Techniques for enhancing the spectral response of hydrothermal alteration minerals in Thematic Mapper images of Central Mexico

Abstract

The use of satellite images during the early stages of mineral exploration has been very successful in pointing out the presence of hydrothermally altered rocks and the main structural features that can be related with ore deposition. Here we compare several methods used for spectral enhancement of the images in order to detect rocks containing hydrothermal alteration in an area in the western section of the Transmexican Volcanic Belt, where recent unaltered volcanic and sedimentary rocks and Tertiary age altered volcanic rocks outcrop. The study area is covered by different types of vegetation: crops, bushes and pine trees. The techniques presented here allow the identification of hydrothermally altered rocks in areas covered with different vegetation types that do not have a similar spectral response. The methods that proved to be the most efficient were the Object Oriented Principal Component Analysis (Crosta Technique) using four TM bands combined with the HSI transformation. The results obtained with this method point out the areas identified in the field.