Infrared reflectance spectroscopy is effective at identifying many rock forming minerals, thus it is useful for characterizing lithologies and formations encountered in wells. Characterizing mineralogy and its variability within a formation or with depth can also provide information about past temperatures and rock physical properties that are important for Enhanced or Engineered Geothermal System (EGS) assessment. Advances in hyperspectral imaging technology allow for rapid analyses and the creation of high-resolution mineral maps of geothermal drill core or cuttings samples. This provides the ability to evaluate spatial relationships of minerals within the sample. We performed a new study on core and cuttings from several wells on the Fallon FORGE EGS site using automated high-resolution imaging spectroscopy. Our analysis focuses on well 21-31 that was drilled in early 2018. Spectral maps were acquired using a TerraCore Hyperspectral Core Imaging System (HCIS), with a pixel size of 1.2 mm, equipped with FENIX VNIR-SWIR (400-2500 nm) and OWL LWIR (8-12 μm) cameras, as well as an RGB camera to create a high resolution (0.12 mm pixel size) image of the same drill core or cuttings sample. We interpreted these data for dominant mineralogy, as well as spectral scalars that are related to the mineral structure. In addition, new X-Ray Diffraction (XRD) and thin section analyses were performed on samples from well 21-31 to validate and expand on our hyperspectral interpretation. These data were compared to the extensive existing dataset produced during the Fallon FORGE EGS project, including well log datasets (e.g. temperature and other wireline logs), formation characteristics, and existing mineral and hydrothermal alteration datasets. Finally, we evaluate our data alongside the current conceptual model of the Fallon EGS site.

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