MULTI-SULFUR ISOTOPE RECONNAISSANCE STUDIES OF SLAVE PROVINCE VMS DEPOSITS

Multi-sulfur isotope (³²S, ³³S, ³⁴S and ³⁶S) analyses of galena, sphalerite and pyrite from 30 Archean volcanogenic massive sulfide deposits and occurrences across the Slave Province reveal a variable contribution from Archean atmosphere-derived sulfur. Mass-independent fractionation of the sulfur isotopes produced anomalous abundances of the sulfur isotopes (i.e., non-zero values of Δ³³S) that were incorporated to varying degrees in deposits that formed in different tectonic settings. Nearly all samples fall within Δ³³S = -1.03 to +1.24‰, and δ³⁴S = -1.94 to +2.54‰). Our data indicate that deposits of the bimodal-mafic type (bimodal rift setting) are characterized by a restricted range of Δ³³S values from -0.3 to 0.1 ‰, whereas deposits of the bimodal-felsic type (arc-like settings) exhibit a broader range in Δ³³S values, from -0.8 to 0.6 ‰. Mantle-derived (juvenile) sulfur is essentially the sole source of sulfur in deposits of the bimodal-mafic type, whether derived directly by magmatic degassing, or indirectly by leaching of magmatic sulfides in the associated hydrothermal system; these deposits are also characterized by relatively low silver contents. Bimodal-felsic type deposits, typified by high silver contents, contain variable amounts of atmospheric derived sulfur that was more readily available in arc-like settings. Our current multi-sulfur isotope data set displays no regional variation with respect to previously inferred Pb- and Nd-isotopic crustal variations, or correlation with respect to Pb-isotope ratios measured on the same samples.