Chemical-isotopic analyses and hydrogeologic modeling of the geothermal System of Rosario de la Frontera (Salta, Argentina): preliminary results.

AGOSTINA CHIODI; FRANCO TASSI; WALTER BAEZ; ROBERTA MAFFUCCI; LEA DI PAOLO; JOSÉ VIRAMONTE

Pisa

Congreso; 86º Congresso Nazionale della Società Geologica Italiana (SGI).; 2012

Società Geologica Italiana

The present study is a part of a multidisciplinary investigation of the thermal springs in the area of Rosario de la Frontera, carried out in order to produce a preliminary evaluation of geothermal potential of this system. These thermal manifestations, whose temperature varies from 22.7 to 93.3 °C, are located in the northern sector of the La Candelaria Range, Salta province, Argentina (Moreno et al. 1975). This study is based on analytical evidence of the chemical and isotopic composition (d18O2, dD e d13C-CO2) of 13 water and 5 gas samples taken from the springs. The values of the isotopic ratios of water (respectively -6.7 e -37 ‰ V-SMOW for d18O2 dD), suggest predominantly meteoric origin for these fluids (Gonfiantini 1978; Clark & Fritz, 1997; Craig 1961.) The gaseous phases associated to the thermal water as a bubbling gas, are mainly constituted by CO2 (between 550 and 960 mmol / mol) with significant concentrations of N2 (>28 mmol/mol), that in the case of Zarza and Silicosa samples (385 and 415 mmol / mol) are comparable to the CO2 content. The 3 gas samples with high CO2 content (Sulfurosa de la ViejaQuemada, Sulfurosa and Aguas Chicas) presents higher concentration of H2S (up to 3.6 mmol / mol), H2 (up to 0022 mmol / mol) and CH4 (up to 0087 mmol / mol), and the lowest concentrations in atmospheric gases (O2, Ar and Ne), compared to the 2 gas samples rich in N2. The 13C/12C ratios in CO2 (d13CCO2 from -5.16 to -3.66 ‰ V-PDB) are consistent with a mantlesource for that gases.