Geological and Geochemical Reconnaissance of a Non-Volcanic Geothermal Prospect in Guatemala - Joaquina Geothermal Field

Abstract

The results of a geological and geochemical survey of the Joaquina geothermal field in Guatemala are summarized. Structural mapping, soil chemistry including CO2 (soil gas), and shallow temperature measurements were employed in conjunction with petrographic and bulk rock chemical analyses of drill cutting samples to identify regions of hydrothermal fluid upwelling and outflow in the Joaquina system. A chemical reconnaissance of thermal manifestations provided evidence for the presence of a meteorically-derived Na-bicarbonate(-sulfate) geothermal fluid, similar to those in neighboring geothermal systems in Honduras. Geothermometric analyses of the Joaquina fluids yielded reservoir temperature estimates (Tsilica-adiabatic) of ~180°C. Sulphur and carbon isotopic analyses of soil gas and sulfide minerals in drill core indicate that the sulfur, CO2, and CH4 were likely derived from hydrothermal alteration of organicrich metasediments of the El Tambor Complex. The natural thermal output of the Joaquina system is estimated conservatively at 29.4 MWth. This study represents the first detailed field investigation of a non-volcanic geothermal system in Guatemala.