Hydrothermal alteration and main structures mapping using TM images in La Primavera geothermal field (Mexico)

Abstract

Landsat TM images of the La Primavera geothermal field area were used to identify the main structures within the field, and to locate areas that show hydrothermal alteration. The methods used in the processing of the images include univariate and multivariate statistical analysis, spectral and spatial enhancement. Vegetation in the area is not composed by wide leaf plants; however, there is interference between the spectra of vegetation and hydrothermal alteration. In order to overcome this interfer- ence, the Crosta technique and the Loughlin method were used (Crosta and Moore 1989; Loughlin 1991). As a result, iron oxides and hydroxyl minerals were detected in the area. The resulting images were displayed in gray tones and false color composites to enhance main structures and the altered rocks respectively.
The identified alteration zones were correlated with the discharged flows from the geothermal reservoir, and with the main structures that control the permeability of the reservoir and the cap rock; therefore, locating hydrothermally altered rocks in the surface will help to determine the presence of upflows from the geothermal reservoir.