The geothermal system of Rosario de La Frontera (La Candelaria Ridge -NW Argentina): methods and preliminary results

Within the Sierra Sub-andina and Santa Barbara System (Jujuy and Salta Provinces, NW Argentina), we focused our attention on La Candelaria Ridge a broad N-S trending anticline, strongly plunging both to the North and to the South. The ridge is cored by neo-Proterozoic phyllite basement and draped by a Cretaceous-Quaternary sedimentary succession (SEGGIARO et alii, 1997), and it has a complex structural history (CRISTALLINI et alii, 1997 and reference therein). Several hot springs, whose temperatures at surface range from 22.7 to 93.3 °C, occur in correspondence of the northern plunge of the Ridge, in the localities of Los Banos and Las Termas, close to the town of Rosario de la Frontera. This project intends to contribute to the sustainable development of the town of Rosario de La Frontera by means of medium enthalpy (90o<T<150°C) geothermal resources. Main goals of our study are: (i) to constrain the origin of the geothermal anomaly; (ii) to evaluate the size, fracture network and permeability of the potential geothermal reservoir; (iii) to identify the recharge areas and deep fluid flow; (iv) to model the geothermal system. To achieve these goals, we apply a robust set of methodologies (traditional structural analyses, geological, geochemical and geophysical survey, paleothermometry and dedicate software) to explore the geothermal potential of the area. Preliminary results related to structural analyses are here presented. Four different fracture sets and their relative chronology have been recognised: N-S, NE-SW, NNW-SSE and E-W. N-S and E-W trending fractures are particularly concentrated in the northern plunging area of the anticline where the hot springs occur. This pervasive orthogonal fracture system gives rise to a structural control on the distribution of the chemical and physical features of waters. Main reservoir and cap-rock units have been also recognised by means of structural analyses.