Deciphering the Way Ratai geothermal system, Lampung, Indonesia: A comprehensive geochemical and isotopic analysis

This study investigates the geochemistry and isotopic characteristics of geothermal manifestations in the Way Ratai geothermal field, Lampung, Indonesia, to elucidate the system's fluid flow, reservoir temperature, and the origins of its thermal waters. Fourteen samples were collected from Way Ratai, with three additional from Jatimulyo and four from Natar. The major ion contents and stable isotope ratios (δ¹⁸O and δD) were examined. The Way Ratai hot springs are classified as chloride-type waters based on the Cl-SO₄-HCO₃ concentration ratios, whereas the Natar and Jatimulyo hot springs are characterized as bicarbonate-type waters. The estimated reservoir temperature for the Way Ratai system ranges from approximately 174 °C to 210 °C, with a depth between 600 and 1000 m. Isotopic analysis indicates that the thermal waters at Way Ratai predominantly originate from meteoric sources. The recharge area for the Way Ratai geothermal fluid is estimated to be at an elevation of 1200 m above sea level, corresponding precisely to the location of Mt. Ratai. Through geochemical and isotopic analysis, it is inferred that the hot springs at Natar and Jatimulyo are connected to the Way Ratai reservoir, having undergone mixing and dilution processes. This research is integral to effective exploration and development strategies in the region, offering key insights into the potential of the Way Ratai geothermal field. The detailed geochemical and isotopic analyses contribute to a deeper understanding of the geothermal systems in the area and their viability for sustainable energy exploitation.