Geochemical Study of Water and Gas in The Wayang Windu Geothermal System

Abstract

This study presents a comprehensive geochemical and hydrogeological characterization of the Wayang Windu Geothermal System in West Java, Indonesia. The research aims to identify water and gas chemistry patterns, to determine fluid origins, and to estimate reservoir temperatures to support conceptual modeling of the geothermal field. Field sampling was conducted on hot and cold springs and fumarolic gases, complemented by laboratory analyses of major ions (Cl⁻, SO42⁻, HCO3⁻; Na⁺, K⁺, Mg2+), stable isotopes (δ2H, δ18O), and gas compositions (CO2, N2, Ar). Data interpretation employed standard geochemical tools, including Cl-SO4-HCO3 and Na-K-Mg diagrams for water classification, δ2H-δ18O plots for recharge source identification, and N2-CO2-Ar ternary diagrams for gas origin assessment. The results indicate that sulphate-type hot springs mark upflow zones, while bicarbonate-type warm and cold springs reflect lateral outflow and mixing processes. The isotopic signatures confirm predominantly meteoric recharge with localized steam-heated and magmatic influences. The gas geothermometers estimate reservoir temperatures between 225° and 286° C, and Cl-Li-B relationships reveal three distinct reservoir clusters: Gambung, Wayang, and Windu. These findings provide critical insights into fluid pathways, reservoir structure, and recharge dynamics, forming a robust basis for sustainable geothermal resource management in volcanic settings.