Application of natural isotope tracers to geothermal research in the Ranong fault zone (S-Thailand)

Northeast-southwest trending fault in the southern part of Thailand, Ranong fault, exposes six hot springs along that faults line. These hot springs are utilised for health spa and water consumption. In this contribution, we present a comprehensive survey of chemical and isotopic compositions of thermal waters from five hot springs, well water, and cold surface water samples. We aim to identify sources of the geothermal waters, hydrodynamic processes and the thermal capacity of the hot springs along the Ranong fault zone. Field parameters, major ions, stable isotopes of hydrogen, oxygen, and carbon, as well as radiocarbon and tritium are investigated. The chemical composition of both thermal waters and cold surface waters is dominated by the Na-HCO₃ type. δ²H _SMOW and δ¹⁸O_SMOW data of thermal water and cold surface water plot along a local meteoric water line, suggesting local precipitation as the source of thermal water in the area. δ¹³C_PDB values between -23.55 to -25.59 ‰ indicate that dissolved carbon in the thermal water samples is mainly from organic carbon sources, but some mixture with inorganic carbon may occur. Radiocarbon analyses (54-61 pMC) suggest ages from 3,600 to 4,800 years for the formation of the thermal waters. Additionally, tritium concentrations range between 0-0.2 TU.