| Abstract: |
Reflectance spectra were collected from the cores of two geothermal wells (HSB2 and HSB4) drilled during Summer 2010 as part of the Akutan geothermal exploration project on Akutan Island, AK. Spectra were collected using an Analytical Spectral Devices (ASD) portable spectrometer and used to identify mineralogy based on characteristic absorption features in the visible to shortwave infrared (0.35-2.5 ?m) region of the electromagnetic spectrum. The cores were previously studied in detail by Stelling and Kent (2011) who produced a thorough summary of the mineralogy identified in thin sections and by using X-ray diffraction (XRD) and a scanning electron microscope (SEM). The purpose of this study was to further understand the value of reflectance spectroscopy as a geothermal core-logging method by comparing findings with results from Stelling and Kent (2011). In addition, this study was done to identify any additional alteration minerals and characterize the mineralogy in core sections between samples studied by the previous authors. Reflectance spectroscopy is particularly sensitive to hydrothermal alteration minerals and precipitates, including clays, carbonates, and sulfates. Mineralogy may be used as a temperature index to characterize the thermal regime at depth and thus act as an indicator for geothermal potential. Muscovite, kaolinite, calcite, epidote, prehnite, hematite, montmorillonite, illite, chlorite, and zeolites were identified in this study using reflectance spectroscopy. Petrography, XRD, and SEM allowed for more specific discrimination of minerals and the identification of some minerals not possible using reflectance spectroscopy (quartz, adularia, pyrite), but the large amount of spectral data allowed for basic mineral identification over the entire length of the cores. |