Geology and Geophysics of the Zunil Geothermal System, Guatemala

Abstract

The Zunil geothermal system in western Guatemala is located adjacent to the active volcanic centers of Santa Mari and Cerro Quemado, where the northeast trending Zunil fault system transects the proposed Quetzaltenango caldera. The volcanic and intrusive host rocks of the geothermal system are highly altered, with the degree of alteration and veining increasing with depth. The effects of hydrothermal alteration are reflected in both the resistivity and gravity data. The electrical soundings define the presence of a resistive basement at depths of 200-400 m that correlates with a change in the clay mineralogy of the volcanic rocks. Trends in conductivity thickness products also may reflect an increase in the development of electrically conductive clays away from the upwelling center. Hydrothermal alteration may be reflected in the gravity data as low amplitude gravity highs. Both the field mapping and gravity studies define a series of northwest and northeast trending faults.