Geology of part of the Wollaston Lake Fold Belt, North Wollaston Lake, Saskatchewan

The map-area straddles the Wollaston Lake Fold Belt at Wollaston Lake, Sa skatchewan. The rocks of the area consist almost entirely of pre- Hudsonian migmatized paragneiss overlain nonconf ormably at the west margin of the area by the Helikian Athabasca Formation. On the basis of the field characteristics the paragneiss falls into three subdivisions, the western, the central, and the eastern zones of migmatites. The central migmatites, which farm a northeast-striking belt with similarly oriented internal structures, have been correlated with the Daly Lake Group. They have been derived mainly from pelite and greywacke with a significant amount of impure calcareous sediments including probable evaporites and lesser amounts of f eldspathic psammite-like rocks, quartz arenite and lean iron formation. Regional metamorphic assemblages, of high grade and moderate pressure, show effects of retrograde metamorphism. Igneous rocks which have intruded the central zone consist of amphibolite (mafic sill or sill s), the layered Sandy Islands Gabbro and the Shaganappie Granite. Whit e, massive granodiorite and granodiorite pegmatite, probably products of anatexis, are interlayered with the metasediments and are particularly abundant near the boundary with the western zone of migmatites. The eastern migmatite zone is separated from the central zone by a gradational boundary, marked by an increase in the amount of leucosome and a change in its character to granitic. The strong northeast erly-striking structure of the central migmatites is also present in the eastern z one. Though restitelithologies similar to those in the central zone are present, fine grained "metaclastics" are more quartzo-feldspathic, granular, pink, magnetic, and relatively biotite-poor, in contrast with the irdrab equivalents in the central zone. This arkosic appearance is consistent with formation of Kfeldspar, magnetite and hematite by the destruction of biotite during advanced anatexis. The western migmatite zone is separated from the central zone by a sharp boundary at which mylonite has been found. Instead of the northeast-striking linear structures of the other two z ones of migmatites there is no well-defined structural grain. Though metasedimentary relics are present, homogenization app ears to be more advanced in these pink swirled nebulitic migmatites than in the eastern zone. Though the central zone in general comprises lithologies similar to those described from the Daly Lake Group, a thick quartz arenite unit in the sequence is more comparable with the rocks of the Meyers Lake Group and assignment of the central migmatite zone as a whole to the Daly Lake Group appears to be incorrect. The quartzite outcrops close to amphibolite (mafic sills) as well as calc-silicates interlayered with greywacke-pelite type rocks, an association reminiscent of the Kinga Formation and the post-Ameto complex and included mafic sills of the Aphebian Hurwitz Group. The presence in the central zone of thick pure quartzite, abundant carbonate, probable evaporites and lean iron formation - if of Superior type, point to deposition of the original sediments in the later half of Aphebian time if the atmosphere became significantly oxygenized in the middle of the Aphebian. The composition of the rocks of the central zone and the size and shape of the Wollaston Lake Fold Belt give, in the simplest analysis, the impression that these rocks, were deposited as a shelfslop e-rise complex at the tectonically inactive margin of a continent of some size.