Geology and origin of copper-nickel sulphide deposits of the Bird River area of Manitoba

Abstract

The origin of copper-nickel mineralization in the Bird River area of southeastern Manitoba was investigated within the context of regionai evolution by mapping, the logging of diamond drill core, and petrographic, mineralographic, sulphur isotope and metal ratio studies. The region has had a complex geological history involving deposition of a volcanic-sedimentary eugeosynclinal Sequence, penecontemporaneous intrusion and differentiation of a mafic-ultramafic sill, followed by the intrusion of two granitic diapirs. These were separated by an episode of mafic-ultramafic intrusions. Pyrrhotite-rich Algoma type iron formations are an integral part of the sedimentary-volcanic sequence. The sulphide facies are essentjaily barren of valuable base metal values within the sedimentary belts, but appreciable copper and zinc are found in belts where volcanic rocks predominate... It is concluded that nickel ions released at the time of dehydration and metamorphism of the ultrabasic rocks of the Bird River Sill were superimposed upon existing sulphide facies of iron formation. The nickel ions reacted with existing pyrrhotite to produce pentlanditerich deposits, some of them ore grade. Copper and zinc sulphides found in iron formations within greenstone belts are interpreted as iron formation microfacies.