1. MLR Key Laboratory of Metallogeny and Mineral Assessment, Institute of Mineral Resources, Chinese Academy of Geological Sciences, Beijing 100037, China
2. China University of Geosciences (Beijing), Beijing 100083, China
Abstract：Hyperspectral technology is a new non-damaging method for mineral detection and identification. In recent years, short-wave infrared (SWIR) technology with a wavelength of 1.1~2.5 μm had been successfully applied in alteration minerals and correlated ore deposits studies. However, SWIR technology was more suitable for hydrated and hydroxyl-bearing minerals, and was not sensitive for minerals containing SinOk, SO4, CO3, PO4. Then thermal-infrared technology with the wavelength of 3~14 μm could remedy the technical defect, and was more detectable for minerals without hydro and hydroxyl. Garnet is an important neosilicate mineral containing SinOk, divided into many groups according to the chemical components including grossular, andradite, pyrope, almandine, spessartine et al., and garnet is indicative for temperature, pressure and other mineral forming conditions and ore prospecting. Recently, little research on thermal-infrared spectroscopy of garnet minerals has been conducted. In this paper, sixteen garnet minerals with different components and colors were collected, and thermal-infrared spectroscopy of these garnet minerals was firstly studied using Agilent 4300 thermal-infrared spectrometer. What’s more, the content of principal elements including SiO2，MgO，Al2O3，K2O，CaO，Fe2O3 of these garnet minerals was measured using Niton XRF analyzer at the same position, and the relationship between the content of principal elements and absorption wavelength were analyzed. The result indicated that garnet minerals had diagnostic features with twin peaks in the thermal-infrared band region of 10~13 μm, which presented the main absorption at about 11.5 μm and a secondary absorption at about 12 μm. The wavelength at these two absorption was well correlated with the Al2O3 and Fe2O3 content of garnet minerals, which was linear negative correlated with the content of Al2O3, and was linear positive correlated with the content of Fe2O3. The results can help quickly identify the chemical components of garnet minerals and add alteration zoning of skarn ore deposits in the field that indicate ore prospecting. The study started an application of Agilent4300 thermal-infrared spectrometer in the mineral study and gave a good example of thermal-infrared spectroscopy of garnet minerals study, which could provide the fundamental basis for thermal-infrared spectroscopy of other tectosilicates, neosilicates, single-chain silicates, carbonates and sulphates.
Key words：Garnet; Thermal-infrared spectroscopy; Chemical content; Correlation analysis
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