Basement-hosted geothermal systems in the Sierras Pampeanas (NW Argentina): Evidence from new geochemical and isotopic characterization

Abstract

Basement-hosted geothermal systems are increasingly relevant in the context of the energy transition, due to the large thermal storage capacity of crystalline rocks, controlled fluid circulation, and their potential as sources of critical elements. This study investigates geothermal systems hosted in the Sierras Pampeanas, one of the largest geological units of Argentina. This area exhibits several geothermal systems associated with fractured Precambrian-Paleozoic metamorphic and granitic basement blocks exposed across an area of approximately 1.5 × 106 km2. Despite their geologic and strategic significance, the geothermal systems in this region remain poorly characterized. This study presents new hydrochemical and isotopic data and updated conceptual models for three of the main geothermal systems in this region, named Sierra de Hualfín, Sierra de Fiambal´a, and Sierra de Narv´aez-Las Planchadas, located in Catamarca province. The proposed conceptual models suggest local circulation loops strongly controlled by fault networks. The fluids are of meteoric origin and temperatures between ~22 ◦C and ~60 ◦C at their discharge. In Sierra de Hualfín and Sierra de Fiambal´a, calculated reservoir temperatures reach ~106 ◦C and 87 ◦C, corresponding to theoretical circulation depths of about 2000–3000 m assuming a normal geothermal gradient. In Sierra de Narv´aez-Las Planchadas, estimated temperatures are lower(37 ◦C), suggesting shallow circulation depths (~1000 m). Waters are predominantly Na+-HCO3 -, reflecting water-rock interaction within the crystalline basement. In some cases, Na+-Cl- end members reflect mixing with shallow aquifers and circulation in sedimentary deposits. The presence of SO42- in Sierra de Fiambal´a is linked to the oxidation of sulfide minerals within the granite, whereas in Sierra de Narv´aez-Las Planchadas it derives from interaction with volcano-sedimentary units. The trace element composition is dominated by Li and B, followedby Rb, Fe, Sr, Mn, As, Ba, Zn, and Mo, which show marked enrichments in the eastern flank of the Sierra de Hualfín system. This study provides a refined basis for future geophysical, hydrological, and exploration studies aimed at improving the understanding of heat sources, fluid pathways, and reservoir geometry in basementhosted geothermal resources of the Sierras Pampeanas.