Estimation of the Deep Geothermal Reservoir Temperature of the Thermal Waters of the Active Continental Margin (Okhotsk Sea Coast, Far East of Asia)

Low-enthalpy thermal waters (30–70 °C) with nitrogen as a dominant associated gas are spread within the active continental margin of Russian Far East (east and north Okhotsk Sea Coast) traditionally great importance for recreation balneology facilities. The chemically classified into three groups: (i) Na–HCO3(SO4) type, low TDS (0.2 g/L) lowest temperature (<50 high pH (9.1–9.3), (ii) Na–SO4 type (~1 g/L), highest (70 weak alkaline (8.7) (iii) Ca–Na–Cl (15 moderate T (59 neutral (7.5). ?18O ?D values suggest that originate from meteoric water, they not isotopically fractionated. Silica cation geothermometers thermodynamic equilibrium calculations using GeoT PHREEQC programs indicate reservoir 103–121 °C types 136 153 °C, respectively. evaluation mixing degree water cold groundwater shows equilibration ranges between 148 °C. Estimated circulation depths manifestations range 2.7 to 4.3 km may be 6 km.