THE IMPACT OF VOISEY’S BAY: TWENTY FIVE YEARS FROM GREENFIELDS DISCOVERY TO A NEW TYPE EXAMPLE

The Voisey’s Bay Ni-Cu-Co discovery had a profound impact upon our understanding of magmatic sulfide deposits, and led to new ideas that became important themes for exploration. In many respects, it has become the new type example for this deposit clan. This review traces these critical “threads of evidence” and their impact.

The deposit illustrates key ingredients for a world-class magmatic sulfide deposit, but questions some of them. The host mafic rocks are compositionally evolved compared to other examples, and likely were products of sulfur-saturated mantle melting. Several lines of evidence implicate crustal contamination, but derivation of external sulfur from country rocks remains hard to prove, as is how it was distilled from gneisses that contain mere traces of pyrrhotite. Voisey’s Bay was the first deposit of its kind for which three-dimensional geometry was understood prior to exploitation, and these data are the most influential. Sulfide mineralization is localized within a magma conduit, and at its intersections with larger chamber-like bodies, perhaps controlled by preexisting structures in the wall rocks. Within these first-order controls are more local geometric and fluid-dynamic controls, in part analogous to those of sedimentary environments. These findings implied that a conduit model might apply to other deposits, and it became a successful exploration strategy. The model also led to a shift from simple closed-system models to open-system concepts that visualized interaction of sulfide liquids with multiple magma batches. The redissolution of sulfide liquids in such environments may circumvent limiting factors in closed systems, and this might be a key process for PGE-rich deposits. Finally, some of the massive sulfide deposits at Voisey’s Bay are zoned, demonstrating progressive fractional crystallization of accumulated sulfide liquids.

The Voisey’s Bay story underlines the value of integrating research and exploration, but it also highlights the need to share and publish ideas, and for open discussion and peer review. The recent announcement for future underground development of the deposit holds much promise for continued scientific impact if such principles can be maintained.