Geothermal Exploration of the Mesillas Zone, Nayarit, Mexico

Abstract

As part of the project between the IDEEA group of the Institute of Engineering and the Geothermal Research Group of the Geophysics Institute, UNAM, first exploration fieldwork has been carried out in the Mesillas geothermal system, Nayarit, Mexico with the long-term objective of developing a direct use geothermal project. A geological survey, chemical characterization of geothermal samples, diffuse flux analysis (CO2, H2S and CH4) as well as reservoir temperature estimations in the geothermal system were performed. The Mesillas geothermal area (~ 420 m.a.s.l.) is in the southern part of the state of Nayarit, approximately 30 km west of San Pedro Lagunillas, where the geothermal field San Pedro Dome is located, which is currently under exploitation. In general, the following preliminary results were obtained: (i) five andesitic units were identified in an area of ~1.5 km2, with 25 thermal springs with discharge temperatures between 47-90 °C, pH ~ 9 and Na-CO3 water type; (ii) andesites show high permeability given the intense fracturing derived from the normal faulting systems with trend NW-SE, SW-NE, NS, and EW; (iii) the surface hydrothermal alteration is argillic and (iv) degassing of CO2 is restricted to the springs area with no preferential degassing direction.