<![CDATA[The Gunung Kapur area in Jambi is part of a geothermal region characterized by volcanic, plutonic, and hydrothermal alteration features. This study evaluates the hydrogeochemical characteristics, fluid types, equilibrium conditions, and inferred reservoir temperatures of the Gunung Kapur geothermal system and surrounding thermal waters using pH, major-ion chemistry, Cl–SO₄–HCO₃ classification, silica and cation geothermometers, and the Na–K–Mg geoindicator. The dataset includes thermal waters from Idung Mancung, Sapan Melolong, Semurup 1, and Semurup 2, together with Kerinci cold water as a reference. The hydrochemical data indicate contrasting fluid characteristics. Idung Mancung is strongly acidic and sulfate-rich, consistent with shallow steam-heated water, whereas Sapan Melolong and Semurup 1 exhibit chloride-bearing characteristics and lower Mg concentrations, suggesting greater interaction with deeper geothermal fluids. Semurup 2 shows a more mixed and immature signature, while Kerinci cold water is dominated by bicarbonate and represents a shallow meteoric or peripheral component. Geothermometric estimates vary according to fluid maturity and water type. Semurup 1 yields the most consistent high-temperature indications, with estimated reservoir temperatures generally ranging from approximately 194 to 243 °C, whereas Sapan Melolong indicates moderate-temperature conditions of approximately 169–188 °C. In contrast, cation geothermometer estimates for strongly acidic or immature waters should be interpreted cautiously because of shallow alteration, mixing, and disequilibrium effects. The results indicate that the regional geothermal system contains chemically heterogeneous waters representing steam-heated, deeper chloride-bearing, mixed, and meteoric components. These findings provide a hydrogeochemical basis for understanding subsurface fluid circulation and geothermal potential in the Gunung Kapur region, although direct confirmation of reservoir conditions requires additional site-specific geochemical, geophysical, and subsurface data.]]>
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