The igneous petrology, thermal history, and genesis of sedimentary rock-hosted Au deposits in the northern Battle Mountain mining district, Nevada

The Battle Mountain mining district in north-central Nevada hosts deposits of magmatic-hydrothermal origin, including porphyry, skarn, and distal disseminated deposits, as well as sedimentary-rock hosted Au deposits of uncertain origin. This dissertation examines the ages of magmatism and mineralization in the Battle Mountain mining district, the characteristics of hypogene sedimentary rock-hosted Au mineralization at the deposit scale, and potential novel techniques for dating alteration associated with this deposit style. Zircon U-Pb geochronology indicates that magmatism occurred during the Jurassic, Cretaceous, and Eocene in the district, and that these sedimentary-rock hosted Au deposits are spatially associated with Cretaceous and Eocene intrusions. Apatite and zircon (U-Th)/He thermochronology applied to intrusion samples from throughout the district reveal a widespread Eocene thermal event interpreted to represent hydrothermal fluid flow. The (U-Th)/He dates are contemporaneous with the formation of magmatic-hydrothermal deposits elsewhere in the district, providing a proxy age for Au mineralization at the sedimentary rock-hosted deposits. Geophysical data reveal that the development of the structural fabric within the Battle Mountain district was influenced by basement structures and that this crustal architecture forced successive generations of magmatism and hydrothermal fluid flow to repeatedly exploit the same structural pathways. This led to complex overprinting of alteration and mineralization in both space and time, which we propose explains why individual deposits display characteristics that meet classification criteria for multiple deposit styles and contributes to the diversity of deposit types observed in the district. These district-scale processes are also evident at the deposit-scale. Red Dot is the single largest sedimentary rock-hosted Au deposit at Marigold Mine and extends below the redox boundary, where we observe evidence that reactivation of the same fluid pathways through time leads to spatially overprinting hypogene alteration and mineralization styles. Red Dot displays multiple quartz generations in veinlets. Although the absolute timing of the earlier quartz generations is uncertain, their textures and characteristics are consistent with D and E veins in porphyry systems. Ore-stage quartz is the youngest quartz generation and contains no fluid inclusions, but produces a bright yellow, highly zoned cathodoluminescence response, typical of low-temperature hydrothermal environments. Early-stage pyrite displays porphyry textures and is enriched in Hg and Ni. Ore-stage sulfides consist of arsenian pyrite rims on earlier pyrite cores. The rims are enriched in Au, As, Ag, Cu, and Sb and show complex chemical zonation. Base metal sulfides show inconclusive paragenetic textural relationships with ore-stage pyrite and may either pre-date or post-date the Au mineralization event. Apatite and zircon (U-Th)/He dates indicate the most recent hydrothermal fluid flow event, i.e. ore-stage quartz…