The geothermal system of Las Tres Virgenes is related to a Plio-Quaternary volcanic complex, in an active tectonic zone associated with Gulf of California opening. Since 1984, intensive exploration studies were conducted by the Comision Federal de Electricidad of Mexico. This paper summarizes the geological, geophysical and geochemical studies, as well as the exploratory drilling results. The hydrothermal active zone is related to the most recent igneous activity, between 0.44 Ma and present time. The youngest tectonic structures control the principal permeability zones and hydrothermal activity. The geoelectrical methods applied, defined an interesting geothermal zone of small size, coincident with the most intensive fumarolic activity and hot soil sites. A broader area of secondary interest was delineated, but more detailed studies are required. Geochemically estimated temperatures agrees well with the 266 "C measured during drill-hole evaluation. Discharged fluids are of acid-sulphate character, having quartz, calcite, chlorite, epidote and clays assemblages. These results represent the first mexican experience in the evaluation of low permeability reservoirs contained in granitic fracturated rocks. The accumulated knowledge is a valuable guide for the design of future exploratory strategies in some similar areas, reducing the risk of failure and the exploration costs.

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