Nature and origin of mineral occurrences inside the Sudbury Basin
Rocks of the Whitewater Group (Aphebian age) occur within the Sudbury Basin and consist of three formations which are, from oldest to youngest: Onaping, heterolithic breccias /lus an igneous-textured component; Onwatin, argillite and silt-stone; and Chelmsford, greywacke with minor argillite with silts tone. Mineralization in these rocks is as follows:1) Sulphides are disseminated throughout the Onaping Formation. Pyrrhotite, the major sulphide mineral, occurs mainly as fragments; other sulphides are chalcopyrite, sphalerite, galena, pyrite and marcasite.2) Zn, Pb, Cu, Ag and Au mineralization in the Vermilion member, a carbonate-chert unit near the base of the Onwatin Formation (Vermilion and Errington mines).3) Pyrite and minor base metals in the Onwatin Formation.4) Mineralized quartz veins, located at or near the base of the Onaping Formation, include such deposits as Moore Lake (Pb, Zn and Ag), Foisey (Zn, Pb), Papineau (Cu, Au and Co) and Proulx (Pb, Zn, and Cu). Quartz-carbonate veins in a meta-gabbro sill contain Cu, Zn, As and Au. Material from quartz veins from two former "gold mines" (Gordon Lake and Creighton) yielded no Au values.5) Anthraxolite veins in the Onwatin Formation.
The mineral occurrences can be explained in terms of either the volcanic theory or meteorite-impact theory of basin formation. According to the latter theory, the sulphide fragments in the Onaping Formation may have been formed by the breccia-tion of sulphide-rich pods located in the upper mantle and at the base of the transient crater; some of the sulphides may have been derived from target rocks of the Huronian Supergroup. The Vermillion-Errington deposits may represent sedimentary exhalative deposits of the Remac type; mineral-rich brines, trapped at the base of the transient crater, rose upward and precipitated the mineralized carbonate-chert under reducing conditions. These conditions continued throughout the deposition of the upper Onwatin Formation but pyrite was the only sulphide that formed.
The quartz veins were emplaced during the time of basin deformation. Metamorphism remobilized and concentrated carbonaceous material in the Onwatin Formation to form the anthraxolite veins.
Mineral exploration, Sudbury Basin, Sulphide deposits, Pyrrhotite fragments, Sedimentary exhalative deposits, Quartz veins, Base metals, Anthraxolite, Meteorite impact