Resumo

CHIODI, Agostina L et al. Modelo conceptual preliminar del sistema geotermal El Sauce (Salta) a partir de estudios de geoquímica de fluidos. Rev. Asoc. Geol. Argent. [online]. 2016, vol.73, n.1, pp.93-103. ISSN 0004-4822.

There are numerous interesting sites for the exploitation of the geothermal resource in the northern Argentina; however, most of them only have reconnaissance studies. The present contribution reports the chemical and isotopic composition of thermal fluids from the El Sauce geothermal system used to construct a preliminary conceptual model describing the compounds source regions and the P-T condition of the fluid within the reservoir. The geochemical characterization of the fluid phase was carried out by direct sampling of waters and gases, and subsequent analysis of their chemical and isotopic composition. The geothermal reservoir, hosted within Yacoraite Formation, acquires a HCO3¯-Na+ composition by water-rock interaction, likely favored by crustal CO2 contribution. The gas phase associated with the hot springs is dominated by atmospheric gases dissolved in meteoric water recharging the geothermal aquifer. The deep geothermal reservoir mixes with saline Na+-Cl¯(SO42-)-aquifers (located within the Metán Subgroup) during the uprising through the structures. Finally, the thermal waters are subject to mixing and cooling processes with the shallow cold HCO3¯-Ca2+/Na+-aquifers with low salinity contents present within quaternary deposits. Considering that geothermal reservoir is ~2.6 km depth, recharging meteoric water can reach the cation-geothermometer temperature (~106 ºC) in a normal geothermal gradient (~33 °C/km). The latter together with the gas isotopic signature allows to reject the hypothesis proposed in previous studies that assigned a magmatic origin for both gas and heat anomaly.

Palavras-chave : Gas-water geochemistry; Geothermal reservoir; Deep circulation; Geothermal resource; Northern Argentina.

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