of major magmatic bodies and metallogeny in the region of the study area. Chapter 3 describes the geology of the Whistler corridor. This includes descriptions of all lithologies, alteration, veins, breccias, and the main mineralising bodies studied in this thesis. This chapter is heavy on rock descriptions.  9  Chapter 4 describes the whole-rock chemical characteristics of the major intrusive and extrusive phases of the Whistler corridor. It syntheses the nature of metasomatism associated with hydrothermal alteration as well as attempts to distinguish between different intrusive phases of the Whistler corridor. Chapter 5 characterises the mineral chemistry of feldspar-stable alteration in the Whistler corridor. This includes K+ and Na+ metasomatism. The presence of Na+ metasomatism was not established prior to this study. Chapter 6 relates feldspar-destructive sericitic crystallinity to alteration assemblages containing sericite. This provides some interpretations regarding paragenesis and fluid evolution. Chapter 7 characterises the sulphur isotopic signature of sulphides of the Whistler deposit. This is compared to other deposits and some interpretation about fluid evolution is provided. Chapter 8 provides isotopic ages for three mineralised intrusive bodies of the Whistler corridor, as well as for molybdenite associated with mineralisation. These data are compared to the ages of unmineralised intrusive rocks previously dated in the Whistler corridor, and regionally. Chapter 9 provides a synthesis of the major discoveries of this thesis. This includes a detailed paragenesis and interpretive model for the development of the Whistler corridor. This chapter also includes exploration implications and suggestions for further work.   10  2 Regional Geology 2.1  Introduction This chapter provides a synthesis of the regional geology and terranes of the North American Cordillera with a developing focus on the Mesozoic development of basinal strata and arc magmatism in southern Alaska. This provides the necessary background geological context for the deposit-scale study at Whistler.  The North American Cordillera comprises a semi-linear 7000 km by 800-1600 km accretionary orogen along the western Laurentian, now North American margin (NAM). Today, the North American Cordillera is expressed geographically as several mountain ranges including, but not limited to, the Sierra Nevada, Cascade Range, American and Canadian Rockies, Columbia Mountains, Coast Mountains, Yukon Ranges, Chugach Mountains, Talkeetna Mountains and the Alaska Range. These individual mountain ranges represent distinct orogenic processes, and are dispersed spatially and temporally across this great orogenic belt. The story of this continental margin begins with the mid-cratonic rifting of Rodinia through the Proterozoic and Cambrian, transitioning to a passive margin through the Cambrian to Devonian. Subduction and accretionary orogenesis of the Cordillera began in the Devonian and continues to the present. This summary begins with a brief overview of the Neoproterozoic to Triassic rifting, passive margin, and final convergent-margin orogenesis of the Intermontane belt. This provides the background information necessary to understand the nature of the NAM prior to the orogenesis associated with magmatism and metallogeny relevant to this project.  A descriptive summary of the major terranes associated with this Mesozoic and Cenozoic orogenesis is then provided. This includes stratigraphic, provenance, and structural descriptions of accreted basinal strata, and an overview of magmatism relevant to this project. This information is then presented in a temporal summary of Mesozoic and early Cenozoic tectonic history of southern Alaska.   11   Figure 2.1 Regional geology maps. (a) (© 2013 Society of Economic Geologists, adapted with permission). Southern Alaskan terrane map. Modified from Goldfarb et al. (2013); (b) (© 1994 Geological Society of America, adapted with permission). Outcrop map demonstrating major Mesozoic and early Cenozoic basins and intrusive bodies discussed in text. Modified from Nokleberg et al. (1994) with significant input from Trop and Ridgway (2007) Cole et al. (1999) and Young (2005).   12  2.2  Neoproterozoic to Triassic summary of the North American Cordillera 2.2.1  Neoproterozoic to Cambrian formation of the continental margin The story of the North American Cordillera begins with the formation of a continental margin during Neoproterozoic rifting of the supercontinent Rodinia. The breakup of Rodinia likely occurred in two stages. The first occurred in the northern Cordillera between ca. 755 Ma and ca. 700 Ma (Powell et al., 1993; Ross et al., 1995; Wingate and Giddings, 2000). The southern breakup event was ca. 570 Ma (Bond and Kominz, 1984; Colpron et al., 2002). The intermittent period was associated with passive margin sedimentation in the north, which extended southwards as rifting propagated. More detailed examination of the Proterozoic basins of Rodinia, as well as metallogeny associated with rift-related processes can be found in Nelson and Colpron (2007). 2.2.2  Cambrian to Devonian passive margin evolution By the earliest Cambrian the continental margin of western Laurentia was formed. This margin remained relatively passive through to the Devonian, comprising rift-controlled continental platform and shelf to basinal deposition. Sedimentation here was controlled by sea-level transgressive/regressive cyclicity and localised rift-related half and full graben tectonics. These early to mid Paleozoic continental margin successions are also host to sedimentary-rock hosted mineralisation including SEDEX, VMS, MVT, and other carbonate or sedimentary hosted deposits (Nelson and Colpron, 2007). 2.2.3  Devonian and Carboniferous arc magmatism  Subduction was initiated from the northernmost parts of the continental margin and propagated southwards throughout the Devonian. Subduction was associated with arc-related magmatism with radiometric U-Pb derived ages of magmatism and volcanism ranging from ca. 390 to ca. 320 Ma and peaking between 360 and 350 Ma (Nelson et al., 2006). This magmatism was compositionally diverse including arc tholeiites, calc-alkalic, MORB, E-MORB, OIB, boninitic, BABB, and continentally contaminated felsic magmas (Piercey et al., 2006). Rollback of the subducting plate led to increasing back-arc magmatism and eventual opening of the Slide Mountain Ocean by early Carboniferous time. This rifting separated the pericratonic Yukon-Tanana Terrane (YTT) from the Laurentian margin and migrated the eastwardly-dipping  13  subduction zone into the Panthalassa Ocean, with the Slide Mountain Ocean forming in the back-arc. Subduction-related arc magmatism now formed a continental-arc on the YTT and compositionally intermediate island-arc magmatism formed the arcs of Stikine, Quesnellia, East Klamath and North Sierra well outboard of the western Laurentian margin.  2.2.4  Permian to Jurassic subduction and arc accretion By the mid-Permian westwards-dipping subduction had been initiated under the eastern margin of the YTT. This is evident by the continentally-influenced felsic magmatism and a belt of high-pressure metamorphic rocks on the east side of the YTT (Nelson et al., 2006; Nelson and Colpron, 2007). As the Slide Mountain Ocean was subducted westward, the N. Sierra, E. Klamath, and Quesnellia arcs were accreted to the continental margin with the YTT accreted in the northernmost position. Initiation of eastwards-dipping subduction facilitated the obduction of the Cache Creek accretionary prism outboard of the Quesnellia terrane. This complex subduction arrangement with both east and west-dipping subduction migrated the Stikine arc southwards outboard of the Quesnellia and Cache Creek terranes where it collided with the continental margin and was accreted by the mid-Jurassic (Mihalynuk et al., 2004). This ‘sandwiched’ the Cache Creek terrane between the Stikine and Quesnellia terranes. The amalgamation of the accreted arcs, and the YTT, has been collectively referred to as the Intermontane Belt (Monger and Price, 2002). This complicated subduction environment has modern analogues in the Philippines. A detailed examination of this well-studied accretionary orogenesis is provided by Nelson and Colpron (2007). 2.3  Jurassic and Cretaceous accretion of the Wrangellia Composite Terrane By the mid-Jurassic the North American margin (NAM) was defined by a series of accreted arcs collectively referred to as the Intermontane Belt. In the north this was represented by the pericratonic YTT. Orogenesis continued through the Mesozoic and Cenozoic with the accretion and collision of the Wrangellia Composite Terrane (WCT) and the intervening basinal strata to the NAM. As a preface to this chapter a description of the YTT, the WCT and the basins that separate the two is provided here. This information is then summarised in a temporal geologic history of Mesozoic and Cenozoic collision and accretion of the WCT to the NAM.  14  2.3.1  The Yukon Tanana Terrane (YTT) As discussed, the YTT is a block of ancestral cratonic crust that was rifted from the NAM during the Devonian, hosted east- and west-facing arcs, before being accreted back to the NAM by the Triassic. The basement to the YTT has been historically enigmatic, with magnetotelluric interpretations suggesting underthrust Mesozoic flysch (Stanley et al., 1990). This interpretation was largely disproved by Pb, Nd, Sr and O isotopic studies of Cretaceous and Tertiary granites which suggest anatexis of continental crust (Aleinikoff et al., 2000). Furthermore, Piercey and Colpron (2009) determine a Paleoproterozoic provenance age by Nd-Hf and U-Pb systematics for the continental margin metasedimentary Snowcap assemblage as being representative of YTT basement.   Early-mid Paleozoic rocks of the YTT are dominated by metamorphosed passive continental margin sedimentary assemblages, with an early Proterozoic source (Mortensen, 1992). However, during the mid-Devonian, peraluminous magmatism and cogenetic submarine volcanism became widespread (Mortensen and Jilson, 1985) and have been interpreted as products of a continental magmatic arc that continued until the early Carboniferous (Mortensen, 1992; Colpron et al., 2005). This was followed by a temporary lull in magmatism until the mid-Permian. This cyclical passive margin-continental arc continued, with pulses of arc magmatism occurring during the mid-Permian and also Late Triassic to Early Jurassic (Mortensen, 1992). Mid-Late Mesozoic deformation and magmatism was dominated by accretion of the Wrangellia Composite Terrane and associated basins of the Farallon Ocean basin (Nokleberg and Richter, 2007). The current extent and orientation of the YTT was facilitated by Cenozoic dextral translation along the Tintina fault. 2.3.2  The Wrangellia Composite Terrane (WCT) The Wrangellia Composite Terrane comprises the amalgamated Wrangellia, Alexander and Peninsular Terranes. This amalgamation likely occurred during the late Paleozoic (Plafker and Berg, 1994). The Insular Belt of Nelson and Colpron (2007, and references therein) marks the most outboard belt of the North American Cordillera, and includes the amalgamated Wrangellia/Alexander/Peninsular terranes from Alaska to British Columbia, as well as those  15  accreted subsequently. In general, the WCT represents oceanic island-arc terranes allochthonous to North America. In slightly more detail, it contains late Precambrian to early Paleozoic volcanic arc assemblages with continental basement in southeast Alaska. In northern British Columbia and Yukon Territory early Paleozoic platform sequences are overlain by late Paleozoic arcs, and elsewhere in British Columbia Mesozoic continental flood basalts such as those of the Nikolai group were dominant (Jones et al., 1977). In south-central Alaska, the WCT comprises the Peninsula Terrane (Figure 2.1). In summary, the WCT is a long-lived, multi-episodic Paleozoic and younger arc terrane. In the Late Triassic, the WCT was located at low latitudes, and moved northward and westward to converge with the North American margin between the latest Triassic and earliest Cenozoic (Jones et al., 1977). For the purposes of this synthesis the Wrangellia, Alexander and Peninsular terranes are considered as one allochthonous body, the WCT. 2.3.3  The Alaska Range Suture Zone (ARSZ) By the mid-Jurassic, the NAM was defined by the YTT in southern Alaska. The Nutzotin and Kahiltna ocean basins separated the NAM from the WCT, and NE-dipping subduction under the NAM was associated with magmatism of the Coast Plutonic Complex. This subduction through the Late Jurassic led to complete ocean closure by the mid Cretaceous. Much of the Nutzotin and Kahiltna flysch sedimentary rocks were accreted to the NAM/YTT to form the Nutzotin and Kahiltna terranes respectively. The term Alaska Range Suture Zone (ARSZ) was coined by Ridgway et al. (2002) to refer to geologic units comprising the suture zone between the NAM/YTT and the WCT in Alaska. The ARSZ comprises accreted ophiolites (Patton et al., 1994; Amato et al., 2007), sedimentary basins (Jones et al., 1982; McClelland et al., 1992; Eastham and Ridgway, 2002; Kalbas et al., 2007; Manuszak et al., 2007; Nokleberg and Richter, 2007), and plutonic and volcanic assemblages with associated mineral deposits (Reed and Lanphere, 1973; Lanphere and Reed, 1985; Moll-Stalcup, 1994; Young et al., 1997). It ranges up to hundreds of kilometres in width and includes relatively un-metamorphosed sedimentary basins comprising over thousands of metres of thickness (Nokleberg et al., 1994; Kalbas et al., 2007; Manuszak et al., 2007). The term ARSZ is henceforth  16  used in this synthesis to represent all accreted sedimentary basins, subduction-related igneous rocks, and major structures located between the YTT and WCT in Alaska.  2.3.4  The Denali-Farewell fault system The Denali Fault is major fault system that extends over 2000 km along-strike distance from northern British Columbia to south-central Alaska (Lanphere, 1978; Csejtey et al., 1982). The fault system separates the Laurentian continental margin (eg. YTT) from the accreted terranes (e.g., WCT). Estimates of displacement along the Denali Fault and its splays vary significantly (Lanphere, 1978) from a few to several hundred kilometres (Eisbacher, 1976; Nokleberg et al., 1985). Initial right-lateral translation on the Denali fault probably began during the Late Cretaceous (Eisbacher, 1976; Nokleberg et al., 1985) and continues today (Eberhart-Phillips et al., 2003; Fisher et al., 2004) Evidently the Denali Fault is a major crustal-scale fault system. Seismic surveys such as the Trans-Alaska Crustal Transect (TACT) demonstrate a deep conductivity anomaly (Fuis and Clowes, 1993; Fisher et al., 2004; Hammer and Clowes, 2007). Brocher et al.  (2004) describe a near-vertical fault with a 5 km-wide zone of fault gouge extending to around 1 km-depth, a 40 km-wide damage zone extending to 5 km-depth, and a total depth of at least 30 km. Fisher et al. (2004) compare the Denali Fault to the Altyn Tagh Fault in Tibet because both may facilitate the tectonic escape of large crustal blocks, emphasising the regional importance of this structure. The Denali Fault can define the entire thickness of the ARSZ where the NAM and WCT are directly abutting, or may mark the NAM/ARSZ boundary where the ARSZ comprise sedimentary or igneous sequences. The maps in Figures 2.1 and 2.5 demonstrate the variation in lateral extent of the ARSZ. 2.4  Stratigraphic and structural synthesis of ARSZ basinal terranes Stratigraphic and structural analyses of ARSZ basins demonstrate Mesozoic-Cenozoic tectonic processes associated with accretionary and collisional orogenesis. Each basinal terrane examined here provides insights into the pre-, syn-, and post- WCT collisional tectonics depending on whether they are autochthonous or allochthonous to the NAM, changes in their provenance, or  17  the structural deformation and metamorphic history. Many basins of the ARSZ (eg. Wrangell Mountain, Dezadeash, Copper River terranes) are tectonically significant but excluded from this discussion as they are not integral to the story of WT accretion from the perspective of this project. The basins (Cantwell, Macleren, Aurora Peak, Windy, Pingston, Nutzotin and the laterally extensive Kahiltna terrane) described here were selected as they provide insights into the nature and timing of accretion and WCT collision with the NAM. The locations of these terranes are outlined in Figure 2.1. 2.4.1  Cantwell basin: structurally deformed autochthonous terrane  The following stratigraphic and structural synthesis of the Cantwell basin is summarised from Cole et al. (1999) Ridgway et al. (2002) and Trop and Ridgway (2007). The Cantwell basin is located between the Denali Fault and its splay – the Hines Creek Fault, and is truncated by both. The basin is 135 km long and 45 km wide. The stratigraphy of the basin includes two major sequences; the Lower and Upper Cantwell formations. The Lower Cantwell Formation comprises 4000 m of 80 to 70 Ma conglomerate, sandstone, shale and coal. These fluvial-lacustrine to shallow marine sediments were shed from uplifted crust associated with orogenesis and the Cantwell is thus a thrust-top basin. Evidence for this orogenesis includes 70 to 60 Ma east-west trending folds and north-verging thrust faults representing north-south compression, interpreted to have formed during suturing of the WCT to the YTT. Paleocurrent directions and grain compositions suggest that the Lower Cantwell Formation received sediments from the YTT in the north and from the Kahiltna Terrane to the south (Ridgway et al., 2002) that deposited in-situ and can thus be considered autochthonous. The Lower Cantwell Formation overlies the Kahiltna Formation along an angular unconformity. The Upper Cantwell Formation comprises a 7000 m sequence of 60 to 55 Ma mafic to felsic volcanic flows and lesser volcaniclastic rocks which post-date earlier deformation. These volcanic rocks may represent the end of subduction-related magmatism or be related to the outboard subduction of an active spreading centre (Trop and Ridgway, 2007). It is likely that magma migration occurring along the WCT suture. The volcanic sequence is structurally deformed by complex set of faults consistent with right-lateral transpression along a strand of the Denali Fault. Thus, the Cantwell Formation records; (1) uplift, erosion and thrust-top sedimentary  18  deposition, with a YTT provenance in the north and Kahiltna provenance in the south; (2) north-south oriented compressional deformation associated with accretionary and collisional orogenesis; (3) volcanism associated with the end of subduction; and (4) deformation associated with the onset of right-lateral strike-slip faulting in the Cenozoic. 2.4.2  Macleren and Aurora Peak: metamorphic terranes The Maclaren terrane, originally “Maclaren metamorphic belt” (Smith, 1971), is bounded to the north by the Denali fault and to the south by the Boxson Gulch fault abutting the WCT in the central Alaskan Range (Nokleberg et al., 1985). The lithology of the Maclaren terrane is dominated by amphibolite-grade metamorphosed plutonic (East Susitna Batholith) and sedimentary rocks (Maclaren Glacier Metamorphic Belt). While the sedimentary provenance is unknown, it is thought to be a metamorphosed section of the Kahiltna terrane (Nokleberg et al., 1994; Davidson and McPhillips, 2007). Ridgway et al. (2002) have provided an age of ca. 74 Ma for metamorphism suggesting it is associated with the same orogenic event that deformed the Cantwell basin at ca. 70 Ma. The age of magmatism has not been well constrained but Aleinikoff et al. (1980) suggest an age of 70 ± 7 Ma. The WCT was transported over the Macleren terrane along the Talkeetna thrust fault. The Macleren terrane represent subduction-related magmatism associated with accretionary orogenesis, and a date for major regional metamorphism associated with WCT collisional orogenesis.   The Aurora Peak Terrane occurs in the east-central Alaskan Range as a sliver bounded by the Denali fault to the south and a branch of the Denali to the north. It is dominated by Silurian to Triassic metasedimentary and Late Cretaceous to early Cenozoic metaplutonic rocks, dated at 71 Ma, thus broadly synchronous to those of the Macleren terrane (Nokleberg et al., 2000; Nokleberg and Richter, 2007). In addition, K-Ar ages of ca. 37, 27, 24, and 18 Ma are interpreted to represent greenschist facies metamorphism that occurred during dextral strike-slip transportation of the terrane along the Denali Fault. Similarly to the Macleren terrane, the Aurora Peak terrane is allochthonous, and records not just a subduction-related magmatic and accretionary metamorphic event, but also Cenozoic strike-slip movement of the Denali Fault.  19  2.4.3  The Windy and Pingston terranes: victims of Denali fault translation The Windy terrane is tectonically juxtaposed along the Denali fault as narrow, discontinuous lenses spread over several hundred kilometres. At its western extent it lies between the Aurora Peak and Maclaren terranes and in the east directly juxtaposes the WCT and YTT (Nokleberg et al., 1985; Nokleberg and Richter, 2007). The Windy terrane comprises structural mélange of Silurian-Devonian limestone and marl as large (0.5 m) conglomeritic clasts, Triassic limestone, Jurassic basalt and chert, and Cretaceous flysch, volcanic rocks and gabbro. This mélange includes faulting and shearing, phyllonite and protomylonite with intense schistosity formed at lower greenschist facies, although primary sedimentary structures are preserved (Nokleberg et al., 1994). Sedimentary rocks are interpreted to have WCT and YTT provenance, although exotic limestone and marl have an unknown origin demonstrating a complex structural history (Nokleberg et al., 1994; Nokleberg and Richter, 2007) with no stratal continuity between major lithic units (Jones et al., 1982). Deformation that formed mélange is associated with dextral strike-slip tectonics along the Denali fault.  The Pingston terrane forms several narrow, discontinuous lenses, generally less than 50 km in length, over 700 km strike-length of the Denali fault (Nokleberg and Richter, 2007). Lithology includes weakly metamorphosed, structurally disrupted sequence of (1) mid Carboniferous and Permian phyllite, marble, and chert, (2) Late Triassic limestone, shale, calcareous sandstone and quartzite, and (3) Early Cretaceous gabbro, dolerite and diorite (Nokleberg et al., 1994). Stratigraphy suggests the Pingston terrane was originally deposited as a turbidite sequence adjacent to the NAM passive margin (Gilbert et al., 1984). This defines the Pingston terrane as parautochthonous to the NAM compared to the Windy terrane, thus originated proximal to the NAM/YTT suture zone. This may explain the extreme structural disruption of this terrane and current dispersion over such long strike length, demonstrating the significant offset attributable to the Denali fault.  2.4.4  Nutzotin terrane: stratigraphic analysis The Nutzotin terrane represents an accreted basin 15-35 km wide by 250 km long in eastern Alaska. It is bounded by the Denali fault in the north and a splay – the Totschunda fault – in the  20  south (Figure 2.1). The Nutzotin Mountains sequence represent marine deposition in a forearc basin overlain by collisional foreland subaerial volcanic rocks of the Chisana Formation (Trop and Ridgway, 2007). Facies analyses of the Nutzotin Mountains sequence provide an insight into the development of the Nutzotin basin. Five facies associations (FA) are described by Manuszak et al. (2007) and their depositional environment is summarised in Figure 2.2. FA1 includes coarse-grained lithic-rich sandstone and conglomerate with limestone and chert clasts. This assemblage combined with northward paleocurrent directions suggest that FA1 represents a proximal submarine fan with sediment sourced from the uppermost units of the WCT (Nizina and McCarthy limestones). FA1 has a depositional contact with the WCT. FA2 comprises mainly deep-water (Nereites ichnofacies) hemipelagic sediments with minor lenticular conglomerate. Depositional environment is interpreted as a distal submarine-fan, with conglomeratic channels, laterally equivalent to FA1. Macrofossil biostratigraphy suggest an upper Jurassic age for FA1 and FA2. FA3 comprises normally graded sandstone to shale (distal) and FA4 tabular sandstone and clast-supported conglomerate (proximal). These are transverse and eastward trench-parallel axial, medial to distal submarine-fan systems representing the main phase of sedimentation and subsidence in the Nutzotin basin (Figure 2.2). Stratigraphically higher within FA3 and FA4 an increase in metabasalt clasts reflects exhumation of deeper levels of the WCT (Chitina arc). Macrofossil biostratigraphy suggests an Upper Jurassic to Lower Cretaceous age for FA3 and FA4. FA5 comprises a fossil-rich bioturbated mudstone. This unit is also upper Jurassic to lower Cretaceous. FA5 represents shallow marine shelf deposition proximal to the southern margin of the Nutzotin basin. The compositional and paleocurrent variations demonstrate an evolving sedimentary source in the Nutzotin basin. FA1 and FA2 represent the proximal and distal northwards paleocurrent of sediments shed from the WCT with a predominantly sedimentary source. FA3 and FA4 comprise a significant component of volcanic material becoming more plutonic higher in stratigraphy. This represents the exhumation of the Chitina arc on the WCT suggesting crustal thickening, possibly associated with collisional tectonics. The paleocurrent direction associated with FA3 and FA4 becomes increasing eastward suggesting crustal thickening is most significant  21  to the west and thus this progression to axially-oriented sedimentation may be attributed to oblique collision of the WCT with the NAM. FA5 represents a shallow marine shelf, consistent with the infilling of the ocean basin as oblique collision continued.    Figure 2.2  Nutzotin basin stratigraphic and structural development. (© 2007 Geological Society of America, by permission). (A) FA1/FA2 were deposited proximal and distal to the Wrangellia Composite Terrane (WCT) with sediment flowing directly off the WCT. (B) FA3/FA4 represent the most significant phase of deposition with sediment sourced from the WCT flowing axially to the trench. (C) FA5 was deposited in a shallow-marine environment assiated with final uplift of the basin.  (D) Final accretion of the basin to the North American Margin (NAM) was completed by structural imbrication associated with WCT collision to the NAM. (E) Final structural emplacement by right-lateral translation was completed during the Cenozoic.View is to the northwest. Image modified after Manuszsak et al. (2007).   22  2.4.5  Kahiltna terrane: stratigraphy and provenance analysis The Kahiltna terrane crops out along a 800 km by 200 km NE-SW trending belt (Figure 2.1). The Kahiltna terrane (or basin) has been described as a “thick, tectonically collapsed, isoclinally folded flysch sequence” (Nokleberg et al., 1994; Bundtzen et al., 1997). It has long been recognised that there are varied lithofacies within this terrane, and it has been subdivided (Wallace et al., 1989, and references therein) into the northern (Talkeetna Mountains) and southern Kahiltna assemblage (Alaska Range). These subdivisions are separated by Broad Pass, the structurally emplaced (thrusted) shallow marine Chulitna terrane (Figure 2.1) – dominated by black shale, chert and fossiliferous limestone (Eastham and Ridgway, 2002). Unlike in the Nutzotin Basin, there is evidence of a variation in sediment source throughout the Kahiltna terrane. In the northern Kahiltna (Talkeetna Mountains) assemblage the depositional environment was mud-rich submarine fan systems (Eastham and Ridgway, 2002). Ridgway et al. (2002) go on to subdivide the Talkeetna Moutnains into three sections. In the southern areas, adjacent to the Talkeetna thrust an assemblage of conglomerate, sandstone and laminated siltstone with normal grading and tabular bed geometry represent proximal submarine fan deposits. The central Talkeetna Mountains comprise normally graded calcareous sandstone interbedded with siltstone and chert, representing medial submarine fan deposition. The northern Talkeetna Mountains comprise normally graded siltstone and mudstone representing distal submarine fan deposition. This sequence is broadly Late Cretaceous to Early Jurassic in age (Kalbas et al., 2007). Incorporation of these data demonstrate a northwestward paleocurrent direction with the WCT as the primary sedimentary provenance for the northern Kahiltna terrane. The southern Kahiltna (Alaska Range) is Early to Late Cretaceous in age (Kalbas et al., 2007) and broadly demonstrates the same stratigraphic assemblages as the Talkeetna Mountains but in a reversed northeast-to-southwest arrangement. Thus, proximal submarine fan-style turbidity current conglomerates and sandstones are found in the northeast, grading to interbedded siltstone and mudstone, and massive mudstone in the southwest. This suggests a southeasterly paleocurrent direction with the NAM as the primary sedimentary provenance.   