Carbon dioxide diffuse degassing as a tool for computing the thermal energy release at Cerro Blanco Geothermal System, Southern Puna (NW Argentina)

This work presents the first carbon dioxide diffuse degassing survey carried out in the Cerro Blanco GeothermalSystem (CBGS; Southern Puna plateau, NW Argentina) with the aim to estimate the thermal energy release. Thesurvey was divided into (i) a prospecting stage of the degassing sites within the CBGS and (ii) mapping of theselected diffuse degassing sites. The purpose of the prospecting stage was to elaborate two transects, crosscuttingthe nested caldera of Cerro Blanco Volcanic Complex (CBVC) and Los Hornitos thermal site, both belonging toCBGS. More than 60 soil diffuse CO2 flux and soil temperature measurements were carried out in the 16-km and1-km long transects. Significant soil diffuse emissions were only found within the Cerro Blanco caldera, where adetailed mapping of CO2 flux was produced. In this site, named CBa, a single diffuse degassing structure releasing22.44 kg d- 1 of deep-sourced CO2 into the atmosphere was identified. Any other geologic feature of the CBVCand Los Hornitos hydrothermal site presented very low CO2 flux values. According to statistical and geochemicalanalyses, soil diffuse CO2 degassing is fed by a deep-seated (hydrothermal) and a soil respiration source, whichmix each other at different degree. The thermal energy release associated with the diffuse degassing process atCBa is estimated to be ~2.4 kJ/s. This low magnitude thermal energy release is probably a consequence of anefficient cap-rock that likely buffer the surficial expressions of the geothermal resource potentially occurring atdepth.