Estimation of Fluid-rock Interaction Process and Recharge Area of the Tampomas Geothermal Field, West Java, Indonesia by Water Chemistry

Abstract

Geochemistry is one of the most effective methods used in the geothermal exploration process, especially related to subsurface temperature, interaction process, and geothermal fluid source. This preliminary research is aimed to clarify the origin and process of rock and fluid interaction that occurred in the Tampomas geothermal field in the northern the Bandung Basin, one of the geothermal potential fields in this basin. The potential in the northern Bandung basin is estimated to be lower than the southern basin in which several fields such as Kamojang, Darajat, and Wayang Windu produce considerable geothermal energy, ranging from 200 to 300 MWe. To reveal this potential difference is an important issue for the geothermal system in the subduction zone. Geochemical analysis was applied to it. Generally, water type of hot spring in the Tampomas area is dominated by chloride-bicarbonate water, where water is formed in the marginal area near the surface. CO2 gas and water vapor are condensed into cold groundwater as well as steam heated processes. The low B / Cl ratio in the hot springs indicates a close relationship with the magmatic geothermal system. The Ciuyah hot spring has the highest concentrations of chloride, calcium, and lithium among the other manifestations, which is probably due to fluid interaction with the Tertiary marine sedimentary rocks in this area, in particular the Tertiary claystone of the Subang Formation. The maximum subsurface temperature in the Tampomas area is 168 ℃ based on a silica geothermometer. Study on stable isotopes of oxygen and deuterium suggest that the recharge area in the Tampomas geothermal manifestation is located in the elevation range from 425 to 900 m a.s.l. Consequently, through our geochemical data, the geothermal fluids originating from meteoric water have been influenced by the volcanic process of the Tampomas mountain and interacting with the sedimentary rocks around it.