Chemical and isotopic composition of CO2-rich magnesium- sodium-bicarbonate-sulphate-type mineral waters from volcanoclastic aquifer in Rogaška Slatina, Slovenia

Bottled natural mineral waters from an andesitic aquifer in Slovenia are enriched in magnesium (1.1 g/l), sulphate (2.2 g/l) and dissolved inorganic carbon (204 g/l). We analysed major ions, trace elements, tritium activity, 14 C, d18 OH2O , d2 HH2O, d13 CDIC, gas composition and noble gases in six wells. In addition, 87 Sr/ /86 Sr, d34 SSO4 and d11 B were analysed here for the first time. Stable isotopes with d18 O = -11.97 to -10.30% and d2 H = -77.3 to -63.8 confirm meteoric origin. CO2 degassing is evident at three wells, causing the oxygen shift of about -1.3%. Tritium activity was detectable only in the shallowest well, where the freshwater component was dated to the 1960s. d13 CDIC in five waters is -1.78 to ? 1.33%, typical of carbonate dissolution. Radiocarbon is low, 1.03–5.16 pMC. Chemical correction with bicarbonate concentration and d13 C correction methods gave best mean residence times, slightly longer than previously published. Sulphate has d34 S 26.6–28.9% and d18 O 8.9–11.1% due to dissolution of evaporites in carbonate rocks. Boron at concentrations of 1.2–6.1 mg/l has two origins: d11 B = 11.3–16.4% from hydrothermal alteration and d11 B = 26.6–31.7% from carbonate dissolution. Strontium at concentrations of 0.5–22.0 mg/l has 87 Sr/ /86 Sr, indicating three sources: 0.7106 for Miocene clastic rocks, 0.7082 for Triassic carbonates and 0.7070 for Lower Oligocene andesitic rocks. CO 2 represents the majority of the dissolved ([ 98.84 vol%) and separated gas ([ 95.23 vol%). Methane is only found in two wells with a max. of 0.30 vol%. All waters show excess helium and 16–97% of mantlederived helium. Since all show subsurface degassing, the paleo-infiltration temperature could not be calculated