Ore Fluid Properties and Sources from Quartz-Associated Gold at the Betze-Post Carlin-Type Gold Deposit, Nevada, United States

摘要

Quartz at the Betze-Post deposit, the largest Carlin-type gold system in the world, was examined to better understand ore fluid properties and sources that generated Carlin-type gold deposits. Detailed petrography and paragenesis investigations distinguished textural relationships, luminescence, various generations of quartz, and fluid inclusion populations; microthermometry, chemical analyses of quartz, and in situ and conventional oxygen isotope analyses of quartz provided information about hydrothermal fluid conditions as well as fluid sources and ore formation processes. Pre-, syn-, late-, and post-ore stages of quartz were distinguished during petrographic studies and confirmed by cathodoluminescence analyses. Ore-stage jasperoid and late-ore drusy quartz are spatially associated with Au-bearing pyrite; both lack luminescence. Two generations of post-ore drusy quartz overgrew ore and late-ore quartz and exhibit bright and multiply zoned luminescence. Electron probe microanalyses determined that nonluminescing ore and late-ore quartz have elevated concentrations of Al, in contrast to post-ore luminescent quartz that contains low trace element concentrations. Fluid inclusion microthermometry determined that ore-staee fluids had low salinities, generally <5 wt % NaCl equiv, and were trapped at 180° to 240°C.