Distribution of 222Rn and CO2 across faults and its origin in Wayang Windu geothermal area, West Java']Java- Indonesia

As a geogenic gas, 222Rn (radon) has been widely utilized to infer permeability zones in some geological settings such as fault zones, volcanic and geothermal areas. In this study, soil 222Rn was measured in Wayang Windu geothermal area to infer the relation between fault and permeability. In addition, measurement of soil CO2 and its 813C composition were also performed to infer transport mechanism and the origin of soil CO2. The high and anomaly soil 222Rn, i.e., above 8,500 Bq/m3, were found in the south -southwest area and related to Pejaten Fault, Banjarsari Fault and Cibitung Fault. In contrast, low soil 222Rn was found in the northern area, where several highly productive geothermal wells are located. The high and anomaly soil CO2 concentrations were also found in a relatively similar area with high 222Rn, but not closely related to the fault structures. Furthermore, the 813C composition showed that the origin of soil CO2 in the area was magmatic, biogenic and atmospheric. Based on the 222Rn/CO2 values and its 813C compositions, the mechanism of 222Rn transport was interpreted as in-dependent from CO2 as carrier gas.