The Geochemistry of the Mt. Balut Island Geothermal Prospect, Davao Del Sur, Philippines

Abstract

The acidic waters of Mt. Balut Island precludes the use of cation geothermometry for the calculation of its reservoir temperature. Instead, the silica mixing plot was used to predict the subsurface temperature, assuming that a chloriderich reservoir exists. In the absence of a suitable cold water sample from the area, an assumption was made that the composition of surface waters, in terms of SiO2 concentration, is similar. Based on eleven cold water samples from different provinces in the Philippines, an average SiO2 concentration of 33 ppm was obtained. This, together with the SiO2 concentration of the warm waters in Mt. Balut were plotted against the corresponding enthalpy equivalent of the measured water temperatures.

The silica-enthalpy mixing model shows that it is possible that a reservoir with a temperature of 196oC exists. Hydrologically, the chloride-rich water could be submerged under the sea. But how do we prove this and do we have the technology to tap such resources? In the meantime, we can only surmise that the geothermal resource in Mt. Balut Island can only be used for domestic as well as recreational purposes.