Sulfur Isotope Analyses of Some Sudbury, Ontario, Ores

Cu-Ni ores from seven mines in the Sudbury ore camp have been analyzed. Together with older analyses, they indicate a weighted mean δ 34 S for all ore of + 2.1‰ (CDT), a range from + 0.5 to 7.2‰. Individual deposits have characteristic δ 34 S means, and small dispersions compared to whole camp. 34 S-content is not correlated with ore type, as defined by sulfide-silicate association; δ 34 S increases with depth in south-range deposits; north-range ores are heavier still, as if deposits had been uplifted relative to south-range, contrary to conventional structural interpretation.Fractionation between pyrrhotite and chalcopyrite (Δ pc  = δS Po – δS cp ) ranges from − 0.8 to + 0.9‰. Negative fractionations may be quenched in from high temperatures. Δ pc is positively correlated with δS po . Both variables may be responding to increasing depth of emplacement, δS po by progressive fractionation through extraction of S-32 enriched crystals from sulfide magma; Δ pc through decreased cooling (quenching) rate. Alternately, Δ pc – δ po variations may represent partial exchange of pyrrhotite with an 32 S-rich fluid after ore deposition.Overall δS of ore suggests that primary sulfide magma is fractionated with respect to primitive basaltic sulfur, possibly by loss of S-32 enriched vapor.