zone is displaced from the sulfides, it is often the product of tectonic deformation, or the formation of a hybrid SEDEX-like distal pool of sulfides. The alteration assemblages of the footwall alteration zone is, from core outwards; Silica alteration zone, found in the most intensely altered examples, resulting in complete silica replacement of the host rocks, and associated with chalcopyrite-pyrite stringer zones. Chlorite zone, found in nearly all examples, consisting of chlorite +/- sericite +/- silica. Often the host rock is entirely replaced by chlorite, which may appear as a chlorite schist in deformed examples. Sericite zone, found in nearly all examples, consisting of sericite +/- chlorite +/- silica, Silicification zone, often gradational with background silica-albite metasomatism. In all cases these alteration zones are metasomatism effects in the strictest sense, resulting in addition of potassium, silica, magnesium, and depletion of sodium. Chlorite minerals are usually more magnesian in composition within the footwall alteration zone of a VMS deposit than equivalent rocks within the same formation distally. The hangingwall to a VMS deposit is often weakly sodium depleted. Alteration not associated with the ore forming process may also be omnipresent both above and below the massive sulfide deposit. Typical alteration textures associated with devitrification of submarine volcanic rocks such as rhyolitic glasses, notably formation of spherulites, of perlite, lithophysae, and low-temperature prehnite-pumpellyite facies sub-seafloor alteration is ubiquitous though often overprinted by later metamorphic events. Metamorphic mineralogical, textural and structural changes within the host volcanic sequence may also further serve to disguise original metasomatic mineral assemblages. Classification Deposits of this class have been classified by numerous workers in different ways (e.g., metal sources, type examples, geodynamic setting - see Franklin et al. (1981) and Lydon (1984)). The magmatic assemblages of VMS deposits are associated with varying tectonic setting and geological environment during the formation of the VMS. The following five subclasses have specific petrochemical assemblages that resemble a specific geodynamic environment, during the event of formation: Mafic associated VMS deposits associated with geological environments dominated by mafic rocks, commonly ophiolite sequences. The Cyprus and Oman ophiolites host examples and ophiolite-hosted deposits are found in the Newfoundland Appalachians represent classic districts of this subclass. Bimodal-mafic VMS deposits associated with environments dominated by mafic volcanic rocks, but with up to 25% felsic volcanic rocks, the latter often hosting the deposits. The Noranda, Flin Flon-Snow Lake and Kidd Creek camps would be classic districts of