Characterizing Geothermal System of the Tampomas Area, West Java, Indonesia by Water Chemistry and Stable Isotope Analyses

Abstract

The Tampomas geothermal area is located at 42 km northeast of the Bandung basin, West Java, Indonesia and seated in the intra-volcanic basin by the Indonesian subduction system. This study aims to clarify the geothermal system and resource potential of the Tampomas geothermal area. Dominant directions of fractures, northeast and northwest, inferred from the lineament data are in agreement with the regional pattern of west Java structure. The fluid path from the geothermal reservoir to the surface may be formed in the high-density zone of fractures in the northeastern part. The hot spring manifestations are situated in the transition domain between the geothermal water and groundwater, and their waters are mostly Cl-HCO3 type originated from the mixing of Cl water with the groundwater in the flow process. The δ13C (CO2) stable isotope data suggest CO2 origins are magmatic and marine bicarbonate, while the source of geothermal fluids is meteoric water indicated by the δ18O and deuterium isotope data. Furthemore, the subsurface temperature in the Tampomas geothermal area is estimated in the range from 142 to 167 ºC by a silica geothermometer. Consequently, the study area is classified as medium enthalpy geothermal system.