Geochemical Characterization of the Calacoa Geothermal Zone

The Calacoa geothermal zone (CGZ) is located in the western Cordillera of the Andes in southern Peru, approximately 10 km on the western slope of Ticsani Volcano. In Calacoa there are mainly volcanic rocks that have been deposited over a sedimentary Cretaceous basement. The geochemical interpretation of the results shows that thermal waters are an alkaline-chloride-sulphate water type. The Cl-SO4-HCO3 diagram shows that most of the geothermal waters plot close to the mature water portion, which is typical of geothermal deep fluids. High B concentrations lead to a relatively high B/Cl ratios as shown on a B-Cl binary diagram. This can be used to elucidate the reactions of waters with sedimentary marine rocks at deep depths. The δ18O vs δD plot indicates that the geothermal water originates by a mixing of meteoric water with magmatic water. The results for chemical geothermometry allowed us to estimate temperatures between 170 and 230°C at the depth of the geothermal resources.