2015 GSA Annual Meeting in Baltimore, Maryland, USA (1-4 November 2015)

Paper No. 206-21
Presentation Time: 9:00 AM-6:30 PM


TAYLOR, Bruce E.1, PETER, Jan M.1 and WING, Boswell A.2, (1)Geological Survey of Canada, 601 Booth Street, Ottawa, ON K1A0E8, Canada, (2)Department of Earth and Planetary Science, McGill University, 3450 University Street, Montreal, QC H3A 0E8, Canada, Bruce.Taylor@nrcan-rncan.gc.ca

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.