Recent Cooling in Los Humeros Geothermal Field (Mexico), Inferred from Clay Minerals Distribution

Abstract

Samples of cutting form 12 exploration wells drilled in the Los Humeros geothermal field, were analyzed using X-ray diffraction for the identification of clay minerals. The results yield the flowing assemblages of clay minerals with increasing depth: 1 - Ca-montmorillonite zone; 2- interstratified illite-montmorillonite zone; 3 - illite and chlorite zone; 4 - illite, chlorite an dmonmorillonite zone. In some wells the illite chlorite zone can be identified also below the illite-chlorite-monmorillonite zone. The presence of montmorillonite in zone 4 is related to a temperature inversion. The temperature inversion inferred from the clay minerals distribution correlates well with the available data on hydrothermal alteration and fluid inclusion (Viggiano and Robles, 1988; Prol-Ledesma and Browne, 1989).