VMS Deposits

Volcanogenic massive sulphide (VMS) deposits are an important base metal deposit type, typically with combinations of Zn, Cu, Pb, Ag, and Au. They often occur as lenses of polymetallic massive sulphide that form at or near the seafloor in submarine volcanic environments. As many as 800 different deposits are known worldwide. VMS deposits are found in rocks of nearly all ages - in submarine volcanic terranes, with examples that are actively forming deposits in modern seafloor environments. 

The most common feature among all types of VMS deposits is that they are formed in extensional tectonic settings, including both oceanic seafloor spreading and arc environments. Most significant VMS mining districts are defined by deposit clusters formed within rifts or calderas. Their clustering is further attributed to a common heat source that triggers large-scale subseafloor fluid convection systems. As a result of large-scale fluid flow, VMS mining districts are commonly characterized by extensive semi-conformable zones of hydrothermal alteration that intensifies into zones of discordant alteration in the immediate footwall and hanging wall of individual deposits. VMS camps can be further characterised by the presence of thin, but extensive, units of ferruginous chemical sediment formed from exhalation of fluids and distribution of hydrothermal particulates.

VMS deposits are present in the Lachlan Fold Belt near Cobar (at May Day, Overflow and Yellow Mountain) and prospective rock types have been encountered in Thomson Resources tenements, particularly the Warraweena area of ELs 7252 and 7253.

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Typical VMS massive sulphide mound (after Galley et al and Hannington et al)

References:


Galley A.G., Hannington M.D., and Jonasson I.R.  2007. Volcanogenic massive sulphide deposits. in Goodfellow, W.D., ed Mineral deposits of Canada: A synthesis of major deposit types, district metallogeny, the evolution of geological provinces, and exploration methods: Geological Association of Canada, Mineral Deposits Division, Special Publication 5, p. 141-161. 

Hannington, M.D., Galley, A.G., Herzig, P.M., and Petersen, S., 1998, Comparison of the TAG mound and stockwork complex with Cyprus type massive sulfide deposits; Proceedings of the Ocean Drilling Program, Scientific Results Volume 158, College Station, TX, p. 389-415.