Resource assessment of the Cerro Blanco geothermal system

Abstract

Over the past three decades, studies have provided important information on the current volcanic activity and the associated thermal anomalies spread over the southern Puna in Argentina, as in the Cerro Blanco Volcanic Complex case. The volcanic-hosted geothermal systems have received critical attention since they are low-carbon energy sources and are frequently linked to geothermal lithium deposits. A key issue in developing productive projects is quantifying the thermal resource because this value determines investor interest. Our research aims to estimate the power capacity of the Cerro Blanco geothermal system in terms of MWe. Two methods were employed: a conductive cooling of the magmatic chamber and the classical volumetric method, coupled with Montecarlo simulations. After a rigorous analysis of recently published data, a 3D structural mapping supported by a series of analogue models, combined with a deep fluid compositional reconstruction, was employed to estimate the reservoir temperature and to support the resource assessment. Our experimental calderas show that the collapse onset is controlled by a combination of internal reverse faults and peripheral ring faults; concentric inner faults propagate outward from the caldera structure's central part. The 3D structural mapping highlights that the main structures of the Cerro Blanco geothermal system constrain the reservoir area. The estimation obtained by the magmatic heat transfer method indicates that Cerro Blanco might produce 6 MWe per km2 at 50% confidence and that it hosts a total power capacity of 127 MWe. Also, it was calculated that there are >18 km2 above 200 °C at 2 km depth. By the volumetric method, a power capacity of 6 MWe and 32 MWe at 90% and 50% confidence were estimated, respectively. These results should be interpreted cautiously considering that, for example, 1% of the unknown recovery factor correlates with 4.1 MWe in the power capacity. These estimations do not confirm the existence of the geothermal resource but raise encouraging results. Moreover, they become relevant because the Cerro Blanco geothermal system has few thermal manifestations and might be considered a blind geothermal system.