Surface Exploration at Pampa Lirima Geothermal Project, Central Andes of Northern Chile

摘要

Pampa Lirima geothermal project is located in the Altiplano of northern Chile, ca. 1,700 km north from Santiago, within the Central Andes Volcanic chain. Energia Andina, a Chilean geothermal company, obtained the exploration concession through a bidding process in June 2009. Since then, Energia Andina has developed an extensive and rapid surface exploration program, together with a successful communication program with local communities in the area. Surface exploration has been focused in understanding the geology of the area and generating geochemical and geophysical models. The superb results found through this rapid program have led the company to the next step, and a series of slim-hole wells have been programmed for 2010. Local communities have been involved from the beginning of the project in the acquisition of the different data, as well as in the environmental issues associated to the development of a possible future geothermal power plant. Pampa Lirima project is located on the western edge of this high plateau, with an average elevation of 4000 m asl. Geothermal features known for many years consist essentially on hotsprings located in the lower southwestern part of the Lirima basin (Banos Lirima) and at the lower flank of a Plio-Pleistocene volcanic chain (Banos Andres Jiguata). The geology of the area is constituted by Jurassic to Paleogene volcanoclastic sequences, partially covered by Middle Miocene ignimbrite sheets as well as eroded volcanic edifices of the same age. The youngest units cropping out in the area consist of volcanic complexes of Pliocene to Pleistocene in age, located on the northern part of the Lirima basin. These volcanic complexes have been interpreted originally as the possible heat source for the geothermal system in the area. Thermal waters from Banos Lirima are characterized by high Cl and B concentrations and δO~(-18) enriched, and relatively low Mg concentration, consistent with deep circulation from a geothermal reservoir, and low mixing degree. Minimum temperatures from water and gas geothermometers range from 200-240°C. MT/TDEM geophysical survey carried out in the area of the project (82 sites) revealing a large conductivity anomaly interpreted as being associated to an important geothermal system at depth, consistent with the geochemical data at surface. Slim holes drilling will be carried out during 2011 for proving the existence of an exploitable geothermal system.