ABSTRACT

D/H ratios of molecular hydrogen and chemical composition were analyzed for well and fumarole steam from the Matsukawa, Takinoue and Onikobe active geothermal fields in Northeast Japan. The δD values ranged from -364 to -594‰. The temperatures estimated from the hydrogen-water deuterium isotope equilibrium fractionation are 200 to 300°C for most samples. The relationship between H₂/H₂S ratios and the hydrogen isotope geothermometer suggests that hydrogen and hydrogen sulfide concentrations in geothermal waters are controlled by equilibria with iron mineral buffers.