| Abstract |
From 2023 to 2025, Transmark Renewables completed a two-year geothermal exploration program in the Cachapoal concession area of Chile. The project was co-financed by the Federal Republic of Germany through KfW and with funding by the European Union via the Geothermal Development Facility for Latin America. The prospect has been identified from its widespread 32.7°C to 67°C neutral chloride hot springs. Due to the influence of evaporites, the cation chemistry of the springs constrains hydrology but not temperature. Silica geothermometry from 97°C to 176°C suggests the existence of moderate temperature deep-circulation geothermal reservoirs, consistent with elevated heat flow indicated by the recent eruption of a lava flow 8 km to the east. However, most volcanics have been eroded by glaciation in this part of the Andes, exposing Tertiary intrusive and metamorphosed sedimentary rocks that tend to be impermeable except where intersecting structures locally increase stress and fracturing. MT surveys detected <70 ohm-m retrograde hydrothermal clay alteration associated with the hot springs, contrasting with surrounding >300 ohm-m rocks. Based on an integration of geothermometry, hydrology, MT resistivity, and a 3D Leapfrog model of geology and structures from surface mapping and core logs from mining industry wells, a geothermal conceptual model has been developed, and three target zones have been identified. Although the novel characteristics of Cachapoal support an estimate of a 16% probability of success for discovering a geothermal resource using slim hole wells, such a success would demonstrate a new geothermal play type and would create opportunities at analogous prospects. |