Chemical and isotopic composition of hot spring waters in the Tacna region, Southern Peru

Abstract

The Tacna region hosts the most promising geothermal zones of Southern Peru, comprising five main geothermal areas: Tutupaca, Calientes, Borateras, Ancocollo and Chungara- Kallapuma located along the Quaternary volcanic chain at a height of 4000-4400 m on the Cordillera de los Andes. In these areas, we studied the chemical and isotopic composition of thermal waters. The geochemical characterization of the thermal discharges shows, the presence of two different types of thermal spring in Tacna region Na+ -Cland Ca2+ -SO4 2- waters. The Na+ -Clsprings, controlled by magma degassing and by water-rock interaction processes. Ca2+ -SO4 2- waters are supply by shallow meteoric water heated by ascending gases and are characterized by a low pH. Chloride water is rich in B, As and SiO2, suggesting interactions of deep-originated fluids with meteoric waters at shallow depth. The relatively high boron concentrations in the geothermal waters may be due to deep circulation paths that interacted with different lithologies at depth associated to sedimentary rocks. The isotopic composition δ2H and δ18O indicates that the geothermal reservoir waters originate from a mixture of meteoric and magmatic water, with temperatures exceeding 200°C estimated by geothermometry, indicate that geothermal areas can be regarded as the most promising areas and deserve more detailed geological and geophysical investigations for determination the geothermal potential.