(Special session) Resource exploration and big-data processing

[3301-05-02] Specifying upwelling zone in a field of hidden geothermal system in Indonesia by combining soil-properties and lineament data

○Mochamad Iqbal¹, Katsuaki Koike Koike¹ (1. Kyoto University)

Chairman:Akihisa Kizaki (Akita University)

Keywords:hidden geothermal system, Mt. Endut, 1 m depth temperature , mercury concentration, CO2 concentration

Mt. Endut area in Banten, West Java, Indonesia has been known as a potential hidden geothermal system, where only four hot springs (53-88°C) were found, with a total natural heat loss of about 1.9 MW. This area consists of the Tertiary sedimentary rocks such as sandstone, claystone, and limestone. The younger Quaternary Endut volcanic product veils the older product and complex geological structure, including faults and folds that were found in the sedimentary rocks mainly trending NE-SW and E-W. This study aims to specify upwelling zone where the geothermal fluid reaches the surface using soil survey and lineament density data. Soil samples were collected mainly from the western part of Mt. Endut along a line passing through the hot springs at 500 m interval. In addition, lineament density was mapped in a broader area around Mt. Endut to reveal the regional structure. The soil pH ranges from 2.98 to 6.90 with slightly acidity of the Cikawah hot spring. Soil temperature at the 1 m depth ranges from 24.3 to 36.2 °C. Soil mercury and CO₂ show high concentrations around the Cikawah hot spring, 1.6-1.8% and 349-391 ppb, respectively. Lineament density is also large around Mt. Endut and the Cikawah hot spring. Those results suggest that the upwelling zone is located around the Cikawah hot spring by the geologic structure, which is covered by the Endut volcanic product that probably formed the caprock in the geothermal system. Therefore, geophysical exploration and 3D geologic modeling are indispensable to demonstrate this interpretation and unravel the geological structure controlling the system.