23   Figure 2.3  Alaska Range and Talkeetna Mountains provenance study. (© 2010 American Geophysical Union, adapted with permission). Upsection temporal trend correlated with increased component of Paleozoic and Precambrian populations indicating increased component of Intermontane provenance with time. Maximum depositional ages (MDA) are from Hampton et al. (2010) and ranges determined where more than once sample used, incorporating error. MDA values include youngest single grain (ysg), youngest graphical peak age (ypk), and weighted mean age (wma) from youngest cluster of three or more grains. From Hampton et al. (2010).  24   The provenance interpretations based on stratigraphic analyses in these two zones of the Kahiltna terrane have been examined using detrital zircon geochronology. As lithostratigraphic and biostratigraphic evidence has suggested, the northeastern (Talkeetna Mountains) section is older than the southwestern (Alaskan Range) section (Eastham and Ridgway, 2002; Ridgway et al., 2002; Kalbas et al., 2007). Hampton et al. (2010) provide a summary of detrital zircon geochronology of samples across both sections of the Kahiltna terrane and is outlined in Figure 2.3. These data show: (1) a clear northeast to southwest younging in the maximum depositional ages within each part of the Kahiltna as well across the whole terrane evident from biostratigraphy; (2) an increased Paleozoic and Precambrian provenance in younger sequences; (3) Only Mesozoic provenance (nothing older) in the oldest, easternmost sample from the Talkeetna Mountains; (4) A mix of known WCT and YTT magmatic ages in the northwest Talkeetna Mountains ; (5) Age populations matching known YTT magmatism in samples from the younger Alaska Range part of the Kahiltna terrane. These observations, and the following interpretations, are broadly similar to the earlier detrital zircon provenance study of Kalbas et al. (2007) Hampton et al. (2010) describe three main stages of sedimentation in the Kahiltna Basin.  The first Late Jurassic to Early Cretaceous stage is characterised by foreland basin development along the margin of the WCT. At this stage, only Mesozoic zircons were deposited (Mz 100%, Pz 0%, Pc, 0%) as is reflected in Figure 2.3 and expected from a WCT source. This was followed by an early Cretaceous stage with an increase of Precambrian and Paleozoic aged zircons (Mz 84%, Pz 11%, Pc 5%) from the YTT. This stage can be identified in both the Alaska Range and Talkeetna Mountains. The final Early to Late Cretaceous stage show significant increase in YTT aged zircons grains (Mz 65%, Pz 11%, Pc 24%). This would represent the transition from a remnant ocean basin to a peripheral foreland or strike-slip basin. All evidence leads to the conclusion that there was a westwardly younging suture zone forming as a result of oblique collision between the NAM and the WCT. As the WCT and Kahiltna basin moved towards the NAM, the Kahiltna terrane received YTT aged sediments, which increased in proportion during the final stages of ocean close in a westerly direction.  This is  25  essentially a mirror image of the Nutzotin basin, with the primary difference being the WCT-only sediment source in the Nutzotin. However, no radiometric geochronologic provenance studies have been conducted in the Nutzotin terrane to date.  Figure 2.4  Kahiltna basin evolution and accretion. (© 2010 American Geophysical Union, by permission). Three-stage model for Kahiltna basin evolution associated with accretion of the Wrangellia Composite Terrane (WCT) to the North American Margin (NAM). Intermontane belt from the Upper Jurrassic to Upper Cretaceous. Initial detrital contribution is exclusively Mesozoic suggesting WCT was the dominant source in the late Jurassic. Oblique convergence facilitates an increase of Precambrian and Paleozoic detrital material sourced from the NAM in the early Cretaceous, initially form east. Progressive basin closure increased NAM provenance accross the basin and convergent tectonics created late Cretaceous structural disruption in an east-to-west progression across the Kahiltna assemblage. View is roughly westward. Image from Hampton et al. (2010).    26  2.5  Southwestern Alaska regional Cretaceous magmatism Continuous magmatism along the NAM in Alaska and western Canada, throughout the Cretaceous resulted in approximately 25 distinct magmatic belts between 145 and 90 Ma (Hart et al., 2004). In southwestern Alaska magmatic belts have historically been less well defined. Recently Graham et al. (2013) defined three distinct magmatic and metallogenic epochs; mid-Cretacous 117-112 Ma and 100-89 Ma epochs; and Late Cretaceous 76-75 Ma magmatism. The earliest of the mid-Cretaceous magmatic events is hosted in the Nyac terrane. Later mid-Cretaceous and Late Cretaceous magmatism is hosted by the Kahiltna terrane. In both cases, southwestern Alaskan magmatism has been previously referred to as the Alaska-Aleutian Range Batholith (Reed and Lanphere, 1973) or the  Alaska Range-Talkeetna Mountain magmatic belt (Moll-Stalcup, 1990, 1994). 2.5.1  Mid-Cretaceous magmatism 2.5.1.1  Nyac magmatism The earliest phase of magmatism (111-108 Ma) has been associated with the Ruby-Kaiyuh-Nyac arc of the Nyac terrane (Hart et al., 2004). The tectonic setting of this magmatism is equivocal, having been associated with collisional (Flanigan et al., 2000) and volcanic arc tectonics (Graham et al., 2013). Magmatism of the Nyac terrane hosts considerable mineral, and especially gold, resources. The most significant of these is the Bonanza vein deposit (Wenz, 2005). However, the focus of this section is of Cretaceous magmatism and metallogeny associated with the WCT accretion to the NAM within the Kahiltna terrane and the Nyac is not discussed further. 2.5.1.2  Kaskanak Batholith  The Kaskakanak Batholith is hosted within the Kahiltna terrane. The batholith consists of quartz monzodiorite to granodiorite. A date for the batholith, as determined from U-Pb in zircon, is 89.7±0.2 Ma (Bouley et al., 1995; Rebagliati and Payne, 2004).  It has been suggested that this, and associated, magmatism at 100-90 Ma formed during a shift towards right-lateral transpression, on the inboard side of the WCT, equivalent to the outboard regions of the Kahiltna terrane  27  (Goldfarb et al., 2013). The resulting strike-slip deformation and extensional zones such as in pull-apart basins is thought to have facilitated magma ascent (eg. Richards, 2003). The Kaskanak Batholith is associated with the world-class Pebble porphyry Cu-Au-Mo system (Bouley et al., 1995; Lang et al., 2013). Mineralisation is characterised by porphyry-style quartz-sulphide veins with an advanced argillic (supergene) cap. A 2008 resource estimate of the Pebble deposit suggests an indicated and inferred resource of 49 Glbs Cu, 57 Moz Au, and 2.9 Glbs Mo at 0.3% CuEq. cut off.  (Rebagliati et al., 2008) making Pebble one of the largest undeveloped resources in the world.  2.5.2  Late Cretaceous and Paleocene magmatism After an apparent lull in magmatism, Alaska and western Canada underwent a surge of magmatic activity beginning at 75 Ma. The earliest of these intrusions, the gold-rich Whistler Igneous Suite, was highly localised along major regional structures and is of an oxidised nature. More regionally extensive reduced magmatic suites followed over the next 10-20 Ma, including metallogenically prospective Composite plutons including Mt Estelle, Summit Lake/Kichatna plutons, and less metallogenic McKinkley Series and Crystal Creek plutons. 2.5.2.1  Whistler Igneous Suite The Whistler Igneous Suite (WIS) comprises diorite and coeval andesitic volcanic units (Young, 2005; Couture and Siddorn, 2007; Roberts, 2011). It is geochemically calc-alkalic of intermediate basaltic-andesite to andesite and diorite composition. Previous hornblende Ar-Ar geochronology determined least-altered diorites as being 75.5 ± 0.3 Ma (Layer and Drake, 2005) and data presented in this thesis (Chapter 8) indicate a 76.4  ± 0.3 Ma age for mineralised diorite. Magnetite-rich intrusive and extrusive phases of the WIS suggest Whistler has a more oxidised redox state than the later Late Cretaceous magmatic phases. Intrusive centres are associated with Au-rich porphyry-style Au-Cu mineralisation. A 2011 resource estimate of the Whistler deposit suggests an indicated and inferred resource of 768 Mlbs Cu and 3.13Moz Au at 0.3% AuEq. cut off (Morris, 2011). The WIS and associated mineralisation is the focus of this thesis and is discussed in detail in subsequent Chapters.  28  2.5.2.2  Composite plutons and Mt Estelle The Composite plutons occur along a 150 km belt from the Lacuna dunite sills in the north to the Emerald pluton in the South (Young, 2005). The Composite plutons include the Cascade,  Emerald, Kohlsaat, Lacuna, Mount Estelle, Ptarmigan, Shellabarger, Stoney and Yentna plutons (Reed and Nelson, 1980; Crowe et al., 1991; Reiners et al., 1996). The gross form of the Composite plutons comprises several en-echelon mega-dykes with trend rotating from ~035 in the northern parts to ~000 in the southern sections as a function of oroclinal bending (Johnston, 2001; Young, 2006). These intrusions are compositionally diverse with concentric zonation tending from ultramafic or mafic margins to intermediate to felsic cores. The Mount Estelle pluton is zoned from diorite at the margins, through quartz monzodiorite, quartz monzonite to granite in the core (Reiners et al., 1996). It has been dated by K-Ar of biotite at approximately 62 Ma (Reed and Lanphere, 1973). Two granodiorites from the composite plutons yield zircon U-Pb ages of 69 ± 1 and 67 ± 1 Ma (Hung et al., 2007). Isotopic (87Sr/86Sr and εNd values) suggest the incorporation of enriched mantle, as well as a general trend towards crustally contaminated signatures with increasing differentiation (Reiners et al., 1996). Mineralisation is extensive and generally gold-rich. Specifically, ellipsoidal structures defined by close-spaced concentric fractures of gold, sulphides, quarts and sericitic alteration have been described (Crowe et al., 1991). Elsewhere, quartz-arsenopyrite stockworks and breccias with quartz, tourmaline and sulphide matrices exhibit significant gold contents (Millrock, 2010). These represent an intrusion-related style of mineralisation.  2.5.2.3  Summit Lake/Kichatna plutons Originally considered part of the Composite plutons (Reed and Lanphere, 1973), the Summit Lake or Kichatna plutons have been distinguished based on lithology and age (Reed and Nelson, 1980). These plutons are calc-alkalic and comprise diorite to granodiorite and monzonite and are commonly associated with pyrite, pyrrhotite, chalcopyrite and gold-rich vein and breccia systems in the Whistler area. They are considered to be 74 to 61 Ma with a 67.4 ± 2 Ma biotite K-Ar age (Reed and Lanphere, 1973). The presence of pyrrhotite suggests a relatively reduced redox state and it is likely these are of similar affinity to the Composite plutons.    29  2.5.2.4  McKinley Series Plutons  McKinley Series plutons crop out in the northern section of the Alaska Range-Talkeetna Mountain magmatic belt and comprise coarse-grained granite and granodiorite (Lanphere and Reed, 1985). Biotite K-Ar geochronology suggest an average age of 57.3 Ma and whole-rock Rb-Sr dating suggests a maximum age of 64.4 ± 1.9 Ma (Lanphere and Reed, 1985). Some recent unpublished data give zircon 206Pb/238U ages for two peraluminous granites of 62 ± 1 and 60 ± 1 Ma and two A-type granites of 57 ± 1 and 51 ± 1 Ma (Hung et al., 2007) suggesting that magmatism became progressively more alkaline. Initial Sr ratios range from 0.7054 – 0.7085, interpreted to reflect sourcing from mixing mantle-derived magma and melted flysch (Lanphere and Reed, 1985). Associated mineralisation includes minor tin anomalies including a quartz-tourmaline-muscovite greisen zone and some stockworks are present. Tin-related granites are typically found in continental collision fold belts (Groves and Bierlein, 2007). 2.5.2.4  Crystal Creek Sequence The Crystal Creek Sequence comprises calc-alkalic quartz monzonite and granite. It has been dated by K-Ar methods at between 60.5 and 55.7 Ma (Reed and Lanphere, 1973). The Crystal Creek sequence is not considered prospective for copper-gold or base metals, but has been explored for molybdenum (Fernette and Cleveland, 1984). 2.6  Summary of WCT collision and terrane accretion The accretion of the WCT is the most significant addition of crust to the western NAM in 200 Myr (Plafker and Berg, 1994). A temporal summary of this Jurassic to Cretaceous accretion and collision of the WCT to the NAM is presented here.  The record of accretion of allochthonous terranes to a continental margin is commonly best preserved in the sedimentary basin (Hampton et al., 2010). This record is evident in stratigraphic facies analyses and provenance studies, including detrital zircon geochronology. When combined with studies of subduction-related magmatism a detailed description of orogenesis is possible. The Middle Jurassic NAM was defined by the YTT terrane is SW Alaska. North-dipping subduction under the YTT was associated with a Jurassic arc (Figure 2.3). The subduction of the  30  oceanic lithosphere progressively closed the Kahiltna and Nutzotin ocean basin carrying the WCT towards the NAM (Figure 2.5a). Outboard of the WCT, a second north-dipping subduction zone was associated with Jurassic arc magmatism of the WCT. This included volcanic activity that was to exclusively provide the earliest sediment source for the Kahiltna (NE Talkeetna Mountains) and Nutzotin (FA1/FA2) basins (Figures 2.2, 2.3, 2.4 and 2.5). This WCT-outboard subduction was also associated with a developing accretionary prism – the McHugh Complex.  As these processes continued through the Late Cretaceous, initial collision of the central WCT divided the Kahiltna and Nutzotin basins. Exhumation associated with this collision provided abundant sediment source for the Kahiltna and Nutzotin (FA3/FA4) basins (Figures 2.2, 2.3, 2.4 and 2.5). This crustal thickening also provided the mechanism for trench-parallel sediment flow represented by westward and eastward paleodrainage in the Kahiltna and Nutzotin basins respectively. Collisional orogenesis was also likely responsible for the metamorphism of the Macleren and Aurora Peak terranes (Figure 2.5b). As this continued in the Early Cretaceous the Kahiltna basin received an increasing component of sediment sourced from the YTT, especially directly adjacent to the NAM. Provenance of sediments in the Nutzotin is not well constrained, although a YTT input may be likely. At this time, uplift of the Nutzotin basin formed a marine shelf with fossiliferous muddy sedimentation.  Magmatism associated with north-dipping subduction under the WCT continued to migrate inboard throughout the Cretaceous. This may be associated with a flattening of the subducting slab and/or shortening and thickening of the WCT.  Magmatism in the Kuskokwin in the early mid-Cretaceous (118-112 Ma) is found in the Nyac terrane. Within the Kahiltna terrane the most significant mid-Cretaceous magmatism is of the Kaskanak batholith at ca. 90 Ma, associated with the giant Pebble porphyry Cu-Au-Mo deposit (Figure 2.5b).  Magmatism through the latest Cretaceous included the Crystal, McKinley, Composite (Estelle), Summit Lake, and Whistler Igneous Suite intrusions of the Alaska Range-Talkeetna Mountains   31   Figure 2.5  Temporal evolution of the ARSZ.(continued on next page) (© 2007 Geological Society of America, adapted with permission). Four-part temporal sequence of Middle to Upper Jurassic (A) Lower to mid-Upper Cretaceous (B) latest Cretaceous (C) and Paleogene (D) accretionary and collisional orogenesis associated with the convergence of the Wrangellia Composite Terrane (WCT) with the North American Margin (NAM). Major events discussed in-text are presented in schematic map cross-section view. Figures are heavily modified from Trop and Ridgway (2007).  32    Figure 2.5 (cont.)  33  magmatic belt (Figure 2.5b). Of these, the WIS is the oldest. It is also the only one hosted by coeval volcanic rocks, and exhibiting an oxidised redox state. This ca. 76 to 65 Ma transition from oxidised to reduced state is reminiscent of the regional scale transition in magmatic chemistry of Jurassic and early Cretaceous magmatism described by Hart et al. (2004). It is not clear whether a similar temporal transition occurred in these latest Cretaceous intrusions, or whether this anomaly is due to particularly rapid ascent of magma, and thus less reduction by continental contamination. This second option may be substantiated by the position of the WIS on major regional structures.  Inboard of the focus of Kahiltna magmatism, deposition in the Cantwell thrust sheet was facilitated by exhumation of the Kahiltna and YTTs (Figure 2.5c). These terranes provided sediment to the Cantwell basin from the south and north respectively, between 80 and 70 Ma.  The lower Cantwell basin was then structurally disrupted by east-west trending folds and north-verging thrust faults associated with regional collisional orogenesis between 70 and 60 Ma. This orogenesis is also preserved in the Maclaren terrane to the east in Barrovian-type amphibolite-grade metamorphism at ca. 74 Ma. Widespread volcanism in the upper Cantwell basin may be associated with slab breakoff and remnant mantle wedge melting or subduction of an active spreading centre (Figure 2.5d).  Transpressive stress associated with collision was also likely responsible for the development of the right-lateral Denali-Farewell fault system (Figures 2.1 and 2.5c) between the paleo-NAM and the ARSZ. The significance of this major structure is evident in; (1) right-lateral faulting of the upper Cantwell volcanic rocks; (2) periodic Cenozoic greenschist metamorphic events in the Aurora Peak terrane at 37, 27, 24 and 18 Ma associated with right-lateral translation; (3) intense mylonite development in the Windy mélange terrrane; (4) internal disruption and displacement of Pingston terrane lenses over 700 km of the Denali fault; and (5) deep crustal-scale seismic anomalies to at least 30 km depth with a 40 km wide damage zone at 5 km depth.  Outboard, the McHugh accretionary prism development continued with the accretion of the Valdez Group in the latest Cretaceous and the Orca Group in the earliest Cenozoic forming the Chugach accretionary complex. Subduction continued to the present and the modern accretionary  34  prism, the Prince William terrane represents active accretionary orogenesis. This transpressive stress is still being accommodated by right-lateral translation along the Denali fault, most recently during the 2002 M7.9 earthquake (Eberhart-Phillips et al., 2003).     35  3 Whistler Property Geology The geology of the Whistler property is described in this chapter. Lithology, alteration, veins, breccias, and specific deposit geometry is described here in detail. Paragenetic relationships are described; however, the interpretation of these data are given in Chapter 9, which summarises the paragenesis of mineralising systems within the Whistler property with reference to the descriptive data of this chapter. The Whistler property comprises a 547 km2 block of 732 State of Alaska mining claims in the Yentna mining district. The property is 100% owned by Kiska Metals Corporation (Kiska) as of September 2010 (Weber, 2010) until the present.  The extent of the Whistler property is outlined in the geographic map of Figure 1.1 and geological map of Figure 3.1. This map also shows the locations of many of the intrusive suites nearby Whistler as discussed in Chapter 2.5. There is active exploration on the property at areas denoted “Old Man Breccia”, “Muddy Creek” and “Island Mountain”. These prospects are associated with the Composite suite of intrusive rocks discussed in Chapter 2.5.2. The Island Mountain prospect is associated with significant Cu-Au mineralisation, possibly of similar size to Whistler and is currently (at time of publication) the focus of a parallel Master’s thesis conducted by Tim Gross at the Colorado School of Mines. The mineralised systems that are the focus of this thesis are associated with the Whistler Igneous Suite (WIS) only, within a geological feature referred to as the Whistler Corridor. 3.1  The Whistler Corridor  The Whistler Corridor is a NNW-trending, fault-bounded volcano-sedimentary sequence emplaced into the regionally extensive Kahiltna terrane (Figure 3.1; 3.2). Topographically the Whistler Corridor forms a depression where the major Skwentna River is joined by the Happy River and Portage Creek (Figure 3.1). Strong hydrothermal alteration of the volcanic package and subsequent susceptibility to weathering is the likely cause for this topographic depression.  The Whistler Corridor includes the intrusive, sub-volcanic (hypabyssal), volcano-sedimentary, and multi-phase intrusive rocks associated with the WIS. Both the intrusive and  36  extrusive phases are of intermediate composition, comprising diorites and andesites respectively. These phases are considered broadly coeval (Young, 2005; Franklin et al., 2006; Young, 2006; Roberts, 2011) and together comprise the WIS. The margins of the Corridor are defined by the most lateral extent of these intermediate intrusive and extrusive rocks, usually defined by steeply-dipping normal faults.   Figure 3.1  Geology map of Whistler and surrounding areas. (© 2011 Kiska Metals Corp., by permission). Coordinates are in the UTM Zone 5 NAD83 grid system. Red line indicates extent of property held by Kiska Metals Corporation as of 2014. Location of intrusive bodies nearby to the WIS is approximate. After Roberts (2011).   37   Figure 3.2  Geology map of the Whistler Corridor. (© 2011 Kiska Metals Corp., adapted with permission). Coordinates are in the UTM Zone 5 NAD83 grid system. After Roberts (2011)    38  The nature of these margins is not well-constrained as they are not exposed in outcrop and have not been intersected by drilling. Geophysical magnetic data and constraints of nearby drilling indicate that the margin is steeply dipping. Other considerations discussed in subsequent Chapters indicate that the volcanic sequence is likely down-dropped relative to the surrounding Kahiltna sedimentary rocks. This has led to the interpretation that the Whistler Corridor represents a graben, half-graben, or pull-apart basin setting. An overall westward younging direction is interpreted here by examining the field relationships evident in Figure 3.2. WIS rocks in the western Whistler Corridor (Whistler ridge, Snow Ridge) comprise diorite intruding lithic sandstone of the Kahiltna Terrane. This includes the Whistler deposit. In the central Whistler Corridor WIS rocks comprise diorite intruding the WIS volcanic package. This includes the Raintree and Rainmaker deposits. In the eastern Whistler Corridor (Long Lake Hills area) volcanic rocks of the WIS are rarely intruded by mineralised diorite and show less indication of strong hydrothermal alteration. Additionally, an S-shaped structure (identified by magnetics) on the far eastern Whistler Corridor likely represents a channelised volcanic flow. Overall these relationships represent a west-to-eastward progression to higher stratigraphic levels, and thus a west-to-east younging direction of the Whistler Corridor.  The Kahiltna terrane hosts the WIS as well as the nearby Composite plutons. Locally, these Kahiltna rocks have been subdivided into several facies; the Lower Greywacke, Middle Greywacke, Upper Greywacke, and Feldspathic Sandstone (Young, 2005). These units are described below. 3.2  Lithology As discussed, the Whistler Corridor comprises a suite of igneous rocks hosted by the regionally extensive greywacke sandstone flysch of the Kahiltna Terrane. These sedimentary rocks were not examined in detail in this study, but a summary from previous work is included. Igneous rocks include an extensive intermediate volcanic, hypabyssal, volcanic breccia, and volcaniclastic package, and a suite of intermediate intrusive rocks, broadly divided into mineralised and  39  unmineralised diorite. There are also some minor intermediate and mafic dykes that post-date the main phases of intermediate magmatism. 3.2.1  Sedimentary rocks Four sedimentary units were identified by Young (2005, 2006). These include three greywacke units (lower, middle and upper) and an overlying lithic sandstone unit that is the direct host to both the volcanic package and several intrusive bodies, including the Whistler deposit. 3.2.1.1  Lower, middle and upper greywacke units These units are broadly correlative to the regionally extensive Kahiltna terrane. A detailed facies analysis of these units is not in the scope of this thesis, and descriptions given here are primarily sourced from Young (2006). The lower greywacke unit is dominant in the north of the Whistler Corridor and constitutes a SW to NE belt of sedimentary rocks (Figure 3.2). It is comprised of dark grey to black argillite and siltstone, and olive-grey greywacke and sandstone and includes normally graded bedding. The sandy component varies in abundance significantly from 5-70%, and is of similar mineralogy to the lithic sandstone described below. Sandstone is well-bedded, light-grey to brown-grey to olive-grey. It is fine to medium grained. It includes detrital white mica, dark lithic chips, chlorite, and it is matrix-rich. Lower Cretaceous (Valanginian to Hauterivian) 140-130 Ma Buchia sublaevis fossils have been found in correlative units of the Kahiltna terrane to the northwest of the Whistler region (Bundtzen et al., 1997; Young, 2005). The presence of fairly complete Bouma sequences associated with turbidity currents suggests a slope depositional environment. The middle greywacke unit is dominant to the south of the Whistler Corridor. Speculatively, it surrounds and underlies the upper greywacke and lithic sandstone units. It conformable overlies the lower greywacke unit and is lithologically similar. The middle greywacke unit however, includes greater proportions of carbonate, detrital white mica, lithic grains, and more feldspathic sandstone layers. It also includes a fine to medium grained, orange-ochre coloured ankeritic sandstone not identified in the lower greywacke unit. Buchia sublaevis is also present in the middle greywacke unit and “appears to have been deposited below storm wave base on the  40  outer shelf or perhaps upper slope” (Young, 2006). Low angle cross-bedding can be present which may represent a transitional depositional environment between the lower greywacke and lithic sandstone. Glauconitic sandstone is also present within the middle greywacke unit thus an upper slope to proximal shelf (shallow water) depositional environment is suggested. The upper greywacke unit is spatially restricted to a WSW-ENE trending belt along the southern flank of the Whistle Corridor. It is probably conformable with the underlying middle greywacke unit and gradational with the overlying lithic sandstone. The upper greywacke is characterised by Bouma cycles of black shale, mudstone, siltstone to feldspathic and tuffaceous sandstone. Fossils of Inoceramus anglicus or possible Inoceramus pictus suggest a mid-Cretaceous (Albian to Cenomanian) 112-93 Ma age of deposition although this is tenuous (Young, 2006). Abundant detrital white mica, carbonised plant impressions, and the fine-grained rock types suggest a pro-delta depositional environment. The three major greywacke units appear to represent an overall regressive sequence in the local Kahiltna terrane. 