Utilizing thermal infrared spectroscopy data to map lithology and mineral alteration in geothermally active areas

Mapping hydrothermal alteration mineralogy is essential for characterizing active geothermal systems and identifying prospects for geothermal energy and mineral resource assessment. The potential of thermal infrared (TIR: 8 to 13 μm) imaging spectroscopy for geothermal mineral mapping remains largely under-explored. Here we present the first ever lithological and mineralogical maps of Parco Naturalistico delle Biancane (PNB), part of the Larderello geothermal field, derived from TIR imaging spectroscopy data collected by the Hyperspectral Thermal Emission Spectrometer (HyTES). TIR data provides simultaneous information on both surface composition and temperature, enabling the combined mapping of alteration mineralogy and thermal anomalies from a single dataset. The limited rock exposure and strong lithological and alteration heterogeneity make PNB a rigorous test environment. We mapped the dominant mineralogical assemblages associated with geothermal alteration at PNB, including clays, silicate and hydrothermal alteration assemblages. By integrating TIR-derived surface mineralogy with surface temperature, we demonstrate a spatial correlation, linking mineralogical alteration to geothermal activity. We also compare two independent mineral mapping approaches, the Mineral Identification and Characterization Algorithms (MICA), extended to the longwave infrared and the recently developed Surface Mineralogy code (SM-code), based on Multiple Endmember Spectral Mixture Analysis (MESMA), adapted for use with HyTES emissivity data. Simulation of laboratory emissivity spectra at the spectral resolution of the future spaceborne TIR missions, such as SBG/EAGLE-TIR, TRISHNA, and LSTM, reveals that SBG/EAGLE-TIR has the highest discriminative capability. These results establish a validated methodological and spectral reference framework for next-generation spaceborne TIR missions, advancing the use of TIR imaging spectroscopy for geothermal exploration and mineral resource assessment.