New geochemical and isotopic insights to evaluate the geothermal resource of the hydrothermal system of Rosario de la Frontera (Salta, northern Argentina)

AGOSTINA CHIODI; FRANCO TASSI; WALTER BAEZ; ROBERTA MAFFUCCI; INVERNIZZI CHIARA; GUIDO GIORDANO; SVEVA CORRADO; GABRIELE BICOCCHI; ORLANDO VASELLI; JOSÉ VIRAMONTE; PIETROPABLO PIERANTONI

JOURNAL OF VOLCANOLOGY AND GEOTHERMAL RESEARCH

ELSEVIER SCIENCE BV

Lugar: Amsterdam; Año: 2015 vol. 295 p. 16 - 25

0377-0273

In this study, the chemical and isotopic composition of thermo-mineral springs from the Rosario de la Fronterahydrothermal system was used to construct a conceptual model describing the source regions the thermalfluids and the chemical?physical processes controlling the chemistry of waters and dissolved gases duringtheir underground circulation. The main hydrothermal reservoir, hosted within the Cretaceous Pirgua Subgroupdeposits, is fed by meteoric water and shows a Na-HCO3 composition produced by water?rock interactionsinvolving sedimentary formations mostly consisting of conglomerates and sandstones, which are interbeddedwith alkaline volcanic rocks and shales and limestone deposits. This aquifer also receives significant contributionsof crustal CO2 and He from mantle degassing, the latter being likely favored by the regional tectonic assessmentthat is characterized by a deep detachment (at about 10 km depth) in the basement of the Santa Bárbara thickskinnedthrust system and a thinned lithosphere. The uprising thermal fluids mix with a relatively high salinityNa-Cl dominated aquifer produced by the interaction of meteoric water with the Tertiary Anta Formation evaporite.The temperatures of the hydrothermal reservoir, estimatedwithwater geothermometers, are up to 130 °C,which are consistent with the thickness of the hydrothermal circuit (2700-3000 m) and the relatively high localgeothermal gradient (~40 °C/km). These results suggest that the heat stored in the fluid phase of RFHS is up to~1 × 1018 J, a value significantly higher (20%) than that previously estimated assuming an average reservoirtemperature of 90 °C.