Comparison Between Two Contrasting Geothermal Fields in Mexico: Los Azufres and Los Humeros

Abstract

A comparison between the Los Azufres and the Los Humeros geothermal fields in the Mexican Volcanic Belt (MVB) is made. The Los Azufres geothermal field is located at the center of the MVB and is a typical boiling system lying entirely within Pliocene and quaternary volcanics. This field has been subdivided in two zones, namely North and South. At the center of the field lies a rhyolitic dome which permits fluid to discharge in two directions. Thus the fluid moves up from the aquitard, which contains only compressed liquid to the producer aquifer, where it flashes in situ to constitute a two phase zone, and later, above the level of alkali chloride water, steam segregates in pockets to discharge as fumaroles and hot springs. In some places the steam condenses to produce intense alteration with kaolinite and residual silica. On the other hand the Los Humeros geothermal field is locatd at the Eastern side of the MVB. Its lithology is more complex, being grouped into four units including hornblende and augite andesites, basalts, ignimbrites, limestones, granirir rocks, marbles, hornfels and diabases. Thus although this system is also a high relief one, its hydrology is quite different from Los Azufres. Here fluid of variable composition, moves up from the aquitard (local basement) to the aquifer (Unit III) to constitute a narrow compressed liquid zone, with temperatures near to critical, but steam does not separate in-situ. Its superficial discharge is very low.