3.2.1.2  Lithic sandstone This unit has been traditionally referred to as a felspathic sandstone (Young, 2005; Franklin et al., 2006; Young, 2006; Couture and Siddorn, 2007; Roberts, 2011); however, feldspar is significantly subordinate to lithic fragments and quartz (Appendix B) and thus this rock is correctly classified as a litharenite or lithic sandstone. Descriptions given here are from the author’s field and petrographic examinations with contributions referenced as appropriate. In outcrop lithic sandstone occurs in cm-scale wavy or ropy beds, commonly with cross-bedding. It exhibits a salt-and-pepper texture. Bedding is defined by interbedded thin-bedded siltstone, mudstone and shale. Mineralogy comprises fine to coarse grained unsorted angular to subangular grains of quartz (40%); lithic material (35%) – including; chert (12%) muddy chert (10%) mesochert (8%) and mudstone (5%) – plagioclase feldspar (5%); carbonate (3%); detrital muscovite (2%); and sericite (5%). Grains are tightly packed with minimal cement (~10%) of quartz and calcite. Bioturbation is common parallel to bedding planes.  41  The following description and interpretation is based on Young (2005, 2006). The lithic sandstone unit has some spatial variation in composition and could sometimes be classified as biotite-bearing arenaceous sandstone, quartz arenite, or arkose although these compositions were not identified in this study. Young (2006) describes metre-scale andesite flows within layers of the lithic sandstone, and suggests that this unit was deposited simultaneously with volcanism of the Whistler Corridor.  However, the absence of intermediate-mafic detrital lithic material or detrital magnetite disassociates the lithic sandstone unit from the volcanic package. Lithic sandstone is quartz and chert rich, unlikely related to WIS volcanism. Andesite ‘flows’ are most likely sills. Overall, the lithology, bedding style and common bioturbation suggest the lithic sandstone unit represents “tidally-influenced shoreface to offshore deposition, with deeper-water shelf incursions represented by dark argillite” probably deposited semi-conformably over the greywacke units. It most likely predates volcanism of the WIS and is thus probably associated with the Kahiltna Terrane. 3.2.2  Intermediate volcanic rocks of the WIS The volcano-sedimentary sequence of the Whistler Corridor includes; hornblende-phyric andesitic flows, dykes, and sills, rarer pyroxene-phyric andesite, volcanic breccias, and undivided volcanic/subvolcanic intermediate rocks. Previous work grouped these volcanic rocks as ‘Extrusive Andesite’ (Young, 2005). This name is not used in this thesis because: (1) it does not differentiate between volcanic facies; and (2) the designation of extrusive is redundant when describing andesite. The term ‘intermediate volcanic package’ is proposed to represent these rocks and is used throughout this thesis. To date, there has been little success in correlating these units spatially due to apparent lateral variation and strong alteration obscuring primary lithology.   42   Figure 3.3  Sedimentary rocks of the Whistler Corridor. (a) Outcrop of interbedded sandstone and dark argillite of the lower greywacke unit, west of Whistler. Image courtesy of Young (2006); (b) outcrop of sub-metre scale interbedded light orange-ochre weathered sandstone and dark shale of the middle-greywacke unit southwest of Whistler. Image courtesy of Young (2006); (c) outcrop of glauconitic sandstone of the middle greywacke unit to the southeast of the Whistler corridor. Image courtesy of Young (2006); (d) outcrop of crossbedding in the lithic sandstone unit directly adjacent and west of the Whistler deposit; (e) handsample of the lithic sandstone unit from WH10-21-28m; and (f) cross-polarized petrographic image of lithic sandstone from WH10-21-28m. Note, grains include quartz, white mica and lithic fragments; mudstone, chert, with minimal feldspar.   43  3.2.2.1  Andesite Coherent volcanic rocks of the Whistler Corridor exhibit a basaltic-andesite to andesitic chemical composition (Chapter 4). These andesites are, when least altered, buff to dark brown or green coloured, porphyritic with fine to medium grained phenocrysts of feldspar or amphibole in a dark green or brown aphanitic groundmass (Figure 3.4a,b). Feldspar phenocrysts generally comprise 10-50% rock volume and are 0.2 to 3.0 mm long euhedral crystals, usually lathlike. Amphibole phenocrysts comprise 5-20% rock volume and are 0.2 to 2.0 euhedral laths. Groundmass is typically >50% abundant but in some cases can be up to 80%. Magnetite is a common accessory mineral and these andesites are typically magnetic when unaltered. Volcanic flows can be amygdaloidal with carbonate-filled vesicles, although are often non-vesicular. Trachytic flow textured feldspar phenocrysts are sometimes present. These andesites are rarely unaltered and feldspars are generally sericitised, amphiboles chloritised, and groundmass can be altered to hematite, chlorite, sericite or a mixture of these. 3.2.2.2  Pyroxene-phyric andesite Volcanic flows locally contain pyroxene phenocrysts in addition to plagioclase and hornblende described in Chapter 3.2.2.1. Pyroxene phenocrysts are blocky 0.5-5.0 mm octagonal subhedral to euhedral crystals (Figure 3.4c,d) typically strongly altered to chlorite, sericite and clay. Plagioclase and hornblende phenocrysts are similar to the other andesites, although hornblende is less abundant. Plagioclase is typically 30% abundant, with pyroxene 15% and hornblende 10% and magnetite 5% of rock volume. Magnetite is present as an accessory primary mineral, and is typically euhedral and 3-5% abundant. Groundmass is 20-40% abundant, and comprises plagioclase, with lesser mafic minerals, usually altered to chlorite and sericite. Pyroxene-phryic andesite may be more abundant than appreciated at Whistler, as pyroxene is usually obscured by alteration and may be mistaken for amphibole. 3.2.2.3  Undivided intermediate volcanic rocks There are significant intermediate volcanic rocks in the Whistler corridor that are not easily categorised into specific genetic classifications. ‘Undivided intermediate volcanic’ rock is a term used to encompass a variety of volcanic and/or subvolcanic rocks that are superficially similar to  44  the diorites described in Chapter 3.2.3. These volcanic rocks have a crowded porphyritic texture with 20-50% phenocrysts of 0.2-3.0mm plagioclase and 10-40% phenocrysts 0.2-3.0mm hornblende laths in a fine- to medium-grained groundmass. Groundmass varies significantly in abundance from 10-60% and is dominated by plagioclase. Groundmass is commonly fine- to medium-grained and thus exhibits a less porphyritic texture than the andesites described above, and is better described as inequigranular. Furthermore, significant heterogeneity in texture (including wispy flow or trachytic features) phenocryst abundance and size, and groundmass grainsize can occur over a few metres. In occurances containing a significant crystalline component, coarse groundmass, and is obscured by alteration, this rock type can be difficult to differentiate from intrusive diorite associated with mineralisation. However, it is the inherent heterogeneity which is most distinguishing, as true diorite bodies are typically texturally homogenous. These undivided intermediate volcanic rocks are interpreted to represent different parts of thick volcanic flows, hypabyssal/subvolcanic sills and dykes, and occasionally may be misidentified strongly altered andesites, pyroxene andesites, or volcanic breccias. 3.2.2.4  Intermediate volcanic breccia These rocks encompass a variety of volcanic breccias comprising a significant component of the volcanic package stratigraphy. These breccias are typically clast supported with 0.2-10 cm or sometimes >25 cm clasts. Clasts are most typically angular, but can be subangular to rounded (Figure 3.4e,f). Clasts are usually andesite or ‘undivided intermediate volcanic’ hypabyssal type, but can include mudstones. The matrix is usually igneous or volcaniclastic, and while clast-supported matrices are common, matrix-supported breccia is also present. In the absence of the commonly overprinting chlorite-sericite or sericite-pyrite alteration these rocks are typically hematite altered. When fresh (rare) they can be magnetic. The diverse styles of these volcanic breccias, and the significant variation in alteration of these, facilitate a huge diversity of rocks that fall under this classification.   45  These breccias are interpreted to represent autoclastic brecciation of volcanic and volcaniclastic flows in a highly diverse, heterogenic volcanic and hypabyssal environment. They may also represent diatreme pipes or miscategorised volcanic conglomerates. 3.2.2.5  Volcaniclastic tuff/sandstone/conglomerates These volcaniclastic rocks typically comprise large grains/clasts up to 2 cm of mudstone/siltstone and altered andesite in a fine-grained sandy groundmass (Figure 3.5g). Groundmass is commonly difficult to identify due to strong alteration, but is likely comprised primary of lithic fragments including andesite and mudstone, as well as plagioclase crystals. These volcaniclastic are typically intermixed with volcanic flows and breccias. When conglomeratic and altered, these are difficult to distinguish from volcanic breccias.                46     47  Figure 3.4  Volcanic rocks of the WIS. (previous page) (a) Hand-sample of fairly unaltered andesite with plagioclase and hornblende phenocrysts. Samle WH10-10-39m; (b) XPL image of the same andesite sample. Note trachitic texture of plagioclase phenocrysts; (c) hand-sample of pyroxene-phyric andesite. Sample WH10-11-154m; (d) XPL image of same pyroxene-phyric andesite shows strong sericite-clay alteration of pyroxene. Sample WH10-11-154m; (e) outcrop of volcanic breccia/conglomerate in the Long Lake Hills area. Angular clasts of andesitic rock in a similar composition matrix; (f) similar volcanic breccia/conglomeratge as in (e) although slabbed section shows clasts are strongly sericitically altered (common) and groundmass is significantly altered to hematite; (g) hand-sample of volcaniclastic conglomerate with polymictic clasts of siltstone and andesite in a granular matrix; and (f) (© 2006 Kiska Metals Corp., by permission) outcrop of andesitic flow disrupting argillite beds in the Snow Ridge area. Image from Young (2006).   3.2.3  Intrusive rocks of the WIS Intrusive rocks of the WIS are almost exclusively dioritic. Traditionally, these diorites have been categorised based on a variety of attributes; hue (olive diorite, leucocratic diorite); phenocryst type and size (megacrystic diorite, hornblende diorite); or presence of mineralisation, xenoliths and cross-cutting relationships (main-stage, intermineral, late-stage diorite); or dykes (intrusive andesite). Some of these variations are likely due to secondary processes such as hydrothermal alteration. In some cases, they occur only in localised areas. For example, hornblende diorite and megacrystic diorite are only found in the ‘Round Mountain’ area to the NNW of the main Whistler diorite. These lithologies were not observed in this study and as such are not examined here. For more detail of these lithologies see Young (2005, 2006). It is important to note that no diorite phases have been positively distinguished based on their primary mineralogy, but rather by; presence of alteration, presence of xenoliths, and cross-cutting relationships. Intrusive rock designations are revised here and are as follows; (1) Unmineralised diorite: not associated with mineralisation, and characterised by a lack of significant alteration. (2) Mineralised diorite: associated with mineralisation and can exhibit a spectrum of porphyry-related alteration types, described below.  (3) Main-stage porphyry (MSP): A sub-type of ‘mineralised diorite’ identified only in the Whistler deposit (to date) associated with the most volumetrically significant magmatism, mineralisation and feldspar-stable alteration  48  (4) Inter-mineral porphyry (IMP): A sub-type of ‘mineralised diorite’ identified only in the Whistler deposit (to date) associated with volumetrically minor magmatism, low-grade mineralisation (except when associated with high-grade mineralised breccias), and feldspar-destructive sericite-pyrite alteration. Regularly contains xenoliths of mineralised MSP. (5) Late-stage porphyry (LSP): A sub-type of ‘mineralised diorite’ identified only in the Whistler deposit (to date) associated with volumetrically minor magmatism, lack of mineralisation, and chlorite-sericite or sericite-pyrite alteration. Often exhibits chilled-margin textures. (6) Intermediate dykes (7) Mafic dykes  3.2.3.1  Unmineralised diorite Unmineralised diorite represents a phase of magmatism that post-dates the main mineralizing phase of dioritic magmatism (see Chapter 8). ‘Unmineralised diorite’ has been classified previously as ‘olive diorite’ (Young, 2005, 2006). These occur across the Whistler Corridor and also within the lithic sandstone, including nearby to the mineralised diorite of the Whistler deposit. Rocks described here were gathered from a fresh outcrop ~1 km ENE of the Whistler deposit. These rocks exhibit an inequigranular to weakly porphyritic texture (Figure 3.5). Phenocrysts comprise subhedral to euhedral 0.1-3.0mm stubby to lath-like crystals of plagioclase feldspar (40-60%) and subhedral to euhedral 0.1-3.0 mm stubby to lath-like crystals of hornblende (40-50%). In some cases, pyroxene was identified petrographically as being 10-20% abundant. Where present, pyroxene exhibit prismatic to acicular 0.2-3.0mm crystals and are often rimmed by an alteration mix of clay, chlorite, and an unidentified opaque mineral. Plagioclase often exhibits a sericite/carbonate ‘dusting’ style of alteration. Phenocrysts are set in a very fine-grained  49  groundmass (10-20%) comprising dominantly feldspar, with minor amphibole. This groundmass is commonly altered to sericite, even in these relatively fresh rocks.   Figure 3.5  Unmineralised diorite of the WIS. (a) Hand-sample of fairly unaltered unmineralised diorite with plagioclase and hornblende phenocrysts. Samle 209 from unmineralised diorite near to Whistler deposit; (b) XPL image of the same diorite sample. Plagioclase shows slight sericite ‘dusting’. Hornblende phenocrysts are fairly unaltered; (c) Hand-sample of basaltic andesite dyke with carbonate altered amphibole and plagioclase in a very fine grained (aphanitc) groundmass. Sample 201; (d) XPL image of basaltic andesite dyke. Carbonate replacement of amphibole is evident. Laths of plagioclase comprise groundmass. Sample 201.  3.2.3.2  Mineralised diorite Mineralised diorite is, where least-altered, mineralogically similar to ‘unmineralised diorite’. ‘Mineralised diorite’ has been previously classified as either ‘olive diorite’ or ‘leucocratic diorite’, largely based on the degree of chloritic/phyllic alteration. It occurs across the Whistler Corridor as well as in the lithic sandstone on the fringes of the volcanic package (Figure 3.2).  50  Mineralised diorite is the magmatic phase associated with all porphyry-style mineral deposits of the Whistler Corridor.  Similarly to unmineralised diorite, these rocks exhibit an inequigranular to weakly porphyritic texture. Phenocrysts comprise subhedral to euhedral 0.1-3.0mm stubby to lath-like crystals of plagioclase feldspar (40-60%) and subhedral to euhedral 0.1-3.0 mm stubby to lath-like crystals of hornblende (40-50%). Plagioclase phenocrysts may be altered to albite, and are invariably altered significantly to sericite or calcite. Hornblende is commonly altered to chlorite, locally exhibiting a ‘shreddy’ texture suggesting chlorite has replaced hydrothermal biotite. Where phyllic alteration is strong, all mafic minerals are altered to pyrite. Groundmass (10-20%) is presumably similar to ‘unmineralised diorite’ but is commonly altered to potassium feldspar, albite, or quartz, and strongly overprinted by chlorite and sericite. Groundmass can appear aphanitic and medium to dark olive-grey due to this ubiquitous alteration.  In the Whistler deposit, three phases of ‘mineralised diorite’ have been identified. These include a Main-stage (MSP), Inter-mineral (IMP), and Late-stage (LSP) porphyry diorite. The lithology and diagnostic characteristics of these intrusive phases are described in this chapter. The geometry, alteration, and mineralisation are outlined in Chapter 3.7.1. These designations are used when describing different diorites of the Whistler deposit as they have only been positively identified there thus far. Multiple phases have been identified at Raintree West but further work is necessary to classify these. ‘Mineralised diorite’ is used to describe altered diorite intrusion associated with mineralisation elsewhere in the Whistler Corridor. It should be noted that the primary mineralogy of these phases has not been distinguished from ‘mineralised diorite’.  3.2.3.3  Mineralised diorite: main-stage porphyry (MSP) This is the most volumetrically significant diorite phase in the Whistler deposit. It is lithologically and mineralogically identical to ‘mineralised diorite’ described above. In the Whistler deposit, this unit is given a specific designation (MSP) to differentiate it from the IMP and LSP phases identified in the deposit. MSP is ubiquitously altered. Alteration varies from  51  sericite-pyrite±quartz (phyllic) at the periphery, to albite-magnetite (sodic-ferric) or potassium feldspar-magnetite±biotite (potassic) centrally. A chlorite-sericite overprint is ubiquitous, except where sericite-pyrite±quartz is strongest. MSP is associated with the majority of porphyry-style Au-Cu mineralisation at the Whistler deposit.  3.2.3.4  Mineralised diorite: inter-mineral porphyry (IMP) Inter-mineral porphyry is lithologically similar to MSP exhibiting the same primary mineralogy. It can exhibit similar feldspar-stable alteration assemblages and mineralised veins, including M-, A-, and B veins, although typically of lower grade than the surrounding MSP. Intrusive contacts are difficult to identify lithologically, as sharp boundaries or chilled margins are generally absent. Contacts can be distinguished by abutting veins of the MSP, sharp change in alteration, or the presence of xenoliths. These xenoliths are typically quartz-vein fragments or mineralised MSP diorite fragments, generally close to the contact (Figure 3.6). IMP phases in the Whistler deposit are spatially associated with a magmatic-hydrothermal breccia bearing high-grade Au-Cu mineralisation and strong sericite-pyrite alteration. IMP is considered to be a magmatic injection into MSP during the cooling and high-temperature alteration and mineralizing stage of the paragenesis. 3.2.3.5  Mineralised diorite: late-stage porphyry (LSP) Late-stage porphyry diorite is lithologically and mineralogically similar to MSP. This unit is characterised by a complete lack of mineralisation and sharp, chilled-margins. It never displays feldspar-stable alteration, and is typically fresh, chlorite-sericite, or sericite-pyrite±quartz altered. LSP is considered to be a magmatic injection late in the paragenesis. 3.2.3.6  Basaltic andesite dykes Discrete dykes of aphanitic, moderate to dark grey-green rock, probably andesite or basalt. Whole-rock geochemistry suggests these are basaltic andesite (Chapter 4).They can contain hornblende phenocrysts up to 2 mm long. These are observed in outcrop and drill-core and vary in thickness from several centimetres to several metres. They commonly contain igneous magnetite. They often exhibit chlorite and/or carbonate alteration or can be unaltered (Figure 3.5c,d).   52   Figure 3.6  Mineralised diorite phases of the WIS. (a)-(d) from Whistler, (e)-(f) from Raintree West. (a) Chilled margin contact between MSP diorite with mineralised quartz veining and unmineralised LSP diorite. Sample WH07-02-283.6m; (b) chilled margin contact betwen same MSP and LSP diorite as in (a) but approximately 200 vertically below. Note alteration is sericite-pyrite below and chlorite-sericite above. Sample WH07-03-593.2m; (c) contact between mineralised diorite with quartz vein xenoliths and unmineralised dorite. It is not clear exactly which phases are present but probably a IMP/LSP contact. Sample WH07-04-49.7m; (d) diorite with quartz vein xenoliths is typical of IMP. The IMP in this area is transitional to a magmatic-hydrothermal breccia with quartz-vein fragments in an intrusive matrix. Sample WH07-04-90m; (e) intrusive contact between mineralised MSP diorite with quartz-pyrite B3-vein and an unidentified later phase of intrusion. Sample WH09-02-418m; and (f) intrusive contact between same phases of intrusive as (e) but the later phase is cross-cut by a quartz-carbonate-sphalerite-pyrite D3-style vein. Sample WH09-02-425.6m.   53  3.3  Alteration In general, the alteration associated with mineralizing hydrothermal fluids within the Whistler Corridor is typical of gold-rich porphyry systems. For field identification, they have been grouped into different mineral associations and assemblages; potassic, sodic-ferric, chlorite-sericite, phyllic, propyllitic and iron-carbonate. The hydrothermal minerals and alteration assemblages described herein have generally all formed from a diorite protolith. In some cases the protolith was host rock to the diorite – either sandstone or andesitic volcanic or volcaniclastic rocks – but the assemblages remain broadly similar. A summary of alteration and vein types is presented with paragenetic interpretation in Chapter 9, Table 9.1.  3.3.1  Potassic (magnetite-potassium feldspar±biotite) alteration Potassic alteration is characterised by the presence of a potassium feldspar and magnetite. This alteration assemblage is also strongly associated with chalcopyrite as well as pyrite mineralisation. Pervasive potassic alteration can be characteristically texturally destructive (Figure 3.7), but is commonly restricted to zones of intense magnetite and quartz vein stockworks.  Potassium feldspar commonly partially replaces the groundmass at Whistler, as evident in Figure 3.7b. This groundmass replacement may be overemphasised by staining, as SEM work by Le Couteur (2012) suggests is often a mixture of ankerite, Fe-(Mn) oxides, quartz, potassium feldspar and probably sericite. Full replacement of plagioclase by K-feldspar appears to be rare. Magnetite is found in in wormy veinlets as well as in anhedral to subhedral disseminated grains. When in veinlets it is often associated with quartz or chalcopyrite and may have a K-feldspar alteration halo. It is likely that these minerals are co-precipitative. In some cases magnetite has altered to hematite. Biotite has been interpreted (Young, 2005) to have been present based on the presence of “shreddy” chlorite textures in hand samples. Although this feature is locally observable it is possible these have altered directly from hornblende. Therefore the presence of hydrothermal biotite as part of the potassic alteration assemblage is not discussed further here.   54  Chlorite is ubiquitous in potassic and sodic-ferric alteration, replacing groundmass and mafic minerals. It is not completely clear whether this is part of a potassic/sodic-ferric alteration mineral association or due to overprinting chlorite-sericite assemblage.  Sulphides associated with potassic alteration include chalcopyrite and pyrite, and rarely bornite. Chalcopyrite is commonly associated with magnetite, mostly in veins but also in disseminations. Electrum as inclusions in this chalcopyrite is the primary site of gold deportment associated with the high-T porphyry mineralisation at Whistler (Petersen, 2004; Proffett, 2009). Bornite occurs rarely with chalcopyrite in A-, and B-veins. 3.3.2  Sodic-ferric (albite-magnetite) alteration Sodic-ferric alteration is similar to potassic alteration in texture, distribution and mineralogy, but lacks potassium feldspar. Whole-rock (Chapter 4) and feldspar mineral geochemistry (Chapter 5) suggest significant Na enrichment in the form of introduced albite. This albite-magnetite assemblage facilitates the designation of sodic-ferric alteration. The distribution of sodic-ferric alteration is enigmatically intermixed with potassic alteration. No control has been identified on whether potassic or sodium feldspar-stable alteration will be dominant in a given area, but is discussed in Chapter 5. As with potassic alteration, chlorite groundmass and magnetite-chlorite mafic replacement is ubiquitous giving sodic-ferric alteration a characteristic dark green colour evident in Figure 3.7. This ubiquitous chlorite is presumed to be part of a late chlorite-sericite overprint, but it is possible that chlorite is part of the sodic-ferric assemblage, in which case the assemblage is albite-magnetite-chlorite. 3.3.3  Phyllic (sericite-pyrite±quartz) alteration Phyllic alteration is the most texturally destructive alteration at Whistler. It comprises dominantly sericite-pyrite±quartz (known generally as QSP). Where strongest, silicification is a major constituent, and when weakest there is very little quartz. Phyllic alteration without quartz can be referred to as sericite-pyrite alteration. In these cases, original rock texture is often preserved (eg. Figure 3.6b).    55  Where present, quartz can be patchy but when pervasive generally fills the interstitial zones between sericitised feldspars as anhedral grain mosaics (Figure 3.8b). The hardening of the rock is characteristic of this silicification, and likely hindered further fluid flow or overprinting alteration. Strong phyllically altered zones are the only rocks at the Whistler deposit not overprinted by chlorite-sericite. Pyrite replacement and nucleation at mafic sites is highly characteristic of phyllic alteration. This represents a significant sulphur input, as can be seen in Figure 3.8. Sulphur assay values can, with care, be used as a proxy for phyllic alteration intensity. Pyrite can form cubes or relatively subhedral to anhedral grains, usually nucleating from mafic sites. Pyrite can occupy up to 15% of the rock volume in some cases, and 5-10% is typical. Sericite alteration of feldspars and groundmass is a major part of the phyllic alteration assemblage. As discussed below, sericite alteration in the phyllic zone is more crystalline than that in chlorite-sericite alteration, however this is not determinable in hand samples. There are transition zones where phyllic and chlorite-sericite alteration assemblages are present together (Figure 3.8c). In these zones, chlorite and pyrite replacement of mafic minerals occur but cross-cutting relationships are not clear. These zones commonly represent the transition from pyrite, to magnetite-chlorite as the dominant ferromagnesian replacement mineral and as such may be considered as a vector to more oxidised and less acidic metasomatism, and thus towards mineralisation. 3.3.4  Chlorite-sericite alteration As the name suggests, this alteration assemblage comprises chlorite and sericite. Here, the term ‘sericite’ is a field term used to refer to hydrothermal phyllosilicate minerals including muscovite, illite and an illite-smectite mixture. Spectral and XRD analyses of these phyllosilicate minerals has determined them to most likely be illite with varying degrees of crystallinity (Chapter 6).  Feldspars alter to sericite, varying from weak alteration ‘dusting’ of grain margins to stronger alteration partially to completely replacing phenocrysts and groundmass. Chlorite  56  generally replaces mafic sites which are most commonly hornblende or pyroxene. This replacement can result in blotchy anhedral chlorite. Both sericite and chlorite alteration strongly replace groundmass. Chlorite-sericite alteration causes an exaggeration of the original weakly porphyritic texture of these diorites (Figure 3.8d). This is due to the contrasting darkening effect of chlorite replacing groundmass and lightening effect of feldspar sericitisation.  When chlorite-sericite overprints potassic alteration, chloritised mafic sites can exhibit a “shreddy” texture (Figure 3.7e,f). This is interpreted to represent chlorite overprinting hydrothermal biotite. The chlorite-sericite alteration assemblage described here is equivalent to Sillitoe and Gappe’s (1984) sericite-chlorite-clay assemblage, and to the intermediate argillic assemblage of Seedorff et al. (2005). Figure 3.8 provides some examples of chlorite-sericite alteration. 