Hydrogeochemical exploration of geothermal prospects in the Tecuamburro Volcano region, Guatemala

Abstract Chemical and isotopic analyses of thermal and nonthermal waters and of gases from springs and fumaroles are used to evaluate the geothermal potential of the Tecuamburro Volcano region, Guatemala. Chemically distinct geothermal surface manifestations generally occur in separate hydrogeologic areas within this 400 km 2 region: low-pressure fumaroles with temperatures near local boiling occur at 1470 m elevation in a sulfur mine near the summit of Tecuamburro Volcano; non-boiling acid-sulfate hot springs and mud pots are restricted to the Laguna Ixpaco area, about 5 km NNW of the sulfur mine and 350–400 m lower in elevation; steam-heated and thermal-meteoric waters are found on the flanks of Tecuamburro Volcano and several kilometers to the north in the andesitic highland, where the Infernitos fumarole (97°C at 1180 m) is the primary feature; neutral-chloride hot springs discharge along Rio Los Esclavos, principally near Colmenares at 490 m elevation, about 8–10 km SE of Infernitos. Maximum geothermometer temperatures calculated from Colmenares neutral-chloride spring compositions are ∼180° C , whereas maximum subsurface temperatures based on Laguna Ixpaco gas compositions are ∼310° C . An exploration core hole drilled to a depth of 808 m about 0.3 km south of Laguna Ixpaco had a bottom-hole temperature of 238°C but did not produce sufficient fluids to confirm or chemically characterize a geothermal reservoir. Hydrogeochemical data combined with regional geologic interpretations indicate that there are probably two hydrothermal-convection systems, which are separated by a major NW-trending structural boundary, the Ixpaco fault. One system with reservoir temperatures near 300°C lies beneath Tecuamburro Volcano and consists of a large vapor zone that feeds steam to the Laguna Ixpaco area, with underlying hot water that flows laterally to feed a small group of warm, chloriderich springs SE of Tecuamburro Volcano. The other system is located beneath the Infernitos area in the andesitic highland and consists of a lower-temperature (150–190°C) reservoir with a large natural discharge that feeds the Colmenares hot springs.