Identification of Hydrothermal Alteration Using Satellite Images in Areas with Dense Vegetation Cover

Abstract

TM images were used in order to characterize areas with hydrothermal alteration. Processing of the images included principal components analysis and False color composition (RGB). The studied area is located in the western border of the Mexican Volcanic Belt and hosts still unexploited ore deposits (mainly opal and precious metals) of hydrothermal origin. The stratigraphic column includes products of the volcanic activity that formed the Sierra Madre Occidental during the Tertiary, and of the recent volcanic activity related to the still active Ceboruco Volcano. The main problem is to differentiate the hydrothermally altered rocks from vegetation covered areas in the satellite image. The band ratios did not yield good results in removing the spectral effect of the vegetation cover in areas that contained hydrothermally altered rocks, this was due to the high correlation between the bands as was shown when they were analyzed using the principal components approach. The of the vegetation spectral effect was done using the technique for bands: 1, and for oxides analysis; and 1, 4, 7, for hydroxyls analysis. All the zones of alteration mapped in the field coincide with the areas marked hydrothermally altered in the resulting images