The application of near-infared spectral data in studying the chloritized rocks

Chlorite minerals present in altered rocks could characterised by field portable near-infrared spectroscopy. It is a kind of low-temperature altered mineral that cristal at between 100 to 400 degree centigrade. Six kinds of major alteration rocks, andesite, dacite, sillite, granite, sandstone and phyllite are shown the spectruml characteristic of chlorite. The characteristic absorption bands of chlorite are always due to OH stretch absorption and metal-OH bend absorption, but different lithology behaves different wavelengths of the absorption bands espetially for basic rocks, intermediate rocks and acid rocks. This behavior could help geologists to study the lithology and diagenetic environment. The diagnostic absorption bands of chlorite are appear at wavelengths between 2249nm and 2260nm, it dues to Fe-OH absorption and called Fe-OH band; and another important absorption band between 2335nm to 2355nm, it is caused by Mg-OH absorption and named Mg-OH band. Fe-OH band and Mg-OH band are always existence proof of chlorite. Basic rocks such as andesite and sillite, their Fe-OH bands are occured at wavelength between 2256nm and 2260nm; Mg-OH bands are located at wavelength between 2338nm to 2339nm. Intermediate rocks such as dacite and sandstone, their Fe-OH bands are appeared at wavelength between 2253nm and 2256nm; Mg-OH bands are shown at between 2237nm and 2251nm. Acid rocks such as granite and phyllite, their Fe-OH bands are shown at wavelength between 2249nm and 2252nm; Mg-OH bands are occurred at wavelength between 2340nm and 2351nm. Contrast with X-Ray Fluorescence Spectrometer measurement, the wavelength of the Fe-OH band correlates positively with the (FeO+Fe2O3) values. It varies from Mg-rich to Fe-rich varieties, and it can help us to analysis the diagenetic environment, and it could also distinguish basic rocks, intermediate rocks and acid rocks that be rich in chlorite.