Metamorphosed Proterozoic Zn-Pb-Ag Mineralization in the Foster River Area, Northern Saskatchewan, Canada

Abstract

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 lowtemperature (≤250°C), near-neutral pH and high fO 2 fluids. Sulfur isotope compositions of sulfides at Foster River are highly enriched in 34 S (δ 34 S = 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 δ 34 Ssulfide 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.

The origin of the sediment-hosted Kanmantoo Cu-Au deposit, South Australia: Mineralogical considerations

“…All of these exhalative rocks occur at the same stratigraphic level within the Tapanappa Formation (the so-called Angas Garnet Member of Gum, 1998). Similar rocks have been described elsewhere in the world spatially associated with metamorphosed exhalative/inhalative massive sulfide deposits (i.e., Broken Hill-type, VHMS, and SEDEX; Spry, 2000;Spry et al, 2000;Slack, 2012;Steadman and Spry, 2015). Given that such exhalites are generally associated with metamorphosed syn-sedimentary deposits, it would be remarkable that the same types of exhalative units spatially associated with metamorphosed Pb-Zn-Ag-(Cu-Au) SEDEX deposits are also spatially associated with the Kanmantoo deposit if it has a syn-deformational origin (Marshall and Spry, 2000).…”

Paleoproterozoic manganese oxide precipitation in oxic seawater surface and reductive enrichment in anoxic seafloor

“…The systematic negative to low positive Eu anomalies (0.38-1.27) in our rock samples suggests that high-temperature hydrothermal processes did not contribute significantly to the manganese precipitation since positive Eu anomalies are a diagnostic feature of hightemperature hydrothermal fluids (>250ºC; e.g., Derry and Jacobsen, 1990;Douville et al, 1999;German and Von Damm, 2003;Frei et al, 2017;Schier et al, 2020). Considering the paleogeography and the distribution of mafic rocks in the Northern Borborema Province, the distal deposition of manganese-rich rocks from the hydrothermal source might explain the diminished intensity of the positive Eu anomaly (Steadman and Spry, 2015). Other possibilities are Eu anomalies imprint by submarine weathering of a fractionated oceanic basaltic source (Towell et al, 1969;Menzias et al, 1977;Rudnick, 1992) as suggested previously or lower temperature hydrothermal fluids (e.g., Schier et al, 2020).…”

Hydrothermally altered volcanic rocks metamorphosed at granulite-facies conditions: an example from the Grenville Province

“…Similar features were reported by Bonnet et al (2005) in amphibolite-to granulite-facies aluminous gneisses associated with 1.50 Ga felsic-dominated volcanic rocks in the La Romaine Supracrustal Belt of the southern Grenville Province and were inferred to be fingerprints of metamorphosed volcanogenic massive sulfide environments (Bonnet and Corriveau 2007). Aluminous nodules in amphibolite-to granulite-facies hydrothermal alteration zones have been mostly described as dominated by sillimanite with lesser quartz ± muscovite ± Fe oxide (Bonnet et al 2005;Spry et al 2010;Steadman and Spry 2015). However, in the aluminous rocks of the LBS, they show a more complex mineralogy, also including spinel and corundum (but no muscovite) largely overgrown by garnet, likely as a result of partial melting at granulite-facies conditions.…”