Geothermal exploration in Mexico 1968–1969

Abstract

The Federal Electricity Commission is developing a second geothermal field in the Cerro Prieto area, near Mexicali, Baja California, with twenty-two producing drill holles. Exploration is concentrated south-east of Cerro Prieto where hot water and steam at high temperature and pressure are present in the reservoir. To the north and south of Cerro Prieto there are three further areas of surface manifestations. During the period from the beginning of 1968 to August 1969, the Research Institute for the Electrical Industry, a branch of the Federal Electricity Commission, has carried out geological, geophysical, and geochemical studies in four geothermal fields in the central volcanic belt, located approximately between parallels 18 and 21 north latitude, and composed of volcanic rocks of ages ranging from Tertiary to Recent. All of them have very good contrast in their physiographic expression, intimately connected with active volcanic and tectonic zones of Mexico. The fields of Los Negritos and Ixtlán de los Hervores, State of Michoacán, (1535 metres a.m.s.l.) are at the intersection of the western Sierra Madre and the west-central part of the neovolcanic axis. They are about 27 km apart and separated by the Pajacuarán Ridge, on the eastern side of Lake Chapala, 130 km east of Guadalajara. The lake Chapala region is structurally a tectonic trench formed by the Chapala-Acambay system of E-W faults, partially covered by lacustrian sediments and pyroclastic materials. It is a very rich agricultural valley, and there are zones of intense surface thermal activity in areas of recent volcanic activity. The field of Los Humeros, State of Puebla, (2700 metres a.m.s.l.) is at the center of a caldera in the eastern part cf the neovolcanic axis, and the activity consists of dry steam manifestations distributed along three small N-S faults. In these three areas, geological mapping (photogeology and surface sampling) surface temperature, heat flux and resistivity surveys, and also chemical sampling, have been completed. Los Azufres (2800 metres a.m.s.l.) is the highest and most mountainous of these geothermal fields. Preliminary surveys have been made of some hot springs and fumaroles, including temperature measurements, chemical sampling, photogeology, and establishment of a network of benchmarks. The programme is well advanced in Ixtlán de los Hervores, where five exploration drill holes have been sited, and drilling has commenced on the first two sites.