δ34S values determined for dissolved sulfate in water discharged by sulfurous springs near Paige Mountain identify gypsum beds in the Lower Devonian Bear Rock Formation as the sulfate source, whereas relatively low δ18O values show that as much as 30% of the sulfate may have gone through a reduction–re-oxidation cycle. Reduced sulfur species in the spring water have negative δ34S values as a result of microbiological isotope fractionation during sulfate reduction; airborne sulfur species (H2S, SO2, H2SO4) and gypsum formed through reaction of H2SO4 fallout with exposed carbonate rocks show similar negative δ34S values. Negative δ18O values for the sulfate radical in H2SO4 fallout and in the alteration product indicate that more than half of the oxygen reacting with airborne H2S is derived from water vapour.

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