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This institution reserves the right to refuse to accept a copying order if, in its judgment, fulfillment of the order would involve violation of copyright law. GRC Transactions, Vol. 35, 2011 Surface Exploration at Pampa Lirima Geothermal Project, Central Andes of Northern Chile R. Arcos1, J. Clavero1, A. Giavelli1, S. Simmons2, I. Aguirre1, S. Martini1, C. Mayorga1, G. Pineda1, J. Parra1, J. Soffia1 1Energía Andina, Chile 2Hot Solutions, New Zealand Keywords low mixing degree. Minimum temperatures from water and gas Central Andes, Chile, geothermal project, surface exploration, geothermometers range from 200-240°C. Pampa Lirima MT/TDEM geophysical survey carried out in the area of the project (82 sites) revealing a large conductivity anomaly inter- preted as being associated to an important geothermal system at ABSTRACT depth, consistent with the geochemical data at surface. Slim holes drilling will be carried out during 2011 for proving the existence Pampa Lirima geothermal project is located in the Altiplano of an exploitable geothermal system. of northern Chile, ca. 1,700 km north from Santiago, within the Central Andes Volcanic chain. Introduction Energía Andina, a Chilean geothermal company, obtained the exploration concession through a bidding process in June 2009. Pampa Lirima geothermal project is located in the Altiplano Since then, Energía Andina has developed an extensive and rapid of northern Chile, ca. 1,700 km north from Santiago, within the surface exploration program, together with a successful com- Central Andes Volcanic chain. munication program with local communities in the area. Surface Energía Andina, a Chilean geothermal company, obtained the exploration has been focused in understanding the geology of exploration concession through a bidding process in June 2009. the area and generating geochemical and geophysical models. Since then, Energía Andina has developed an extensive and rapid The superb results found through this rapid program have led the surface exploration program, together with a successful com- company to the next step, and a series of slim-hole wells have munication program with local communities in the area. Surface been programmed for 2010. Local communities have been in- exploration has been focused in understanding the geology of volved from the beginning of the project in the acquisition of the the area and generating geochemical and geophysical models. different data, as well as in the environmental issues associated The superb results found through this rapid program have led the to the development of a possible future geothermal power plant. company to the next step, and a series of slim-hole wells have Pampa Lirima project is located on the western edge of this been programmed for 2011. Local communities have been in- high plateau, with an average elevation of 4000 m asl. Geothermal volved from the beginning of the project in the acquisition of the features known for many years consist essentially on hotsprings different data, as well as in the environmental issues associated located in the lower southwestern part of the Lirima basin (Baños to the development of a possible future geothermal power plant. Lirima) and at the lower flank of a Plio-Pleistocene volcanic chain (Baños Andrés Jiguata). The geology of the area is constituted by Geology Jurassic to Paleogene volcanoclastic sequences, partially covered by Middle Miocene ignimbrite sheets as well as eroded volcanic The geology of the area of the geothermal exploration conces- edifices of the same age. The youngest units cropping out in the sions Pampa Lirima 1, 2, 3 and 4, and its immediate surroundings area consist of volcanic complexes of Pliocene to Pleistocene in especially west of them is characterized by the following (Arcos, age, located on the northern part of the Lirima basin. These vol- 2010): 1) Mesozoic basement rocks, 2) coverage of volcanic canic complexes have been interpreted originally as the possible and sedimentary rocks of Oligocene-Miocene, and 3) middle heat source for the geothermal system in the area. Thermal waters Miocene to Pleistocene volcanic edifices. (Figure 1: Geological from Baños Lirima are characterized by high Cl and B concen- Map by cycles.) trations and δO18 enriched, and relatively low Mg concentration, The Mesozoic basement recognized to the west of concessions consistent with deep circulation from a geothermal reservoir, and Pampa Lirima 1 and 2 consists of clastic-carbonate sequences 689 Arcos, et al. Oligocene to Miocene units consist of pyroclastic rocks with interbedded sedimentary units grouped in the Altos de Pica Fm. (“Estratos de Cultane” together with the Huasco Ignimbrite aged Oligocene to Middle Miocene), reaching a thickness between 500 and 700 m, including as well the Cordon Saitoco and Loma Chislaca volcanic complexes, both from lower Mio- cene. The units that form this structural domain are found in angular unconformity overlying Mesozoic basement units, and also are partially covered by the volcanic edifices and their products ranging in age from the middle Miocene to Recent. Such unconformity covers a wide timespan from the Paleocene (65 Ma) to Early Oligocene (28 ma). The set of ignimbrites, sediments and lavas of the Oligo-Miocene coverage present a structural style characterized by a succession of anticlinal and synclinal folds with submeridional axis, some of them with greater wave amplitude than others, with their hinges either plunging to the N or double plunging. It is also observed that the folding axes are in turn folded, varying from NE direction to NS or even folded up to a NW orientation in their southern ends. In the structural model of the Pampa Lirima area (Radic, 2010; Fig. 2), the deformation style that shows this Oligo - Miocene sequence has been interpreted as the surface expression of a strike slip dextral fault that would affect in depth at least the Mesozoic basement rocks and developing a positive “flower-like” structure in the volcanic coverage. From the surface distribution of this fold and thrust belt in the southern area (S of Lagunillas Pampa), we infer that the possible trace of this strike slip fault south of 20° S, could be aligned or connected with the Collacagua river valley and the depression of the Huasco lagoons, whose NS features lengthen this path to the south until ​​Pampa Caya in Figure 1. Geological map of the Lirima area, showing (red circle) the area of the geophysi- Guatacondo valley, where this structure could be linked cal anomaly found by the MT survey. with the N-terminus of the West Fault System (Arcos et al, 2009). from the Jurassic to Early Cretaceous, forming a folded and Regarding the structural domain formed by the wide range of thrusted belt, and a Cretaceous volcanic sequence, covering the middle Miocene to Pleistocene volcanoes, they are all overlying older units in angular unconformity (Figure 2: Structural Model in angular unconformity the rocks of the Oligo-Miocene coverage Profile Radic, 2010). and distributed in 3 NW-SE strips. Miocene complexes occupy the southwestern strip, the upper Miocene corresponds to the immediate NE strip (central strip), whereas the Pliocene units occupy the north-eastern strip (Polanco and Gardeweg, 2000, Arcos, 2010, Polanco, 2011, Martini, 2011). Only Porquesa dome complex (Pleistocene), is located outside of this disposition in NW-SE strips, not only due to its geographical position but also because its morphology shows NE- SW elongation axes, indicating different Figure 2. Deformation style in Pampa Lirima area (Radic, 2010). 1) Jurassic to Lower Cretacic sedimen- tary rocks (fold and thrust belt); 2) Upper Cretacic volcanic rocks Oligocene to Lower Miocene Cover; structural control than the older ones. 3) Ignimbrites and epiclastic (=Altos de Pica Fm.), 4) Huasco Ignimbrite Middle Miocene to Pliocene The structural style of this domain is Volcanism; 5) Middle Miocene volcanism; 6) Upper Miocene volcanic edifices; 7) Pliocene volcanic characterized solely by the morphology of edifices ; 8) Eocene Intrusives. the volcanic edifices, some reaching great 690 Arcos, et al. altitudes above their bases (Pliocene), all with varying degrees Its chloride content varies between 250 and 310 mg / l, sulfate of erosion (the more ancient and, therefore, less preserved their between 260 and 330 mg / l and pH levels between 6 and 7. original morphology) and large volume of accumulated material The Baños de San Andres hot springs, are waters that outcrop (op. cit., 2000, 2010 and 2011). in the upper basin (4380 m asl) show a sulphate calcium-sodium