Geochemical Interpretation of Bicarbonate Thermal Springs for the Comprehension of a Geothermal System: A Case Study at Cerro Machin Volcano, Colombia

Abstract

Cerro Machin volcano is an active volcano located on the eastern flank of the Cordillera Central of Colombia with thermal springs dominated by two types of bicarbonate waters; Na-HCO3 and Ca-HCO3 waters. The chemical components and δ18O and δ2H isotopes analyses were used to characterize the waters and their relationship with the geothermal system. Na-HCO3 springs are less affected by the dilutions/mixing processes and they were suitable for some geothermometers, whereas the Ca-HCO3 springs are more strongly affected by this subsurface process, and not suitable for geothermometry. The equilibration temperatures determined by geothermometry is between 158°C to 246°C. Application of the chloride enthalpy model suggests a hot parent water of about 282°C. The stable isotope compositions of the geothermal waters indicate a meteoric origin, and the waters became enriched in CO2 by steam-heating and gas adsorption. The geothermal system is a convection-dominated geothermal play associated to recent volcanism and, with an intermediate reservoir temperature around 200 - 230°C and, a possible deep high enthalpy reservoir around 280°C.