Mapping REE-minerals at the Mountain Pass Mine, California USA, using DESIS imaging spectroscopy data

Abstract:

DLR Earth Sensing Imaging Spectrometer (DESIS) data acquired in 2019 were used to spectrally map the distribution of Rare Earth Element (REE) minerals at the Mountain Pass Mine in California. DESIS data are acquired from the International Space Station covering the visible/near-infrared (VNIR) spectral range (0.4 to 1.0 microns) in 235 channels with a 3.5 nm bandpass and at a 30 m pixel size. Most minerals with Lanthanide series elements (i.e., Pr, Nd, Sm, Eu, Tb, Dy, Ho, Er, Tm, and Yb) have 4f-f transition absorptions over the VNIR range. These absorptions change shape and wavelength position with mineral type. Theoretically, DESIS data have fine enough spectral resolution to resolve these changes and could be used to differentiate between REE minerals from orbit. We applied the U.S. Geological Survey’s Material Identification and Classification Algorithm (MICA) to the DESIS data and detected neodymium’s spectral absorptions, confirmed by field sample measurements, in the mine pit, product stockpiles, waste rock and tailings piles. Detection of neodymium’s spectral signature in materials covering areas smaller than the relatively coarse 30 m pixel size of DESIS implies the ability to detect deposits with high concentrations of REEs at the subpixel level from orbit. Evaluation of the utility of DESIS data for spectrally differentiating between individual REE mineral types is ongoing. If DESIS data can be used to successfully differentiate between REE minerals at Mountain Pass, then this instrument may potentially contribute to finding economic REE deposits in other areas. Such a success would further demonstrate that orbital measurements can assist in defining economic mineral deposits worldwide.