GEOLOGY OF THE VOISEY BAY NI-CU-CO DEPOSIT, LABRADOR, CANADA

The Voisey's Bay Ni-Cu-Co deposit was discovered in late 1994 as the r esult of prospecting initiated in the summer of 1993. By July 1995, pr oven mineable reserves were 31.7 x 10(6) tonnes grading 2.83% Ni, 1.68 % Cu and 0.12% Co, and current total resources in all categories are q uoted to be in the order of 150 x 10(6) tonnes. The deposit is associa ted with a body of troctolite belonging to the Nain Anorthosite (1.35 Ga - 1.29 Ga) suite, which was emplaced across the boundary between th e Proterozoic ''Rae'' Province to the west and Archean ''Nain'' Provin ce to the east. The deposit can be described in terms of three geologi cal settings. The ''Ovoid'' is a 600 m long by 350 m wide by 100 m dee p lens of massive sulfide, covered by 10 m to 20 m of glacial overburd en, 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 ''Wes tern Extension'', comprising disseminated and massive sulfides in a no rth-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 Bas al Breccia Sequence. East of the Ovoid, the troctolite sheet broadens out into a troctolite intrusion, within which occurs the ''Eastern Dee ps'', a zone of massive and disseminated sulfide up to 100 m thick tha t is currently being explored. The mineralization of the Eastern Deeps lies along the line of intersection of a feeder sheet with the base o f the intrusion. The current interpretation is that the three geologic al 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 repr esents 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. Sulfi des and gneissic fragments were brought up by magma flowing quickly th rough the feeder, and settled out where the flow rate decreased as the sulfide-bearing magma mixed with magma already emplaced in the intrus ive body. Copyright (C) 1996 Canadian Institute of Mining, Metallurgy and Petroleum.