Hydrogeochemical characteristics and genesis of geothermal waters in Qingyuan, northern Guangdong, China

Qingyuan City, Guangdong, possesses abundant geothermal resources; however, systematic investigations into the hydrogeochemical characteristics and genesis of these thermal fluids remain scarce, hindering their scientific development and efficient utilization. This study conducted hydrochemical analyses of 16 representative geothermal water samples, supplemented by hydrogen and oxygen stable isotope analyses of five of these samples, to elucidate their hydrogeochemical evolution and genetic mechanisms. The results indicate that the major ion chemistry of these thermal waters is predominantly governed by water–rock reactions, which manifest as the dissolution of carbonate and silicate minerals in conjunction with cation exchange; a meteoric origin is further corroborated by the stable isotopic compositions (δD and δ 18 O), with estimated recharge elevations of 193–635 m a.s.l. and a recharge area located in the low-mountain and hilly region of the study area; reservoir temperatures estimated using the quartz geothermometer (no steam loss) range from 46 °C to 146 °C, consistent with a low- to moderate-temperature geothermal system. Corresponding circulation depths are estimated at 1,113–5,442 m. The findings support a conceptual model in which meteoric water infiltrates and circulates to depth, where it is heated and reacts with the surrounding rocks, before ascending along faults and discharging at the surface. Taken together, these results refine the conceptual understanding of the origin and hydrogeochemical evolution of geothermal waters in the study area, while providing a hydrogeochemical basis for future geothermal exploration and resource assessment.