Juan Camilo Mejía-Fragoso , José David Sanabria-Gómez, Rocio Bernal-Olaya

The Aguas de Vichy thermal spring (SAN-001), identified by the Colombian Geological Service (SGC) and located in Santander, Colombia, represents a significant yet underexplored geothermal resource. This study is the first to conduct subsurface imaging of the geothermal system, employing Electrical Resistivity Tomography (ERT) and Induced Polarization (IP) methods to investigate the hydrogeological framework. Geochemical analyses of the spring water indicate high salinity and elevated temperatures, suggesting a substantial energy capacity. The geological setting is characterized by north-south (N-S) and northeast-southwest (NE-SW) faults, intersecting Cretaceous and Precambrian formations, along with a Quaternary aquifer.

Three ERT transects were conducted around the inferred fault, which was hypothesized to be the main conduit for geothermal fluids. Two transects crossing the fault revealed resistivity values ranging from near zero to over 1500 ohm-meters, suggesting the presence of zones of clay, groundwater accumulation, and geothermal fluids. High resistivity anomalies at depths of 5 to 10 meters indicate the lower boundaries of the Quaternary deposits. The third transect, situated within the Quaternary deposit but distant from the fault, exhibited elevated resistivities and a diminished prevalence of anomalies, indicating a possible clay deposit with reduced influence of water. IP measurements validated the presence of geothermal fluids and illuminated areas with elevated chargeability, suggesting the presence of clay levels within the aquifer.

Our findings support the existence of a geothermal system where convection plays a significant role, alongside notable advective movements within the aquifer. This suggests a complex interaction of subsurface fluid dynamics, integrating both fault-mediated fluid transport and advection processes rather than being solely advection-dominated as suggested initially. The complexity observed in these findings underscores the necessity for further detailed studies to enhance our understanding of the geothermal system's dynamics and potential, which could make a valuable contribution to Colombia’s energy sustainability objectives.