Origin of sulfur species in acid sulfate-chloride thermal waters,northeastern Japan

Acid sulfate-chloride thermal water samples collected together with fumarolic gases from various volcanic areas in northeastern Japan were studied chemically and isotogdically. δ³⁴S (COT) values of sulfate and hydrogen sulfide from these volcanic hot springs range from +4.0 to +31 and from ?15.0 to ?2.0% respectively, with δ³⁴S_ys value of +2.5 to +31. The δ³⁴S of the sulfate in the more saline waters tends to become smaller with increasing ratio of SO₄ to Cl, although the chemical and isotopic composition of acid thermal water within some areas may be altered by secondary processes during the discharge of the thermal waters. This trend can be explained by the reaction of the volcanic gases, having S/Cl of 4 ~ 7 and total sulfur of ~0% in δ³⁴S, with ground water at 200°C, and/or the removal of sulfide phase depleted in ³⁴S from the acid thermal water formed by the disproportionation of volcanic sulfur. The sulfur species in acid sulfate-chloride thermal water are shown to be volcanic exhalations.