VMS - volcanogenic massive sulphide
A VMS is a large geological feature creatured by the upwelling of magma (to the earth's surface in the case of McFauld's). It may consist of numerous metals. Here's a PDF link:
http://gsc.nrcan.gc.ca/mindep/synth_dep/vms/pdf/deposit_synthesis.vms.galley.pdf
This link shows a VMS associated with volcano activity under the ocean. Although the James Bay Lowlands where McFauld's resides is no longer under the ocean (although it is very wet), it may have been at one time.
Snug