3.3.5  Propyllitic (chlorite-epidote-carbonate) alteration Propyllitic alteration at Whistler is rare, most common in the Whistler Orbit distal to mineralisation. The assemblage comprises chlorite, epidote and calcite. Chlorite primarily replaces the groundmass an anhedral masses, and also partially replaces mafic minerals. Epidote replaces groundmass and rarely feldspar, and often forms characteristics rosettes. Feldspars are partially altered to calcite and sericite, and will react with weak HCl. Calcite is also present in veinlets that may be part of the propyllitic assemblage but probably post-date alteration associated with mineralisation. Figure 3.9d shows the appearance of propyllitic alteration of diorite and Figure 3.9,e,f demonstrate the assemblage in thin section. 3.3.6  Iron carbonate (ankerite/siderite) alteration An overprinting of mineralised zones with iron carbonate alteration is very common at Whistler. In Figure 3.9a an iron carbonate front is replacing potassic and chlorite-sericite alteration. This type of alteration is most commonly found in mineralised zones, but also spatially associated with fault zones. This suggests that these are areas of high permeability, presumable associated  57  with the intense vein stockworks of the mineralised areas. Veins associated with iron carbonate alteration show that this is the latest alteration event.  In detail, iron carbonate alteration is characterised primarily by ankerite and siderite replacement of relict feldspar sites and groundmass (Figure 3.9c), hematisation and iron-hydroxide replacement of magnetite and relict mafic sites. This alteration can be texturally destructive, although it occurs primarily in rocks that are already strongly altered so this is not clear. It is interesting to note that iron carbonate alteration can be difficult to identify in fresh drill core. It does not react well with HCl unless powdered and then only elicits a weak reaction. After several days, or ideally months, the exposure to air and moisture creates the characteristic orange-brown colour evident in Figure 3.9a,b. It is probable that the iron carbonate alteration represents a post-mineralizing event, and is not genetically related to the mineralizing system. Furthermore, difficulty identifying it in fresh drill-core has resulted in a poor understanding of the distribution. Thus, iron carbonate alteration is not examined in further detail in this thesis. 3.4  Veins The veins described below are consistently found throughout the Whistler Corridor and are associated with diorite intrusive bodies. Some vein types have only been found in specific areas as discussed below. Vein types are summarised in Table 3.2. 3.4.1  Magnetite-dominant veins (M1, M2) Magnetite-dominant veins (M-veins) are classified here as those with greater than 50% magnetite. In order of abundance; quartz, chalcopyrite and anhydrite may also be present. Rarely, bornite or molybdenite is present.  M1 veins are defined here as magnetite-dominant veins with little or no quartz. M2 veins can include up to 50% quartz. Veins with quartz as the most abundant mineral are classified as quartz-dominant veins (see below). M-veins with greater quartz content are often observed to cross-cut those with lesser quartz. Thus M-veins represent a temporal transition to increased quartz content. M-veins are 0.1-1.0 mm wide. They typically comprise aligned subhedral magnetite and are often discontinuous. They can occur as isolated wispy veins or as part of dense sheeted vein  58  sets (Figure 3.10). Quartz, if present, is generally equant subhedral to euhedral where most abundant. Grain size is dependent on vein width but is rarely above 0.1mm. Chalcopyrite is commonly present in these veins as anhedral to subhedral, elongate to equant grains or inclusions within magnetite.  Anhydrite is rarer and can usually only be identified petrographically. These grains occur isolated or as masses of several grains within an individual vein. More rarely they occur along the entire length of a vein. Grains are equant, subhedral to euhedral and usually around 0.1 mm. Pyrite may also be present in these veins although it is likely a later overprint of magnetite or chalcopyrite. M-veins often have an alteration halo several centimetres wide comprising either; albite-magnetite or potassium feldspar-magnetite alteration. These correlate with zones of potassic or ferric-sodic alteration (see Chapter 3.3 for a description of these alteration types). M-veins are also correlated with chlorite alteration. It is not clear whether chlorite alteration occurs as part of this assemblage or as a later overprint.  3.4.2  Quartz-dominant veins (A1, A2, A3, B1, B2, B3, D1, D2, D3) Quartz-dominant veins are the most abundant types of veins at Whistler. These include subdivisions similar to the A, B and D types of veins of Gustafson and Hunt (1975) with details discussed below. Quartz-dominant veins can also include; magnetite, chalcopyrite, pyrite, bornite, sphalerite, galena, molybdenite, anhydrite, dolomite, calcite, chlorite and epidote. The categorisation of quartz-dominant veins into A, B or D types is dependent on a variety of factors including mineralogy, crystal habit and associated alteration. 3.4.3  Quartz-dominant A-veins (A1, A2, A3) The most characteristic feature of A-veins is the crystal habit of the quartz and the vein morphology. Quartz grains are typically equant and equigranular with a grainsize ≤0.3 mm and exhibiting a “granular” or “sugary” texture. The second diagnostic characteristics of A-veins are irregular vein edges, having never formed parallel vein walls. Similarly to M-veins, A-veins can be discontinuous, comprising aligned subhedral quartz grains. These can be aligned to form a straight but irregular vein, or to form wispy meandering veins that may deviate around igneous  59  phenocrysts. In all cases A-veins lack the straight-edges expected in fracture-fill vein types. Examples of A-veins are given in Figure 3.11. Mineralogically A-veins are similar to M-veins although with subsidiary magnetite in A1 and absent in A2 and A3 veins. Chalcopyrite may be present in all three A-vein subdivisions usually as anhedral grain equant or elongate grains or inclusions in magnetite. Anhydrite is rarely present, usually as masses of several subhedral grains. Pyrite may also be present in these veins although it is likely a later overprint of magnetite or chalcopyrite. The subdivision of A1, A2 and A3 is purely mineralogical. A1 and A2 types are the most abundant, with the latter lacking magnetite. A3 veins are very rare and include molybdenite, although this has not been identified petrographically it has been observed in field observations using portable X-Ray Florescence (XRF) devices. A3-veins are wormy, comprise “glassy” quartz and very fine-grained molybdenite. These Mo-rich A3-veins seem to be concentrated in the periphery of the Au-Cu zone in a molybdenum ‘halo’ as shown in Figure 3.25. Similarly to M-veins, A-veins often have an alteration halo several centimetres wide comprising either; albite-magnetite or potassium feldspar-magnetite alteration. These correlate with broader zones of potassic or ferric-sodic alteration. A-veins are also correlated with chlorite and sericite alteration. It is not clear whether chlorite alteration occurs as part of this assemblage or as a later overprint.  3.4.4  Quartz-dominant B-veins (B1, B2, B3) B-veins are defined primarily by vein morphology at Whistler. B-veins typically have very straight vein margins with quartz crystals growing from the walls towards the centre, commonly with a mineralogically diverse centreline. This cockscomb texture is typical of B-veins in porphyry systems (Gustafson and Hunt, 1975; Seedorff et al., 2005). Quartz grain morphology varies from highly euhedral and pyramidal (cockscomb textured) and cm scale to subhedral, equant grains at sub-mm scale. Grain size is generally significantly smaller that A-veins, with the exception of pyramidal quartz where present. In many cases, characteristics of both A and B veins can be present within a single vein, for example, a straight-edged vein may contain no cockscomb textures or  60  centreline, or a “sugary” textured quartz vein may have a centreline. These may be transitional veins or A-veins broken by a secondary B-vein phase. Examples of B-veins are given in Figure 3.12. Mineralogically, B-veins are similar to A-veins. They are dominated by quartz, with secondary magnetite or pyrite, with chalcopyrite and lessor anhydrite, bornite and molybdenite. The subdivision of B1, B2, B3 refers to the transition from magnetite to pyrite as the dominant iron mineral. B1-veins comprise quartz-magnetite, B2-veins transition from zones of quartz-magnetite to zones of quartz-pyrite, and B3-veins are quartz-pyrite. All three phases can include chalcopyrite or rarer anhydrite or bornite. B3-veins are observed to cross-cut B1-veins (Figure 3.10a). Distinct alteration halos around B-veins are less obvious than around M- or A-veins. In many cases, feldspar-stable sodic-ferric or potassic alteration assemblages are broadly associated with B-veins. Where pyrite is prevalent, feldspar-destructive sericitic alteration may be present. This alteration is rarely in halos correlated with veins but is more pervasive.  It should be noted that many quartz-rich veins exhibit characteristics of both A-, and B-veins. For example some veins have straight edges but are dominated by “sugary” textured quartz and magnetite. Other examples include wormy, irregular, “sugary” textured quartz veins but with centrelines of pyrite and/or chalcopyrite. These have been referred to as AB-veins, and represent a transitional stage from A- to B-veins. 3.4.5  Quartz-dominant D-veins (D1, D2, D3) D-veins at Whistler are most succinctly defined as those with feldspar-destructive alteration halos. D1-, D2-, and D3-veins are quartz dominant with significantly variable amounts of quartz, dolomite, calcite, rhodochrosite, ankerite, pyrite, chalcopyrite, sphalerite, galena or molybdenite. D1- and D2-veins are typically 1-30 mm wide, with straight margins. D-veins represent a transition from feldspar-stable to feldspar-destructive alteration halos and the onset of Zn-Pb-(Au-Ag) mineralisation.   61  D1-veins are essentially a continuum from B3 veins, and a correlation with feldspar-destructive sericitic alteration is now evident in a discreet cm-scale alteration selvage (Figure 3.13). Quartz is typically equant subhedral to euhedral, fine-grained 0.05-0.3 mm. While quartz is still dominant, pyrite is ubiquitous and may comprise from 5-50% in D1- and D2-veins. Pyrite occurs as tiny 0.05 mm flecks to 10 mm anhedral masses to euhedral cubic crystals.  D2-veins include a significant carbonate component, usually as dolomite but calcite, rhodochrosite or ankerite are also locally present. The presence of a significant carbonate component separates D2- from D1-veins. This carbonate can be present within a centreline or evenly distributed within the vein (Figure 3.13d,e). D2-veins are also more likely to include a greater sphalerite or galena component. In both cases, grains are subhedral to euhedral, usually equant and up to 1 to 10 mm in size. Both D1- and D2- veins include significant chalcopyrite, often occurring as mm- to cm-scale anhedral “clumps”. Molybdenite in a D2-vein has been analysed for Re-Os systematics and the results discussed in Chapter 8.  D3-veins refer to base-metal rich D-veins. D3-veins are referred to as Dbm veins for the purposes of logging by onsite geologists. ‘Dbm’ refers to D-veins with base-metals. D3-veins are typically dominated by a quart-carbonate-pyrite-chalcopyrite-sphalerite-galena assemblage (Figure 3.13c,d,e,f). Crystals are typically medium to very coarse grained, up to several cm. Chalcopyrite occurs as anhedral masses or more commonly as inclusions within sphalerite along cleavage planes (Figure 3.13f). D3-veins occur sporadically distributed across the entire deposits, but are the only mineralised veins that occur significantly distal to porphyry-style mineralisation – up to two hundred metres from porphyry mineralisation. 3.4.6  Pyrite-dominant D-veins (D4, D5) D4-veins are narrow 0.5 to 3.0 mm wide pyrite veins with a strong feldspar-destructive sericite-pyrite alteration halo (Figure 3.14). D4-veins are referred to Dpy veins for the purposes of logging by onsite geologists. D4-veins are the closest representation to the D-veins defined by Gustafson and Hunt (1975). These veins are straight, with edges defined by individual pyrite crystals. Pyrite is typically euhedral and cubic, although can be anhedral occurring as masses. They  62  are observed to cross-cut all M-, A-, and B-veins and most D1- and D2-veins. Usually D4-veins are observed to cross-cut D2-, and D-3 veins. However, D3-veins have been observed to cross-cut D4/D5-veins (Figure 3.14b) suggesting multiple phases or synchronous D-veins mineralisation. D4-veins exhibit a discrete zone 1-10 cm wide with strong sericitisation of feldspar and pyritisation of mafic minerals.  In some cases pyrite stringers can also host tourmaline (Figure 3.14c,d). In these cases they pyrite-tourmaline veinlets are referred to as D5-veins. D5 veins are narrow 0.5 to 3.0 mm wide and like D4-veins are associated with feldspar-destructive sericite-pyrite alteration halos. The paragenetic relationship between D4 and D5 is not known but assumed to be synchronous. D4- and D5-vein types are paragenetically later than M-, A-, B-, and most D-veins. They are also peripheral to zones of dense magnetite- and quartz-rich veining. D4-veins occur with greatest density in the zones of strongest sericite-pyrite alteration.  3.4.7  Sulphide-dominant epithermal-style E-veins (E) E-veins are mineralogically similar to base-metal rich quartz-carbonate D3-veins although E-veins are typically dominated by sulphides, especially sphalerite. E-veins differ texturally from D3-veins in that they exhibit crustiform, cockade, colloform and comb banded growth textures and breccia infill (Figure 3.15). E-veins have been referred to as Dbm (grouped with D3-veins) or “D-bling” veins by onsite geologists due to the spectacularly textured base metals. They have here been reclassified as E-veins due to their significantly differences from D3-veins and for constancy of vein naming convention. This is a new classification suggested here as they have a substantially different morphology to the mineralogically similar D3-veins. The ‘E’ refers to ‘epithermal’ as these textures suggest a much shallower, open-space filling style of formation than D3-veins.  E-veins comprise predominantly sphalerite, quartz, and carbonate, with lesser pyrite, galena, chalcopyrite and tetrahedrite. Sphalerite and galena typically exhibit crustiform, cockade or colloform textures while quartz and carbonate exhibit comb and zoned textures. Crustiform and colloform colour banding of translucent red, brown and opaque sphalerite does not represent a significant compositional variation (Le Couteur, 2012). Au-Ag (electrum) is most likely present as  63  inclusions within sphalerite and chalcopyrite as observed in brecciated E-veins (Figure 3.19). This electrum comprises 66% Au and 34% Ag (Le Couteur, 2012).  E-veins can be laterally extensive over several metres and may be associated with sericitic alteration of the surrounding rock. The paragenetic relationship of E-veins to other veins is uncertain, but considered to be the most peripheral and shallow-level time-equivalents of D3-veins. As yet, E-veins have only been identified in drill-core approximately 200 m vertically above the deep Raintree West porphyry deposit. They have been identified in outcrop (Young, 2012, personal communication) although their overall distribution and density is currently unknown.  The mineralogy, vein and associated breccia infill textures of the E-veins in the Whistler corridor are all typical of an intermediate-sulphidation (IS) epithermal style of mineralisation (Sillitoe, 2010). Although polymetallic massive sulphide E-veins were described at Rosario, Chile by Masterman et al. (2005) they are mineralogically and texturally different. E-veins at Whistler are similar to the Victoria veins associated with the Far-Southeast porphyry and Lepanto high-sulphidation (HS) magmatic-hydrothermal system in the Mankayan mineral district, Philippines (Claveria, 2001; Sajona et al., 2002). A detailed structural study of E-vein density in the Whistler corridor is recommended to determine if these IS ‘E-veins’ represent a significant Au-Ag resource. 3.4.8  Chlorite-muscovite veinlets (SC) SC-veins are very narrow (0.2 mm) veinlets of chlorite and muscovite and are rarely observed. These veins have only been identified petrographically (Figure 3.16a,b) due to their size and unobtrusive nature. Chlorite in SC-veins is elongate in the vein direction and muscovite forms radiating laths. These veinlets include a very strong sericite alteration halo with chloritisation of mafic minerals 1 cm either side. Few cross-cutting relationships have been observed for these veinlets. Figure 3.16a,b demonstrate an SC-veinlet cross-cutting an A-vein. It is possible that SC-veinlets are associated with the ubiquitous chlorite-sericite alteration found at Whistler. SC-veins are mineralogically similar to the SCC-alteration of Sillitoe and Gappe (1984).   64  3.4.9  Iron carbonate-dominant veins (FeCarb) FeCarb-veins comprise carbonate filled tension gashes, cross-cutting all M-, A-, B-, and D-veins. They are usually 2 – 15 mm wide and comprise ankerite or siderite. They are spatially associated with an iron carbonate alteration which partially replaces feldspar phenocrysts and groundmass with iron carbonate, and magnetite with hematite. These alteration zones are concentrated in densely veined zones, including the Au-Cu mineralised porphyry cores. This phenomenon is probably related to the structural weakness of these zones and associated increased permeability relative to the surrounding silicified phyllic alteration. FeCarb-veins and alteration is best identified in weathered outcrop or drill-core due to a distinctive yellow-orange-brown hue associated with Fe oxidation (Figure 3.16c,d). 3.4.10 Gypsum veins (G) G-veins comprise narrow planar to irregular 0.5 – 2 mm wide gypsum veins (Figure 3.16e,f). These cross-cut all M-, A-, B-, D-, and FeCarb-veins. These are best observed in hand sample, as the soft gypsum rarely survives the thin-section making process. G-veins probably represent remobilisation of sulphur in pyrite by meteoric fluids. 3.4.11 Calcite veins (C) Late planar calcite veins 0.5 – 3 mm wide are present across the Whistler corridor, and are likely unrelated to mineralisation. These cross-cut all M-, A-, B-, D-, and FeCarb-veins.  3.5  Hydrothermal breccias Several breccia types have been identified in the Whistler corridor. These include intermineral magmatic-hydrothermal and hydrothermal, late-stage hydrothermal, and tectonic breccias. Many breccias at Whistler and in the Whistler corridor are difficult to classify. Some of these may; have an intrusive or volcanic origin; be related to diatremes; involve multiple phases of brecciation; have a structural origin; and/or be strongly overprinted by alteration. These are typically described as ‘undifferentiated breccia’ in field observations. Breccias described in this chapter are hydrothermal (or magmatic-hydrothermal) in origin, and can be linked to specific phases in the paragenesis and alteration history of the Whistler magmatic-hydrothermal system.   65  3.5.1  Magnetite-chlorite-chalcopyrite intermineral hydrothermal breccia This breccia is not laterally extensive, having been found only in one drill-hole (WH07-02) over a few metres, near the magmatic-hydrothermal breccia described in Chapter 2.5.1. Similar to the main body of magmatic-hydrothermal breccia, it comprises brecciated mineralised diorite. It is polymictic, with clasts consisting primarily of diorite, locally veined, and quartz-vein fragments (Figure 3.18a,c,e). Clasts are typically subangular and not well endowed in chalcopyrite. The breccia matrix comprises an interesting assemblage of subhedral bladed magnetite, anhedral chalcopyrite interstitial to bladed magnetite, and anhedral masses of chalcopyrite (Figure 3.18b,d,f). This bladed magnetite is unusual and is rarely documented in porphyry deposits. The matrix transitions into zones dominated by anhydrite/gypsum, probably overprinting or as late open-space filling.     The presence of magnetite-chlorite-chalcopyrite in the breccia matrix is significant at Whistler for paragenetic reasons. Mineralised quartz-veins (A-, B-veins) consistently cross-cut magnetite (M-vein) and are thus paragenetically later. As this breccia has clasts of these quartz-veins and a magnetite matrix, this indicates an additional magnetite mineralising event after quartz veining. This suggests this breccia formed in an intermineral phase. Similarly to the magmatic-hydrothermal breccia described in Section 3.5.2, this magnetite breccia has mineralised quartz-vein clasts, a hydrothermal matrix, and is spatially associated with IMP intrusions thus it is classified as in intermineral breccia. The paragenetic relationship between this and the magmatic-hydrothermal breccia is unknown. However, as the magmatic-hydrothermal breccia is sericite-pyrite altered, and this type of alteration is associated with a later stage of paragenesis and fluid evolution, it is likely that this magnetite-chalcopyrite-chlorite intermineral hydrothermal breccia formed slightly earlier than the quartz-sericite-pyrite intermineral magmatic-hydrothermal breccia.  3.5.2  Quartz-sericite-pyrite intermineral magmatic-hydrothermal breccia This brecciated rock is associated with the highest grade of mineralisation at Whistler. It is brecciated mineralised diorite and is typically strongly sericite-pyrite±quartz altered. It is polymictic to monomict and the breccia matrix transitions on a cm-, to m-scale between quartz and  66  sericite-pyrite altered diorite. Clasts are angular to rounded and can comprise clasts of; diorite fragments; quartz-vein fragments; or veined diorite. Clasts are typically between 0.5 cm and 5 cm.  Where breccia matrix is siliceous, clasts are typically larger (up to 5 cm), more rounded, and monomict; diorite clasts (Figure 3.17a,b). These diorite clasts often contain truncated quartz (A-style) veins.  Where matrix comprises strongly phyllically altered diorite, clasts are smaller (1-2 cm), angular, and polymictic; diorite and quartz-vein clasts (Figure 3.17a,c,d) but are typically dominated by quartz-vein clasts. These quartz-vein clasts are often endowed with chalcopyrite and magnetite (Figure 3.17d,e). Where the concentration of quartz-vein clasts is densest, Au-Cu grade (especially Au) are the highest. It is not clear whether Au is also associated with pyrite in the strong sericite-pyrite altered matrix of these breccia zones, or just in the clasts. It is the variable nature of this breccia matrix that warrants the classification as a magmatic-hydrothermal breccia. As this breccia clearly post-dates quartz-vein mineralisation, but is itself strongly sericite-pyrite altered, it most have occurred during active hydrothermal activity and can thus be considered intermineral (Kirkham, 1971). Spatial correlation with IMP intrusions suggests that this intermineral breccia is associated with the intermineral phase of dioritic intrusion in the Whistler deposit. 3.5.3  Quartz-carbonate-pyrite-sphalerite-galena hydrothermal breccia This breccia has been observed to be spatially associated with the E-veins described in Chapter 3.4.7. Figure 3.19a demonstrates the spatial correlation with this breccia forming in direct contact with E-veins over a 2 cm interval dominated by sphalerite-galena. This breccia comprises sub-angular clasts of 0.2-3.0 cm (typically 0.3-0.5 cm) of sphalerite, pyrite, galena, carbonate, Mn-rich siderite, and chalcopyrite in a matrix comprising mostly quartz with wispy interstitial and also nebulous patches of sericite (Figure 3.19a,b,d). Electrum has been identified in inclusions within sphalerite and quartz (Figure 3.19c,d,f). This electrum comprises 66% Au and 34% Ag (Le Couteur, 2012). The dissociation of electrum and chalcopyrite in these base-metal rich breccias (and E-veins) is evident in the Cu:Au ratios, which  67  are much lower (<1000) than in the typical zones of M-, A-, and B-veined mineralisation (2000-5000) or magmatic-hydrothermal breccia (1000-4000). It is not clear whether these quartz-carbonate-pyrite-sphalerite-galena breccias represent brecciated E-veins or open-space filling associated with the same phase of mineralisation as E-veins. However, the mineralogical similarity indicates an indisputable genetic link with either D3-, or E-veins.  3.5.4  Tourmaline-pyrite breccia This breccia monomict, with angular, 0.2-5.0 cm clasts of diorite (Figure 3.20). In all cases, diorite clasts and associated wallrock are sericite-pyrite±quartz altered. The matrix of this breccia is dominated by tourmaline and pyrite with anhydrite possibly overprinting. This breccia type is most abundant on the western contact of the eastern sericite-pyrite-quartz altered LSP body in Figure 3.25 and 3.26, intersected in drill hole WH10-20.  Tourmaline-pyrite breccia is associated with D5-veins, both mineralogically and spatially as shown in Figure 3.20d. While cross-cutting relationships are not abundant, tourmaline-pyrite breccia is thought to be in association with D5-veining, and sericite-pyrite-quartz alteration associated with IMP and LSP dioritic intrusions.  The angularity and monomictic nature of clasts is notable compared to other hydrothermal breccias described above. This suggests these breccias formed explosively in-situ with little-to-no reworking of material. It remains unclear whether this hydrothermal breccia was formed by the exsolution and over pressuring of fluids from a rapidly-cooling LSP intrusive (eg. Skewes et al., 2003); or as a result of hydrothermal collapse associated with dissolution of feldspar-destructive phyllic hydrothermal fluids (eg. Sillitoe and Sawkins, 1971). It is clear that it is spatially associated with the emplacement of phyllically altered LSP, and genetically associated with D5-veining. 3.6  Structurally deformed rocks and tectonic breccia Faults are typically defined by three lithological types; fault gouge, sheared rock, or rock-flour breccias.  68  3.6.1  Fault gouge Fault gouge is marked by significant clay alteration and loss of rock strength. In drill-core this can be represented by loss of core, or by soft, spongy rock dominated by sticky clay. These structurally disrupted rocks have become a focus of fluid causing this significant clay alteration. Slickenlines/slickensides can be evident on some surfaces. 3.6.1  Sheared rocks Many structurally disrupted rocks are marked by a distinctive shear fabric (Figure 3.21). These are typically oblique to drill-core axis although fault orientations are often enigmatic.  In some cases, S- and C- fabrics typical of mylonite development are evident. Slickenlines/slickensides can be evident on some surfaces. 3.6.2  Rock-flour breccia Tectonically-derived breccia is associated with faulting. This breccia typically comprises angular to sub-angular monomictic wall-rock fragments in a very fine-gained rock-flour matrix. It can be matrix- or clast-supported, depending on extent of deformation. Where hydrothermal pyrite alteration overprints, rock-flour breccia is referred to as pyritic rock-flour breccia. In this case, breccia matrix comprises rock-flour, pyrite, sericite, and quartz (Figure 3.21c). In some cases, D-veins are observed to cross-cut pyritic rock-flour breccia. Rock-flour breccia is commonly associated with zones of fault gouge and/or sheared rock.    69      70  Figure 3.7  Potassic and sodic-ferric alteration.