Carbon dioxide diffuse degassing and hydrothermal alteration in the soils of the Cerro Galán geothermal system (Catamarca, Puna Austral)

Abstract

Cerro Galán, located in the Puna Austral, is a caldera formed during a Pleistocene-Holocene super-eruption. It is characterised by silicic volcanism, which could host a high potential geothermal system. However, this system has been little explored. The main objective of this paper is to contribute to the understanding of the geothermal system and to add new data to the geochemical conceptual model. The paper presents the first study of diffuse CO₂ degassing, temperature and hydrothermal ground disturbance of the three hydrothermal areas of the Cerro Galán caldera: La Colcha, Aguas Calientes and Piscinas Burbujeantes. A total of 148 CO₂ flux and soil temperature measurements were made. In addition, eight samples of precipitates and alteration clays were collected at the La Colcha and Piscinas Burbujeantes sites. CO₂ flux values ranged from 0 to 21.66 g/m²/d and temperature values from -5.2 to 35 ºC. Diffuse degassing structures were identified at La Colcha and Aguas Calientes in spatial relation to the thermal springs. We propose two sources of CO₂: a hydrothermal aquifer and one related to soil respiration. The diffuse degassing rate of hydrothermal CO₂ was 0.44 kg/day. The mineralogy of hydrothermal alteration was characterised by the presence of calcium carbonate, salts, clays, oxides and iron sulphides. Taken together, our results suggest a significant interaction of hydrothermal fluids with shallow water bodies during their ascent to the surface.