MAPPING SULFATE SYSTEMS USING ADVANCED REMOTE SENSING TECHNIQUES

The discovery of jarosite on Mars has created interest in terrestrial analogs where similar mineralogy can be found. The remote sensing group at Univeristy of Nevda - Reno has used a wide variety of airborne and spaceborne sensors to map the occurrence of sulfates using both reflected solar wavelengths (0.4 to 2.5 µm) and emitted thermal wavelengths (7 to 14 µm). Data sets range in spatial resolution from 2m to 30m/pixel and spectral fidelity varies from hyperspectral systems (hundreds of channels) to multi-channel systems. We have used a variety of airborne hyperspectral systems: AVIRIS, HyMAP, HyperSpecTIR, all measuring the optical and shortwave infrared, and SEBASS, measuring the thermal infrared. Multi-channel spaceborne data from ASTER, ALI and airborne data from MASTER have also been used to map mineralogy at varying spatial scales. We perform extensive field validation of remotely mapped mineralogy using portable field spectrometers and collect samples for laboratory measurements and XRD corroboration of mineral species.

Data sets have been acquired over active geothermal systems where sulfates tend to concentrate near old vent structures or around current fumaroles. In the regions historic mining districts Virginia City economic mineralization appeared during a low-sulfidation hydrothermal phase, but many sub-economic minerals contain sulfides that weather in mine tailing piles to form hydrated sulfate minerals. At Leviathan, the region is hosted by intrusive volcanics with former open pit mining of elemental sulfur. We have mapped common sulfate species at these locations, including alunite, gypsum, and jarosite. In all cases the most diagnostic spectral features were identified using hyperspectral airborne data at high spatial resolution corroborated with field measurements. Coarse spatial resolution and low spectral fidelity can broadly identify alteration zones, but are not capable of uniquely identifying specific sulfate minerals. In many instances, mixed sulfates were identified in remote data sets, but field and laboratory measurements were needed to confirm individual species. Sulfates are identified in both shortwave and thermal infrared data and using measurements from both spectral regions allows greater mineral identification ability.