Metallogenesis of an early Proterozoic foreland sequence, eastern Hudson Bay, Canada

Abstract

On the E side of Hudson Bay, the NW margin of the Archaean Superior Structural Province is overlain by an unmetamorphosed, little deformed, Early Proterozoic supracrustal sequence. The sequence is divisible into three parts, possible tectosomes, each characterized by a distinct style of mineralization. The arkosic, alluvial Richmond Gulf Group was shed eastward from a thermal uplift and has been preserved only in a later aulacogen, the Richmond Gulf Graben. It contains an apatite-cemented redbed. Secondly, a widespread post-aulacogen, carbonate-rich, W-facing miogeocline blanketed the region. A pyritic zone developed at its basal contact is particularly thick and hosts disseminated copper mineralization where formed on the arkose in the graben. A pyritic, brecciated, stromatolite-rich horizon within the carbonate contains galena and sphalerite. Thirdly, widespread iron formation and a local 60 cm thick manganese carbonate bed, overlying W-derived basalt flows, flysch and arkosic molasse, all of uncertain tectonic affinity, terminate the sequence.

Iron Formation: The Sedimentary Product of a Complex Interplay among Mantle, Tectonic, Oceanic, and Biospheric Processes

“…Recognized now to be correlative based on high-precision geochronology (Findlay et al, 1995;Fralick et al, 2002;Schneider et al, 2002), these iron formations extend discontinuously for more than 3,000 km along the southern and eastern margins of the Superior craton, from Thunder Bay, Ontario, through Minnesota, Wisconsin, and Michigan, to Quebec (Mistassini basin) and to the Labrador trough. Correlative and texturally similar GIFs are also recognized along the western margin of the Superior craton in the Hudson Bay region (Chandler, 1984;Hamilton et al, 2009). All of these iron formations are considered to have been deposited in extensional basins with coeval submarine basaltic volcanism (Ricketts et al, 1982;Fralick et al, 2002;Schulz and Cannon, 2007).…”

“…This is an important issue because the occurrence and ages of these iron formations have been used by some workers to infer deep-water anoxic conditions in the coeval global ocean (e.g., Poulton et al, 2004;Slack and Cannon, 2009); if these iron formations reflect more restricted, basin-scale conditions, our understanding of the ocean redox state might be incorrect. Paleogeographic reconstructions are not detailed enough to answer this question; however, tidal signatures have been observed in iron formations and interbedded sedimentary rocks in Minnesota and the Hudson Bay region (Ojakangas, 1983;Chandler, 1984), which are consistent with at least periodic open-marine conditions during iron deposition. Two independent approaches can be used to address this issue.…”

Iron Formations: Their Origins and Implications for Ancient Seawater Chemistry

“…IFs extend discontinuously for more than 3000 km along the southern and eastern margins of the Superior craton, from Minnesota, Wisconsin, and Michigan, to Quebec (Mistassini basin), and northward to the Labrador Trough. Correlative and texturally similar GIFs also occur in the center of the Superior craton in the Hudson Bay region (Richmond Bay and Belcher Islands) and in Sutton Inliers, NW part of Ontario (Chandler, 1984;Hamilton et al, 2009;Hawley, 1926;Stott et al, 2010). This group of IFs is considered to have been deposited in extensional settings with coeval submarine mafic volcanism Ricketts et al, 1982;Schulz and Cannon, 2007).…”

“…This is a critical issue because occurrences and ages of these IFs have been used by some workers to infer deep-water anoxic conditions in the coeval global ocean (e.g., Poulton et al, 2004;Slack and Cannon, 2009); if these IFs instead reflect more restricted, basin-scale conditions, our understanding of the global ocean redox state might be incorrect. Paleogeographic reconstructions are not adequately detailed to answer this question; however, tidal signatures have been observed in IFs and interbedded sedimentary rocks of this age in Minnesota and the Hudson Bay region (Ojakangas, 1983;Chandler, 1984), which are consistent with at least episodically open-marine conditions during IF deposition. Two independent questions can be asked as a basis to address this issue.…”

Iron formations: A global record of Neoarchaean to Palaeoproterozoic environmental history

“…Present palaeogeographic reconstructions are insufficient to answer this question; although tidal signatures have been observed in GIF and interbedded sedimentary rocks in Minnesota and the Hudson Bay region (Ojakangas, 1983;Chandler, 1984), which is consistent with at least periodically open-marine conditions, albeit very shallow, during IF deposition.…”