Prefeasibility Geothermal Assessment of Platanares, Department of Copan, Honduras

Abstract

The Platanares geothermal system is located in a region of active Quaternary tectonism in western Honduras. Although the geothermal area is partially blanketed by Miocene ignimbrites (14.5 m.y.), there are no nearby Quaternary volcanic rocks to act as a young magmatic heat source. No acid-sulfate waters, indicative of vapor-dominated conditions, exist in the area. Hot spring activity is most vigorous along a 2 km stretch of the Quebrada del Agua Caliente fault zone. Natural discharge is high (-3300 l/min), temperatures range from 35 to lOO"C, pH ranges from 7 to 9, and total dissolved solids are low (-1100 mg/kg). Chemical geothennometers indicate a subsurface reservoir temperature of about 225°C. Three exploration core holes (7.8 cm diameter) have been drilled to a maximum depth of 680 m and maximum temperature of 165°C. Two holes produce copious amounts of water under artesian conditions (-500 l/min max.; 5 bars flowing) from fractured red beds of Cretaceous to Eocene age (Valle de Angeles Group).Maximum power output is -4.5 MW (thermal) but C02 released during flashing formed some aragonite scale in one hole. The third core hole has an "apparent" conductive gradient of 139" C/km at 400 m. Downward continuation of this gradient implies that the minimum depth to the geothermal resource (225°C) is 1.5 to 2.0 km.