New Isotope-Hydrogeochemical Data on the Bang Spring (Kuang Binh Province, Central Vietnam)

—New isotope hydrogeochemical data on two types of thermal water from the Bang spring (Kuang Binh province, central Vietnam) are reported in the work. The first type includes HCO 3 –Cl–Na–Mg water with extremely low mineralization (44–87 mg/dm 3 ) and pH variations from weakly acidic to weakly alkaline values (5.71–7.84). The second type includes HCO 3 –Na water with mineralization up to 256–659 mg/dm 3 and pH 8.03 to 8.51. The studied types differ significantly in temperature: 24.3–34.5°C in the first type and 62.1–97.1°C in the second type. The analysis of the distribution of oxygen (δ 18 O) and hydrogen (δD) isotopes carried out for the first time confirms different genetic nature of these hydrogeochemical water types. The first type has an atmospheric genesis (δ 18 O = –7.3…–6.2‰ and δD = –51.4…–39.3‰), while the second type restricted to the Kien Giang–Bang intersection zone has a deeper source (δ 18 O = –1.6…–1.3‰ and δD = –22.2…–21.4‰). The tritium ( 3 H) data also point to different circulation times of these waters. The formation time of the HCO 3 –Cl–Na–Mg waters does not exceed 50 years ( 3 H = 4.3–11.1 ТЕ), while that of HCO 3 –Na water may reach more than 1000 years ( 3 H = 0.5 ТЕ).