Genesis of the Late Triassic Southwest Zone Breccia-Hosted Alkalic Porphyry Cu-Au Deposit, Galore Creek, British Columbia, Canada

Research Article| June 01, 2014 Genesis of the Late Triassic Southwest Zone Breccia-Hosted Alkalic Porphyry Cu-Au Deposit, Galore Creek, British Columbia, Canada Kevin Byrne; Kevin Byrne † Mineral Deposit Research Unit, University of British Columbia, 6339 Stores Road, Vancouver, BC V6T 1Z4, Canada *Present address: Teck Resources Limited, 550 Burrard St., Vancouver, BC V6C 0B3, Canada. †Corresponding author: e-mail, kevinbyrne@gmail.com Search for other works by this author on: GSW Google Scholar Richard M. Tosdal Richard M. Tosdal Mineral Deposit Research Unit, University of British Columbia, 6339 Stores Road, Vancouver, BC V6T 1Z4, Canada Search for other works by this author on: GSW Google Scholar Economic Geology (2014) 109 (4): 915–938. https://doi.org/10.2113/econgeo.109.4.915 Article history first online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Kevin Byrne, Richard M. Tosdal; Genesis of the Late Triassic Southwest Zone Breccia-Hosted Alkalic Porphyry Cu-Au Deposit, Galore Creek, British Columbia, Canada. Economic Geology 2014;; 109 (4): 915–938. doi: https://doi.org/10.2113/econgeo.109.4.915 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyEconomic Geology Search Advanced Search Abstract The Late Triassic Southwest zone alkalic porphyry Cu-Au deposit in the Galore Creek district, northwestern British Columbia, is hosted in hydrothermally cemented breccias that overprinted older matrix-rich breccia and megacrystic orthoclase-phyric syenite and monzonite dikes. Synmineralization cemented breccias and biotite-phyric monzodiorite dikes are localized at the contact of the matrix-rich breccia and host syenite and monzonite dikes, as well as in crosscutting faults. Regional shortening tilted the Southwest zone deposit so that the cemented breccias now dip 50° to 60° southwest.Four paragenetic stages formed the deposit. A premineralization stage (1) consists of the emplacement of coherent syenite and monzonite host rocks that are cut by a matrix-rich breccia. The synmineralization stage (2) produced potassic-altered rocks and phlogopite-magnetite-K-feldspar–cemented breccia and veins, and most of the Cu-Fe sulfides. A halo of stage 2 diopside-magnetite-grandite-phlogopite calcic-potassic veins and altered rocks formed around the potassic domains and Cu ore zones. Alteration during stage 2 probably formed at temperatures of about 500° to 425°C from oxidized saline magmatic-hydrothermal fluids. Contemporaneous high (aCa2+)/(aH+)2 conditions peripheral to the potassic domains are required to form the marginal calcic-potassic and calcic assemblages. The potassic and calcic-potassic alteration domains were overprinted by propylitic and calcic alteration assemblages due to the retrograde influx of an admixture of cooler magmatic and nonmagmatic fluids. Sphene from a stage 2 calcic-potassic vein yielded a 202.8 ± 2.1 Ma age (U-Pb SHRIMP-RG) that is interpreted to reflect the approximate time of hydrothermal alteration.Late-mineralization stage (3) alteration overprinted the cemented breccias and comprises sericite-anhydrite (sericitic), grandite (calcic), and chlorite-epidote-carbonate-pyrite (propylitic) assemblages. Localized late-mineralization and Cu-poor stage (4) K-feldspar-Fe carbonate-specularite (carbonate-potassic) and quartz-pyrite veins (quartz veins) cut stage 2 and 3 assemblages.Chalcopyrite and bornite dominate the core of the deposit, and grade outward to chalcopyrite > pyrite and to pyrite > chalcopyrite, flanked by a pyrite-only halo. The core of the system is Cu-Au rich, grading outward to an Au-enriched, Cu-poor halo coincident with pyrite-bearing propylitic alteration. Gold-copper ratios increase upward within stage 2 potassic zones and outward from the core. Variations in pH, redox, and temperature along and across fluid flow paths best explain the change to higher Au/Cu values upward and away from the Cu-rich potassic domains. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.