| Abstract |
The geothermal system associated with the Pleistocene-Holocene Sierra Nevada volcano in the Araucanía Region of Chile has surface manifestations extending from the north-western flank of the volcano to Manzanar and Malalcahuello. Baños del Toro, located on the northwestern flank of the volcano, has numerous fumaroles and acid pools (acid sulfate waters, T=~90°C, pH=2.1, TDS=3080 mg/L); while Aguas de la Vaca, near the base of the volcano, has a bubbling spring (chloride-sulfate waters, T=~60°C, pH=7.0, TDS=950 mg/L). Five shallow (<120m) wells (2 at Manzanar and 3 at Malalcahuello) in the Cautín River Valley discharge alkaline (pH= 9-10) waters with relatively low TDS (130-210mg/L). The main heat source of the geothermal system is apparently the magmatic system of the Sierra Nevada volcano. Liquiñe-Ofqui Fault Zone (LOFZ) that transects the area provides conduits for the flow of the geothermal waters. The geothermal reservoirs are mainly hosted in the volcanic rocks interbedded with glacial deposits that cover the North Patagonian Batholith. This batholith forms an impermeable barrier, and thus constitutes the lower boundary of the geothermal system and also controls the lateral flow of fluids. An equilibrium temperature of 210°C is derived from the gas geothermometry (CO2/Ar-H2/Ar) of the Baños del Toro fumaroles. Geothermal fluids from the upflow area on the northwestern flank of the volcano migrate northwards to the Cautín River Valley. This northward migration of the geothermal water is stopped by the Melipeuco Pluton, causing its accumulation to form reservoirs near Manzanar and Malalcahuello. This geothermal system thus has, (1) high enthalpy aquifers (>200°C) on the northwestern flank of the Sierra Nevada volcano and 2) low-enthalpy resources (<100°C) in the Cautín River Valley that have been tapped to form spas at Manzanar and Malalcahuello. |