Preliminary Hydrogeological Conceptual Model of the Tocomar Geothermal System (Puna, Argentina)

Detailed stratigraphic and structural studies together with hydrogeological and geochemical reconstruction, monitored during time, are fundamental for understanding the relationships among cap rocks, reservoir and fluids circulation in geothermal areas and for planning resource exploitation. The Tocomar volcanic area (Puna plateau, Central Andes, NW Argentina) has a high geothermal potential testified by several thermal springs whose temperature values are between 30.3 and 70 °C, pH between 5.78 and 7.86 and Electric Conductivity between 0.82 and 20 mS/cm. The area is characterized by a dry climate (average rainfall lower than 100 mm per year) and it is crossed by the active NW-SE trans-Andean tectonic lineament known as the Calama-Olacapato-Toro (COT) fault system, which induces a high secondary permeability. Previous study (Giordano et al. 2013) suggest that the main geothermal reservoir is located within or below the Pre-Palaeozoic-Ordovician basement units, characterised by unevenly distributed secondary permeability. The reservoir is recharged by infiltration in the ridges above 4500 m asl. (Giordano et al. 2013), where basement rocks crop out. Below 4500 m asl., the reservoir is covered by low permeable Miocene-Quaternary units with poor circulation of shallow groundwater. Geothermal fluids upwell in areas with more intense fracturing, especially where main regional structures (particularly the COT-parallel lineaments) intersect secondary structures, such as at the Tocomar field. A multidisciplinary study on the Tocomar area integrating geological, structural, vulcanological, hydrogeological and geochemical field-based analysis, together with a geophysical investigation allowed us to produce the first results for the definition of the geothermal and hydrogeological conceptual model. Session S3.1 - Aqua 2015 - 42nd IAH Congress 1