(previous page) (a) hand sample of potassic alteration at Raintree North. The strong hydrothermal magnetite mineralisation and k-feldspar wash of groundmass produce a typical potassic alteration texture, replacing groundmass more strongly than phenocrysts. Sample WH11-37-443m; (b) stained hand sample of potassic alteration at the Whistler discover outcrop. Note, K+ metasomatism is strongest in groundmass with very little phenocryst alteration. Pink hue is visible in small unstained section on the right of image. Sample 204; (c) hand sample of sodic-ferric alteration at Whistler. Textural “wash” is stronger than in potassic alteration, possible due to Na+ metasomatism of groundmass and phenocrysts. Sample WH07-04-254m; (d) hand sample displaying enigmatic feldspar-stable alteration. This sample has a pink hue of groundmass suggestive of potassic alteration but probe analyses of this sample shows Na+ introduction suggestive of sodic-ferric. Sample WH07-03-418m; (e) PPL thin-section view of an ex-amphibole phenocryst in potassic alteration. The “shreddy” texture suggests chlorite alteration is replacing hydrothermal biotite of a potassic assemblage. WH11-33-573m; and (f) XPL view of the same sample shows chlorite, calcite probably replacing hydrothermal bioite and k-feldspar groundmass with magnetite. Sample WH11-33-573m.  71     72  Figure 3.8  Phyllic and chlorite-sericite alteration. (previous page) (a) hand sample of quartz-sericite-pyrite alteration. Igneous textures including phenocrysts preserved here, but are often completely obliterated. Sample WH10-20-556m; (b) XPL image of quartz-sericite-pyrite alteration. Silica can be seen to form interstitial to sericitised feldspar, probably as a by-product of that metasomatism. Sample WH10-20-669m; (c) hand sample of a transitional zone between quartz-sericite-pyrite alteration and chlorite-sericite alteration. Pyrite is ubiquitous in this sample but becomes subordinate and eventually replaced by chlorite in chlorite-sericite alteration. Sample WH10-20-679m; (d) hand sample of chlorite-sericite alteration in otherwise unaltered rock. Note, sericitisation of phenocrysts and chloritisation of groundmass enhances the porphyritic appearance of this diorite. Sample WH10-19-531.6m; and (e) PPL image of same sample as (d) showing partial sericitisation of feldspar and complete chloritisation of amphibole. Sample WH10-20-692m; (f) “blotchy” chlorite alteration from near chlorite-sericite and phyllic transitional zone. Sample WH10-20-305m; and (g) PPL image of “blotchy” chlorite as in (f) made up of chlorite, quartz and sericite.                 73   Figure 3.9  Iron carbonate and propyllitic alteration.(a) hand sample with potassically altered diorite being overprinted by an advancing iron carbonate, here ankerite, alteration front. When freshly exposed, iron carbonate is difficult to identify in hand sample, but when weathered it becomes characteristically red-orange coloured. Sample WH11-030-748m; (b) iron carbonate alteration is spatially concentrated in zones of intense veining associated with mineralisation. This is likely due to the structural weakness of these zones for fluid permeability. Veins here show sequential overprinting M1, A1, B3 and D5 veins. Sample WH04-01-191.7m; (c) XPL image of same sample as (a) demonstrating carbonate replacement of groundmass and phenocrysts. Sample WH11-030-748m; (d) hand sample of chlorite-calcite-epidote-albite(?) altered rock of a propyllitic assemblage. Degree of albitic alteration uncertain although this sample demonstates an elevated geochemical Na abundance. Sample WH05-07-106m; (e) PPL image of chlorite and epidote groundmass replacement of same sample as (d) Sample WH05-07-106m; and (f) XPL image of chlorite, epidote, calcite, and possible alteration. Same sample as (d) and (e) WH05-07-106m.   74   Figure 3.10  M-veins. (a) hand sample showing sheeted magnetite M1-veinlets. These are cross-cut by a straight-sided quartz-magnetite-chalcolpyrite B1-vein, cross-cut by a later quartz vein, possibly late B-, or early D- stage vein, cross cut by a narrow pyrite D4-veinlet. Sample WH07-02-229.1m; (b) hand sample showing a relatively wide (0.4mm) wormy magnetite (M1/M2) vein with a weakly developed potassic halo in sodic-ferric / chlorite-sericite altered diorite. Sample WH07-02-216m; (c) PPL image of same samle as (a) above  showing sheeted whispy M1 veinlets have edges defined by individual magnetite crystals; (d) REF image showing inclusions of chalcopyrite in magnetite in an M-vein. Magnetite is slightly altered to hematite. Sample WH11-030-504.6m; (e) wormy M-, and A1 veinlets are cross-cut by B1 to B3 quartz veins. Sample WH07-01-266.5m; and (f) highly irregular wormy magnetite M1-veins with potassic halo are cross cut by a quartz-pyrite-chalcopyrite B3 vein. Sample WH07-03-418.5m.  75   Figure 3.11  A-veins. (a) hand sample of irregular wormy quartz-molybdenite(?). Sample WH11-33-487m; (b) PPL and REF image showing wormy irregular quartz-chalcopyrite veins with some pyrite. Hematite is present replacing magnetite in these veins. Same sample as (a) WH11-33-487m; (c) hand sample of stockwork of wormy irregular quartz veins. These A-veins cross-cut a magnetite M1-vein which is disrupted by a D2-vein which cross-cuts all. Colours artificially saturated to highlight veins. Sample WH11-34-243.4m; (d) hand sample of irregular wormy quartz-magnetite-chalcopyrite veins forming an irregular stockwork. A later D3 vein cross-cuts all wormy quartz A-veins. Sample WH11-30-674.3m; (e) PPL image of stockworked quartz-magnetite-chalcopyrite veinlets. NE-SW oriented vein has straighter edges than others, may be transitional to B1-vein. Sample WH11-34-221m; (f) XPL of same position as (e) showing porphyritic texture of rock and k-feldspar groundmass alteration.    76   Figure 3.12  B-veins. (a) hand sample of straight-edged quartz-pyrite-chalcopyrite B3-veins. These veins have centreline pyrite-chalcopyrite and appear to represent multiple phases of vein growth. Sample WH08-08-133m; (b) hand sample of stockworked quartz-pyrite-chalcopyrite B3-veins with centreline sulphides. Some minor A1-veinlets are cross-cut by B3-vein stockwork. Diorite is strongly albite(?)-magnetite and chlorite-sericite altered. Sample WH07-03-614m ; (c) hand sample of quartz-pyrite-chalcopyrite B3-vein cross-cutting and offsetting a quartz-pyrite A-vein in turn cross-cutting M1-veinlets. Diorite is albite-magnetite-epidote (propyllitic) altered. Sample WH11-037-424m; (d) hand sample of straight-edged quartz vein with transitional magnetite-to-pyrite B2-vein. This cross-cuts a stockwork of M- and A-veins. Diorite is K-feldspar-magnetite altered and replaced with Fe-carbonate, hematite and sericite. Sample WH11-034-245.9m;    77  Figure 3.12 (cont.) (e) hand sample showing unusual quartz-calcite-chalcopyrite-bornite-magnetite vein. The significant carbonate component suggests categorisation as a D-vein, however this vein has a significant component of magnetite and also bornite not associated with D-veins. A lack of phyllic halo (this vein has magnetite halo) suggests this vein has more characteristics of a B1-vein. Sample WH07-03-451m; and (f) PPL and REF image showing a centreline chalcopyrite-bornite in a quartz vein. This vein does not have characteristic straight-edges of a B-vein but does centreline sulphides. Sample WH07-03-418m.   Figure 3.13  D-veins: Quartz dominant. (a) HF etched hand sample of quartz-carbonate D2-vein with a quartz-sericite-pyrite alteration halo. Sample WH11-030-755.3m; (b) hand sample of a D2-vein cross-cutting some M/A1 magnetite and B3-veins with centreline pyrite. D2-vein comprises comb textured quartz-carbonate-pyrite with a strong pyritic halo. Sample WH10-019-712.6m;   78  Figure 3.13 (cont.) (c) hand sample of comb textured quartz-carbonate vein with sphalerite, galena and ankerite(?) cross-cutting B3-vein with centreline pyrite. Rock surrounding this D3-vein is strongly sericite-pyrite altered. Sample WH07-01-283m. d) hand sample of diorite with milkly white very fine-grained quartz-carbonate vein with zoned sphalerite. This D3-vein has much finer grained quartz and carbonate than (c) and also truncates a B3-vein with centreline pyrite. Sample WH07-04-175m; (e) XPL image demonstrating comb textured quartz on grain margins and calcite vein infill in a D2 or D3-vein. Sample WH11-030-674.3m; (f) REF image demonstrating how chalcopyrite blebs occur in streaks along cleavage lines within sphalerite in a D3-vein. Sample WH11-030-674.3.     Figure 3.14  D-veins: Pyrite dominant. (a) hand sample of pyrite-quartz D4-vein crosscutting magnetite M1-veinlets. Sample WH09-02-420m; (b) hand sample of pyrite (D4-vein) with possible tourmaline edges (D5-vein) truncated by a D3-vein. Suggests D4/D5 veining begun earlier than D3-veining. Sample WH10-020-370m; (c) hand samle of pyrite-tourmaline D5-veins cross-cutting earlier D1-veins. Sample WH07-01-254m; (d) XPL image of same sample as (c) showing pyrite-tourmaline D5-vein. This vein has a sericite (muscovite?) halo and is assoicated with quartz-sericite-pyrite alteration. Sample WH07-01-254m.   79   Figure 3.15  E-veins. (a) hand sample of spectacular open-space filling textured sphalerite-galena-quartz-carbonate vein. Sample WH11-030-269m; (b) hand sample of same sample as (a) showing crustiform and colloform textured sphalerite and comb-textured quartz and carbonate. Sample WH11-030-269m; (c) (© 2012 Kiska Metals Corp., by permission). PPL image demonstrating colour variations in crustiform and collorform banded sphalerite. Colour variation does not coincide with major compositional variation. Sample WH11-030-269m. Image modified from Le Couteur (2012); (d) (© 2012 Kiska Metals Corp., by permission). REF image demonstrating crustiform banding of galena, carbonate, sphalerite, and intergrown quartz-pyrite. Sample WH11-030-269m. Image modified from Le Couteur (2012).     80   Figure 3.16  Late veins. (a) SC-veinlet. PPL and REF image of a chlorite-muscovite veinlet cross-cutting a quartz-magnetite A1-veinlet. These SC-veins may be associated with sericite-chlorite alteration although SC-veins have only been identified petrographically. Sample WH07-02-311m; (b) SC-veinlet. XPL image of same area as (a) shows high birefringence muscovite. Sample WH07-02-311m; (c) Fe-Carb vein. Hand sample showing Fe-carbonate vein cross-cutting earlier M-, and D-veins associated with Fe-carbonate groundmass alteration. Sample WH11-030-602m; (d) Fe-Carb vein. Hand sample showing narrow carbonate veinlet cross-cutting earlier M-veins and associated with a 2-3cm halo of Fe-carbonate alteration. Plagioclase phenocrysts are strongly altered to a green sericite. Sample WH04-01-236.7m; (e) G-veins. Hand sample showing gypsum veins cross-cutting M-, and A-, veins. Sample WH07-04-254m; and (f) G-veins. PPL (above) and XPL (below) images of a gypsum vein. Note vein-perpendicular bladed gypsum. Parts of the vein were lost in the thin-section production as in common with G-veins from Whistler. Sample WH10-20-305.5m.  81   Figure 3.17  Magmatic-hydrothermal breccia. (a) hand sample image demonstrating ambiguous nature of this breccia. Left portion of this image shows sericite-pyrite altered diorite clasts in a siliceous matrix transitioning into fragmental quartz-vein clasts in a strongly sericite-pyrite altered igneous(?) matrix. This ambiguity leads to the classification of this breccia as magmatic-hydrothermal. This 2m interval has 3.01 ppm Au, although it is not clear whether Au is associated with chalcopyrite in quartz or pyrite in diorite. Sample WH07-02-432.5m; (b) hand sample of hydrothermal breccia with sub-rounded diorite clasts with truncated quartz-veins in a quartz-dominant matrix. This sample is from the same brecciated body as (a). Sample WH07-02-436.9m; (c) hand sample showing quartz-vein and diorite clasts in an sericite-pyrite dominated matrix. Quartz fragments include centreline sulphides confirming their vein-related origin. Sample WH07-01-216m; (d) REF image demonstrating nature of sulphide distribution in magmatic-hydrothermal breccia. Chalcopyrite is primarily restricted to quartz-vein fragments and pyrite to the breccia matrix. Same sample as (a) WH07-02-432.5m; and (e) REF image demonstrating overprinting sulphide growth within a quartz-vein clast. Chalcopyrite-magnetite is overgrown by later pyrite. Same sample as (c). Sample WH07-01-216m.  82   Figure 3.18  Magnetite-chlorite-chalcopyrite hydrothermal breccia. All images from sample WH07-02-411m (a) hand sample of hydrothermal breccia showing altered diorite clasts and fragmented quart-vein clasts in a magnetite-rich matrix; (b) PPL and REF image showing breccia matrix comprising magnetite-chalcopyrite-chlorite. Note bladed habit of magnetite; (c) XPL image showing polymictic clasts including quartz (with and without sulphides) and quartz-sericite±pyrite altered diorite; (d) REF image demonstrating bladed magnetite habit with intergrown chalcopyrite in breccia matrix; (e) XPL image demonstrating quartz-veins, possibly A-veins, in quartz-sericite altered diorite clasts are truncated by breccia matrix; and (f) PPL and REF image at same position as (e) demonstrating magnetite-chlorite-chalcopyrite matrix components.   83   Figure 3.19  Quartz-carbonate-pyrite-base metal hydrothermal breccia. (© 2012 Kiska Metals Corp., by permission). (a) hand sample demonstrating the spatial correlation between E-veins and these base-metal hydrothermal breccias. Breccia zone separated from epithermal-textured E-veins by 1-2 cm of sphalerite-galena. Sample WH11-30-269m; (b) hand sample of typical quartz-Mn-siderite-pyrite-sphalerite-galena breccia zone. Sample WH11-30-280m; (c) REF image of electrum as inclusions with chalcopyrite within sphalerite. Samle WH11-30-280m; (d) REF image magnified of area highlighted in (c) showing form of electrum; (e) REF image of chalcopyrite, pyrite, sphalerite, and deformed galena together in breccia. Sample WH11-30-280m; and (f) BSE image of electrum and sphalerite within quartz in breccia matrix. Sample WH11-30-280m. Images (b,c,d,e) from Le Couteur (2012).    84   Figure 3.20  Tourmaline-pyrite hydrothermal breccia. (a) hand sample showing sharp contact from sericite-pyrite-quartz altered diorite into monomictic angular clast-supported tourmaline-pyrite breccia. Sample WH10-20-506m; (b) hand sample of tourmaline-pyrite breccia cross-cutting and disrupting a pyrite vein with sericitic halo (D1/2-vein). Sample WH10-20-596.2m; (c) hand sample of tourmaline-pyrite breccia transitioning into pseudobrecciated tourmaline-pyrite D5-veins. Sample WH10-20-578.7m; (d) PPL and REF image of a zone of tourmaline-pyrite breccia; Sample WH10-20-578.7m; and (e) XPL of same area as (d) showing breccia matrix to include altered diorite fragments as well as tourmaline and pyrite, and is overprinted by anhydrite. Sample WH10-20-578.7m.   85   Figure 3.21  Faults and structurally disrupted rocks. (a) hand sample demonstrating a shear fabric exhibiting minor folds in a fault zone. Sample WH11-33-196.8m; (b) hand sample demonstrating S- and C- mylonitic fabric in a fault zone. Sample WH11-36-480m;  (c) hand sample showing a 15 cm interval of rock-flour breccia with pyrite truncating and off-setting a quartz vein, but being cut by a pyrite D4-vein. In this case this structure formed interminerally, between A/B veining and D4-veins. Sample WH07-04-55m; and (d) hand sample of rock-flour and pyritic matrix breccia with clasts of andesite/diorite and siltstone. A quartz-carbonate-base metal vein is present, possibly as a partial open-space infill. This suggest this faulting may have occured synchronously with quartz-carbonate-base metal veining. Sample WH11-33-471m.    86  3.7  Mineralisation  Mineralisation associated with the WIS is dominated by porphyry-style Au-Cu with some indication of distal epithermal-style base-metal veins with Au-Ag. Porphyry mineralisation occurs at the Whistler deposit, as well as the Raintree West, Raintree North, Raintree South, Rainmaker, and Round Mountain prospects. There are indications of porphyry mineralisation also at Snow Ridge and Dagwood prospects.  Porphyry-style mineralisation display the same style of alteration and vein paragenesis in all instances, although specific phases of ‘mineralised diorite’ (MSP, IMP, LSP) have only been identified in the Whistler Deposit. This suggests a common genetic link between the different deposits although they are spatially separated by lithic sandstone and facies of the volcanic package. No geologic connection has been observed between the deposits at surface or in drill core. Magnetic 3-D inversion models suggest that all dioritic bodies may represent separate cupolas sourced from a common batholith approximately 1 km below surface (Figure 3.22). This is likely the common link between porphyry deposits associated with the WIS. ‘Mineralised diorite’ intrusions and Whistler, Raintree North and Raintree West occur simultaneously ca. 76.4 ± 0.3 Ma (Chapter 8) substantiating a genetic link. 3.7.1  Whistler deposit The Whistler deposit is located on the Western edge of the Whistler Corridor. It comprises a dioritic intrusive body hosted by ‘lithic sandstone’. The diorite type is ‘mineralised diorite’ as described in Chapter 3.2 and includes Main-stage (MSP), Inter-mineral (IMP), and Late-stage (LSP) porphyry phases. The intrusive body is approximately 1.6 km long and 1.25 km wide, elongated in a NNW direction (Figure 3.23). It has steep westward to near-vertical plunge. Deep drilling below 700 m below surface has failed to locate the bottom of the ‘mineralised diorite’ although Au and Cu grades appear to slightly diminish at these depths. The summary of the Whistler deposit given here is primarily based on the geology outlines in Figures 3.23, 3.24, 3.25, 3.26, and 3.27.  87   Figure 3.22  Aeromagnetic 3-D inversion model of the Whistler Corridor. (© 2011 Kiska Metals Corp., by permission). Facing north. This model predicts a batholith approximately 1 km below the surface with porphyry mineralisation associated with several cupolas. No drilling has tested the prospectivity of this batholith although the deepest drilling of diorite bodies at Raintree West (~700 m below surface) are mineralised. After Roberts (2011).  3.7.1.1  Main-stage porphyry (MSP): geometry, alteration, mineralisation The MSP diorite is the most volumetrically significant intrusive phase of the Whistler deposit. It is also the most significant host of Au and Cu mineralisation. The core of the MSP exhibits feldspar-stable alteration (potassic and sodic-ferric) with hydrothermal magnetite and occasional hydrothermal biotite. These alteration assemblages are associated with M-, A-, and B- veins (Chapter 3.4) hosting chalcopyrite and magnetite associated with Cu and Au mineralisation. The introduction of hydrothermal magnetite in this alteration assemblage bequeaths this zone a significant magnetic anomaly. The potassic and sodic-ferric mineralised core of the MSP is invariably overprinted by a chlorite-sericite assemblage (Figure 3.24).  Mineralised MSP grades into peripheral feldspar-destructive sericite-pyrite±quartz (phyllic) altered MSP. This is associated with D- veins. These individual veins can be mineralised (chalcopyrite, sphalerite, galena); however, the phyllic zone is poorly mineralised as a whole.  88  Pyrite is a major component (5-10%) of this phyllic alteration and this zone is a significant sulphur and geophysical resistivity and chargeability anomaly.  The transition between feldspar-stable and feldspar-destructive alteration zones of MSP has distinctive characteristics. This transitional zone is significant as it marks the edge of the mineralised core of the porphyry system, and thus has vectoring implications for exploration. These characteristics can include;  (1) chlorite and pyrite alteration of mafics, or transitional phases between each on a metre scale (Figure 3.8c);  (2) ‘blotchy’ 2-8 mm chlorite-rich blebs (Figure 3.8f,g);   (3) molybdenum values ≥20ppm over a few metres at this transition (Figure 3.27) A combined chlorite and pyrite alteration association is really transitional between sericite-pyrite±quartz and chlorite-sericite alteration assemblages. However, in the MSP chlorite-sericite almost ubiquitously overprints the feldspar-stable potassic and sodic-ferric assemblages. Thus this transition can represent a proxy for a transition between feldspar-stable and phyllic alteration. The ‘blotchy’ chlorite alteration actually comprises fine-grained quartz, chlorite, carbonate and sericite. This style of alteration has not been extensively observed, but is present on the eastern side of the deposit in MSP in drill-hole WH10-20 (Figure 3.8f,g). These ‘blotches are hypothesised to represent texturally destructive silica liberation associated with sericitisation of feldspar, as occurs in phyllic alteration, but without adequate sulphur for the formation of pyrite. This leaves a locally texturally destructive ‘bleb’ of chlorite, quartz and sericite.  The molybdenum anomalies in this transition zone are enigmatic. Rare molybdenite has been observed with magnetite in M- veins, with pyrite and sphalerite in D- veins, and anomalous Mo values have been recorded by field-based portable XRF analyses of glassy quartz veins (A3) considered transitional between A- and B- veins. It is not currently well established how this molybdenum anomaly relates to the paragenesis but is suggested here that A3 veins are spatially restricted to this zone.   89  3.7.1.2  Inter-mineral porphyry (IMP): geometry, alteration, mineralisation Chapter 3.2.3.4 describes generally the diagnostic characteristics of the IMP and emphasises that it can be difficult to distinguish from MSP. It can exhibit the same style of alteration and veining as MSP. The primary method of identification of IMP as distinct from MSP is the presence of xenoliths, including mineralised MSP diorite and quartz-vein fragments, or the intrusive cross-cutting of veins in MSP.  Figure 3.25 shows the distribution of IMP in cross-section. This shows two IMP bodies located in the centre of the main MSP body. These may in fact represent one IMP intrusive body with an intermediary brecciated zone. This brecciated zone comprises the high-grade magmatic-hydrothermal breccia described in Chapter 3.5.2. This spatial correlation with the breccia suggests a genetic link. At depth, IMP becomes more difficult to differentiate from MSP. It is possible that higher-level IMP is a late upwards injection of lower-level MSP syn-mineralisation in a high-temperature ‘mushy’ diorite.   One historical report (Franklin, 2007) suggests a large body of IMP on the north-eastern flange of the main MSP body, but no evidence for this was found in this study. It is possible that weakly mineralised peripheral MSP has previously been mistakenly identified as IMP. Future studies should prioritise the delineation of IMP bodies, as they may have a genetic relationship with high-grade magmatic-hydrothermal brecciation. 3.7.1.3  Late-stage porphyry (LSP): geometry, alteration, mineralisation Chapter 3.2.3.5 describes generally the diagnostic characteristics of the LSP. A lack of mineralisation and sharp chilled-contacts are the diagnostic feature of this intrusive body. Figure 3.25 demonstrates the position of LSP bodies within the Whistler deposit. LSP has not been identified elsewhere in the deposit however it is likely more widespread than indicated in the map of Figure 3.23. On the eastern LSP occurrence the contact between LSP and MSP is marked by a zone of tourmaline matrix breccia (Figure 3.20) described in Chapter 3.5.4. LSP is typically strongly sericite-pyrite altered and this grade-destructive alteration can be seen to strip MSP-hosted mineralisation either side of the LSP body on the eastern side of the deposit in Figure 3.25. Future  90  studies should prioritize the delineation of LSP bodies, as they are grade-destructive and thus affect resource models and estimation. 3.7.2  Raintree North Raintree North is a ‘pencil porphyry’ style of deposit located 2.2 km northeast of the Whistler deposit. The deposit does not crop out at surface and is obscured by 40-50 m of glacial till. It is defined by a ~50-100 m diameter circular diorite pipe plunging down at approximately 50° towards the northeast. A 565 m southwest-northeast cross-section through the Raintree North deposit from 6,872,300 mN, 520,700 mE to 6,872,700 mN, 521,100 mE is shown in Figures 3.28 and 3.29. This diorite pipe narrows vertically closer to surface. Internal chilled-margin contacts within the diorite body suggest multiple phases of diorite intrusions, although these have not been defined. The diorite body intrudes the volcanic package, including andesite and volcanic breccia.  The diorite body exhibits strong feldspar-stable alteration including potassic and sodic-ferric alteration. It includes Whistler-style porphyry mineralisation including M-, A- and B- vein stockworks. This central mineralised zone is overprinted by chlorite-sericite alteration which extends into the surrounding volcanic package  approximately 100 m. Sericite-pyrite alteration extends further into the volcanic package at least approximately 250 m. Significantly, this pyritisation extends further from the diorite body than in the Whistler deposit itself (≤200 m). This suggests that the local volcanic package has a greater fluid permeability than the ‘lithic sandstone’ host of Whistler. Metal zonation is typical of Whistler-style Au-rich porphyry mineralisation. The Au-Cu zone is represented by the core of the system and is mostly restricted to the diorite body. As the diorite pipe narrows nearer to surface, Au-Cu mineralisation extends beyond the diorite into the volcanic package. Au-Cu grade is controlled by the distribution of M-, A-, and B-veins. Fringing the Au-Cu zone is a halo of Mo with 20-50 ppm Mo occurring on both shoulders of the diorite body.  Pb-Zn occurs on the periphery of the Au-Cu zone, partially coincident to the Mo zone but also extends in an intermittent manner to a distal position at least 200 m from the diorite body. Pb-Zn mineralisation is also sporadically present in the Au-Cu zone. This Pb-Zn distribution  91  represents the distribution of sphalerite and galena in D3-veins, cross-cutting the M-. A-, and B- veins controlling Au-Cu and Mo distribution. This is representative of metal zonation in the Whistler Corridor (see Section 3.7.5). For more information regarding specific drill-hole intersections, assay results and exploration methods at Raintree North see Roberts (2011). 3.7.3  Raintree West Raintree West is a large, structurally disrupted, porphyry deposit on the western edge of the volcanic package, approximately 1800 metres east of the Whistler deposit. It comprises two zones of porphyry-style mineralisation; a deep (≥450 m), larger, body unconstrained at depth, and a smaller, near-surface, likely structurally controlled body. A NW-trending regional structure, the Alger Peak fault subdivides deposits and this, and associated splays, are the likely cause of the structural disruption and enigmatic geometry of Raintree West. Geologic relationships at Raintree West are poorly understood but best summarised by Roberts (2011). The deep zone of mineralisation is the most volumetrically significant. It has a lateral extent of approximately 300 by 300 metres and is open at depth. At its shallowest point it is 470 metres below the surface, making it a very deep target. Mineralisation is truncated by a fault on the western margin, and by a later-phase of diorite on the eastern margin. The deposit is open at depth. The near-surface zone of mineralisation trends northwest and comprises a 250 m long by 150 wide lenticular body of diorite. It is coincident with an aeromagnetic high anomaly. This near-surface porphyry mineralisation is likely to be fault-controlled as it is truncated by a fault zone (Figure 3.21a) on its eastern margin. In both cases, mineralisation is of a Whistler porphyry-type character. M-, A-, and B-style veins are hosted by feldspar-stable (potassic and sodic-ferric) altered diorite and overprinted by a chlorite-sericite assemblage. Peripheral sericite-pyrite±quartz alteration is associated primarily with D-veins including base-metal assemblages. Probable syn- and post-mineralisation structural  92  disruption has complicated the alteration zonation at Raintree West. However, the general patter is constant with Whistler and Raintree North. Drilling the great depth to the main Raintree West porphyry has provided the opportunity to evaluate the stratigraphy of the volcanic package, as well as view the most distal, and shallow, effects of this magmatic-hydrothermal system. This is the primary area of study for the descriptions given in Chapter 3.2.2. However, there was little-to-no success in correlating volcanic facies between drill-holes suggesting a complex, laterally heterogeneous volcanic package, representing highly dynamic volcanism. Approximately 200 m above the main porphyry mineralisation significant E-vein mineralisation occurs over an approximately 20 metre interval. This represents a potential target for intermediate-sulphidation epithermal style of mineralisation (Chapter 3.7.6). For more information regarding specific drill-hole intersections, assay results and exploration methods at Raintree West see Roberts (2011). 