Although not the world’s primary source of copper, volcanogenic massive sulfide (VMS) deposits are an important source of the metal. These deposits also supply significant zinc, lead, gold and silver. VMS deposits haven't always been miners' first choice, as they are generally small and can be difficult to process. However, technological advances and the recent bull run in the copper price has piqued explorers' interest.
While VMS deposits can take on a variety of morphologies, they typically occur as lenses of polymetallic massive sulfide that form at or near the seafloor in submarine volcanic environments. The most distinguishing feature among all types of VMS deposits is that they are formed in extensional tectonic settings, including both oceanic seafloor spreading and arc environments.
VMS deposits are grouped according to host rock type and on the basis of ore composition. In terms of host rock type classification, VMS deposits have been classified in three ways:
- Felsic volcanic hosted, which are the most popular category and account for 50% of deposits.
- Mafic volcanic hosted, which accounts for 30% of deposits.
- Mixed volcanic/sedimentary association, which account for 20% of deposits.
VMS deposits are particularly prevalent in Canada. Out of the world's ~800 known VMS deposits, nearly 350 are in Canada. Canadian VMS deposits account for 27% of the country's copper production, 49% of its zinc and 40% of its silver. Worldwide, VMS deposits account for much less copper production, at an estimated 6%. However, 22% of the world's zinc, 9.7% of lead, 8.7% of silver and 2.2% of gold are extracted from VMS deposits.