Copper-nickel-platinum group element mineralization and petrogenesis of mafic-ultramafic intrusions in the western Quetico and Wabigoon Subprovinces, northwestern Ontario, Canada

Abstract

This project focused on Cu-Ni-PGE mineralization and petrogenesis of mafic-ultramafic intrusions in the western Quetico and Wabigoon Subprovinces of the Superior Province. Two intrusions were singled out for detailed study: the Legris Lake Complex, part of circular series of mafic-ultramafic complexes, which includes the Lac des Iles Complex, located in the Wabigoon Subprovince, and the Samuels Lake Intrusion, part of the Quetico Intrusions, located in the Quetico Subprovince. Legris Lake complex. The Legris Lake Complex is a northeast-trending 7.3 by 3.5 kilometre mafic-ultramafic intrusive complex. It is part of a circular series of mafic-ultramafic complexes, the most notable of which is the Lac des Iles Complex, which is host to Canada's only palladium mine. The Legris Lake Complex consists of mostly gabbroic rocks, but also contains lithologies ranging from anorthosite to wehrlite, and, variety of igneous breccias. The gabbroic rocks vary from melanogabbro to porphyritic leucogabbro. Medium grained, massive, biotite-rich leucogabbro is the predominant exposed variety and probably caps the complex. Samuels Lake intrusion. The Samuels Lake intrusion, ca 2688 +6/-5 Ma, located in the centre of the Quetico Subprovince possesses a northeast-southwest elliptical form (500 m by 250 m) and displays rough concentric zoning with a wehrlite core grading into clinopyroxenite border zone, which has been intruded by later homblendite. Olivine-rich rocks commonly contain blebs of pyrrhotite + chalcopyrite + pentlandite with anomalous PGE values, ranging from 50 to 300 ppb, whereas the clinopyroxenite border zone contains disseminated to blebby PGE-rich Cu-sulphide mineralization. (Abstract shortened by UMI.)