Thermal infrared spectroscopy studies on skarn minerals for exploration of the Jiama Cu-Mo deposit, Tibet, China

The zonation patterns of skarn minerals, including garnet, diopside, and wollastonite, are important for exploration of skarn deposits. Thermal infrared (TIR) spectroscopy, which covers the wavelength range of 6-14 mu m, is a new eco-friendly technology for skarn mineral identification. In this study, the TIR spectra data were collected, using an Agilent 4300 Handheld FTIR Spectrometer from nine drill holes within Jiama Cu-Mo deposit in Tibet, China. This study focuses on the TIR characteristics of grandite-series garnets (i.e., grossular to andradite), which have twin peaks in the 10-13 mu m range and a diagnostic absorption valley (T absorption valley) at around 11.5 mu m shifting based on the contents of Al2O3 and Fe2O3. The T absorption valley in the zoned garnet sample showed an undulating pattern, shifting towards longer wavelengths from the core to the rim, indicating the increase in Fe2O3 content and a decrease in Al2O3, MnO, and TiO2 content. The mixed spectral features of three significant skarn minerals including garnet, diopside, and wollastonite were used to classify the skarn zonation into garnet skarns, diopside-garnet skarns, and wollastonite-garnet skarns. The results from nine drill holes of the No. 24 exploration line in the cross section showed that the garnet T absorption valley shifted towards shorter wavelengths from the proximal to the distal skarn, as well as from the lower to the upper skarn. Furthermore, intensive copper mineralization occurred in the skarn when the garnet T absorption valley exceeded 11.50 mu m. In comparison, the garnet T absorption valley at 11.35-11.50 mu m is related to more intense molybdenum mineralization. This study suggests that TIR spectroscopy has the potential to rapidly identify skarn zonation in the field, and providing a suitable vector tool for skarn ore exploration.