Infrared Spectral Mineralogy for Geothermal Exploration: a Preliminary Study Using Cutting Edge Technology Infrared Imaging Spectroscopy (IRIS)

Abstract

Infrared spectroscopy is a non-destructive mineralogical analysis with minimum sample treatment required. The mineral identification in this method is based on the energy reflected by molecular vibrational processes upon incoming infrared radiation which is a proxy for mineralogy and mineral chemistry. With this method, we can identify minerals that are difficult to distinguish using some other methods (i.e. methylene blue stain test, binocular microscopy, and petrography), particularly clay minerals which are the important temperature indicator minerals in geothermal systems. Therefore, it is a promising mineralogy analytic method to be applied in geothermal subsurface samples. However, the application of the method in geothermal studies is still limited, especially the recently-developed infrared imaging spectroscopy (IRIS), which is the extension of the conventional (non-imaging) infrared spectroscopy. This paper reviews the current use of infrared spectroscopy for geothermal exploration and present preliminary results of our work using infrared imaging spectroscopy. Our preliminary results show that infrared imaging spectroscopy can identify much more minerals compared to non-imaging infrared spectroscopy, including minerals which are present only in a small amount. Spatial relationships between hydrothermal alteration minerals might be visible in bigger cuttings grains. However, the initial mineral map classification using Spectral Angle Mapper (SAM) shows that it is difficult to determine the threshold which will give an accurate assignment of minerals.