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Evolution of alteration and mineralization at the Red Chris copper-gold porphyry deposit East zone, northwestern British Columbia, Canada

University of British Columbia

Located in northwestern British Columbia within the Stikine terrane, the Red Chris Cu-Au porphyry deposit is hosted in the Late Triassic Red Stock (~203.8 Ma). The Red Stock is a quartz monzodiorite to monzonite intrusion hosted in the broadly contemporaneous volcanic rocks of the Stuhini Group. Red Chris has features that are characteristic of calc-alkalic and alkalic porphyry deposits and shares many similarities with the Ridgeway deposit of the Cadia district in New South Wales, Australia. A combined measured and indicated resource of 936 million tonnes at 0.374 % Cu, 0.385 g/t Au, and 1.224 g/t Ag has been outlined from the Main and East zones. Copper and gold are associated with bornite, chalcopyrite and lesser pyrite, hosted in quartz veins and stockworks as disseminations and fracture-controlled veinlets. High-grade mineralization is directly associated with high quartz vein density. Copper-iron sulphide minerals are laterally zoned, with a bornite > chalcopyrite core, grading outward to a chalcopyrite > pyrite shell and outward and upward to a pyrite > chalcopyrite halo. Five major groups of veins are recognized, of which the oldest two sets contain much of the copper and gold. Stable isotopic analysis indicates the presence of magmatic and mixed magmatic-meteoric hydrothermal fluids. Evidence from sulphur isotopes demonstrates a high temperature oxidized magmatic fluid was responsible for transporting and depositing much of the copper and gold. A vertical and lateral zonation in sulphur isotopes exists, whereby deep regions exhibit δ34S values between -1.9 to -0.9 % and transition to near-surface regions in the pyrite halo that exhibit δ34S values between +0.9 to +1.9 %. Isotopic analysis of oxygen and deuterium of hydrothermal alteration minerals provide evidence for a magmatic fluid (secondary biotite and muscovite) and a mixed magmatic-meteoric fluid (illite and kaolinite). Low temperature clay alteration (illite-kaolinite; intermediate argillic assemblage) significantly overprinted high temperature alteration (K-silicate, phyllic) in the upper levels of the system and gradually diminished intensity with depth. Carbonate veins and alteration also characterize the shallow levels and isotopic analysis of carbon and oxygen suggest a magmatic source with the possibility of minor mixing with an external meteoric fluid.

Text

2012-04-23

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/42207

Geological Sciences

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/