The Voisey's Bay nickel deposit is located on the Labrador coast of the Canadian Province of Labrador and Newfoundland, some 1500 km to the north-east of Montreal.
It is hosted by a 1334 Ma troctolite sheet belonging to the extensive 1350 to 1290 Ma Nain Plutonic Suite (NPS) emplaced at the boundary between the Nain Archaean Province to the east and the NNW trending 1850 to 1730 Ma Torngat Orogen to the west. The Torngat Orogen is a zone of deformation separating the Nain Province from the Rae Archaean Province further to the west. Archaean granitic, quartzo-feldspathic and mafic orthogneisses of the Nain Province are found to the east at Voisey's Bay. In the west garnet-sillimanite, and sulphide and graphite bearing quartzo-feldspathic paragneisses represent both reworked Archaean gneisses, and Lower Proterozoic intrusives and shelf sediments of the Torngat Orogen.
The NPS is batholithic and covers some 20 000 sq. km in the district. It comprises a broad spectrum of compositions including anorthosite, granite, troctolite and ferro-diorite representing the episodic coalescence of multiple plutons in an extensional environment, tapping the mantle.
The troctolite host to the Voisey's Bay mineralisation comprises two east plunging intrusions, the lower Reid Brook and the upper Eastern Deeps intrusions. These originally had a 2 km vertical separation. They are linked by a steeply dipping dyke, the Feeder Sheet, that varies from 10 to 100 m in thickness. There are a number of different rock types within these three intrusive bodies, as follows:
i). The higher Eastern Deeps intrusive has an upper olivine-gabbro (OG), grading downwards progressively into a medium grained, even textured troctolite (NT), to a varied texture troctolite (VTT) containing wall rock clasts, to a basal breccia (BBS) at the base, composed of abundant clasts of wall rock and mafics in a troctolite gangue. Various of these lithologies are cut by syenite and granite dykes.
ii). The Feeder Sheet generally comprises the following across its thickness in the upper sections, from the hangingwall - an upper chill zone to an un-mineralised feeder olivine gabbro (FOG), to the leopard troctolite (LT) which has 30 to 50% interstitial sulphides with a sharp contact to a basal breccia (BBS) on the footwall. Lower, towards the Reid Brook intrusive, the BBS may occur anywhere in the feeder and grades into the feeder breccia (FB) which is similar, but much more packed, while the FOG and LT are concentric to massive sulphides, where developed.
iii). The Reid Brook intrusive - the confluence of the Feeder Sheet in the roof of the Reid Brook intrusive is commonly choked by feeder breccia (FB), which also extends for a distance along the roof of the intrusive. This is underlain by a varied texture troctolite (VTT), which grades into the LT of the feeder sheet. The main mass of the intrusive is a leuco troctolite (LUT) similar in some respects to the olivine gabbro of the Eastern Deeps intrusive. Again the intrusive is cut by granite dykes.
Economic mineralisation, mainly massive sulphides occurs both within the Feeder Sheet and at the base of the Eastern Deeps intrusive, adjacent to the entry point of the Feeder Sheet. Within the Feeder Sheet, massive sulphides are restricted to the wider sections and occur as a series of elongate lenses in the plane of the linking sheet, all raking to the east. These include the Mini-Ovoid orebody and the Discovery Hill zone which are within the leopard troctolite (LT), above the basal breccia (BBS). Further to the west and deeper in the Feeder Sheet, the Western Extensions comprise disseminated mineralisation grading towards the footwall into massive sulphides.
The richest body, the Ovoid occupies a 350x600 m basin shaped body that is up to 110 m deep at the thickest point, tapering upwards towards the margins. It overlies a thin band of leopard troctolite (LT) and basal breccia (BBS). This is interpreted to be a depression at the base of the Eastern Deeps intrusive, above the confluence with the Feeder Sheet. Other mineralisation, the Eastern Deeps, is also known from similar positions in the Eastern Deeps intrusive.
The massive sulphides of the Ovoid are 75% pyrrhotite (2 to 5 cm crystals), 12% pentlandite (1 to 2 cm eyes), with irregular chalcopyrite and cubanite. Magnetite is scattered through the pyrrhotite. Disseminated ores of the Western Extension are in a similar proportion, but finer.
The reserve at the Ovoid body is: 32 Mt @ 2.83% Ni, 1.68% Cu, 0.12% Co,
The indicated resource at Eastern Deeps is: 50 Mt @ 1.36% Ni, 0.67% Cu, 0.09% Co,:
The resource at Western Deeps is in excess of 15 to 20 Mt.
The total reserve + inferred and indicated resource was stated as 124.4 Mt @ 1.66% Ni at the end of 1998 and 77.6 Mt @ 2.28% Ni, 1.19% Cu, 0.13% Co in 2005.
The deposit is now in production (2005) and is owned by Inco Limited.
(Source: Porter Geoconsultancy, www.portergeo.com.au, 2005)
