Links between volcanism and the distribution and timing of massive sulphide (VMS) deposits

The links between volcanism and massive sulphide deposits are being studied as part of the "Global Volcanic-hosted Massive Sulphide (VMS) Project", which is IGCP project 502. Different types and settings of VMS deposit show different degrees of influence from volcanic or magmatic processes, with the most distinct genetic connection shown by some felsic-hosted deposits. These influences include:(1) Basin-wide volcano-tectonic events cause deposition of VMS on specific time-stratigraphic horizons. (2) With the exception of mid-ocean ridge settings, major VMS deposits are mainly associated with felsic volcanic rocks, even where felsic rocks form a minor component of the region. (3) Most VMS deposits form in proximal volcanic settings. (4) Most VMS deposits form at a particular stage in the evolution of their host volcanoes, typically late in the magmatic-hydrothermal cycle following a significant felsic eruptive event. The specific relationship in time and place implied by these last two points indicate that either the magmatic-hydrothermal cycle creates an important part of the ore solution, or controls when and where a metal-bearing geothermal solution can be focused and expelled to the sea floor, or both.(5) VMS deposits occur preferentially at times and places where both felsic and mafic magmas were erupted. In felsic-dominated regions, eruption of the mafic rocks commonly closely followed deposition of the ore-host felsic package. (6) Volcanic host rocks influence the morphology and stratigraphic position of VMS. Volcaniclastic and especially pumiceous strata promote deposition of VMS below the sea floor via replacement, whereas coherent lava flows and intrusions promote deposition of VMS on the sea floor. (7) Volcanic rocks and/or magmas are probably the source of metals in most VMS deposits.Godkänd; 2006; 20111007 (andbra