3.7.4  Other deposits Other positively identified porphyry-style deposits of the Whistler corridor include Raintree South, Rainmaker, Dagwood, and Round Mountain. These are described by Roberts (Roberts, 2011) in detail and a brief overview is provided here. The locations of these deposits are indicated in Figure 3.2 and 3.22. Raintree South, similar to Raintree North, is a 100 metre wide “pencil-porphyry”. Hosted by a diorite pipe, it plunges to the NNE. It is hosted by the volcanic package including volcanic breccias and pyroxene-phyric andesite. Strong sericite-pyrite alteration of these volcanic rocks includes up to 15% pyrite forming a semi-circular IP chargeability halo around the porphyry. Au-Cu mineralisation is associated with M-, A-, and B-veins with feldspar-stable and magnetite alteration. However, vein density and Au-Cu grades are less significant than Raintree North. Rainmaker is another probable “pencil-porphyry” approximately 100 metres in diameter. The overall geometry of Rainmaker is not well constrained due to structural disruption and faulting. This faulting is controlled by northwest-trending faults similar to those in the Raintree  93  West area. Au-Cu mineralisation is associated with M-, A-, and B-veins with feldspar-stable and magnetite alteration. Dagwood is the only prospect lacking definitive porphyry-style mineralisation. However, is defined by a 1.5 km wide chargeability high and aeromagnetic low, donut surrounding a 650 m wide chargeability low. The limited drilling done has intercepted sericite-pyrite altered diorite with glassy quartz vein stockworks and B-style quartz veins with sulphide centrelines. These veins carry 20-50 ppm Mo, as well as elevated Ag-Pb-Zn. This is similar to the peripheral Mo halo present on the margins of all other porphyry occurrences in the Whistler corridor, and the Whistler deposit itself. Dagwood thus remains an underexplored porphyry target. 3.7.5 Metal zonation  In all porphyry deposits of the Whistler Corridor a distinct metal zonation is evident. Figure 3.27 demonstrates how this metals are distributed in the Whistler deposit. An inner zone of Au-Cu represents the main phase of porphyry-style mineralisation. Copper sulphides with electrum inclusions (Section 3.7.7) are hosted by magnetite and quartz veins (M-, A-, B-). Directly on the periphery of the Au-Cu zone, a discrete zone 10’s of metres wide hosts anomalous Mo (>20 ppm). This Mo is found in very fine-grained molybdenite in glassy quartz (A3-) veins. Peripheral to, and overprinting the Au-Cu and Mo zone is sporadic Pb and Zn. This represents galena and sphalerite hosted within D3-veins.   3.7.6  Epithermal-style mineralisation and Au deportment As mentioned in Chapter 3.6.3 an intersected zone approximately 25 metres wide and 200 metres above Raintree West was intercepted by WH11-030m. This zone contained significant epithermal-style carbonate-sphalerite-quartz-galena-pyrite veins containing significant gold-silver mineralisation. Carbonate can be Fe- and/or Mn-bearing and is commonly subordinate to sphalerite. These E-veins exhibit comb, crustiform, banded and breccia infilling textures over this interval (Figures 3.15 and 3.19).  The interval from 260.8 m to 285.4 m in WH11-030 contains 0.56 ppm Au, 64.8 ppm Ag, 8.2% Zn and 3.8% Pb. Electrum was identified as inclusions, along with chalcopyrite, within  94  sphalerite in a brecciated portion of this E-vein interval (Figure 3.15c,d). This electrum comprises 66-73% Au and 27-34% Ag (Le Couteur, 2012).  The mineral assemblage and texture of these veins is characteristic of intermediate-sulphidation epithermal veins (Sillitoe, 2010) such as the Victoria veins associated with the Lepanto high-sulphidation and Far-Southeast porphyry deposit in the Philippines (Claveria, 2001). These E-veins represent the shallow level (<1 km paleodepth) counterparts to the D3 veins described in Chapter 3.4.5 (Sillitoe, 2010).  Although intermediate-style mineralisation has been observed above Raintree West, and in at least one outcrop (Young, 2012, personal communication) they have not been a focus of exploration to date.  3.7.7  Gold deportment at Whistler  Previous workers have identified electrum as inclusions within chalcopyrite as the primary host of Au and Ag associated with the Whistler deposit. Petersen (2004) describes electrum only being found within chalcopyrite in the centres of quartz-veins. Electrum inclusions range in size from 2-16 µm (Figure 3.30a). This electrum is 77% Au and 23% Ag by weight (Petersen, 2004), Electrum was also identified as an 8 µm inclusion of chalcopyrite in a quartz-vein with magnetite and bornite (Proffett, 2009). This electrum was identified petrographically (Figure 3.30b). This previous work substantiates the empirical observations that high Au grades are coincident with zones of dense A-, and B-, quartz-veins.  95   Figure 3.23  Lithologic map of the Whistler deposit at 1:8000. Coordinates are in the UTM Zone 5 NAD83 grid system. Map is primarily interpreted from IP, drill-core, and sparse outcrops under glacial till and tundra. Cross-section A-B in Figure 3.25. Sample locations given are for some samples discussed in the text.  96    Figure 3.24  Alteration map of the Whistler deposit at 1:8000. Coordinates are in the UTM Zone 5 NAD83 grid system. Map is primarily interpreted from magnetic, IP, drillcore, and sparse outcrops under glacial till and tundra. Cross-section A-B in Figure 3.25. Sample locations given are for some samples discussed in lithological descriptions.    97   Figure 3.25  Lithologic cross-section A-B of the Whistler deposit.. Scale is 1:8000. Question marks indicate uncertainty, notably with the IMP intrusions at depth. AuEQ indicates the relative grade and indicates where the majority of Cu-Au mineralisation occurs, in the central zones of the MSP intrusive body with highest grades in the magmatic-hydrothermal breccia. IMP intrusives can be unmineralised or weakly mineralised, especially in quartz-vein xenoliths at the margins. LSP is typically unmineralised.     98   Figure 3.26  Alteration cross-section A-B of the Whistler deposit. Scale is 1:8000. Late-stage porphyry intrusions are typically sericite-pyrite-quartz altered. Intermineral intrusions are similar to main-stage porphyry at depth but become sericite-pyrite-quartz altered  nearer to surface and associated with magnatic-hydrothermal breccia. Core of main-stage porphyry intrusion is altered to either albite-magnetite or k-feldspar-magnetite and overprinted by chlorite-sericite alteration. Peripheries of MSP intrusion are sericite-pyrite-quartz altered, as is surrounding sandstone.      99   Figure 3.27  Metal zonation cross-section A-B of the Whistler deposit. Scale is 1:8000. Core of the deposit hosts bulk of the Au-Cu zone, with the highest grades being in the magmatic-hydrothermal breccia, also host to Mo. Periphery of the deposit is marked by a Mo  halo . Zn-Pb occurs distal to the deposit, but also cross-cuts Au-Cu in late-stage D3-veins.    100    Figure 3.28  Lithologic cross-section of the Raintree North deposit.Scale is 1:4000. Facing northwest. Diorite pipe dips approximately 50° to the northeast. Diorite pipe becomes narrower nearer surface. Au-Cu porphyry mineralisation is proxied and indicated by the relative Cu grade. Porphyry mineralisation extends beyond the diorite pipe nearer to surface. Host volcanic package includes flows, sub-volcanic dykes/sills, and volcanic conglomerate. No correlations of these units were successful between drill-holes.       101     Figure 3.29  Alteration cross-section of the Raintree North deposit.Scale is 1:4000. Facing northwest. Feldspar stable-alteration includes sodic-ferric and potassic and is host the porphry-style mineralisation. Feldspar-stable alteation extends slightly beyound diorite pipe evident in Figure 3.28. This is flanked by an anomalously high Mo zone over severl metres akin to the Whistler deposit as shown in Figure 3.27. Feldapr destructive phyllic alteration flanks both sides of mineralisation. Chlorite-sericite alteration overprints feldspar-stable assemblages.   102    Figure 3.30  Gold deportment in porphyry-style mineralisation of the Whistler deposit. (© 2009 Kiska Metals Corp., adapted with permission). (a) SEM image identifying Au as electrum  as an inclusion in chalcopyrite. Magnification on left is 500x. Large electrum grain is 16 µm. Image from Petersen (2004); and (b) PPL and XPL image of a quartz vein (possible A-vein) with electrum inclusion of chalcopyrite. This vein also contains magnetite (m) and bornite (b). Modified from Proffett (2009).    103  4 Whole-Rock Geochemistry  4.1  Introduction Characterising igneous rocks by evaluating whole-rock geochemistry has been revolutionary in the understanding of geological processes (e.g., Goldschmidt, 1923; Turekian and Wedepohl, 1961) and was later instrumental in understanding plate tectonics (e.g., Dickinson, 1970; Jakesˇ and Gill, 1970). In order to chemically distinguish different major rock types and their lithotectonic origins, major elements ratios are sufficient (e.g., total alkali verses silica diagram). There are a number of situations when major elements are insufficient; where different igneous suites are geochemically similar, including different phases of intrusive activity from the same source; or where secondary metasomatism, such as hydrothermal or seafloor alteration has significantly changed the bulk major element composition. In the Whistler Corridor, both of these situations are applicable, and so trace element geochemistry is applied. Certain trace elements are well-suited for distinguishing primary igneous lithogeochemistry. These elements are typically immobile in hydrothermal alteration. Elements include Al, Ti, Zr, Nb, Y and the rare-earth elements (REEs) (Pearce and Cann, 1973; Pearce and Norry, 1979; MacLean and Kranidiotis, 1987; MacLean and Barrett, 1993). Historically, most of these elements have been difficult to analyse due to instrumental limitations leading to poor precision. Modern methods such as X-ray fluorescence (Johnson et al., 1999) and ICP-MS (Jenner et al., 1990; Eggins et al., 1997)  have enabled an extremely high degree of precision. The trace elements mentioned here are used to evaluate the different igneous phases of the Whistler Corridor. The metasomatism that inhibits primary igneous geochemical characterisation can be chemically characterised using major elements. Evaluating mass transfer in the hydrothermal alteration of porphyry deposits has been conducted since the early 1960’s (Creasey, 1959; Hemley and Jones, 1964). Many studies since then (e.g., Ford, 1978; Taylor and Fryer, 1980; Carten, 1986; Arancibia and Clark, 1996; Ulrich and Heinrich, 2002) have evaluated the mass gain/loss of rocks having undergone a particular alteration assemblage compared to a least-altered sample. By this  104  methods, the whole-rock metasomatism associated with each alteration assemblage in the Whistler Corridor is characterised. There are two primary objectives for conducting an evaluation of whole-rock geochemistry in the Whistler Corridor. The first objective is to evaluate the lithogeochemical characteristics of different igneous phases to determine distinct geochemical traits that may be associated with mineralising intrusive phases. The second objective is to evaluate the effect of metasomatism, in the form of hydrothermal alteration, on whole-rock geochemistry.  For both of these objectives, major, trace and rare element analyses are necessary and examined herein.  4.2  Methods 4.2.1  Sample collection and processing Samples were collected and analysed over two field seasons (2011-2012). Thirty-three samples were collected from field outcrops and drill core. Care was taken when preparing samples to avoid oxidised or otherwise weathered rock, and veins were preferentially cut out where possible.  All samples represent Whistler Igneous Suite (WIS) rocks. Samples include; twenty variably altered diorite samples from the Whistler deposit (nineteen core samples, one outcrop), two moderately strongly potassically altered diorites from Raintree North (core) and one strongly potassically altered diorite from Raintree West (core). There are four samples of unmineralised, younger (Chapter 8) and relatively unaltered, diorite bodies from near Whistler and across the Whistler Corridor. These four samples were taken from outcrop. There are three samples of volcanic rocks from the Whistler Corridor. Two of these, taken from core, exhibit strong chlorite-sericite and clay alteration. The third volcanic rock, taken from core, sourced directly adjacent to Raintree North mineralisation exhibits moderate sericite-pyrite alteration. There are three samples from basaltic andesite dykes (one from core and two from outcrop). These dykes have chlorite, calcite and clay alteration.  The twenty samples taken from Whistler diorites exhibit a range of alteration types and intensity. Of the three potassically altered samples; 1021602 and 73418 exhibit weak K-feldspar-magnetite, overprinted by chlorite-sericite alteration. Sample 204B shows stronger K-feldspar- 105  magnetite overprinted by chlorite-sericite and pyrite. Four samples (72246, 1019696, 74254, 72311) exhibit moderate magnetite alteration, ubiquitously overprinted by chlorite-sericite. Sample 72246 also comprises significant secondary biotite. Two samples (05REC07106/05REC07107) collected from a southern extension of Whistler diorite exhibit chlorite-sericite-calcite-epidote (propyllitic) alteration of weak to moderate strength. The seven samples having sericite-pyrite±quartz±calcite alteration are classified as phyllic according to Lowell and Guilbert (1970). These samples vary in alteration intensity significantly. Samples 1020692, 74326, 1020556, 1020661 and 1020669 are all sourced from the eastern periphery of the Whistler deposit, and all show very strong, texturally destructive quartz-sericite-pyrite-calcite and chlorite alteration. Sample 73172 has moderately strong quartz-sericite-pyrite-calcite alteration. Sample 1019521 has moderately strong chlorite and seritie-pyrite-quartz alteration. Sample 1019531 is similar to 1019521, but has stronger chlorite-sericite alteration and weaker quartz-sericite-pyrite alteration. Samples 1019521 and 1019531 represent a transition zone between chlorite-sericite alteration and quartz-sericite-pyrite alteration. Samples 1020305 and 1020318 show moderate chlorite-sericite alteration overprinting weak quartz-sericite-pyrite and also represent chlorite-sericite to quartz-sericite-pyrite transition zone. Sample 72285 exhibits weak chlorite-sericite and calcite alteration of a late-stage porphyry diorite. A summary of the alteration mineralogy of samples is included in Table 4.1 and petrographic descriptions given in Appendix B. 4.2.2  Analytical methods Analyses were conducted by ALS Chemex in North Vancouver, BC, Canada. A known standard was included in both stages with similar results both times matching known values. The following methods were employed: base metals by 4-acid digestion, whole rock (major element) by ICP-AES, remaining 37 element (trace and REE) by ICP-MS, total S and C by LECO induction furnace with Loss-on-ignition (LOI) at 1000°C. Data presented in Table 4.1 has been recalculated for major elements, including C and S, to total 100% thus excluding LOI. Raw geochemical data, precision calculations (Thompson, 1988) and QAQC analyses are presented in Appendix C.  106  4.3  Observations: overview The geochemical data for all samples are presented in Table 4.1. Major elements are measured in weight percent (%) and trace elements parts-per-million (ppm). The major element composition, presented in %, is recalculated without LOI to 100%. Total C and S is presented independently of LOI. The raw data presented in Appendix C includes total LOI. The major element data presented in Table 4.1 is summarily displayed in Figure 4.1.The overall statistical information is presented in this section.  SiO2 composition varies from 55-65% with an interquartile range (IQR) between 57.5 and 60.8% and a mean of 59.5%. Al2O3 has an IQR of 16.3 to 17.8% and mean of 16.9%. Fe2O3 has an IQR of 5.4 to 8.5% with a mean of 7.0%.  MgO has an IQR of 1.6 to 2.4% and a mean of 2.0%. CaO has an IQR variation between 4.4 and 6.3% with a mean of 5.3%. Na2O has an IQR of 3.1 to 5.2% and a mean of 4.2%. K2O has an IQR of 1.2 to 2.6% and a mean of 2.0%. Total C has an IQR of 0.3 to 1.1% and a mean of 0.8%. Total S has an IQR of 0.1 to 2.1% with a mean at 1.2%. Both C and S have a greater range of values in the upper quartile data giving an asymmetric distribution. Less abundant TiO2 has an IQR 0.61 to 0.85% and a mean of 0.77%. MnO has an IQR between 0.06 and 0.17% with a mean of 0.15% and P2O5 has an IQR of 0.20 to 0.31% with a mean at 0.26%. LOI values have an IQR of 2.9 to 4.8%, a mean of 4.1% and an upper quartile extending to 7.1%.  This compositional variation is evident in the Harker (1965) diagrams of Figure 4.2. Comparisons of Fe2O3, MgO and CaO with SiO2 display a weak negative correlation. This correlation is weak due to significant scatter of data, discussed below. Within these trends, basaltic andesite dykes exhibit higher Fe2O3, MgO and CaO than most diorite samples. This suggests this unit is more mafic than the diorites. In general, a negative correlation is to be expected with these elements as part of a normal fractionation trend. Similarly, K2O and Na2O should exhibit a positive correlation with SiO2 as part of a fractionation trend. This is poorly demonstrated in the data.   107  In the following sections, observations and discussions are presented for the following categories;  (1) Major element primary igneous geochemistry (2) Major element secondary metasomatic geochemistry (3) Trace element geochemistry   Figure 4.1  Tukey diagram displaying major element compositional for all samples . Solid box represents 50% of data, with the upper and lower limits representing the upper and lower quartiles respectively. The line in the box is the median and the circle the mean. The whiskers represent the limit of data except for the outliers. Hollow circles represent outliers at least 1.5 x (UQ-LQ).   4.4 Major element primary igneous geochemistry  4.4.1 Observations In order to best characterise the primary chemical characteristics of these rocks, it is prudent evaluate the characteristics of the least-altered samples. Diorite samples (mineralised diorite) from the Whistler deposit, Raintree West, Raintree North always exhibit alteration while those from elsewhere in the Whistler Corridor (unmineralised diorite) are usually unaltered.   108  Six samples were selected that best represent the least-altered diorites from the Whistler Corridor. These are three ‘unmineralised diorite’; 209, 211, 212 and three chlorite-sericite altered samples from Whistler; 1019531, 72285, 1020318. The fourth sample from ‘unmineralised’ diorite, 220, exhibits ambiguity regarding primary lithology and may have a hypabyssal or volcanic origin (Appendix B). Sample 220 is thus excluded from the ‘unmineralised’ diorite characterisation.   Least altered diorites of the Whistler Corridor have a mean SiO2 composition of 60.45% (σ=0.47). Al2O3 is 17.46% (σ=0.28). Fe2O3 is 6.20% (σ=1.02). MgO is 2.22% (σ=0.28). CaO is 5.44% (σ=0.62).  Na2O is 4.32% (σ=0.52). K2O is 1.82% (σ=0.59). TiO2 is 0.75% (σ=0.07). MnO is 0.12% (σ=0.05). P2O5 is 0.25% (σ=0.02). The C mean content is 0.46% (σ=0.43) but significantly lower in just the unmineralised samples (xˉ=0.09, σ=0.07). The S mean content is 0.61% (σ=0.94) but significantly lower in the unmineralised samples (xˉ=0.01, σ=0.01). These totals have been recalculated to 100% excluding LOI. LOI has a mean value of 3.87% (σ=1.94) but is also lower in the unmineralised samples (xˉ=2.35% σ=0.61). The three samples from basaltic andesite dykes have a mean SiO2 composition of 55.61% (σ=0.45). Al2O3 is 17.72% (σ=0.28). Fe2O3 is 9.03% (σ=0.64). MgO is 3.56% (σ=0.20). CaO is 6.21% (σ=0.83).  Na2O is 4.50% (σ=0.56). K2O is 0.64% (σ=0.22). TiO2 is 1.23% (σ=0.22). MnO is 0.18% (σ=0.02). P2O5 is 0.35% (σ=0.03). The C mean content is 0.83% (σ=0.28). The S mean content is 0.13% (σ=0.12). These totals have been recalculated to 100% excluding LOI. LOI has a mean value of 5.11% (σ=0.64). The basaltic andesite dykes have less silica, and more iron, magnesium, titanium and calcium than least-altered diorites.  The three samples of intermediate volcanic rocks have a mean SiO2 composition of 57.02% (σ=1.43). Al2O3 is 17.80% (σ=1.80). Fe2O3 is 6.57% (σ=0.64). MgO is 1.51% (σ=0.31). CaO is 8.34% (σ=2.39).  Na2O is 1.58% (σ=1.38). K2O is 2.08% (σ=0.82). TiO2 is 0.94% (σ=0.06). MnO is 0.34% (σ=0.34). P2O5 is 0.30% (σ=0.04). The C mean content is 1.43% (σ=0.77). The S mean  109  content is 2.08% (σ=3.52). These totals have been recalculated to 100% excluding LOI. LOI has a mean value of 6.62% (σ=3.35). The volcanic rocks sampled here have less silica, magnesium and sodium, but more iron, calcium and potassium than least-altered diorites. Individual sample data can be plotted on a total alkalis verses silica (TAS) plot as shown in Figure 4.3. Overall these data show significant scatter. The least-altered six fall within the high alkali, high silica portion of the diorite field. One sample of unmineralised diorite (220) from the eastern Whistler Corridor exhibits a chemical character similar to the volcanic package. All other diorite samples show scatter due to alteration, discussed below.  Basaltic andesite dykes fall in the high alkali low silica portion of the diorite field, which corresponds with the basaltic andesite to basaltic trachyandesite field of the volcanic TAS diagram. The intermediate volcanic rocks sampled show greater variance although fall in the basaltic andesite to andesite fields of the volcanic TAS diagram.  The alkali-iron-magnesium (AFM) diagram in Figure 4.4 also exhibits scatter. Samples generally straddle the tholeiite/calc-alkalic boundaries of Kuno (1968) and Irvine and Baragar (1971). The least altered diorite samples fall in the calc-alkalic field. The basaltic andesite dykes also fall in the calc-alkalic field, albeit with greater iron and magnesium content. The volcanic rocks fall in the tholeiitic field, chiefly due to low magnesium content.   110  Table 4.1  Whole-rock geochemical data for all samples.  Alteration mineralogy is simplified, see Appendix B (petrography) for more details. Major elements are recalculated with C and S extracted from raw LOI data and total major elements and LOI at 100%. Raw data, including location information is in Appendix C. Trace elements are presented in ppm.    Sample Locality Lithology Alteration SiO2 Al2O3 Fe2O3 CaO MgO Na2O K2O TiO2 MnO P2O5 C S Cu LOI TotalUnits % % % % % % % % % % % % % % %201 Whistler Andesite dyke wk chl-ser-calc 55.1 17.87 8.31 6.34 3.74 5.14 0.67 1.06 0.18 0.33 1.15 0.05 0.01 5.84 100202 Whistler Andesite dyke wk chl-ser-calc 55.7 17.40 9.23 6.96 3.59 4.22 0.40 1.30 0.20 0.34 0.63 0.07 0.01 4.88 1001019750 Whistler Andesite dyke chl-ser 56.0 17.90 9.54 5.32 3.34 4.14 0.83 1.35 0.17 0.39 0.71 0.27 0.01 4.62 100101039 S Orbit Andesite volc. chl-ser-clay 57.7 17.93 7.22 9.00 1.16 3.09 1.29 0.88 0.12 0.32 1.30 0.01 0.01 5.62 100101052 S Orbit Andesite volc. chl-ser-clay 55.4 19.54 5.94 10.34 1.71 1.25 2.04 0.96 0.18 0.33 2.25 0.09 0.01 10.36 100209 West Orbit Diorite fresh; wk chl-ser 60.7 17.34 6.77 4.66 2.39 4.36 2.46 0.78 0.16 0.25 0.09 0.02 0.00 1.77 100211 West Orbit Diorite fresh; wk chl-ser 60.5 17.45 6.58 5.81 2.44 3.74 2.11 0.78 0.16 0.26 0.17 <0.01 0.00 2.98 100212 West Orbit Diorite fresh; wk chl-ser 60.8 17.39 6.67 5.46 2.50 3.87 2.10 0.80 0.15 0.26 0.02 <0.01 0.00 2.30 100220 East Orbit Diorite chl-ser-clay? 57.5 17.80 8.15 7.46 2.75 3.13 1.41 0.84 0.19 0.32 0.27 0.17 0.00 3.16 1001134091 RTN Andesite volc. ser-py-qtz 58.0 15.93 6.55 5.69 1.67 0.39 2.92 0.99 0.74 0.26 0.74 6.14 0.00 3.88 1001134221 RTN Diorite ksp-ser-mgt-chl-calc 61.2 15.09 7.55 4.41 1.33 4.38 3.29 0.78 0.35 0.31 0.95 0.34 0.15 3.64 1001137443 RTN Diorite ksp-mgt-chl-ser-qtz 55.0 15.47 13.29 2.72 1.46 4.20 5.85 0.93 0.30 0.32 0.25 0.21 0.06 2.19 1001133573 RTW Diorite ksp-mgt-chl-ser-calc-bt? 57.7 14.66 10.30 4.58 2.24 4.32 3.38 0.86 0.35 0.30 0.71 0.61 0.16 3.58 100204 B Whistler Diorite ksp-mgt-chl-ser-clay? 57.1 16.31 10.25 3.59 2.37 5.33 3.29 0.81 0.17 0.28 0.52 0.01 0.11 3.66 1001019696 Whistler Diorite qtz-ser-py-chl-calc 57.8 16.36 7.95 6.95 2.33 5.88 0.79 0.85 0.07 0.33 0.63 0.09 0.15 3.87 1001021602 Whistler Diorite ksp-mgt-chl-ser-anh 60.3 17.77 4.95 5.21 2.32 5.63 1.79 0.65 0.03 0.19 0.02 1.12 0.05 2.95 1001019521 Whistler Diorite qtz-ser-py-chl-clay 62.4 17.83 3.56 4.53 1.94 4.67 1.25 0.72 0.04 0.29 1.14 1.60 0.03 4.75 1001019531 Whistler Diorite qtz-ser-py-chl-clay 60.6 17.52 4.52 6.37 1.91 4.64 1.19 0.72 0.04 0.26 0.90 1.34 0.01 7.05 10074254 Whistler Diorite mgt-chl-ser-py-qtz-ksp? 56.7 15.85 8.45 6.80 1.41 5.18 1.46 0.60 0.07 0.20 0.73 2.54 0.13 3.93 10074326 Whistler Diorite qtz-ser-py-calc 63.9 16.31 3.85 4.60 0.94 4.15 2.06 0.57 0.08 0.16 1.27 2.14 0.00 2.79 10072246 Whistler Diorite mgt-bt-carb-qtz 57.5 14.59 9.36 6.34 1.86 5.76 0.80 0.49 0.05 0.16 0.65 2.42 0.08 5.62 10072285 Whistler Diorite chl-ser-calc-qtz 60.7 16.83 7.23 4.92 1.84 4.15 2.11 0.83 0.11 0.24 1.02 0.07 0.00 4.83 10072311 Whistler Diorite mgt-chl-ser-qtz-calc 59.9 16.34 8.55 3.35 2.20 5.33 1.67 0.74 0.05 0.25 0.38 1.22 0.27 3.78 10073172 Whistler Diorite qtz-ser-py-calc 61.7 17.07 5.35 4.16 1.71 2.34 1.91 0.68 0.06 0.20 1.22 3.61 0.00 2.85 10073418 Whistler Diorite ksp-mgt-chl-ser 60.1 16.76 8.75 3.05 1.67 7.35 0.79 0.56 0.04 0.20 0.10 0.69 0.03 2.68 1001020692 Whistler Diorite chl-ser-qtz-pyrite 63.1 16.68 5.36 4.46 1.47 2.93 2.65 0.55 0.13 0.17 0.98 1.51 0.04 3.60 1001020669 Whistler Diorite qtz-ser-py-calc 59.8 16.29 6.17 4.82 0.97 3.08 2.96 0.53 0.11 0.15 1.16 3.98 0.00 - 1001020661 Whistler Diorite qtz-ser-py-calc-chl-tour 64.8 17.06 4.26 3.55 1.67 3.15 2.54 0.58 0.09 0.17 1.12 0.98 0.04 4.15 1001020556 Whistler Diorite qtz-ser-py-calc 64.2 16.65 3.85 3.27 1.50 3.44 2.90 0.55 0.07 0.22 1.23 2.07 0.00 2.29 1001020318 Whistler Diorite chl-ser-qtz-calc-py 59.5 17.63 5.42 5.38 2.24 5.15 0.97 0.62 0.06 0.21 0.60 2.20 0.03 4.28 1001020305 Whistler Diorite qtz-ser-chl-calc-py 60.9 17.80 5.61 5.57 2.89 2.48 1.76 0.65 0.09 0.24 1.15 0.89 0.01 7.12 1005REC07106 S Whistler Diorite chl-ser-calc-epi 60.8 17.87 5.74 5.37 1.84 5.28 1.70 0.73 0.17 0.31 0.15 0.01 0.00 4.22 1005REC07107 S Whistler Diorite chl-ser-calc-epi 60.0 17.75 5.76 5.58 1.65 5.12 2.35 0.72 0.15 0.30 0.58 <0.01 0.00 5.19 100 111  Table 4.1 (cont)     Sample As Cr Co Ni Ga W Mo V Nb Sb Ta Sn Hf Zr Zn Sc Cu Tb U Lu Se Er Bi Y Hoppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm201 3.1 10 20 7 19.4 3 1 196 13 0.28 0.8 1 3 105 122 n/a 60 0.54 1.24 0.26 0.4 1.7 0.05 16.9 0.61202 2.4 20 20 10 22.9 3 1 255 26.3 0.91 1.7 2 5.1 180 111 n/a 53 0.98 1.91 0.48 1 3.25 0.03 31.4 1.091019750 15.4 30 21 20 22.2 1 <1 209 22.5 1.46 1.3 1 4.1 167 118 n/a 64 0.87 1.86 0.41 0.8 3 0.03 29.1 1.07101039 1.1 10 14 6 19.1 1 <1 135 16.2 3.92 1 1 3.3 139 84 n/a 85 0.53 2.09 0.26 0.3 1.73 0.02 17.3 0.63101052 1 10 21 7 19.5 <1 <1 98 16.6 1.17 1 1 3.4 142 101 n/a 70 0.54 2.22 0.26 0.3 1.78 0.03 17.7 0.66209 2.2 30 13 14 20.3 167 <1 155 18.9 0.56 1.8 1 3.7 163 94 n/a 48 0.56 2.31 0.3 0.5 1.99 0.1 19.4 0.69211 0.5 20 12 12 20.1 2 <1 115 18.9 0.08 1.1 1 3.8 162 103 n/a 39 0.56 2.22 0.32 0.5 1.98 0.05 19.2 0.69212 1.6 20 14 14 18.8 1 <1 113 17.9 0.07 1.1 1 3.5 152 100 n/a 39 0.52 2.07 0.28 0.5 1.8 0.02 18.2 0.64220 5.8 10 16 8 20.8 3 <1 120 20.6 0.21 1.2 1 4.1 178 43 n/a 20 0.63 2.11 0.32 0.4 2.19 0.03 21.7 0.771134091 4.2 20 15 7 20.2 1 <1 126 22 0.39 1.5 6 4.6 170 1345 8 13 0.66 2.13 0.32 9.2 2.36 0.47 22.8 0.761134221 0.8 10 8 <1 22.3 1 15 88 28.7 0.63 1.7 4 5.2 200 222 5 1530 0.73 2.59 0.36 1.1 2.61 0.1 22.8 0.81137443 1.6 10 13 3 21.8 2 23 124 27.9 0.43 2.4 3 5.4 190 280 7 577 0.82 2.22 0.4 1.2 3.08 0.08 27.7 0.961133573 3.6 20 16 4 21.2 4 56 93 18.5 0.56 1.2 5 4.2 170 861 7 1560 0.55 3.05 0.3 1.2 1.91 0.34 20 0.69204 B 1.2 10 20 2 21.5 8 3 164 23.1 0.49 1.4 5 4.1 149 327 n/a 1145 0.65 2.45 0.32 0.6 2.05 0.29 19.6 0.731019696 2.1 <10 1 3 20.8 2 1 137 22.8 0.77 1.2 5 3.3 143 61 n/a 1450 0.6 1.83 0.28 1.2 1.95 1.33 19.2 0.71021602 0.8 10 10 3 19.3 <1 11 100 15.6 0.26 0.7 1 2.5 107 50 n/a 484 0.29 1.29 0.14 0.6 0.93 0.04 9.6 0.341019521 10.3 <10 8 3 19.9 1 7 94 20.8 0.18 1.1 8 3.2 140 38 n/a 296 0.54 1.97 