A Re-Evaluation of the Moyuta Geothermal System, Southern Guatemala

Abstract

Chemical and isotopic data from four fumarole sites combines with prefeasibility assessments obtained in the 1970s have resulted in a reevaluation of the Moyuta geothermal system. Moyuta consists of an east west trending complex of Quaternary andesite/dacite domes and flows cut by north trending faults. Areas of fumaroles, acid springs, and bicarbonate rich thermal springs flank the north and south sides of the volcanic complex. Chloride rich thermal springs discharges along rivers at lower elevations around the Moyuta highland. The distribution of thermal features indicates that deep reservoir fluid rises convectively near the axis of volcanism and flows laterally to the north and south. Geochemical data suggest that there are two subsystems having temperatures of about 210°C (north flank) and 170°C (south flank). Data extrapolations suggest a reservoir fluid containing about 2400 mg/kg C1, with D = -.48% 18O = -.6%, and a tritium content of 0,4 T.U. Exploration well sited near the most northerly fumarole (Azulco) encountered temperatures of <113°C at 1004 m depth. We suggests the fumaroles occur above hydrothermal outflow plumes that are confined to vertical, fault controlled conduits. Higher temperatures occur closer to the intersections of the north trending faults and the Quaternary volcanic axis.