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 for the ∼2.55 Ga Hongtoushan Cu-Zn-Au VMS deposit are reported. Three sulfide minerals (pyrite, pyrrhotite, chalcopyrite) display slightly various δ34S mean values of +0.94 ‰, +0.60 ‰, and +0.57 ‰ and Δ33S mean values of –0.07 ‰, –0.02 ‰, and –0.05 ‰, 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 Δ33S values, the Hongtoushan deposit may have greater prospecting potential. This study also proposes that not only the high Au-grade Archean VMS deposits have relatively high Δ33S values (near-zero) as suggested by Sharman et al. (2015), those low Au-grade Archean VMS deposits might also have high Δ33S values (near-zero). The Cu grades may be also directly linked to Δ33S values for the Archean VMS deposits, as the higher seawater contribution (rapid temperature decrease; more negative Δ33S values) would link to higher Cu grades. These new findings may have great implications in our understanding of Archean VMS deposits genesis, and multiple sulfur isotope analyses may be used to predict the size, the grade of Cu, and the grade of Au for the Archean VMS deposits.