0.23 1.1 1.53 0.65 15.3 0.551019531 1.2 10 4 3 19.2 1 <1 77 20.6 0.36 1.1 2 3.1 139 67 n/a 131 0.5 1.77 0.21 0.5 1.5 0.09 15.5 0.5774254 0.9 20 6 7 18.4 1 12 111 13.6 0.61 0.6 3 2.5 90 89 7 1285 0.31 1.29 0.14 1 1.04 0.2 9.1 0.3274326 20.8 10 9 4 21.3 1 2 72 23 0.41 1.2 1 4.2 170 27 4 32 0.44 3.33 0.23 1.1 1.56 0.05 13.4 0.4672246 0.4 10 6 6 18.1 <1 1 94 12.7 0.83 0.7 1 2.4 90 63 5 784 0.28 0.56 0.11 0.5 0.87 0.18 8.1 0.2872285 1.6 20 8 5 22 1 2 107 25.3 1.14 1.3 1 4.3 170 87 6 6 0.58 3.2 0.26 0.5 1.98 0.57 17.6 0.6372311 2 10 16 7 21.9 1 5 114 18.1 1.02 0.9 2 2.7 100 61 8 2730 0.37 1.13 0.15 1.6 1.19 0.98 10.3 0.3673172 4.8 30 16 16 19.6 1 1 104 14.9 0.67 0.9 2 3.1 120 41 7 22 0.38 1.78 0.17 2.5 1.24 0.99 11.3 0.4173418 1.6 10 12 6 20.6 <1 1 108 14.5 0.78 0.7 1 2.6 100 104 8 321 0.32 0.94 0.14 0.5 1.04 0.09 9.8 0.351020692 128 <10 <1 <1 20 1 <1 61 23.8 1.53 1.2 1 3.8 164 34 n/a 366 0.43 3.25 0.23 0.4 1.46 0.04 14.9 0.521020669 24.6 <10 30 1 15.6 2 <1 49 21.7 0.51 1.1 1 3.4 153 120 n/a 5 0.33 2.47 0.2 10.3 1.14 0.66 10.9 0.371020661 15.1 <10 2 1 22.4 9 <1 70 24.1 0.34 1.2 1 3.8 169 175 n/a 364 0.44 3.83 0.24 0.5 1.51 0.29 14.7 0.531020556 5.6 <10 9 <1 18.6 1 <1 61 23.6 0.36 1.2 <1 3.6 161 43 n/a 2 0.4 3.11 0.21 1.3 1.35 0.17 13 0.471020318 2.3 10 26 5 18.5 2 25 104 16.1 0.33 0.7 1 2.4 107 76 n/a 256 0.32 1.74 0.15 7.2 1.03 0.26 10.5 0.371020305 0.7 10 10 5 18.8 1 4 111 16 0.2 0.7 5 2.5 107 70 n/a 147 0.28 1.78 0.14 0.3 0.96 0.12 10.3 0.355REC07106 0.4 <10 10 1 19.4 1 <1 90 21.6 0.19 1.2 1 3.5 150 83 n/a 17 0.51 2.29 0.24 0.4 1.64 0.01 16.9 0.65REC07107 0.2 <10 10 2 19.5 1 <1 90 21.1 0.16 1.1 1 3.4 146 85 n/a 18 0.52 2.35 0.24 0.4 1.64 0.01 16.8 0.59 112  Table 4.1 (cont) Sample Pr Gd Ce Th Yb Ag Cd Tm Sm Nd Pb Dy La Eu Hg Tl Sr Ba Rb Cs Teppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm201 4.39 3.69 33.8 3.31 1.72 <0.5 <0.5 0.26 3.93 18.1 9 3 16.7 1.21 0.1 <0.5 750 910 23.8 7.06 0.01202 7.27 6.24 56.5 5.06 3.22 <0.5 <0.5 0.48 6.68 29.7 4 5.57 27.6 1.71 0.013 <0.5 1300 244 10.4 2.05 0.011019750 6.61 5.71 51.2 4.7 2.67 <0.5 <0.5 0.43 6.03 25.8 18 5.12 25.1 1.81 0.056 <0.5 597 224 22.1 4.68 0.01101039 5.24 3.6 42.7 5.14 1.6 <0.5 <0.5 0.26 4.31 20.4 4 3.05 21.6 1.22 0.022 1.3 692 548 63.1 16.2 <0.01101052 5.43 3.79 44.2 5.31 1.64 <0.5 0.5 0.26 4.51 21.4 8 3.13 22.2 1.23 0.159 2.2 518 321 90.8 28.8 <0.01209 5.79 3.84 48.4 5.7 1.82 <0.5 <0.5 0.28 4.43 21.9 13 3.29 25.1 1.29 0.031 <0.5 775 757 86.4 2.84 0.01211 5.69 3.79 47.2 5.83 1.86 <0.5 <0.5 0.29 4.38 21.4 9 3.25 24.8 1.35 0.024 <0.5 641 717 72.3 2.82 0.01212 5.35 3.44 44.6 5.24 1.73 <0.5 0.5 0.27 4.24 20.2 17 3.04 23.6 1.23 0.015 <0.5 622 701 67.2 1.73 0.01220 6.76 4.35 56.4 5.9 2 <0.5 <0.5 0.31 5.1 25.6 6 3.73 28.6 1.48 0.014 <0.5 673 518 47.1 1.3 0.011134091 5.74 4.66 45.1 5.53 2.12 0.9 6.2 0.34 4.86 24.6 439 3.62 24 1.32 0.451 3.3 198.5 547 127 8.75 0.081134221 6.56 5.13 53.8 9.38 2.22 <0.5 0.8 0.36 5.67 28.4 24 3.95 25 1.59 0.061 0.8 467 368 102.5 3.55 0.011137443 6.2 5.65 49.2 6.65 2.77 <0.5 <0.5 0.45 5.78 26.9 14 4.62 23 1.47 0.006 0.9 271 1100 169 1.46 0.011133573 5.92 3.81 50 6.3 1.9 1.9 4.9 0.31 5.3 23.9 127 3.31 25.2 1.31 0.036 1.2 434 752 119.5 1.8 0.02204 B 5.38 4.35 43.6 7.59 1.96 1.3 0.5 0.3 4.85 21.9 20 3.52 24.4 1.12 0.417 0.8 538 950 65.6 3.07 0.071019696 5.81 4.13 45.4 6.1 1.71 0.5 <0.5 0.28 4.88 22.8 4 3.41 21.3 1.4 0.171 <0.5 816 225 16.1 5.62 0.51021602 2.91 1.96 23.8 2.88 0.86 <0.5 0.5 0.13 2.46 11.4 9 1.65 12.5 0.74 0.025 <0.5 914 448 74.8 1.68 0.011019521 8.91 3.7 75.9 6.41 1.39 <0.5 <0.5 0.22 5.67 31.2 8 2.94 39.3 1.56 0.512 0.8 559 154 86.2 10.75 0.841019531 6.65 3.57 56.2 5.98 1.35 <0.5 <0.5 0.21 4.88 24.6 7 2.76 31.4 1.31 0.024 0.6 748 256 54.3 7.43 0.0474254 2.49 2.26 20.2 2.85 0.9 0.6 <0.5 0.13 2.33 10.8 9 1.63 10.5 0.85 0.045 0.8 1250 893 63.8 5.47 0.0474326 4.38 3.06 38.5 6.31 1.44 <0.5 <0.5 0.22 3.54 17.8 8 2.4 20.8 1.07 0.172 0.9 526 260 81.4 9.13 0.3972246 2.53 2.15 20.4 3.2 0.72 <0.5 <0.5 0.11 2.3 11.2 7 1.48 10.2 0.73 0.091 <0.5 1305 1530 37.4 4.22 0.0372285 5.16 4.07 43.6 6.33 1.75 <0.5 <0.5 0.29 4.5 21.4 13 3.19 22.6 1.58 0.01 0.7 569 528 81 7.73 <0.0172311 3.04 2.65 24.6 4.41 0.95 0.7 <0.5 0.15 2.9 13.4 7 1.87 12.6 0.84 0.082 0.5 532 287 49.5 2.54 0.2273172 3.91 2.93 32.5 4.39 1.05 <0.5 <0.5 0.17 3.28 16.6 18 2.05 16.3 1.22 0.173 1.3 456 485 91.6 10.7 0.3473418 2.72 2.28 22.1 3.04 0.9 <0.5 <0.5 0.14 2.41 11.5 7 1.72 10.7 0.76 0.171 <0.5 864 351 32.4 2.5 0.011020692 4.84 2.79 41.3 6.13 1.38 0.6 <0.5 0.21 3.57 17.7 5 2.43 23.1 1.42 0.044 1.1 392 1690 135.5 7.84 0.051020669 4.81 2.06 42 5.41 1.22 <0.5 0.8 0.17 3.11 17.5 38 1.81 22 0.97 0.241 1.3 279 945 149.5 8.92 1.741020661 5.08 2.94 43.9 6.23 1.45 0.6 0.6 0.23 3.79 18.7 10 2.48 23.3 1.37 0.128 1.1 433 1905 116 8.75 0.391020556 4.12 2.72 34.9 6.12 1.28 <0.5 <0.5 0.2 3.25 15.4 15 2.32 19.6 0.94 0.286 1.2 425 1580 113.5 8.57 0.291020318 3.52 2.19 29.7 2.96 0.95 <0.5 <0.5 0.15 2.77 13.4 25 1.85 16 0.92 0.025 0.6 824 539 36.2 5.99 0.071020305 2.66 1.84 22.6 2.97 0.92 <0.5 0.5 0.15 2.15 10.3 5 1.59 12 0.73 0.051 1.6 624 454 93.6 12.7 0.025REC07106 6.09 3.5 51.9 6.14 1.5 <0.5 <0.5 0.24 4.5 22.4 10 2.9 28.9 1.32 0.047 <0.5 1080 862 59.7 1.32 0.015REC07107 5.99 3.53 51.5 6.02 1.47 <0.5 <0.5 0.24 4.57 22.6 15 2.95 28.5 1.34 0.03 <0.5 1150 939 88.1 2.74 <0.01 113    114  Figure 4.2  Harker (1965) diagrams for all samples. (previous page) Samples have been colour coded to represent lithology and symbol shape represents alteration, indicated in the key. Vertical and horizontal axes are in weight %. Weak fractionation trends are evident in Fe2O3, MgO, CaO, K2O and Na2O however significant scatter is present. Late andesite dykes display a distinctively more mafic character than the diorites. The highest silica values are associated with phyllic alteration. Highest Na2O values with sodic-ferric alteration. Highest K2O values with potassic alteration. The highest C valuses are associagted with carbonate alteration. Highest S values with pyrite (phyllic alteration) or anyhydrite/gypsum. The highest LOI values are associated with strong chlorite-sericite-clay alteration with probable weathering.    Figure 4.3  Total alkalis and silica diagram. Unmineralised and weakly chlorite-sericite altered diorite samples fall in the diorite field. A significant spread of data are evident. Most notable are the relatively low alkali and high silica content of the phyllically altered diroites (SPADs). High alkali samples are typically potassic or sodic-ferric altered. Rocks of the intermediate volcanic package and late andesitic dykes have intermediate chemistry albeit less alkalic or silicic than the diorites.  115           Figure 4.4  AFM diagram showing general calc-alkalic affinity of the samples. Least altered diorites exhibit a calc-alkalic character. Samples exhibiting tholeiitic tendencies have been affected by alteration. Andesite dykes and intermediate volcanic package rocks have a higher Fe and Mg, lower alkali, albundance than diroites. Blue and red lines are calc-alkaline/tholeiite discrimination lines of Irvine and Baragar (1971) and Kuno (1968) resepectively     116  4.4.1 Discussion Six samples of diorite were selected to represent the least-altered diorite composition in the Whistler Corridor. These included three least-altered (weakly chlorite-sericite altered) from mineralised (MSP and LSP) from the Whistler deposit, and three relatively unaltered samples from unmineralised diorite. These six all exhibit similar major element geochemical compositions. The six samples chosen to reflect least-altered diorites are not completely unaltered. They all display some degree of sericitisation (eg. Figure 4.5a-d). The samples from the ‘unmineralised’ diorite are the least altered, usually with minor sericitisation and relatively unaltered amphibole (Figure 4.5a,b). The three chlorite-sericite altered samples selected from ‘mineralised’ diorite were included in order to ensure that the major element composition of ‘mineralised’ diorite was incorporated into the broad characterisation of WIS diorites. These three samples show variable degrees of sericitisation, and some chloritisation and carbonate alteration of amphibole (Figure 4.5c,d). They are, however, the least altered of samples from diorites from the Whistler deposit. The six least-altered diorites used to represent the diorite composition in the Whistler Corridor are compared to average diorite compositions of LeMaitre (LeMaitre, 1976). In general, WIS diorite has higher silica, aluminium, and sodium. WIS diorite has less iron, calcium, magnesium, and titanium than average diorite values. Potassium exhibits average values. For these reasons, WIS diorite could be considered a high-Si, high-Na, low-Ca intermediate intrusive rock.  The high Na and K, and low Ca (Table 4.1 and discussed above) suggests a possible low-Ca plagioclase. Petrographically derived extinction angle studies suggests andesine (An30-50) composition is typical. This is supported by mineral chemistry (Chapter 5) which suggests a mean CaO value of 7.04% and mean Na2O value of 7.32% for igneous plagioclase. Additive molar CaO, Na2O and K2O concentrations are in excess of molar Al2O3 for: unmineralised and least-altered diorites; least-altered basaltic andesite dykes; and intermediate volcanic rocks. Thus all sampled igneous rocks in the Whistler Corridor are metaluminous. Eight samples with a peraluminous signature are phyllically altered with depleted Na2O and CaO content due to sericitisation of feldspar.  117   Figure 4.5  Petrographic images of selected geochemistry samples. (a) PPL image of ‘unmineralised’ diorite shows only slight incipient sericitic/carbonate alteration of  plagioclase phenocrysts and groundmass, but otherwise unalterd. Sample 209; (b) PPL image of ‘unmineralised’ diorite shows only slight incipient sericitic/carbonate alteration of  plagioclase phenocrysts and groundmass, but otherwise unalterd. Sample 209; (c) PPL image of chlorite-sericite alterated ‘mineralised’ diorite. Amphibole has been completely replaced by chlorite. Sample 1019531; (d) XPL of same sample as (c). Sericite alteration of plagioclase is obvious here; (e) PPL image of strong quartz-sericite-pyrite alteration. Sample 1020669; (f) XPL image of same sample as (e) showing strong sericitisation and pyritisation of phenocrysts and complete groundmass replacement by quartz and sericite.     118  The three samples from the basaltic andesite dykes are relatively unaltered. They exhibit minor seritisation, chloritisation, and carbonate alteration (Figure 3.5c,d). The volcanic package rocks are more strongly altered. Samples 101039 and 101052 are quite strongly chloritised, sericitised and clay and carbonate altered (Figure 3.4). The carbonate alteration may be represented by the relatively elevated CaO values in these volcanic rocks. The third volcanic rock 1134091 is a strongly sericitised and pyritised andesite from Raintree North. This sample has low Na2O, CaO and MgO, and high K2O and S values. This is likely due to the replacement of ferromagnesium minerals (Mg, Fe) with pyrite (Fe, S), and plagioclase (Na, Ca) with sericite (K). The low MgO values due to alteration cause the intermediate volcanic rock to fall into the tholeiitic field of the AFM diagram in Figure 4.4, this is an alteration effect.   4.5  Major element secondary metasomatic geochemistry 4.5.1  Observations The data presented in Figures 4.1, 4.2, 4.3, and 4.4 demonstrate significant compositional variation amongst diorite samples. This is despite most samples being of intermediate composition and from igneous rocks with a common source. The dominant controlling factor of this variation is metasomatism associated with hydrothermal alteration. The hydrothermal minerals that represent this metasomatism are described in Table 4.1.  Figure 4.6, an alteration plot of Davies and Whitehead (2006) shows molar ratios of Na/Al and K/Al demonstrating aluminosilicate associated with alteration. Sodic-ferric altered diorite show albite-muscovite (sericite) alteration. Only one potassically altered diorite shows trend towards plagioclase/K-feldspar alteration, the others show a mixture of albitic and potassic alteration. Quartz-sericite-pyrite altered diorites show a trend towards muscovite alteration, with some clay alteration. Chlorite-sericite altered diorites show a weak alteration to albite, muscovite and/or clays. Volcanic package rocks show trend towards clay alteration. Basaltic andesite dykes show trend towards sericite/clay alteration.  In Figure 4.7 samples have been grouped into their dominant alteration assemblages and major element compositions are compared. It is important to evaluate how specific element  119  mobility is associated with specific types of alteration in order to understand the nature of these alteration types. The following observations are evident in Figure 4.7. 4.3.3.1  Silica (SiO2) Silica mean concentration in unmineralised samples is 60.67% with little variance (n=3; σ=0.14). In chlorite-sericite (n=5; xˉ=60.81%; σ=1.05) and chlorite-sericite-epidote-calcite alteration (n=2; xˉ=60.44%; σ=0.56) this is essentially unchanged, although there is greater variance. Quartz-sericite-pyrite alteration typically has elevated silica (n=8; xˉ=61.66%; σ=2.83) although can be depleted and thus has significant variance. Potassic (n=5; xˉ=58.26%; σ=2.53) and sodic-ferric (n=4; xˉ=58.55%; σ=1.69) alteration demonstrate depleted silica concentrations with significant variance. 4.3.3.2  Alumina (Al2O3) Aluminium mean concentration in unmineralised samples is 17.39% with little variance (n=3; σ=0.05). In chlorite-sericite (n=5; xˉ=17.52%; σ=0.41) and chlorite-sericite-epidote-calcite alteration (n=2; xˉ=17.81%; σ=0.08) it is slightly elevated and there is greater variance in chlorite-sericite. Quartz-sericite-pyrite alteration typically has depleted alumina (n=8; xˉ=16.54%; σ=0.40) with significant variance. Both potassic (n=5; xˉ=15.86%; σ=1.23) and sodic-ferric (n=4; xˉ=15.89%; σ=0.94) alteration demonstrate significantly depleted alumina concentrations with significant variance. 4.3.3.3  Iron (total Fe2O3) Iron mean concentration in unmineralised samples is 6.67% with little variance (n=3; σ=0.10). In chlorite-sericite (n=5; xˉ=5.27%; σ=1.37) and chlorite-sericite-epidote-calcite alteration (n=2; xˉ=5.75%; σ=0.01) it is slightly depleted and there is a significant variance in chlorite-sericite. Quartz-sericite-pyrite alteration also has depleted iron (n=8; xˉ=5.42%; σ=1.44) with significant variance. Both potassic (n=5; xˉ=9.27%; σ=3.16) and sodic-ferric (n=4; xˉ=8.78%; σ=0.41) alteration are typically enriched in iron.  120  4.3.3.4  Calcium (CaO) Calcium mean concentration in unmineralised samples is 5.31% (n=3; σ=0.59). There is little calcium mass gain/loss in any alteration type. In chlorite-sericite (n=5; xˉ=5.36%; σ=0.70) and chlorite-sericite-epidote-calcite alteration (n=2; xˉ=5.47%; σ=0.15) there is little variation from least-altered. Quartz-sericite-pyrite alteration has slightly depleted calcium (n=8; xˉ=4.69%; σ=1.18) especially in strongly altered samples. Both potassic (n=5; xˉ=4.10%; σ=0.96) and sodic-ferric (n=4; xˉ=4.88%; σ=1.96) alteration demonstrate depleted calcium concentrations with significant variance. 4.3.3.5  Magnesium (MgO) Magnesium mean concentration in unmineralised samples is 2.44% with little variance (n=3; σ=0.05). Magnesium is typically depleted in all altered samples. In chlorite-sericite (n=5; xˉ=2.16%; σ=0.43); chlorite-sericite-epidote-calcite (n=2; xˉ=1.74%; σ=0.14); quartz-sericite-pyrite (n=8; xˉ=1.53%; σ=0.44); potassic (n=5; xˉ=1.94%; σ=0.51); and sodic-ferric (n=4; xˉ=1.78%; σ=0.33) alteration magnesium is depleted with a small amount of variance. 4.3.3.6  Sodium (Na2O) Sodium mean concentration in unmineralised samples is 3.99% with little variance (n=3; σ=0.33). In chlorite-sericite (n=5; xˉ=4.22%; σ=1.03) and chlorite-sericite-epidote-calcite alteration (n=2; xˉ=5.2%; σ=0.11) it is slightly elevated and there is greater variance in chlorite-sericite. Quartz-sericite-pyrite alteration typically has depleted sodium (n=8; xˉ=3.17%; σ=1.55) with significant variance. Both potassic (n=5; xˉ=4.77%; σ=0.66) and sodic-ferric alteration (n=4; xˉ=5.91%; σ=0.99) demonstrate elevated sodium concentrations, and sodic-ferric alteration exhibits the highest values.  4.3.3.7  Potassium (K2O) Potassium mean concentration in unmineralised samples is 2.22% with little variance (n=3; σ=0.21). It is typically depleted in chlorite-sericite (n=5; xˉ=1.46%; σ=0.46); chlorite-sericite- 121  epidote-calcite alteration (n=2; xˉ=2.03%; σ=0.46); and sodic-ferric (n=4; xˉ=1.18%; σ=0.45) alteration. Quartz-sericite-pyrite alteration (n=8; xˉ=2.34%; σ=0.74) has similar potassium to unaltered samples although with a significant negative skewness (-1.49) to depleted values. Potassic alteration (n=5; xˉ=3.52%; σ=1.46) is enriched in potassium, although with a significant variance.   4.3.3.8  Titanium (TiO2) Titanium mean concentration in unmineralised samples is 0.79% with little variance (n=3; σ=0.01). In chlorite-sericite (n=5; xˉ=0.71%; σ=0.08) and chlorite-sericite-epidote-calcite alteration (n=2; xˉ=0.73%; σ=0.01) it is slightly depleted and there is greater variance in chlorite-sericite. Quartz-sericite-pyrite alteration typically has depleted titanium (n=8; xˉ=0.66%; σ=0.17) with significant variance. Potassic alteration (n=5; xˉ=0.81%; σ=0.11) has a similar titanium content to unaltered samples although with significant variance around this mean. Sodic-ferric alteration (n=4; xˉ=0.59%; σ=0.11) demonstrate depleted titanium, concentrations with moderate variance. 4.3.3.9  Loss-on-ignition (LOI) The mean LOI in unmineralised samples is 2.35% (n=3; σ=0.61). In chlorite-sericite (n=5; xˉ=5.61%; σ=1.37) and chlorite-sericite-epidote-calcite alteration (n=2; xˉ=4.71%; σ=0.68) it is slightly elevated and there is greater variance in chlorite-sericite. Quartz-sericite-pyrite alteration typically has depleted LOI (n=7; xˉ=3.35%; σ=0.70) with significant variance. Both potassic (n=5; xˉ=3.20%; σ=0.64) and sodic-ferric (n=4; xˉ=4.00%; σ=1.21) alteration demonstrate significantly depleted LOI concentrations with significant variance. LOI incorporates carbon and sulphur compositions. 4.3.3.10   Carbon (C) Carbon mean concentration in unmineralised samples is 0.09% with a significant variance (n=3; σ=0.07). Carbon values are elevated in all altered samples. In chlorite-sericite (n=5; xˉ=0.96%; σ=0.23) and quartz-sericite-pyrite alteration (n=8; xˉ=1.04%; σ=0.24) carbon is  122  moderately elevated. In chlorite-sericite-epidote-calcite alteration (n=2; xˉ=0.37%; σ=0.3) it is slightly elevated. Both potassic (n=5; xˉ=0.49%; σ=0.37) and sodic-ferric alteration (n=4; xˉ=0.47%; σ=0.29) demonstrate slightly elevated carbon concentrations. 4.3.3.11   Sulphur (S) Sulphur mean concentration in unmineralised samples is essentially non-existent 0.01% (n=3; σ=0.01). All altered except chlorite-sericite-epidote-calcite alteration (n=2; xˉ=0.01%; σ=0.01) show sulphur enrichment. In chlorite-sericite alteration (n=5; xˉ=1.22%; σ=0.8) sulphur is moderately elevated. Quartz-sericite-pyrite alteration typically has strongly enriched sulphur (n=8; xˉ=2.57%; σ=1.93) with significant variance. Potassic alteration (n=5; xˉ=0.46%; σ=0.43) has minor enrichment and sodic-ferric alteration (n=4; xˉ=1.72%; σ=0.91) has significantly enriched sulphur concentrations. 4.5.2  Discussion It has been well documented that hydrothermal alteration causes bulk changes in elemental composition (metasomatism) in magmatic-hydrothermal mineral deposits (eg. Lowell and Guilbert, 1970). A correlation between alteration mineralogy and major element chemistry is clearly evident in the data in Figure 4.2 and expressly displayed in Figure 4.7.  The metasomatism associated with sodic-ferric alteration (albite-magnetite) demonstrates significant elemental mobility. Silica, potassium, aluminium and magnesium are typically depleted. Iron and sodium are enriched.  Calcium can be depleted, although remains constant on average. Sulphur is introduced. These bulk changes are representative of the mineralogical change associated with sodic-ferric alteration. Ferromagnesian minerals, primarily amphibole, are replaced by magnetite (Figure 3.7; Figure 4.8a,b). This adds iron and removes some magnesium. Sodium is added by the alteration of andesine plagioclase to albite. Introduced sulphur is in the form of chalcopyrite, bornite and anhydrite.    123   Figure 4.6  Molar Na/Al versus K/Al alteration discrimination plot of Davies and Whitehead (2006). Least-altered diorite samples are in the circle. Arrows indicate trend of alteration towards dominant aluminosilicate mineral. Sodic-ferric altered diorite show albite-muscovite (sericite) alteration. Only one potassically altered diorite shows trend towards plagioclase/K-feldspar alteration, the others show a mixture of albitic and potassic alteration. Quartz-sericite-pyrite altered diorites show a trend towards muscovite alteration, with some clay alteration. Chlorite-sericite altered diorites show a weak alteration to albite, muscovite and/or clays. Volcanic package rocks show trend towards clay alteration. Andesite dykes show trend towards sericite/clay alteration.   124   Figure 4.7  Tukey diagram of diorite samples grouped by alteraiton.Highest silica values associated with phyllic alteration, lowest with feldspar-stable alteration. Highest aluminum values associated with phyllosilicate alteration, lowest with feldspar-stable alteration. Highest iron values associated with feldspar-magnetite assemblages. Sodium is highest in sodic-ferric and potassic alteration, and lowest in phyllic alteration. Potassium is elevated only with potassic alteration. Highest C values are associated with chl-ser and phyllic alteration due to carbonate alteration. Highest S associated with pyrite. Most significant LOI values are associated with chlorite-sericite alteration.   125    Figure 4.8  Petrographic images of altered samples analysed for whole-rock geochemistry. 126  (a) PPL image of sodic-ferric altered ‘mineralised’ diorite. Significant hydrothermal magnetite is present in the groundmass. Sample 74253; (b) XPL of same sample as (a) showing plagioclase phencrysts replaced by fine-grained albite. Sericite alteration overprints; (c) PPL image of potassically altered ‘mineralised’ diorite showing magnetite. Sample 1137443; and (d) XPL same image as (c) showing significant K-feldspar replacement of groundmass with relatively unaltered plagioclase phenocrysts. Potassic alteration (K-feldspar-magnetite) demonstrates a similar chemical profile to sodic-ferric alteration. That is, depletion in silica, aluminium and magnesium, and enrichment in iron, sodium and sulphur. Potassic alteration is also associated with a depletion in calcium and strong potassium enrichment. Ferromagnesian minerals are replaced by magnetite. Potassium enrichment and calcium depletion is associated with the replacement of plagioclase groundmass by potassium feldspar (Figure 3.7; 4.8c,d). The sodium enrichment is probably associated with slight sodic alteration of phenocrysts which may have occurred prior to potassic alteration. Introduced sulphur is in the form of chalcopyrite, bornite and anhydrite.  Phyllic alteration (quartz-sericite-pyrite) demonstrates both silica enrichment and depletion. Aluminium is depleted, as usually is iron, calcium, magnesium and sodium. Sulphur is usually strongly enriched. The mineralogical change that represents this chemical change is dominated by the sericitisation of all feldspar, and the pyritisation of all ferromagnesian minerals. Strong sericitisation removes calcium and sodium from feldspar, but remains relatively potassium neutral. Silica is remobilised in this process, which is deposited unevenly as quartz, creating the variance in the silica values.  Pyritisation of ferromagnesian minerals slightly depletes iron and magnesium and adds significant sulphur. The mineralogical change associated with phyllic alteration is represented petrographically in Figure 3.8 and 4.5e,f. There are four samples with a SiO2 composition above 63%. These four samples are very strongly quartz-sericite-pyrite±calcite (phyllically) altered to the point of complete textural destruction (Appendix B: 1020661, 1020556, 74326, 1020692). Sample 1020669 is also exhibits similar chemical composition with just under 60% SiO2. This group of strongly phyllically altered diorites (SPADs) is chemically distinct in both major and trace element analyses and is evaluated further using trace elements below (Section 4.6).   127  The metasomatism associated with chlorite-sericite alteration demonstrates elemental immobility. Silica, alumina and calcium show only slight variations compared to least-altered samples. Depletion in iron and magnesium is probably due to the closure effects associated with the increase of sulphur. This is represented mineralogically by the replacement of igneous amphibole with chlorite and sulphides (Figure 3.8; 4.5c,d). Similarly chlorite-sericite-epidote-calcite (propyllitic) alteration shows slight depletion in iron and magnesium. This is probably associated with the replacement of amphibole with chlorite (Figure 3.9). There is also significantly greater LOI than unaltered rocks. This is probably due to the low-temperature sericite forming a swelling clay rich illite-smectite mixture. There is silica depletion in rocks associated with early central potassic and magnetite alteration and enrichment in later peripheral phyllic alteration zones. This may suggest that igneous silica from feldspar is mobilised and transported by hydrothermal fluids. Specifically, mobilised during feldspar-stable potassic and sodic-ferric alteration and deposited as part of the phyllic alteration assemblage.  4.6 Trace element geochemistry Three different igneous suites in the Whistler Corridor were identified by major element analysis; diorite, basaltic andesite dykes, and rocks of the intermediate volcanic package. No distinctions between different phases of diorite were identified. This may be due to insignificant/unresolvable differences in major element composition, or obscuration by hydrothermal alteration. Trace element geochemistry is used here to evaluate possible chemical subdivision within WIS diorites, lithotectonic properties, and the influence of alteration on trace element geochemistry is discussed. 4.6.1 Observations  4.6.1.1 Multi-element trace and rare earth element diagrams The relative abundance of trace elements are displayed in the multielement plots of Figure 4.9. All samples have been normalised to primitive mantle of Palme and O’Neill (2003). Figure  128  4.9 shows samples grouped into rock types. Each group is represented by a range one standard deviation above and below the mean. WIS rocks display an overall enrichment of the most incompatible elements. The large ion lithophile elements (LILE; Cs, Rb, Ba, K, Sr) are enriched relative to high field strength elements (HFSE; Nb, Ta, Zr, Hf) and rare earth elements (REE). This relationship is less developed in the basaltic andesite dykes which show a flatter trace element profile (Figure 4.9a). Basaltic andesites are relatively depleted in incompatible elements (LILEs) and enriched in less incompatible REEs (Figure 4.9a; 4.10a). The general trace element profile of WIS rocks strongly correlates with typical intermediate arc rocks of Davidson et al. (2005) as shown in Figure 4.9c. The most significant difference between these traces is a lack of a negative Nb (or Ta) anomaly in WIS rocks. This has implications discussed below.    All WIS rocks exhibit a positive Sr anomaly (Figure 4.9), with the exception of one strong sericite-pyrite altered volcanic sequence rock (1134091). A small negative Ti anomaly is most evident in diorite and intermediate volcanic rocks, and less evident in basaltic andesite dykes. This Ti anomaly is present in all unaltered and altered diorites. This REE profile of Figure 4.10 shows light REE (LREE; La, Ce, Pr, Nd, Sm) enrichment relative to heavy REE (HREE; Eu, Gd, Tb, Dy, Ho, Er, Yb, Lu). Furthermore, the LREEs display a steep profile with significant enrichment and variability of the most incompatible LREEs (eg. La, Ce, Pr) around 10-50 times primitive mantle values. HREEs display a relatively flat profile of similar values 3-10 times those of primitive mantle.  