Exploring the shallow geothermal resources in the Chilean Southern Volcanic Zone: Insight from the Liquiñe thermal springs
Résumé
Southern Volcanic Zone (SVZ) hosts numerous thermal springs (25–85 °C), related to Liquiñe-Ofqui Fault System
(LOFS) and Andean Transverse Faults (ATFs), suggesting the feasibility of low- to high-enthalpy geothermal
exploitation. However, the local understanding of processes and factors controlling the high-temperature
groundwater circulation remained undefined, which limits its exploitation. Following a brief review of SVZ, we
address the previous issue by a hydrogeochemical and isotopic analysis of 15 thermal springs at Liquiñe area
(representative of SVZ), supplemented by geochemical simulations. We demonstrate that fault zones and derived
hydraulic properties have a predominant control on the ascending high-temperature groundwater circulation
and hydrogeochemical processes. Spring discharges and outflowing temperatures are higher along the LOFS
damage-zone and ATF than those along the LOFS fault core-zone. Albite dissolution is the main water-rock
interaction that is enhanced by absorbed geothermal gases (H2S and CO2 in LOFS; CO2 in ATF). Trace element
contents (Li, Rb, Cs, As, Mo) are influenced by hydraulic properties and geothermal gases within faults. Intrinsic
hydraulic properties of fault zones, where damage-zone is more permeable than the core zone, affect the Li, Rb,
Cs contents. While As and Mo solely differ according to the gases presence. Water stable isotopes point that
steam heating processes enhance the hydrogeochemical reactions through the LOFS damage-zone and ATF,
whereas only low-temperature processes occur through the LOFS core-zone. LOFS damage-zone and ATFs are
great targets for the shallow geothermal resource exploitation. But simulations indicate an elevated risk of
scaling with consequences on the operation plants due to silicate mineral precipitations. Finally, Liquiñe thermal
springs provide interesting insights to respond to the current and future energy challenges in Central-South
Chile.