Preliminary conceptual model of the Cerro Blanco caldera-hosted geothermal system (Southern Puna, Argentina): Inferences from geochemical investigations

Abstract

The Cerro Blanco Caldera (CBC) is the youngest collapse caldera system in the Southern Central Andes (Southern Puna, Argentina). The CBC is subsiding with at an average velocity of 0.87 cm/year and hosts an active geothermal system. A geochemical characterization of emitted fluids was carried out based on the chemical and isotopic compositions of fumaroles, and thermal and cold springs discharged in this volcanic area with the aim of constructing the first hydrogeochemical conceptual model and preliminary estimate the geothermal potential. The main hydrothermal reservoir, likely hosted within the pre-caldera basement rocks, has a Na +-Clˉ(HCO 3)c omposition with estimated temperatures ≥135°C. The unconsolidated, fine-grained Cerro Blanco ignimbrite likely acts as the cap-rock of the hydrothermal system. The presence of phreatic eruption breccias in the surrounding area of the geothermal fumaroles supports the effectiveness of the pyroclastic deposit as sealing rocks. The isotopic data of water (δ 18 O and δD) indicate a meteoric recharge of the hydrothermal reservoir, suggesting as recharge areas the sectors surrounding the CBC, mainly towards the W and NW where large outcrops of the pre-caldera basement exist. A fault-controlled hydraulic connection between the hot springs and the hydrothermal reservoir is proposed for the Los Hornitos area. The fumaroles show the typical compositional features of hydrothermal fluids, being dominated by water vapor with significant concentrations of H 2 S, CH 4 and H 2. Considering the high geothermal gradient of this area (∼104°C/km) and the relatively high fraction of mantle He (∼39%) calculated on the basis of the measured R/Ra values, the hydrothermal aquifer likely receives inputs of magmatic fluids from the degassing magma chamber. The preliminary geothermal potential at CBC was evaluated with the Volume Method, calculating up to E = 11.4*10 18 J. Both the scarce presence of superficial thermal manifestations and the occurrence of an efficient cap-rock likely contribute to minimize the loss of thermal energy from the reservoir. The results here presented constitute the necessary base of knowledge for further accurate assessment of the geothermal potential and ultimately the implementation of the geothermal resource as a viable energy alternative for small localities or mining facilities isolated from the National Interconnected System due to their remote localization.

Chemical and isotopic features of Li-rich brines from the Salar de Olaroz, Central Andes of NW Argentina

“…Specific attention was given to the chemistry of brines in Andean salars, providing conceptual geochemical models for circulating fluids (Warren, 2010;Houston et al, 2011;Munk et al, 2018). Hydrothermal fluids, whose chemistry reflects the interaction between meteoric waters and Andean crustal rocks (Perkins et al, 2016;Peralta Arnold et al, 2017;Chiodi et al, 2019;Tapia et al, 2019), were considered to be one of the main sources for the Andean Li-rich brines (Lowenstein and Risacher, 2009;Houston et al, 2011;Munk et al, 2011;Godfrey et al, 2013;L� opez Steinmetz et al, 2018;Garcia et al, 2020). Brines concentrate as evaporation (i.e., water loss) induces salt precipitation (Eugster, 1980;Munk et al, 2018).…”

Using Conceptual Models to Relate Multiparameter Satellite Data to Subsurface Volcanic Processes in Latin America

“…Unfortunately, the dataset from Cerro Blanco does not have a robust dataset and is not suitable for use as a type example. Geochemical analysis identified the signature of an outgassing magma reservoir (Chiodi et al, ), which supports the classification of the mechanism as magma evolution, but suggests that the system may not be closed.…”

AMS and rock magnetism in the Caviahue-Copahue Volcanic Complex (Southern Andes): emission center, flow dynamics, and implications to the emplacement of non-welded PDCs

“…In summary, directional AMS and field data support the southern region of the Caviahue Caldera as the emission center for RBI, likely the Las Mellizas Caldera. This tectonic setting of multiple, nested emission centers and calderas is common in the Andes (e.g., Ort et al, 1993;Chiodi et al, 2019). Despite that, we cannot rule out the possibility of alternative emission areas located both inside and outside the Caviahue Caldera.…”