Geochemical Investigation of Thermal Water Wells in Tebing Tinggi, North Sumatra, Indonesia: Geology and Preliminary Insights into Their Sources
DOI:
https://doi.org/10.17794/rgn.2026.5.8Keywords:
thermal water hydrogeochemistry, geothermometry, low-enthalpy geothermal system, fault fracture density, North SumatraAbstract
This study investigates the hydrogeochemical and isotopic characteristics of thermal waters from artesian wells in Tebing Tinggi, North Sumatra, Indonesia, to determine their origin, reservoir temperature, and structural controls influencing fluid circulation. Water samples from four thermal wells and one cold artesian well were collected and analysed for major ions (Na⁺, K⁺, Ca²⁺, Mg²⁺, Cl⁻, SO₄²⁻, HCO₃⁻), trace elements (Li, B, SiO₂), and stable isotopes (δ¹⁸O and δ²H) using titrimetry, atomic absorption spectrophotometry, ion chromatography, and cavity ring-down spectrometry. The δ¹⁸O–δ²H relationship confirms a meteoric origin for the thermal waters. Hydrochemical analysis classifies the waters as sodium-bicarbonate type, with characteristics of immature waters due to elevated Mg content, indicating mixing with shallow groundwater. Geothermometry using quartz and Na-K-Ca methods estimates reservoir temperatures between 73°C and 123°C, corresponding to a low-enthalpy geothermal system. Reservoir depth is estimated at 1.26–2.67 km based on regional geothermal gradients. Fault and fracture density (FFD) modelling reveals high fracture concentrations in central Tebing Tinggi, aligned with the interpreted NE-SW trending Tebing Tinggi Fault, suggesting structural control on thermal fluid upwelling. These findings indicate that thermal water circulation in Tebing Tinggi is governed by both tectonic fracturing and residual heat from the Toba volcanic complex, providing baseline data for future geothermal resource assessment in the North Sumatra back-arc region.
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Copyright (c) 2026 Eri Sarmantua Sitinjak, Danni Gathot Harbowo
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