The del 34S of H2S in geothermal & volcanic systems is reviewed by Robinson
BW 1987 in IAEA Proceedings of an advisory group on S isotope variations in
nature held Vienna June 1985. page 31-48. 
A few other papers on New Zealand systems are in Geothermics and Jl of
Volcanic and Geothermal Res with BW Robinson as an author.
Also see Giggenbach WF 1982 Bull Volc. 45-3 , p353 for volcanic 34S.
The 2H/1H ratio in H2S will change too rapidly with any water to be useful.
Hope this is useful 
Graeme Lyon
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