Metamorphosed proterozoic Zn-Pb-Ag mineralization in the Foster River area, Northern Saskatchewan, Canada

Metamorphosed Zn-Pb occurrences (Fable Lake, George, Sito South, Sito Southwest, Sito West, Sito East, Robyn Lake, and Mackie Lake) with high Zn:Pb ratios occur in the Foster River area, northern Saskatchewan, on the southeast margin of the Paleoproterozoic Wollaston Domain. The Sito East prospect, the largest of these occurrences, contains ~50,000 tonnes of 4.5% Zn, with one drill intercept containing 11 m of 4.2% Zn and 0.6% Pb. Most prospects are hosted in a thin, areally extensive metaquartzite within a thick sequence of metasiltstones and metaquartzites in the middle of the Paleoproterozoic Wollaston Group. Occurrences in metaquartzites and metaarkoses, which locally contain gahnite, spessartine, and/or graphite, are spatially associated with metaexhalites (iron formation and quartz garnetite) and strata-bound metamorphosed hydrothermal alteration zones (nodular sillimanite rock). Post-Archean Australian shale-normalized rare earth element (REE) patterns of all three rock types are characterized by light REE enrichment, positive Ce anomalies, neutral to strongly negative Eu anomalies, and heavy REE depletion, consistent with an environment of deposition distinguished by a high (>30 wt %) continental detrital component and formation from or interaction with low-temperature (≤250°C), near-neutral pH and high f_O2 fluids. Sulfur isotope compositions of sulfides at Foster River are highly enriched in ³⁴S (δ³⁴S = 26.2–38.1‰, n = 20) and resulted from microbial reduction of partially reduced seawater sulfate in a restricted basin.

The spatial association of spessartine- and gahnite-bearing lithologies and silicate facies iron formation with Paleoproterozoic base metal sulfides in a psammopelitic host sequence implies similarities between sulfide mineralization in the Foster River area and Broken Hill-type Pb-Zn-Ag deposits. However, the markedly enriched δ³⁴S_sulfide compositions, low Pb/(Pb + Zn) and Ag/(Pb + Zn + Ag) ratios, low Ag contents, and apparent absence of metavolcanic and metavolcaniclastic rocks in the dominantly clastic rock sequence hosting the sulfides in the Foster River area suggest that these occurrences are part of a metamorphosed sedimentary exhalative system with Broken Hill-type affinities, similar to that associated with the formation of the Gamsberg Zn (South Africa), Kanmantoo Group Pb-Zn (South Australia), and Sullivan Pb-Zn (Canada) deposits.