The composition of mineralization at the Voisey's Bay Ni-Cu sulfide deposit, with special reference to platinum-group elements

The Ni, Cu, platinum-group element (PGE), and Au contents of massive sulfid e mineralization, leopard-textured mineralization, sulfides in basal brecci a sequence, and sulfides in varied troctolite from four mineralized environ ments (the Reid Brook zone, the Discovery Hill zone, the Ovoid and Mini-Ovo id, and the Eastern Deeps) at Voisey's Bay have been determined. Modeling o f the compositional data indicates that the large zone of massive sulfide c omprising the Ovoid has crystallized from the base upward, with a fractiona ted, residual liquid becoming concentrated toward the top. Massive minerali zation from the Mini-Ovoid, Reid Brook zone, and Eastern Deeps has undergon e postcrystalliztion modification, possibly due to the influence of heat fr om new influxes of magma through the plumbing system; this has resulted in a considerable redistribution of Cu and to a lesser extent of Ni and Au. Le opard-textured mineralization from the Reid Brook and Discovery Hill zones corresponds closely with the postulated sulfide liquid compositions respons ible for the Ovoid and Mini-Ovoid, but mineralization composition from the feeder to the Eastern Deeps is exceptional in having many of the characteri stics of a monosulfide solid solution cumulate. The composition of dissemin ated and blotchy sulfides in the varied troctolite of the Eastern Deeps req uires a variable but generally higher R factor than that affecting most of the sulfides, to have operated here. The compositional variability of the V oisey's Bay mineralization is best explained in terms of a model calling fo r repeated influxes of magma through the plumbing system to the deposit.