MINERAL MAPPING USING WORLDVIEW 3 DATA AT MOUNTAIN PASS, CALIFORNIA

WorldView 3 (WV-3) data were used to map mineralogy in the Mountain Pass, CA area. The northern and eastern parts of the study area consist of Precambrian gneiss, granite, and scarce carbonatite intrusive rocks. The southwestern part of the study area is covered by Paleozoic and Mesozoic carbonate, siliciclastic, volcanic, and granitic rocks. Deposits in the study area include the Rare Earth Element (REE)-rich Sulphide Queen carbonatite, the polymetallic deposit at the Morning Star Mine, and a number of skarn deposits, prospects, and occurrences.

WV-3 is a multispectral sensor that measures reflected radiation in eight visible near-infrared bands between 0.39 and 1.05 mm (VNIR) and in eight shortwave infrared bands from 1.08 to 2.38 mm (SWIR). Because WV-3 can point off nadir, spatial resolution varies from 1.24 m at nadir to 1.38 m at 20^o off-nadir for the VNIR bands and from 3.7 m at nadir to 4.10 m at 20^o off-nadir for the SWIR bands. In this study the SWIR bands were resampled to 7.2 m spatial resolution due to federal government restrictions on public release of SWIR 3 - 4 m spatial resolution data.

Standard2A WV-3 VNIR and SWIR data were converted to radiance using an ENVI radiometric correction algorithm and the WV-3 radiance data were calibrated to reflectance using FLAASH atmospheric correction software. An averaged water vapor value for the study area during acquisition of WV-3 was obtained from MODIS MOD05 water vapor data for use in the FLAASH algorithm. Spectra and mineral maps were validated using sample spectra and spectra measured in the field using a Fieldspec 4 VNIR-SWIR spectrometer.

Logical operator algorithms, which use band ratios and thresholds to map spectral absorption features, successfully mapped mineralogy using either VNIR or SWIR data. Minerals mapped using SWIR data include calcite and dolomite in the Paleozoic carbonate units, epidote-chlorite in the skarn deposits and chlorite-rich Precambrian gneiss, Al-muscovite in the Precambrian granites, and Fe-muscovite in the Morning Star Mine deposit and in some of the Precambrian gneiss. Fe³⁺ -rich minerals including goethite were mapped using VNIR data. Mapping of REE-rich carbonatite was inconclusive, however, due to low WV-3 spectral resolution of neodymium VNIR spectral features.