Mita Geothermal System, Guatemala: Updated Resource Assessment and 3D Geological Model

Abstract

Mita is a moderate temperature geothermal system that was discovered in 1997 during gold exploration in south-eastern Guatemala. This system is associated with bimodal basalt-rhyolite volcanism, and occurs alongside (and overlapping with) the Cerro Blanco 2 million ounce epithermal gold deposit. Four 1000-1500m deep slimholes were drilled in 2008-09 to confirm the nature of the deep reservoir.

This drilling program outlined an intermediate depth reservoir with temperatures in the region of 200°C, with a deeper inferred reservoir with temperatures of around 240°C. The intermediate depth geothermal system has been interpreted to be an outflow of a deeper system which migrates up along a horst fault. A total of six production wells (800-1000m deep) and two additional slimholes have been targeted to intercept the intermediate reservoir along the horst fault. The results of the drilling campaign have indicated temperatures of 185-216°C; however the permeability along the fault is highly variable, with a narrow outflow zone along part of the horst fault.

Following the latest exploration drilling phase, an updated conceptual model and 3D geological model have been created. This reservoir is liquid-dominated with a sodium-chloride-bicarbonate composition, TDS of about 1,900 mg/kg and gas content of 0.4 wt%. The shallow outflow from this system appears to be linked to the thick Salinas rhyolite encountered at shallow depths. Electricity generation is feasible from wells intersecting permeable fractures along the Eastern Horst Fault (EHF). The extraction from these wells will also assist in the dewatering and cooling that is necessary to access the Cerro Blanco gold deposit. Exploration is continuing to establish suitable injection capacity and to evaluate the production potential of the deeper reservoir.