Geology of the Voisey’s Bay Ni-Cu-Co Deposit, Labrador, Canada

Exploration & Mining Geology, Vol. 5, No. 2, 1996
The Voisey’s Bay Ni-Cu-Co deposit was discovered in late 1994 as the result of prospecting
initiated in the summer of 1993. By July 1995, proven mineable reserves were 31.7 x 106 tonnes
grading 2.83% Ni, 1.68% Cu and 0.12% Co, and current total resources in all categories are quoted
to be in the order of 150 ?? 106 tonnes. The deposit is associated with a body of troctolite belonging to the Nain Anorthosite (1.35 Ga – 1.29 Ga) suite, which was emplaced across the boundary between the Proterozoic “Rae” Province to the west and Archean “Nain” Province to the east. The deposit can be described in terms of three geological settings. The “Ovoid” is a 600 m long by 350 m wide by 100 m deep lens of massive sulfide, covered by 10 m to 20 m of glacial overburden, and separated from the underlying country rock quartz-plagioclase-biotite gneiss by a breccia of gneissic fragments in troctolite known as the Basal Breccia Sequence. To the west of the Ovoid lies the “Western Extension”, comprising disseminated and massive sulfides in a north-dipping sheet of troctolite which ranges from upper unmineralized troctolite down through troctolite with increasing amounts of sulfide (up to 50%), to massive sulfide (in some places only), and then to Basal Breccia Sequence. East of the Ovoid, the troctolite sheet broadens out into a troctolite intrusion, within which occurs the “Eastern Deeps”, a zone of massive and disseminated sulfide up to 100 m thick that is currently being explored. The mineralization of the Eastern Deeps lies along the line of intersection of a feeder sheet with the base of the intrusion. The current interpretation is that the three geological environments represent different erosional levels through a single mineralized intrusion. In this model, the deepest erosional level lies to the west and exposes the feeder to surface, whereas the Ovoid represents the base of the intrusion at surface, and the Eastern Deeps the base of the intrusion
overlain by 600 m to 900 m of troctolite. Sulfides and gneissic fragments were brought up by magma flowing quickly through the feeder, and settled out where the flow rate decreased as the sulfide- bearing magma mixed with magma already emplaced in the intrusive body.
Keywords: Geology, Mineable reserve, Ovoid, Western Extension, Eastern Deeps
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