Geochemical and Isotopic Evaluation of San Marcos Geothermal Area, Guatemala

Abstract

San Marcos Geothermal Area lies in the San Marcos Caldera (Pleistocene age), an elliptic depression with axis about 13 and 9 km, in the western part of the country.

Chemical and isotopic analyses were made to 60 spring samples with a surface temperature range from 15 "C to 95 "C (boiling point in the area) and two river samples were chemically analyzed. Results show that there are two different reservoirs; a deeper one with subsurface temperature around 250 "C (chloride content = 600 m a ) and a shallower one with subsurface temperature close to 200 "C (chloride content = 500 mg/l). Chemically the waters are of three types; sodium chloride, calcium bicarbonate and a mixture between them. Isotopically the sodium chloride water seems to be a mixture of 75 % meteoric water and 24 % andesitic water.

Previous gas analyses confirm underground temperature and magmatic origin of the water.