Application of Cl. B tracers and geoindicators to delineate some production characteristics of Mt. Labo geothermal system, Philippines

Abstract

This report focuses on the interpretation of water chemistry in the Mt. Labo area with the aim of delineating the characteristics of the Mt. Labo geothermal system. The types of waters in the area are: a) dilute neutral pH warm springs, b) alkaline Cl hot springs, c) acid to neutral pH SO4-Cl warm springs, d) slightly acid (pH 5.1 at 270 C) Cl well waters, with relatively high SO4. The source of Cl and B in the warm spring waters is the rock with which these waters react. The main source of Cl in the other types of water is considered to be the magma heat source to the geothermal system. However, in these latter water types most of the B is derived from the dissolving rock. The SO4-Cl warm springs are considered to form by the mixing of magmatic gases with surface waters, whereas the alkaline Cl hot spring waters and well fluids are formed by the mixing of magmatic gases at depth. The pH of the aquifer water feeding the wells is calculated to be 5.1 at the aquifer temperature, 270 C. However, at the surface, the discharged waters are strongly acid (pH 3-4). The reason for this is relatively high SO4 in the waters. Dissociation of HSO4- upon cooling ...