Identification of a Potential Geothermal Resource in Colombia through the Application of Geoelectric and time-domain Electromagnetic Methods at the Aguas de Vichy Spring in the Municipality of San Andrés, Santander

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 but underexplored geothermal resource. This study presents the first geophysical imaging of the system, integrating Electrical Resistivity Tomography (ERT), Induced Polarization (IP), and Time-Domain Electromagnetics (TDEM) to characterize its hydrogeological structure. Existing geochemical analyses reveal high salinity and elevated temperatures, indicative of considerable energy potential and an advection-dominated thermal regime. The geological context is marked by north–south (N–S) and northeast–southwest (NE–SW) fault systems intersecting Cretaceous and Precambrian rocks, overlain by a Quaternary aquifer.

Three initial ERT transects were conducted around the inferred fault, which was hypothesized to be the main conduit for geothermal fluids. Two profiles crossing the fault revealed laterally heterogeneous resistivity values ranging from near zero to over 1500 ohm·m, indicating the presence of clay, groundwater accumulation, and thermal anomalies. A third profile, located within the Quaternary unit but away from the fault, exhibited a more resistive background with subdued low-resistivity anomalies, suggesting a saturated clay deposit with limited geothermal influence. IP measurements validated the presence of geothermal fluids and highlighted elevated chargeability zones, consistent with the occurrence of clay-rich layers.

A fourth ERT profile, together with two complementary TDEM soundings, extended the investigation to greater depths and exhibited a low-resistivity zone at approximately 45–100 m depth, interpreted as a geothermal reservoir. The TDEM models revealed deep conductive features beneath the alluvial aquifer, and the ERTs suggested a fault-aligned hot-water plume feeding the aquifer.

These findings support a convective flow driven by vertical fluid ascent along the fault zone in addition to the previous advection-based hypothesis. The integrated geophysical dataset highlights the complexity and geothermal potential of the system, providing critical insights for future exploration and contributing to Colombia’s energy transition roadmap.