High Temperature Alteration Mineral Identification Using ATR Spectroscopy in Kenyan Geothermal Wells

Abstract

Understanding the formation and distribution of hydrothermal alteration minerals is essential for interpreting the thermal evolution, permeability, and fluid–rock interactions in geothermal systems. This study focuses on identifying high-temperature alteration minerals in selected Kenyan geothermal wells using Attenuated Total Reflectance (ATR) Spectroscopy, an advanced form of Fourier Transform Infrared (FTIR) spectroscopy. The method provides a rapid, non-destructive approach for recognizing mineral phases through their diagnostic infrared absorption features. Drill cuttings and core samples collected from different depth intervals and geothermal fields within the Kenyan Rift were analyzed to investigate mineralogical variations associated with increasing temperature and alteration intensity. The ATR spectra revealed prominent vibrational features characteristic of epidote, chlorite, quartz, garnet, and wollastonite, indicating progressive mineral transformations under high-temperature hydrothermal conditions. These spectral interpretations were verified using X-ray Diffraction (XRD) analysis, which confirmed the accuracy of ATR-based mineral identification. Integration of the spectral and mineralogical data delineated distinct alteration zones with depth, reflecting temperature gradients and fluid flow regimes within the geothermal reservoir. The study demonstrates that ATR spectroscopy is a reliable and cost-effective analytical tool that complements traditional methods in geothermal exploration. Its minimal sample preparation, high spectral resolution, and ability to analyze fine-grained mixtures make it suitable for routine characterization of alteration assemblages. These results enhance understanding of the hydrothermal and thermal evolution of Kenyan geothermal systems and provide valuable input for resource evaluation and reservoir development.