MAPPING OF HYDROTHERMAL ALTERATION BY REMOTE SENSING AT 
THE ACOCULCO CALDERA, PUEBLA, MEXICO 
VICENTE TORRES RODRÍGUEZ 1 & GABRIEL ORIGEL GUTIÉRREZ 
Unidad de Geotermia, Instituto de Investigaciones Eléctricas, A.P. 1-475, Cuemavaca, Morelos, 
62001, México 
ABSTRACT 
This paper presents a method to recognize 
mineralogical features in hydrothermal 
alteration zones by means of remote sensing. 
The proposed technique is based on the analysis 
of the principal components of the included 
information for each band of the Landsat 
satélite. The technique of the principal 
components is an interactive tool, where the 
questions are planned in function of field 
knowledges of the study zone, such as 
mineralogical evidences, experimental 
determinations of rocks and minerals, and 
radiometric measurements at the surface. 
The use of digital image processing for the 
reconnaissance and mapping of hydrothermal 
alteration zones at the Acoculco Caldera allows 
to detect zones with the abundance of iron 
oxides and aluminium hydroxides (clays). 
1. INTRODUCTION 
The geothermal zone of the Acoculco Caldera is 
located at the extreme eastern part of the 
Transmexican Volcanic Belt (CVT), between 
the States of Puebla and Hidalgo, Mexico. This 
region is encountered in a straight line 110 km 
northeast of Mexico City. (Fig. 1) 
The geothermal study of the zone initiated in 
1983 as part of a regional inventory of the 
principal thermal sites, realized by the Comisión 
Federal de Electricidad (QUIJANO 1983). Later, 
TELLO (1986) started the investigation of the 
thermal waters of the caldera, conforming the 
geothermal characteristics of the thermal 
Figure 1. Location of study area 
manifestations. Parallel to TELLO's study, 
CASTILLO and DE LA CRUZ (1986) worked a 
primary geological-volcanological map at scale 
1:50,000. Their results are interpretated within a 
model of the caldera evolution, which were 
confirmed by posterior studies (TORRES et al. 
1995). 
In 1995, the Comisión Federal de Electricidad 
(CFE) perforated the exploration well EAC-1 
within the caldera to a depth of 2000 m. A 
temperature of 274 °C was measured at the 
bottom of the well. 
1 E-mail: vtorres@iie.org.mx