In-situ multiple sulfur isotopes of the Archean Hongtoushan Cu-Zn-Au deposit from North China Craton as tracers for the source and the size and grade of the VMS ore deposit

In-situ multiple sulfur isotope analyses of pyrite, pyrrhotite, and chalcopyrite from the -2.55 Ga Hongtoushan Cu-Zn-Au VMS deposit are reported. Three sulfide minerals (pyrite, pyrrhotite, chalcopyrite) display slightly different mean delta 34S values of +0.94 %o, +0.60 %o, and +0.57 %o and mean Delta 33S values of -0.07 %o, -0.02 %o, and -0.05 %o, respectively. The sulfide minerals show obvious signatures of slightly negative mass-independent fractionation for sulfur isotopes, indicating a dominant igneous source of sulfur with -2.5-3.5 % seawater sulfate contribution during the formation of this deposit. According to the suggestion by Chen et al. (2015) that the ore tonnages of Archean VMS deposits are linked to the Delta 33S values, the Hongtoushan deposit may have greater prospecting potential. This study also proposes that not only do high Au-grade Archean VMS deposits have relatively high Delta 33S values (near-zero) as suggested by Sharman et al. (2015), but low Au-grade Archean VMS deposits might also have high Delta 33S values (near-zero). The Cu grades may also be directly linked to the Delta 33S values for the Archean VMS deposits, as a greater seawater contribution (rapid temperature decrease; more negative Delta 33S values) would be linked to higher Cu grades. These new findings may have great implications for our understanding of Archean VMS deposit genesis, and multiple sulfur isotope analyses may be used to predict the size, grade of Cu, and grade of Au for Archean VMS deposits.