PRELIMINARY MINERAL MAPPING OF PLAYAS IN DEATH VALLEY, CALIFORNIA, USING ASTER DATA AND LOGICAL OPERATOR ALGORITHMS

Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) data are being used to map the surficial mineralogy of playas in Death Valley, California in order to field check mineral mapping algorithms that have been used to map lithium brine-rich playas in Chile and Argentina which are not assessable to field studies. Previous remote sensing and field studies indicate that the Death Valley playas are covered with evaporite minerals similar to ASTER-mapped minerals at Salar de Atacama, Chile and Salar de Rincon, Argentina.

Three Visible Near Infrared (VNIR) bands at 15-m spatial resolution, 6 Shortwave Infrared (SWIR) bands at 30-m spatial resolution, and 5 Thermal Infrared (TIR) bands at 90-m spatial resolution are being used to map diagnostic spectral absorption features of minerals. The VNIR, and SWIR reflectance data and TIR emissivity data were resampled to 15-m spatial resolution and were mapped using Logical Operator Algorithms (LOAs). LOAs use multiple band ratios and band ratio values of minerals verified by field data or geologic maps in order to map spectral absorption features.

Mapping evaporites using ASTER SWIR and TIR data has specific advantages over using either SWIR or TIR data. Halite, for example, is spectrally flat in the SWIR region and can be confused with quartz. However, halite has a spectral absorption feature centered at 8.29 micrometers in the ASTER TIR data that is not present in quartz. Gypsum exhibits strong SWIR spectral absorption centered at 2.2 micrometers and can be confused with muscovite which has a similar spectral feature. Despite this, gypsum has a diagnostic spectral absorption feature centered at 8.63 micrometers in the ASTER TIR data. Thus, using SWIR and TIR data allows for more precise discrimination of certain evaporite minerals.

Preliminary mapping of the playas at Cottonball and Badwater basins in Death Valley, California indicate that the surficial mineralogy is similar to the mineralogy mapped at the lithium brine-rich Salar de Atacama, Chile and Salar de Rincon, Argentina. All the playas are covered primarily with halite and gypsum. Other minerals mapped adjacent to the playas include, carbonate, quartz, muscovite, alunite-kaolinite, and epidote-chlorite. Field mapping to verify mineralogy at Death Valley, California is planned for the fall of 2019.