Geothermal Exploration at Irruputuncu and Olca Volcanoes: Pursuing a Sustainable Mining Development in Chile

Abstract

Doña Inés de Collahuasi Mining Company which is the third major copper producer in Chile is pursuing a sustainable development by exploring geothermal resources. Currently the mining operation requires 180MW of electric power, which is derived from fossil fuels. However, the company´s objective is to obtain at least 35MW from renewable energy sources by 2015. The geothermal exploration is focused around the Olca and Irruputuncu volcanoes in the Chilean Altiplano at 4000-5000 m a.s.l. in the vicinity of the copper mine. Irruputuncu is an active dacitic stratovolcano, with fumaroles at the top crater and one acid-sulphate hot spring at the base of the volcano. Two slim boreholes (~800 and ~1430 m depth) evidenced a sequence dominated by tuffs, breccias and minor lava flows, with bottom hole temperatures close to 150ºC and 195ºC (at ~3350 and 3000 m a.s.l., respectively). Both wells are dominated by argillic alteration assemblages and conductive temperature profiles, pointing to a potential deeper reservoir (>220ºC), as suggested by TEM-MT data. Olca is an andesitic volcano with fumaroles at the crater and one neutral warm spring at the base. The 3D inversion of TEM-MT data evidences two conductive layers intercalated with resistive zones. Shallow drilling at the base of the volcano confirms the occurrence of hot water aquifers (up to 70ºC) and a zone dominated by smectite clays which is coincident with the shallow conductor layer. Preliminary results suggest a potential of electric generation between 75 and 450 MWe. Deep drilling is planned for late 2011 to characterize the potential deep reservoir, below the deep conductor.