Understanding hydrogeochemical processes is essential for predicting mineral alteration and carbonate scaling in geothermal and mining environments. However, such studies remain limited in Malifut, North Maluku, where geothermal manifestations and mining activities coexist. This study aims to classify hydrochemical facies and evaluate mineral stability in various thermal waters, including underground mine waters, a hot spring, and borehole thermal waters. Field measurements of temperature, pH, electrical conductivity, and total dissolved solids were conducted, while major ions were analyzed using ion chromatography. Hydrochemical facies were identified using the Cl-SO₄-HCO₃ ternary diagram, and mineral saturation indices were modeled with PHREEQC. The classification revealed that borehole waters belong to the peripheral type, while Shallut and Kencana mine waters are steam-heated, and Toguraci, together with Akesahu hot spring, are volcanic waters. PHREEQC modeling revealed that volcanic and steam-heated waters are oversaturated with calcite and aragonite, indicating a strong potential for carbonate precipitation due to CO₂ degassing and elevated temperatures. Borehole waters were mostly near equilibrium or undersaturated, except PZ-8, which exhibited dolomite oversaturation and a clear geothermal signature. All samples were undersaturated with gypsum and anhydrite, indicating carbonate equilibria as the dominant control. This integrated approach enhances the understanding of water-rock interaction, fluid origin, and scaling risk in geothermal-mining systems, and provides practical insights for water management and scaling mitigation strategies in Malifut.

The karst landscape of Trenggalek Regency, located in several sub-districts including Dongko, Kampak, and Watulimo, is shaped by the Wonosari Formation and is characterized by springs and underground rivers. Due to water scarcity in the region, local communities heavily depend on these natural water sources. This study assesses the groundwater quality of 16 springs and 20 underground rivers to evaluate their suitability for consumption and associated health risks. Using the groundwater quality index (GWQI), human health risk assessment (HHRA), and statistical methods, various physicochemical parameters were analyzed, including pH, total dissolved solids (TDS), electrical conductivity (EC), and concentrations of iron (Fe²⁺), manganese (Mn²⁺), calcium carbonate (CaCO₃), and sulfate (SO₄). Water generally meets the World Health Organization standards for safe drinking. However, correlation analysis reveals notable mineral dissolution and possible anthropogenic influence. TDS strongly correlates with EC (r = 0.97), while Fe²⁺ shows significant relationships with Mn and TDS. Conversely, CaCO₃ shows a negative correlation with EC and TDS, suggesting alternative sources beyond rock weathering. The HHRA indicates higher non-carcinogenic health risks from Fe²⁺ contamination in underground rivers compared to springs. The study’s novelty comes in its integrated assessment of groundwater quality and health hazards in Trenggalek’s karst region, which uses GWQI, HHRA, and statistical analysis to show geochemical interactions and highlight iron-related health issues in underground rivers.