Characterization of the auriferous and barren North Dipper veins at the Sigma mine, Val D'Or, Quebec, based on structural, mineralogical, fluid inclusion and isotopic investigations.

摘要

Auriferous and barren North Dipper veins are the youngest vein systems at the Sigma mine and are interpreted to be shear veins emplaced along east-west trending, low-angle reverse faults during late D2 north-south compression. They comprise highly disrupted quartz and tourmaline layers, which indicate repeated vein opening, filling, and deformation episodes. Auriferous and barren North Dipper veins consist mainly of quartz and tourmaline. In addition, auriferous veins comprise minor calcite, chlorite, muscovite, pyrite, rutile, galena, pyrrhotite, chalcopyrite, bismuth telluride, and gold. Auriferous veins have proximal and distal alteration haloes composed of plagioclase-calcitetourmaline-pyrite-telluride-gold and chlorite-muscovite-calcite-quartz-rutile-pyrite-gold, respectively, whereas barren vein wall alteration is characterized by minor tourmalinization.; Early gold deposition occurred during the main vein-filling event (T 371°C) and was triggered by precipitation of pyrite in the vein and wall-rock. Late gold deposition occurred after main-stage vein filling (during post-D2 exhumation) at a higher temperature (445°C), where pervasive fracturing and increased fluid influx may have prompted mixing of H2O-NaCl-CO2-(CH4) and H2O-NaCl fluids along fractures, causing decrease of aH2S and of gold solubility. (Abstract shortened by UMI.)