Hydrothermal Coprecipitation of Talc and Sulfides in a Sea-Floor Brine Pool Evidence from Geochemistry, 80/60, and Mineral Chemistry

The Mattagami Lake mine is an Archean Zn-Cu massive sulfide deposit located in the Matagami mining district of northwestern Quebec, within the northernmost volcanic center of the Abitibi greenstone belt. Orebody 2 is 21 million metric tons grading 10.5 percent Zn, 0.17 percent Cu, and 0.014 oz Au plus 1.15 oz Ag per short ton. Most of the orebodies in the Matagami district lie at the top of the Watson Lake Group rhyolites and are overlain by the Key Tuffite, a distinctive unit of mixed chemical sediments and epiclastic material of tron-dhiemitic composition. The footwall to the Mattagami Lake mine is a vitroclastic rhyolite possessing the assemblage albite-oligoclase, quartz, and brown biotite. In proximity to the ore zone albite is progressively hydrolyzed to chlorite, which preserves perlitic textures and may comprise up to 90 percent of the rock. Background rhyolites external to the mine plot within the field of rhyolites in Zr/ TiO2-Nb/Y coordinate space. Relative to average Archean rhyolites they are depleted in K20, Cu, and Zn and possess pronounced enrichments of Na203, Fe203, and MnO. Triply concordant oxygen isotope compositions for quartz (10.5%0), albite (7.$%0), and chlorite (1.8%0) signif