Preliminary geothermal conceptual model of Salve Faccha-Oyacachi prospect, Chacana caldera-Ecuador

Abstract

Located at about 60 km east of Ecuador's capital, Chacana is an eroded Plio-Holocene resurgent caldera complex, considered one of the largest rhyolitic centers of the northern Andes. Between 2011 and 2012, two main geothermal prospects in the southern part of Chacana were identified. However, the northern part of the caldera remains unexplored, despite the existence of several geothermal manifestations in Salve Faccha and Oyacachi. Detailed geological mapping was conducted, focused on the identification of structural features, volcanic deposits, and hydrothermal features. Field observations were supplemented by XRD analysis, kinematic analysis, dilation potential estimation and literature review to refine the geochemical interpretation.
The volcanic deposits in the northern part of the Chacana Caldera record a prolonged period of activity during the Quaternary, with sequences of volcanic rocks overlying Paleozoic metamorphic basement. The Rosaspungo center, in particular, exhibits evolved magmatic activity, suggesting the presence of a shallow heat source capable of sustaining a convective geothermal system. Within the caldera, volcanoclastic deposits have developed secondary permeability due to a trans-pressional tectonic regime (ESE-trending ??), hosting a high-temperature (~230°C) geothermal reservoir controlled by NW-SE normal-sinistral faults. These structures, with the E-W faults, also facilitate fluid migration toward a secondary lower-temperature reservoir (~150°C) located beneath Oyacachi village, ~10 km to the east. Overlying the primary reservoir, the geothermal system develops a substantial cap rock characterized by Illite alteration which extends across ~2 km in diameter around the Salve Faccha lake. Approximately 17 hot springs were reported around and beneath the lake, discharging mostly Cl-Na type waters. In addition, HCO3-type hot springs and travertine deposits at Oyacachi village suggest the peripheral part of the system. These results confirm the existence of a convective geothermal system with favorable permeability and high enthalpy, positioning the Salve Faccha–Oyacachi prospect as a strategic resource for renewable energy generation for the capital city of Ecuador.