Structural assessment and geochemistry of thermal waters at the Cerro Machin Volcano (Colombia): An approach to understanding the geothermal system

Abstract

Through a detailed structural assessment of faults, carried out by remote sensing and a slip-dilation tendency analysis along with water geochemistry of thermal waters, it was possible to characterize the geothermal system of Cerro Machin Volcano (CMV) located in the western flank of the Cordillera Central of Colombia. The study shows that the geothermal system presents a favorable structural setting for the transport of fluids (e.g. fault intersection), where the structural component is marked by faults striking NW-SE, NE-SW, and N-S, controlling its deformational model, permeability and therefore, the fluid flow path. In addition, hydro-geochemistry allows identifying two sets of water (i) Na-HCO3 and (ii) Ca-HCO3 types. Na-HCO3 springs are representatives of a more direct upflow in the system, where fluid uses critically stressed areas to ascend. In contrast, Ca-HCO3 springs are more strongly affected by subsurface process such as mixing and water-rock interaction. The geothermal system is characterized of a convection-dominated geothermal play associated with recent volcanism, which is recharged by meteoric waters that flow through fractures and faults and is strongly influenced by a CO2-rich fluid coming from deeper levels. The reservoir occupies a fracture zone within the Cajamarca complex with an estimated temperature of around 220 °C, according to solute and multicomponent geothermometry.