Geochemistry of Thermal Waters of Continental Margin of Far East of Russia

Studied waters belong to warm (T=30-50 degrees C), alkaline (pH=8.9-9.3), low mineralized (TDS<235 mg/l) Na-HCO3 or Na-SO4-HCO3 thermal waters with high content of SiO2 (up to 81 mg/l) and F (up to 3.9 mg/l), occur on modern volcano-tectonic rejuvenated areas of Eastern Sikhote-Alin orogenic belt. Low He-3 concentration as well as N-2/O-2 and N-2/Ar ratios exclude influence of deep mantle fluid. New rare earth element data constrain our understanding of water-rock interaction occurring in the water source region. Meteoric origin of waters is proved by stable isotope values varying from -71 parts per thousand to -136.1 parts per thousand and from -10.8 parts per thousand to -18.8 parts per thousand for delta H-2 and delta O-18 respectively. REE patterns reflect high pH, resultfing from water-rock interaction and oxidative conditions. Calculations of deep aquifer temperature using Na-K and quartz geothermometers show 116.8-131.1 degrees C and 82.2-125.8 degrees C respectively. Presence of deep faults both with abnormal thermal gradient (similar to 45-50 define unique geochemical shape of thermal waters of Sikhote-Alin, area, where no present volcanic activity is registered.