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UBC Theses and Dissertations

Jura-triassic magmatism and porphyry Au-Cu mineralization at the Pine Deposit, Toodoggone District, North-central British Columbia Dickinson, Jenni Michelle

Abstract

The Pine, Fin, and Mex porphyry Au-Cu ± Mo systems are all located within a 10 km² area in the Toodoggone district, along the eastern margin of the Stikine terrane in British Columbia. Multiple episodes of porphyry-style mineralization are associated with these three magmatic centres. The Fin monzogranite is the oldest dated pluton in the district, with a U-Pb zircon emplacement age of 217.8 ± 0.6 Ma. A cross-cutting main-stage quartz-pyrite-chalcopyrite ± molybdenite ± sphalerite vein gives an older Re-Os molybdenite mineralization age of 221.0 ± 1.4 Ma. Hence the vein probably cross-cuts a slightly older, undated magmatic phase. Lead isotope values for sulphide minerals from main-stage veins indicate that magmatic-derived fluids interacted with country rocks and possibly other fluids. The Pine quartz monzonite (U-Pb zircon emplacement age of 197.6 ± 0.5 Ma) intrudes, alters, and locally mineralizes Toodoggone Formation Duncan Member andesite tuff (U-Pb zircon age of 200.9 ± 0.4 Ma). High-grade (0.57 g/t Au and 0.15% Cu) mineralization occurs in main-stage quartz-magnetite chalcopyrite-pyrite veins and disseminated throughout the potassic alteration zone in the Pine quartz monzonite stock. Late-stage anhydrite-pyrite ± specular hematite ± chalcopyrite, quartz-pyrite ± chalcopyrite, and pyrite ± chalcopyrite veins and related phyllic alteration cross-cut earlier veins. Propylitic alteration occurs distal to the potassic core of Pine in the Fin monzogranite and Duncan Member andesite. Limited fluid inclusion data, in combination with S and Pb isotope values for veins and host rocks, suggest that the main-stage fluid was magmatic-derived and deposited metals at 430 to 550 °C and depths of about 5.5 km. Late-stage fluids were also probably derived from the Pine quartz monzonite but interacted with Takla Group country rock prior to metal deposition. Metals were deposited at temperatures of 330 to 430 °C and depths of about 5.0 to 5.5 km. The final mineralization phase of the Pine porphyry system is temporally constrained by the emplacement of weakly mineralized syenite dykes (U-Pb zircon age of 193.8 ± 0.5 Ma). The final stage of magmatism in the Pine-Fin-Mex area is defined by the emplacement of rhyolite dykes (U-Pb zircon age of 193.6±0.4 Ma).

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