MINERAL MAPPING OF THE RARE EARTH ELEMENT DEPOSIT, MOUNTAIN PASS, CALIFORNIA USING SEBASS

Rare Earth Elements are an important commodity for many industrial applications. Carbonate minerals associated with REE Carbonatite Complexes are calcite, dolomite, siderite, and/or ankerite which have absorption features in the LWIR. Bastnaesite and sahamalite (REE carbonates) also have LWIR absorption features. Airborne visible-near infrared (VNIR) and short wave infrared (SWIR) imaging spectrometers can remotely map REE's minerals and carbonates, but other minerals such as epidote, muscovite, biotite, and amphiboles have absorption features that overlap the carbonate absorption features in the SWIR making their identification difficult.

SEBASS (Spatially Enhanced Broadband Array Spectrograph System) is a hyperspectral sensor that measures from 2.5 – 5.3 µm and 7.5-13.5 µm from an aircraft or the ground. Since carbonates, bastnaesite, and sahamalite have LWIR absorption features these minerals can be mapped remotely using SEBASS. This mineral mapping of carbonates, bastnaesite, and sahamalite provides new and complimentary hyperspectral data that may be useful for mineral exploration and lithological classification of carbonatite complexes.

SEBASS was flown over the Rare Earth Element deposit at Mountain Pass, CA in May 2006. At-sensor data were corrected for atmospheric effects using In Scene Atmospheric Correction (ISAC) and the resulting apparent surface radiance data were then corrected to apparent emissivity using an emissivity normalization algorithm. Carbonate mineral maps were created using publicly available spectral signature libraries using a spectral feature analysis algorithm. Bastnaesite, and sahamalite mineral maps were produced using spectral signatures from samples provided by the Smithonsian Institution. This study shows that LWIR hyperspectral data are useful for remotely mapping of carbonates, bastnaesite, and sahamalite.