Characteristic of hydrothermal alteration minerals on MT-1 and MT-2 wells, Mataloko, central Flores, East Nusatenggara, Indonesia by using short-wave infrared reflectance spectroscopy

Abstract

The short-wave infrared reflectance spectroscopy has been used in a wide range of mineral exploration especially to recognize the alteration minerals related with mineralization. The techniques are also very useful in geothermal exploration especially to determine hydrothermal alteration minerals that are related to the physical and chemical characteristics of the geothermal formation. The spectrally detectable major hydrothermal alterations in wells MT-1 and MT-2 are montmorillonite (+/- zeolite), halloysite, kaolinite, illite and dickite. The over print between the smectite group (montmorillonite) and kaolin group (kaolinite，halloysite and dickite) shows the two fluid conditions in the formation. The smectite group occurs in a non-acid condition while the kaolin group occurs in an acid condition. The trend of decreasing Al-OH band wavelength from near the surface to the bottom of the holes reflects to change of state from montmorillonite rich (high Al-OH band absorption) to illite rich (low Al-OH band absorption). Therefore, the Al-OH wavelength data reveal a transition from a smectite dominated zone near the surface to illite dominated zone at the bottom of the well. These features probably also reveal the temperature history of the geothermal formation.