[A-HW23] 同位体水文学2023

[AHW23-02] Geochemical Investigation to Elucidate Fluid Origin, Subsurface Processes, and Recharge for Geothermal Conceptual Modeling

*Nyora Donald Kobare^1,2、 Irwan Iskandar²、Suryantini Suryantini ²、Koki Kashiwaya¹、Katsuaki Koike¹ (1.Environmental Geosphere Engineering Laboratory, Department of Urban Management, Graduate School of Engineering, Kyoto University, Katsura C1-2, Kyoto 615-8540, Japan.、2.Geothermal Engineering Master’s Program, Faculty of Mining and Petroleum Engineering, Bandung Institute of Technology, Jl. Ganesha 10, Bandung 40132, Indonesia)

キーワード：Fluid evolution, Mixing process, Recharge area, Stable isotope geochemistry, Tangkuban Perahu, West Java Indonesia

Tangkuban Perahu and nearby volcano-hosted geothermal prospects are believed to be important for future power generation in West Java, Indonesia. Recharge areas of these prospects and geothermal fluid evolution are not yet fully understood. This study aims to describe the fluid origin, processes, and evolution of geothermal fluids in relation to the recharge and the conceptual model of the Tangkuban Perahu Geothermal Systems (TPGS). Sampling and analyses of geothermal waters, rainwater, and gases collected in fumaroles and other manifestations were implemented in this study. Isotopic results of ¹⁸O and DH collected from thermal and rainwater indicate deep-circulating meteoric origin at an infiltration altitude range between 753 to 850 masl in low terrain. Meanwhile, the high-standing terrain indicates that the recharge zone is within the Sunda Caldera wall and mountain slopes. Chondrite normalized patterns reveal an overall flat trendline that suggests the enrichment of Lower Rare Earth Elements (LREEs) in the central part of Tangkuban Perahu, which is derived from the magmatic influx. The non-atmospheric gases origin was diagnosed by the lower N₂/Ar (~38) and is characterized by meteoric origin. The positive ¹⁸O shifts from Ciater (CT), Batu Gede (BG), and Domas Crater (KwD) geothermal water samples comparatively to the local meteoric lines are influenced by the interaction with wall rocks or magmatic influx. In these geothermal systems, the meteoric water infiltrated to the depth is heated, mixed with near-surface water, and followed by partial discharge as thermal springs along the faults. The resultant Tangkuban Perahu conceptual model has six distinct reservoirs with five geothermal systems hosted in the sedimentary (northern parts) and volcanic rock composition in the central and southern parts.