| Abstract |
The thermal manifestations around Cordillera Sillapaca are hot springs; temperature values are on the range of 18 to 83 °C, pH is between 3.39 to 7.75 and electrical conductivity from 0.053 to 35.7 mS/cm. Hot springs are surrounded by sedimentary and igneous rock units with an age range between Cretaceous and Miocene. The oldest rocks units are sandstone and limestones from Cretaceous (Hualhuani and Arcurquina Formations). The volcanic activity lasted from Oligocene to Miocene ages; the volcanic outcrops are throughout the study area (Tacaza, Palca, Maure and Sillapaca Groups). The structural geology shows that regional faults (Lagunillas NW-SE system) affected rocks units since Mesozoic times, and in recent times developed a visible line parallel to the axis of the Cordillera Sillapaca; permeability is the main factor in meteoric water filtration, circulation, and recharge of the geothermal systems. The hot water emerges in areas with high and low sulphidation processes, associated with epithermal deposits of Au-Ag and Pb-Zn-Cu (related to intrusive and/or subvolcanic bodies of dacite-andesitic composition). According to geochemical interpretations, the water samples are classified in Cl (mature waters), SO4 (volcanic waters) and bicarbonate waters. The Piper diagram groups them into Na.K-Cl and Ca.Mg-Cl.SO4. The waters with high Cl concentration could be associated with deep reservoirs, and during the ascent, it interacts with Paleocene-Eocene detritus, or by evaporite environments associated with marine sedimentary rocks (probably from the Upper Cretaceous) with high B concentration. Geothermometers were used to estimate the temperatures of geothermal reservoirs based on the fluid-mineral equilibrium. In all cases, the chemical components are not in equilibrium with the minerals in the reservoir. The temperature estimation is less 200 ° C for Pinaya, while Jaraña, Atecata and Coline zones are low enthalpy systems, have temperatures below 150 ° C. Is inferred that the reservoir rock constitution is composed of sandstones (Hualhuani Formation) and conglomerates in a calcareous matrix (Puno Group). The δ2H and δ18O isotopic diagram also show that the thermal waters originate mainly from meteoric water. Geological and geochemical exploration results generated a conceptual model for the geothermal source around Cordillera Sillapaca. The source of heat is associated with dacitic - andesitic subvolcanic domical shaped outcrop; the radiometric age is less than 1 Ma |