Mass- spectrometric analyses of material from sulfide ore districts of Sweden, Cornwall, and elsewhere indicate that in general sulfur isotope abundance ratios do not differ significantly in minerals formed during different stages of the same mineralization process, nor can they be correlated with zonal distribution of the ores. Isotope fractionation, evidenced by variations in S 32 /S 34 ratios of coexisting primary sulfides and sulfates, may occur in early stages of mineralization but tends to be more pronounced at lower temperatures; its development may be quite local, as shown by wide ranges in isotopic composition of sulfides in single hand specimens. No appreciable change in isotopic composition occurs during transformation of sulfide to sulfate in the zone of oxidation. The data suggest that a limited number of determinations of isotope abundances in sulfide minerals cannot provide conclusive evidence bearing on the source of the sulfur.

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