REMOTE MAPPING OF QUARTZ VEINS ASSOCIATED WITH GOLD-SILVER MINERALIZATION, AURORA MINING DISTRICT, WESTERN NEVADA

Advances in short wavelength infrared (SWIR) sensors has improved remote mapping of hydrothermal clays associated with shallow, high-sulfidation precious metal deposits. However, the ability to remotely map quartz-rich, low-sulfidation hydrothermal alteration requires thermal infrared (TIR) sensors because characteristic absorption of emission spectra occur well beyond the SWIR at 9.1 microns. We used thermal infrared (TIR) data from the MODIS/ASTER (MASTER) Simulator flown over the Aurora District to map the distribution prominent quartz veins.

The Aurora gold-silver deposit, located in the Bodie Hills near the Nevada-California state border, is classified as a quartz-sericite-adularia deposit. Neogene andesitic to rhyolitic volcanic rocks rest unconformably on Mesozoic basement consisting of Triassic metavolcanics that are intruded Cretaceous plutons. Precious metals are found in quartz veins intruding Miocene andesitic rocks ranging from centimeters to several meters in thickness. Mineralized quartz veins appear to be structurally controlled, related to district-wide N45-75oE trending right lateral strike slip faults.

The location and distribution of quartz veins at Aurora is not apparent on aerial photos, or unprocessed MASTER data. Quartz spectra were isolated from the remainder of the MASTER data using a cascaded Principal Component transformation that generated spectral bands free of instrumental noise. The “spectrally purest” pixels were isolated from mixed pixels and identified as mapping endmembers (e.g., quartz). The resultant map identifies all major quartz veins and several minor veins, many of which are clustered in the Silver Hill area south of most recent mining activities. These results which were verified through field studies, indicate that remote TIR mapping of low-sulfidation deposits provides a valuable exploration tool.