Hydrogeochemical model of Ciseeng geothermal field, Bogor, West Java

Ciseeng geothermal field is located Northwest of West Java 40 km from Jakarta. Three surface manifestations are in Tirta Sayaga, Panjang Mountain, and Peyek Mountain. This study aims to build a hydrogeochemical model based on water analysis. The secondary regional geological data are retrieved to complete geological information of Ciseeng. The research method is divided into several stages: introduction includes the literature study, data collection includes the measurement of temperature and pH in several surface manifestations, rock sampling and structural geology analysis in Ciseeng. The type of manifestation that can be found in Ciseeng is a warm pool with chloride fluid type. Extensive travertine deposits were found in all three locations. The fluid temperature of three surface manifestations is about 30-38 °C with pH 6. According to the measurement of Na-K-Ca geothermometer, the reservoir temperature in Ciseeng geothermal field is 180 °C. The three manifestations of Ciseeng geothermal field are classified as mature water based on a ternary plot diagram. The isotopic analysis shows shifting in O₁₈ indicating hydrothermal process due to magmatic activities in the subsurface. It is predicted that Ciseeng geothermal field is part of Salak/Pangrango Mountain geothermal system. The presence of surface manifestation confirms that geological structure trending from North to South, play a significant role to circulate the heated fluid in the subsurface and subsequently to the surface. The result is a geothermal conceptual model of Ciseeng field that shows the fluid origin and movement in the subsurface.