Geothermal Gradient Characterization at Aguas de Vichy Hot Spring via Thermophysical Analysis and 2D Conductive Modeling (Santander, Colombia)

The Aguas de Vichy hot spring is located in the Eastern Cordillera of northeastern Colombia, on the eastern flank of the Santander Massif, a crystalline basement complex. This hydrothermal manifestation, together with a few others in the region, occurs in an atypical geological setting for geothermal systems, away from active volcanic arcs or extensional basins. At Aguas de Vichy, the heat source and the spatial variation of the local geothermal gradient remain unknown.

To address this knowledge gap, we present an integrated workflow for early-stage geothermal assessment. Our methodology combines (1) the construction of a detailed two-dimensional geological cross-section, (2) laboratory measurements of key thermophysical properties, including thermal conductivity, density, porosity, and radiogenic heat production from K-U-Th, on representative outcrop samples, and (3) cationic geothermometry applied to the thermal waters to estimate reservoir temperature.

These inputs are incorporated into a steady-state two-dimensional conductive heat-flow model solved using the finite-element method. Model outputs include subsurface temperature fields, heat flow, and derived geothermal gradients, allowing the identification of anomalies related to lithological heterogeneity or potential deep-seated heat sources. This conductive model establishes a thermal baseline for the area. By comparing this baseline with reservoir temperatures inferred from geothermometry, we assess whether the observed heat transfer is dominantly conductive or if additional processes need to be considered.

This study provides the first quantitative estimate of the geothermal gradient for the Aguas de Vichy system. More broadly, the proposed workflow offers a cost-effective and replicable approach to reduce uncertainty in geothermal prospects located in underexplored regions lacking borehole data. As such, it constitutes a transferable methodological framework for early-stage geothermal project development where direct subsurface temperature measurements are unavailable.