The spatial distribution of surface geothermal manifestations and hydrothermal alteration reflects the complex interplay of multiple factors controlling fluid circulation. This study aims to understand the different controls on the distribution of surface hydrothermal alteration, using the Nevados de Chillán Geothermal System (NChGS) as a case study. Lineament maps were created at 1:2500 and 1:5000 scales, and orientations of faults, fractures, and veins were measured. The pH measured ranges from 2.6 to 5.4. Surface temperature was measured and analyzed via Inverse Distance Weighted (IDW) interpolation in ArcGIS®. Surface hydrothermal alteration was mapped using drones, and minerals were identified through X-Ray Diffraction of whole rock and clay analysis, including chalcedony, opal, native sulfur, illite, kaolinite, iron oxides, sulfates, and hydrated sulfates. Illite crystallinity measured using the Full Width at Half Maximum index (FWHM) ranged from 0.05 to 1.77, while kaolinite crystallinity measuring using Aparicio-Galán-Ferrell index (AGFI), ranged from 0.73 to 1.15. The results show that the distribution of high temperatures (reaching 95 °C) and intense advanced argillic hydrothermal alteration is heterogeneous, controlled by lithological contact and the interaction between ∼E-W-trending lineaments associated with subvertical faults and NNW-striking surficial low-angle faults. Circulation of acid-sulfate waters rich in Fe, Al, and Cu occur primarily along fault/fracture networks, promoting the formation of high-crystallinity illite and kaolinite at the surface. This study proposes a link between surface geothermal manifestations with fault-fracture network and lithological controls within a fractured geothermal system in the Southern Andes.
CORE (COnnecting REpositories)
CORE (COnnecting REpositories)