Geochemical Analysis of Geothermal Manifestations in Buton Island, Southeast Sulawesi, Indonesia

Abstract

The geochemical characteristics of non-volcanic geothermal energy in Buton Island are still rarely studied despite its location in an active tectonic zone. This study explores the geochemical features of geothermal manifestations in Buton Island, Indonesia, with the aim of identifying fluid characteristics and predicting subsurface temperatures from geothermal manifestations in the study area. Water samples collected from five manifestation locations were analyzed for major cations (Na⁺, K⁺, Ca²⁺, Mg²⁺) and anions (Cl⁻, SO₄²⁻) using atomic absorption spectrophotometry, HCO₃⁻ concentration through titrimetric analysis, and SiO₂ content through spectrophotometry. The ternary diagram of Cl-SO₄-HCO₃ indicates the type of bicarbonate fluid, while the ternary diagram of Na-K-Mg indicates the characteristics of immature geothermal water in the reservoir. Interpretation is clarified through specific findings in the Gonda Baru and Karede samples that show characteristics of a chloride-bicarbonate mixture type due to the influence of seawater intrusion or intensive rock-water interaction during long residence times in the reservoir. Geothermometers such as Na-K-Ca and K-Mg are used to estimate reservoir temperatures. The estimated reservoir temperature indicates a relatively low-temperature system, ranging from 70°C to 120°C. The implications of identifying this low-temperature system indicate that geothermal resources on Buton Island are ideal for direct use, such as in the agro-system sector (drying agricultural products), tourism/therapeutic hot springs, or small-scale binary cycle power plants. This research provides an important scientific contribution as a basic reference in the strategy for developing non-volcanic renewable energy potential in Eastern Indonesia.