The REE profile of basaltic andesite dykes shows a slight enrichment in all REEs relative to WIS diorites or intermediate volcanic rocks. The REE profiles of the ‘unmineralised’ diorite and intermediate volcanic rocks are nearly identical. WIS ‘mineralised’ diorites show the most depleted total REE composition.   129  Within the ‘mineralised’ diorite subgroup of Figures 4.9a and 4.10a there is significant trace element variation corresponding to hydrothermal alteration (Figure 4.9b and 4.10b).    130     131  Figure 4.9  Trace element multielement diagrams of WIS rocks. (previous page) (a) and alteration assemblages (b) compared to reference compositions (c) (© 2003 Elsevier BV, by permission) from Davidson et al. (2005). (a) All rock types in the Whistler Corridor show a similar profile consistent with arc andesites although lack a Nb-Ta anomaly (discussed in text). (b) (Trace elements are enriched in potassic alteration, depleted in sodic-ferric alteration. Phyllic alteration shows a steeper profile. Each group represents one standard deviation plus and minus from the mean. Samples normalised to primitive mantle of Palme and O’Neill (2003).    Figure 4.10  REE multielement diagram.(a) The basaltic andesite dykes show the most significant concentration of REEs and ‘mineralised’ diorite the least. Intermediate volcanic package rocks and ‘unmineralised’ diorite show very similar REE profiles; (b) alteration enriches REE concentrations of in potassically altered rocks. Other assemblages depleted relative to ‘unmineralised’ diorite, except propyllitic. Phyllic alteration is enriched slightly in LREEs but depleted in HREEs.      132  The least-altered ‘mineralised’ diorites, those with chlorite-sericite and chlorite-sericite-epidote-calcite (propyllitic) show REE profiles similar to, or slightly depleted from ‘unmineralised’ diorite profile. In cases where REE profiles are depleted, a degree of sodic alteration is suspected. The most depleted and most enriched trace element compositions belong to the two feldspar-stable alteration assemblage. Sodic-ferric (albite-magnetite) alteration exhibits the most depleted LILE, HFSE and REE profiles relative to primitive mantle (Figure 4.9b and 4.10b). The exception to this rule is Sr, presumably due to introduced Sr with albitic alteration. Potassic (K-feldspar-magnetite) alteration exhibits elevated trace element profiles relative to primitive mantle.  The steepest trace element profile of altered rocks is in quartz-sericite-pyrite altered diorite. These rocks are most enriched in the most incompatible and slightly depleted in the least incompatible trace elements (Figure 4.9b). They exhibit a similarly steep profile in the REEs (Figure 4.10b) with enrichment in the LREEs and depletion in the HREEs. The negative Ti anomaly mentioned above is the most distinct in these quartz-sericite-pyrite altered rocks. 4.6.1.2 Trace element variation diagrams 9ariation diagrams are chemical plots on which two elements’ compositions in a series of magmas are plotted. The ratios of highly incompatible trace elements in a melt do not change during crystal fractionation. Thus when two incompatible trace elements are plotted on a variation diagram, the original signature of the magma can be determined, providing information about the magma’s origin (Lee, 2014). In order to evaluate the primary igneous chemistry of an intrusive suite associated with a magmatic-hydrothermal system, elements that are immobile during hydrothermal alteration should be evaluated. A selection of trace elements have been identified which satisfy this condition, at least in alteration zones associated with volcanogenic massive sulphide (VMS) deposits (Pearce and Cann, 1973; Winchester and Floyd, 1977; Floyd and Winchester, 1978; Pearce and Norry, 1979; MacLean and Kranidiotis, 1987; MacLean and Barrett, 1993).. These elements include Al, Ti, the high-field strength elements (HFSE) Zr, Nb, Y and the rare-earth elements (REE).   133  Aluminium shows significant unpredictable but depletive element mobility as evident in Figures 4.6 and 4.7. It is possible that this aluminium mobility may be related to the sericitisation of feldspar, commonly identified in WIS rocks. Aluminium mobility exempts its use as a lithogeochemical determinant element. TiO2 and Zr have been suggested to represent one of the more robust trace element ratios. These data are displayed in Figure 4.11a. Some distinct fractionation trends can be identified. The basaltic andesite dykes may form a trend which fails to intersect the origin, although only there are only three samples. A similar trend can be identified for the intermediate volcanic rocks, of close affinity to WIS diorites.  The majority of the diorite samples fall within a broad trend intersecting the origin. It should be mentioned that the volcanic samples mentioned above may be included within this broad trend.  There are some outliers to the diorite trend. Three sodic-ferric altered samples (74254, 72311, 1019686) exhibit higher TiO2/Zr ratios. One potassically altered sample from Raintree North (1134221) exhibits a lower TiO2/Zr ratio. There are five samples of SPADs (see above) with very strong, texturally destructive quartz-sericite-pyrite alteration. These samples all exhibit a lower TiO2/Zr ratio than the diorite trend.  Comparing Nb and Zr (Figure 4.11b) two distinct origin-intercepting trends can be identified. Trend 1 includes all the WIS ‘mineralised’ diorites, regardless of alteration, including the two samples from Raintree North. Trend 2 includes all the samples from ‘unmineralised’ diorite, the intermediate volcanic package rocks, and the one sample of potassically altered ‘mineralised’ diorite from Raintree West.  The HFSE Nb, and Zr, facilitates the distinction between ‘mineralised’ and ‘unmineralised’ diorite of the WIS. By contrasting elements with a greater range of magmatic compatibility, a more precise evaluation of trends in magmatic affinity can be conducted.  In Figure 4.12 Nb is plotted against Y (Figure 12a) and Lu (Figure 12c). In the Nb-Y diagram three trends a discernible. The basaltic andesite dykes show a clear origin-intersecting trend. Similar to the Nb-Zr diagram, the WIS can be resolved into two trends; (1) ‘mineralised’   134   Figure 4.11  TiO2-Zr and Nb-Zr variance diagrams.(a) TiO2-Zr diagram distinguishes three trends; basaltic andesite dykes, intermediate volcanic rocks, and WIS diorites. A lack of origin interception in basaltic andesite dykes indicate possible Ti enrichment. The strongly phyllically altered rocks fall off-trend indicating Zr enrichment and/or Ti depletion. (b) Nb-Zr diagram distincguishes two trends of WIS diorites, a ‘mineralised’ diorite and ‘unmineralised’ diorite (plus intermediate volcanics) trend. NB: potassically altered rocks from Whistler, Raintree North and Raintree West show scatter due to variable Nb enrichment (Discussed in text).     135   Figure 4.12  Y-Nb, Lu-Nb, Y-La, Lu-La variance diagrams. (a) Y-Nb diagram. Demonstrates at least three trends. The ‘mineralised’ diorite trend does not intercept the origin suggesting element mobility. Strong phyllically altered diorites vary from the ‘mineralised’ diroite trend due to Nb enrichment and/or Y depletion; (b) Y-La diagram. Shows ‘mineralised’ and ‘unmineralised’ diorite comprise one trend. This suggests that the seperate trends evident in (a) may be due to Nb enrichment; (c) Lu-Nb diagram. The phyllically altered diorites do not deviate in this diagram relative to the Y-Nb diagram. This suggests that the deviation in (a) may be due to Y depletion; and (d) Lu-La diagram. This diagram demonstrates the two main primary magmatic trends; basaltic andesite dykes, and all WIS intrusive and extrusive phases. Element mobility of La and Lu is less significant than Nb or Y (discussed in text).      136  diorite; and (2) ‘unmineralised’ WIS diorites plus the intermediate volcanic package and Raintree West. The ‘mineralised’ diorite trend exhibits a similar slope to ‘unmineralised’ diorite but does not intersect the origin, consistent with Nb enrichment or Y depletion (MacLean and Kranidiotis, 1987). The SPADs exhibit a higher Nb/Y ratio suggesting Nb enrichment or Y depletion. When Nb is contrasted with Lu (Figure 4.12c) the same three trends are evident. The SPADs show less deviation from the Nb/Y ratio of the ‘mineralised’ diorite trend. This suggests the SPAD deviation to higher Nb/Y ratios in Figure 4.12a contains a component of Y depletion.  The LREE La is contrasted to Y and Lu in Figures 4.12b and 4.12d respectively. La is similarly compatible to Nb relative to primitive mantle. Thus these two variation diagrams were chosen to evaluate the extent to which La mobility may vary from Nb. The WIS diorite trend in La trends do not facilitate the distinction of ‘mineralised’ and ‘unmineralised’ diorite phases. Both phases fall on one broad trend that intersects the origin. The SPADs show slight La enrichment or Lu depletion. Elevated La values are present but unexplained in two chlorite-sericite-epidote-calcite (05REC07-106/107), one chlorite-sericite (1019531), and one chlorite, sericite-pyrite (1019521) altered diorites. Nb is enriched, and to a lesser degree La, in ‘mineralised’ diorite relative to ‘unmineralised’ diorite. 4.6.2 Discussion The observations of trace element geochemical data above raise several specific points for discussion, and these are discussed below. Specific points include the;  Primitive profile of basaltic andesites relative to other WIS rocks;  Presence of positive Sr and negative Ti anomalies;  Lack of a negative Nb-Ta anomaly, and lower Nb/La ratios than would be expected in arc-related magmatic rocks;  Enrichment of ‘mineralised’ diorites in HFSEs relative to ‘unmineralised’ diorite: distinct magmatic fractionation trend or metasomatism;  Relative depletion in trace element composition of sodic-ferric altered and enrichment in potassically altered rocks.  137   Poor correlation of trace element ratios in potassically altered rocks from Whistler, Raintree North and Raintree West;  Presence of a small negative titanium anomaly, especially in the presence of quartz-sericite-pyrite alteration;  Steeper trace element profile, HREE depletion, and negative Ti anomaly in quartz-sericite-pyrite altered rocks, especially SPADs; In general, the volcanic and intermediate intrusive rocks of the WIS display a trace element geochemical signature compatible with arc-related andesites. All diorite and intermediate volcanic rocks show a similar trace element and REE profile (Figure 4.9a). The lower trace element concentration in ‘mineralised’ diorite than ‘unmineralised’ diorite is either due to variation in the source magma, or due to an early post-magmatic metasomatism (discussed below). The volumetrically insignificant late basaltic andesite dykes exhibit a flatter trace element profile with lower concentrations of incompatible and higher concentrations of less incompatible elements. These incompatible elements include both LREE and HREEs (Figure 4.10a) which are enriched compared to other WIS rocks. Assuming that basaltic andesite dykes are sourced from the same underlying batholith as WIS rocks (not confirmed) it shows a trend towards more mafic magmatism in the Whistler Corridor post mineralisation. Almost all samples exhibit a positive strontium anomaly. As strontium fractionates preferentially into mid-stage fractionates (Salminen et al., 2005), positive Sr anomalies is to be expected in the intermediate WIS. The strongest diorite Sr anomalies are associated with feldspar-stable alteration due to the substitution of Sr in feldspar. The presence of a ubiquitous negative Ti anomaly is common in arc-related magmatism (Pearce and Norry, 1979). This is particularly applicable where amphibole and magnetite are shown to be major accessory mineral phases, as is the case in the WIS.  All WIS rocks lack a negative Nb-Ta anomaly, as is commonly found in arc-related magmatic rocks. While Nb may be enriched in ‘mineralised’ diorite due to post-magmatic hydrothermal processes (discussed below) ‘unmineralised’ diorite and volcanic rocks show  138  hydrothermal enrichment. A negative Nb-Ta anomaly is usually present in continental crust and the depleted mantle (eg. Hofmann, 1988). This is due to retention of Nb, Ta and Ti in residual minerals in subducting eclogitic oceanic slabs (McDonough, 1991). Other elements are released by partial melting of the subducting slab, fertilizing the mantle wedge and incorporated into arc magmas. As a result the La/Nb ratio in the continental crust is around 2.5 (Rudnick and Gao, 2003) to 2.7 (Barth et al., 2000). In arc andesites they are around 2.3 to 3.2 (Plank and Langmuir, 1988; Kelemen et al., 2007). In the primitive mantle this ratio is around 1.0 (McDonough and Sun, 1995). In the depleted mantle La/Nb is generally 1.1 to 1.3 (Salters and Stracke, 2004; Workman and Hart, 2005). WIS rocks exhibit a mean La/Nb ratio of 1.09 (σ=0.28) and 1.34 (σ=0.04) for ‘unmineralised’ diorite. These values are strongly correlated with the depleted mantle. The lack of the distinctive negative Nb-Ta anomaly. and thus low La/Nb ratio, in arc magmas may be explained by a significantly deep (>300 km) subducting slab with little to no crustal contamination on ascent (Bromiley and Redfern, 2008). The HFSE, especially Nb and Zr, facilitate a chemical distinction between ‘mineralised’ and ‘unmineralised’ diorite. Although all WIS diorites show enriched Nb values relative to typical arc magmas (see above); the ‘mineralised’ diorites are particularly enriched. This distinction is evident on the Nb-Zr (Figure 4.11b) Nb-Y and Nb-Lu (Figure 4.12a,c) variation diagrams. These fractionation trends suggest that the ‘mineralised’ diorite has a distinguishable different source from ‘unmineralised’ diorite. However, the ‘mineralised’ diorite trends do not intersect the origin and suggest either Nb enrichment and/or Y and Lu depletion (Figure 4.12a,c). When La is substituted for Nb in these diagrams (Figure 4.12b,d) distinction is less determinable between ‘mineralised’ and ‘unmineralised’ diorite, although La appears to be slightly enriched. For these reasons it can be concluded that Nb and Zr have been enriched by post-magmatic metasomatism (eg. Salvi and Williams-Jones, 1996; Jiang et al., 2003). Raintree North and Raintree West samples are difficult to categorise into either trend, for reasons discussed below. Regardless of the cause of Nb enrichment, it is a useful tool for discriminating between ‘mineralised’ and ‘unmineralised’ WIS diorite. Nb/Y ratios can be used for this purpose. Nb/Y  139  values >1.1 are from ‘mineralised’ diorite (Figure 4.14b). Where Nb/Y ratios are ≤1 it is ‘unmineralised’ diorite. Similarly, Nb/Lu values >70 denote ‘mineralised diorite, <70 unmineralised diorite. Neither of these ratios, nor any REE elements, can be applied to determine the suite of potassically altered rocks due to element mobility (see below). However, the presence of potassic alteration suggests these would be ‘mineralised’ diorite.   Feldspar-stable alteration has a significant effect on trace element composition. Interestingly, the most depleted and most enriched trace element compositions are found in the two feldspar-stable alteration assemblages (Figures 4.9b, 4.10b). Sodic-ferric alteration exhibits the most depleted LILE, HFSE and REE compositions relative to ‘unmineralised’ diorite. The least-altered (chlorite-sericite and chlorite-sericite-epidote-calcite) WIS ‘mineralised’ diorites also exhibit depleted trace element, especially REE profiles.  Rocks with sodic-ferric alteration show relatively consistent trace element ratios (eg. Figure 4.11, 4.12) suggesting that the depleted trace element profile of these, and the least-altered ‘mineralised’ diorites, is related to a primary characteristic of the source magma.  Potassic alteration is enriched in most trace elements, with higher concentrations of most LILE, HFSE and REEs than ‘unmineralised’ diorite. Enriched trace elements in potassic alteration is most likely due to metasomatism. For example, substitution of K by LILEs (Heier, 1962) and the concentration of REEs in altered K-feldspar (Bi et al., 2002) are possible if hydrothermal fluids are strongly (>1300 ppm) enriched in REEs (Banks et al., 1994). The enrichment of the REEs and other trace elements during potassic alteration is problematic for the use of element variance diagrams. In Figure 4.12 samples from Whistler, Raintree North, and Raintree West plot inconstantly. For example, the two samples from Raintree North could be considered part of the ‘mineralised’, ‘unmineralised’ or basaltic andesite fractionation trends, depending on the specific trace elements. This variation is due to metasomatism associated with the formation of K-feldspar. Potassically altered rocks should be avoided when sampling intrusive rocks for WIS lithogeochemistry.  140  WIS rocks with quartz-sericite-pyrite alteration, especially the SPADs are geochemically unique. They exhibit a steeper trace element and REE profile than other WIS rocks (Figures 4.TR, 4.REE) including a particularly strong negative Ti anomaly (also evident in Figure 4.11a). SPADs are thus associated with a depletion in Y (Figure 4.12a,b). A strong correlation between Y and the other HREEs is evident in the Y-HREE variation diagrams of Figure 4.13. Thus the SPADs are also depleted in the HREEs (also evident in Figure 4.10b) As Y is strongly accommodated into amphibole (Green, 1980) it is possible that the complete pyritisation of hornblende in these rocks (Figure 4.5e,f) has allowed for Y mobility. REE depletion has been observed hydrothermal silica alteration associated with high-sulphidation epithermal mineralisation (Fulignati et al., 1999) as well as with increasing degree of sericitisation (Uysal and Golding, 2003) and the influence of these effects is uncertain.  All WIS diorite, and intermediate volcanic rocks share a common source. The primary magmatic chemical signatures of these igneous rocks are extremely similar. Basaltic andesite dykes exhibit a distinct signature. The discrimination plot of Figure 4.14 demonstrates these two phases of magmatism (labelled). The ‘mineralised’diorites can be resolved using Nb/Y (<1.1) or Nb/Lu (<70) ratios. 4.7  Conclusion  There are at least three distinctive magmatic phases in the Whistler Corridor. These are; the basaltic andesite dykes; the WIS extrusive; and WIS intrusive rocks. The defining chemical characteristics of each is summarised here, followed by an overview of the metasomatism associated with hydrothermal alteration. The basaltic andesite dykes are dark grey-green, aphanitic, centimetre to metre scale dykes. Chemically, basaltic andesite dykes are:  Intermediate composition (55-56% SiO2);  Calc-alkalic;  Metaluminous;  Na-, Fe-, Mg, and Ti-rich;  141   Figure 4.13  Comparison of Yttrium and the HREEs. A strong positive correlation is evident. As a result, the HREEs exhibit a similar chemical behaviour to Yttrium, including element mobility associated with strong phyllic alteration. Lu and Yb show lesser correlation with Y for the strongly phyllically altered rocks.      142   Figure 4.14  La/Y-La/Lu and Nb/Y-Nb/Lu discrimination diagrams. (a) La/Y-La/Lu demonstrates the primary magmatic affinity of all samples. The basaltic andesite dykes form a distinct group. All other WIS intrusive and extrusive phases form a group. Variation from this group is due to La enrichment and Y depletion in altered rocks;   143  Figure 4.14 (cont.) (b) Nb/Y-Nb/Lu diagram shows three distinct igneous suites. Basaltic andesite dykes form a distinct group. All ‘unmineralised’ WIS diorite and intermediate volcanic rocks form a distinct group. The ‘mineralised’ diorite suite forms a trend that is related to variable Nb enrichment in all samples and additional Y depletion in strong phyllically altered rocks. A Nb/Y ratio cut-off of 1.1 can be used to discriminate between ‘mineralised’ and ‘unmineralised’ diorite. Note: this method cannot be applied to potassically altered rocks due to variable REE enrichment.  Basaltic andesite dykes have a more primitive trace element profile than WIS phases, that is, a relative depletion in incompatible and enrichment in less incompatible elements. As a result element ratios such as Nb/Y are lower (<0.9) than WIS (>0.9). Basaltic andesite dykes cross-cut all other rock units (Chapter 3) and are thus inferred to represent a late, post mineralisation, relatively mafic, volumetrically minor intrusive phase. The extrusive rocks of the WIS represent a volcano-sedimentary sequence of andesitic flows, dykes, and sills, volcanic breccias, and undivided volcanic/subvolcanic intermediate rocks (Chapter 3). Chemically, volcanic rocks of the WIS are:  Intermediate composition (55.4-58% SiO2 altered);  Calc-alkalic (tholeiitic signature due to metasomatic MgO depletion);  Metaluminous;  Ca-rich (probably due to carbonate alteration) This intermediate volcanic package displays a trace element profile identical to the ‘unmineralised’ diorite. The volcanic package of the WIS was sourced from an arc-related magma. A lack of Nb-Ta anomaly suggests the source rocks were partially melted from a depleted mantle wedge in a steeply dipping subduction zone, with rapid magmatic ascent imparting little to no crustal contamination. The intrusive rocks of the WIS represent multiples phases of porphyritic to inequigranular, plagioclase- and amphibole-phyric diorite (Chapter 3). Chemically, the intrusive rocks of the WIS are:  Intermediate composition (59-61% SiO2);  144   Calc-alkalic;  Metaluminous;  Na-rich; Ca-poor; and  Comprising plagioclase of andesine (An30-50) composition The trace element profile of WIS diorite demonstrates enrichment in incompatible elements. The profile is consistent with the WIS being sourced from an arc-related intermediate magma. However, a lack of Nb-Ta anomaly suggests the source rocks were partially melted from a depleted mantle wedge in a steeply dipping subduction zone, with rapid magmatic ascent imparting little to no crustal contamination. Trace element ratios involving HFSE, especially Nb, demonstrate a distinction between the ‘mineralised’ diorite and ‘unmineralised’ diorite of Chapter 3. Although Nb is enriched in all WIS rocks relative to typical arc magmas, this enrichment is significantly increased and highly variable in ‘mineralised’ diorite relative to ‘unmineralised’ diorite.  Nb/Y ratio can be used to distinguish between ‘mineralised’ diorite and ‘unmineralised diorite. The ‘mineralised’ diorite always exhibit Nb/Y ratios greater than 1.1. In ‘unmineralised’ diorite Nb/Y is 0.9-1.0. Similarly the Nb/Lu ratio is >70 for ‘mineralised’ and <70 for ‘unmineralised’ diorite. This method cannot be used where potassic alteration is present due to highly variable enrichment in the REE composition. The HFSE enrichment is the result of a post-magmatic metasomatism. The ‘mineralised’ diorites are invariably hydrothermally altered. This alteration causes metasomatism that affects the major and trace element chemical composition of these rocks (Table 4.2). The post-magmatic metasomatism associated with HFSE, especially Nb, enrichment is not included here, as it is not correlated with a specific alteration assemblage. Metasomatism associated with hydrothermal alteration is reflected in the following assemblages:    145   Chlorite-sericite: o Minor major element mobility  o Fe, Mg depletion o S enrichment o Significant LOI o Minor trace element mobility  Propyllitic (chlorite-sericite-epidote-calcite): o Minor major element mobility  o Fe, Mg depletion o Significant LOI o Minor trace element mobility  Sodic-ferric (albite-magnetite):  o Na, Fe, S enrichment; o Si, K, Al, Mg depletion; o All trace elements (except Sr) depleted;  Potassic (K-feldspar-magnetite±biotite): o K, Na, Fe, S enrichment; o Si, Al, Mg depletion; o Trace elements, including REE, variably enriched   Phyllic (quartz-sericite-pyrite±calcite): o Variable (patchy) Si composition o S enrichment o Ti, Al, Fe, Ca, Mg, Na depletion o LILE, HFSE, LREE enrichment o HREE depletion In summary, the rocks at Whistler represent; one stage of WIS intermediate volcanism; two stages of WIS intermediate intrusions, a ‘mineralised’ diorite with HFSE enrichment, and an  146  ‘unmineralised’ diorite; and late minor mafic-intermediate set of dykes. Nb/Y ratio can be used as a geochemical determinant ratio to identify ‘mineralised’ diorite. All magmatic rocks lack the Nb-Ta anomaly suggesting depleted mantle source and lack of continental contamination. The hydrothermal alteration associated with porphyry mineralisation in ‘mineralised’ diorite; depleted Si, Al and Mg and deposited Na, K, Fe and S in feldspar-stable assemblages; trace elements were depleted in sodic-ferric and unpredictably enriched in potassic alteration; remobilised and deposited Si, and S, depleted Ti, Al, Mg, Al, Ca, and Na in phyllic alteration, while incompatible trace elements were enriched and less incompatible elements (HREE) depleted; and depleted Fe and Mg and increased LOI in chlorite-sericite and propyllitic alterations.    147  5 Feldspar-Stable Alteration Mineral Chemistry 5.1  Introduction In the Whistler Corridor, mineralisation is associated with K-feldspar-magnetite±biote (potassic) as well as albite-magnetite (sodic-ferric) altered rocks (Chapter 3). Texturally, sodic-ferric alteration is comparable to potassic alteration, and was previously interpreted to represent a less-intense but analogous style of metasomatism. The presence of albite is difficult to ascertain in hand sample or petrographically due to overprinting alteration in these already plagioclase-rich rocks.  The interpretation of whole-rock geochemical data from altered rocks of the WIS suggested the presence of a previously unidentified Na-rich alteration in some magnetite-altered rocks associated with Cu-Au mineralisation (Chapter 4). These rocks were previously thought to be magnetite and chlorite altered, but without a well-understood alteration assemblage. In order to evaluate the nature of Na+ metasomatism directly, mineral chemistry was necessary. The purpose of this chapter is to chemically characterise this Na enrichment and hypothesise how this may be represented mineralogically as part of an alteration assemblage.  Microprobe analyses of feldspar for whole-rock sodium-enriched, potassium-enriched, and least-altered diorites are outlined here. Analyses were made of phenocrysts and groundmass. The results of these analyses are then discussed and related to other cases of sodic alteration. 5.2  Methodology 5.2.1  Sample selection and preparation Eight samples were selected based on the presence of feldspar-stable alteration. These included two samples with potassium alteration of groundmass (demonstrated by Na-cobaltinitrite stain), five with suspected sodium alteration, and one ‘least-altered’ sample. Samples were selected based on the whole-rock geochemistry, specifically samples with elevated Na2O or K2O were chosen to evaluate the source of these anomalies. Care was taken to select samples with minimal feldspar-destructive serite alteration.   148  Polished sections were produced for each sample, and feldspar phenocrysts and groundmass identified petrographically. Samples were carbon coated before analysis. Sites for analyses were selected using back-scatter electron (BSE) mode and care was taken to avoid non-feldspar alteration such as sericite or carbonate.  5.2.1  Analytical methods The scanning electron microsope / energy-dispersive X-ray spectrometer (SEM/EDS) was a Philips XL30 with Bruker Quantax 200 microanalysis system with light element XFLASH 4010 detector, operating with a silicon drift detector that operates at higher count rates without liquid nitrogen cooling. Electron-probe micro-analyses of feldspar were done on a fully automated CAMECA SX-50 instrument, operating in the wavelength-dispersion mode with the following operating conditions:  excitation voltage, 15 kV; beam current, 20 nA; peak count time, 20 s; background count-time, 10 s; spot diameter, 5 m.  Data reduction was done using the 'PAP' (Z) method (Pouchou and Pichoir, 1985).  For the elements considered, the following standards, X-ray lines and crystals were used: albite, NaK, TAP; anorthite, AlK, TAP; diopside, MgK, TAP; anorthite, SiK, TAP; orthoclase, KK, PET; anorthite, CaK, PET; synthetic rhodonite, MnK, LIF; synthetic fayalite, FeK, LIF. 5.3  Results The relative abundance of Na2O, K2O and CaO in feldspar phenocrysts and groundmass are presented in a ternary plot in Figure 5.1. In this diagram three distinct groups can be easily discerned. Based on their relative Na2O