Geothermal influence on the hydrochemistry of surface streams in Patagonia neuquina

VILLALBA, E.; SANTUCCI, L.; BORGI, G.; PASQUINI, A.I.; PÁEZ, G.; CAROL, E.

Environmental Assessment of Patagonia's Water Resources

Springer International Publishing

Año: 2021; p. 57 - 73

relief with steep valleys carved by both glacial and fluvial processes, where the main water courses are the streams named Manchana Covunco, Aguas Calientes and Covunco, which are tributaries of the Varvarco River. These streams run through an area of intense geothermal manifestations composed by aqueous solutions of high temperature, which determine the chemistry of streams and springs. The surface water courses and springs located upstream the thermal springs are neutral to alkaline, of low temperature and electric conductivity, and Ca-HCO3 / Ca-HCO3-SO4 facies, respectively. Downstream the thermal springs, an increase in pH, temperature, and electrical conductivity is registered, as well as changes towards Na-Cl facies, the dominant composition in the thermal springs. Also, thermal springs increase the As content limiting the potability of the water. The contribution from thermal springs to streams varies between 24 - 47%, while in springs it is close to 10%. In addition to the mixing of water, carbonate, plagioclase, and pyroxene weathering processes are mainly evidenced in both thermal springs and springs, while surface water is associated with carbonate and gypsum-anhydrite dissolution. The dissolved REE contents are 10-4 - 10-7 times lower than the Upper Continental Crust and show a decrease towards the down basin of the geothermal field. Understanding the processes that determine the hydrochemistry is of great relevance in arid mountainous environments with scarce knowledge.