CHEMISTRY, TEXTURES, AND FLUID INCLUSIONS IN QUARTZ: CLUES TO ORE FLUID SOURCES AT THE NORTH BETZE ORE ZONE, GOLDSTRIKE CARLIN-TYPE GOLD SYSTEM, NORTHERN CARLIN TREND, NEVADA

Ore fluid conditions, components, and sources at the Goldstrike deposit, the largest Carlin-type gold system in the world, are not well understood. To improve our knowledge of ore fluids, geochemical, textural, and fluid inclusion characteristics of ore-stage quartz associated with Au-bearing pyrite are being determined. Pre-ore and post-ore quartz, spatially associated with ore but related to other events, are also being characterized. Detailed information on the geochemistry and fluid inclusion characteristics of ore-stage quartz will help refine our model for ore deposition. In addition, the ability to distinguish different generations of quartz and recognize ore quartz will provide a new exploration tool for these systems.

Paragenetic studies focused on the North Betze ore zone identified Au-bearing pyrite grains and ore-stage quartz. Discrete types of pyrite were distinguished based on size, morphology, color, and geologic association. Au-bearing pyrite grains, identified initially by morphology, were confirmed by electron microprobe analysis (EMPA). Various stages of quartz were identified by integrating petrographic, fluid inclusion, and cathodoluminescence studies, and spatial association with Au-bearing pyrite. Cathodoluminescence analyses distinguished generations of quartz that exhibit different intensities of luminosity. Ore stage jasperoid quartz that does not luminesce was overgrown by drusy quartz that also does not luminesce, and which appears to be late-ore stage. These observations indicate that ore-stage quartz is manifested by both jasperoid replacement of limestone and open-space deposition of drusy quartz. Multiple generations of post-ore drusy quartz overgrow ore and late-ore quartz and exhibit luminescence of varying intensities. Preliminary EMPA indicates that decreasing trace Al in quartz corresponds with increasing intensity of luminosity.

Primary, secondary, and pseudosecondary fluid inclusions have been identified in multiple generations of quartz. Ore stage quartz contains sparse two-phase fluid inclusion assemblages in jasperoid and in youngest late ore-stage drusy quartz. Primary inclusion assemblages exhibit consistent liquid-vapor ratios (approximately 5 volume percent vapor) and occur within growth zones in drusy quartz crystals.