Synthesis of high-spatial resolution hyperspectral VNIR/SWIR and TIR image data for mapping weathering and alteration minerals in Virginia City, Nevada

The Comstock mining district, around Virginia City, Nevada, consists of mostly Miocene volcanic rocks that have been subjected to multiple episodes of hydrothermal alteration, extensional faulting, and mineralization. The distribution of alteration zones is related to the occurrence of precious metal deposits. Also, as a result of past mining activity, tailings that are now distributed throughout the town site contain-abundant Fe-sulfide minerals that weather to form secondary Fe-minerals often linked to acid mine drainage. To support research into both precious metal exploration, and environmental site characterization high spatial resolution (∼2 m) hyperspectral VNIR/SWIR and TIR images were acquired over Virginia City using the newly-developed airborne imaging spectrometers HyperSpecTIR and SEBASS. Spectral reflectance data from HyperSpecTIR and spectral emissivity data from SEBASS were used to generate maps of important weathering and alteration minerals. Acid-sulfate alteration minerals were found to be zoned locally and weakly constrained by structures. Jarosite was found to be relatively abundant on mine tailings along with minor occurrences of hydrous Mg-Ca-Al sulfates, indicative of pH conditions around 3-5. Finally, minerals that could not be identified uniquely with one spectral range could be identified using a combination of both VNIR/SWIR and TIR hyperspectral image data.