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TitreThe volcanic setting of VMS and SMS deposits: From the modern ocean floor to Archean examples
AuteurRoss, P -S; Mercier-Langevin, P
SourceL'Association géologique du Canada-L'Association minéralogique du Canada, Réunion annuelle conjointe, Recueil des résumés vol. 37, 2014 p. 236-237
Séries alt.Secteur des sciences de la Terre, Contribution externe 20130530
ÉditeurGAC MAC
Réunion GAC-MAC 2014; Joint annual meeting of Geological Association of Canada and Mineralogical Association of Canada; Fredericton; CA; mai 21-23, 2014
Documentpublication en série
Mediaen ligne; numérique
Sujetsgisements minéraux; assemblages de minéraux; minéralisation; or; gîtes volcanogènes; sulfures; roches ignées; gîtes stratoïdes; altération; géologie économique
ProgrammeÉtude des gîtes de sulfures massifs volcaniques, Initiative géoscientifique ciblée (IGC-4)
LiensOnline - En ligne
Résumé(disponible en anglais seulement)
Volcanogenic massive sulfide (VMS) deposits and seafloor massive sulfide (SMS) deposits are "strata-bound accumulations of sulfide minerals that precipitated at or near the sea floor in spatial, temporal and genetic association with contemporaneous volcanism" (Franklin et al. 2005). The control exerted by the volcanic succession (e.g., rock type, architecture and facies) on the nature and style of the ore and alteration (e.g., subsea-floor replacement vs. exhalative, conformable vs. discordant) is major, making it primordial to better understand volcanology in developing genetic and exploration models. Three groupings which likely cover a good proportion of cases are discussed. First, complexes of submarine felsic domes, cryptodomes and/or blocky lavas, and their reworked equivalents, are often spatially associated with VMS and SMS deposits, especially of the bimodal-mafic and bimodal-felsic types. In addition lobe-hyaloclastite flows, which are really more extensive and associated with lesser proportions of hyaloclastite than domes, can also be associated with VMS deposits. The facies architecture of felsic domes and lavas is well known, relatively simple, and distinctive. A felsic dome is limited in size and the spatial association with an ore deposit should therefore be clear on maps and cross-sections, not only on interpretative sketches. Five series of examples are reviewed in this category, ranging in age from modern to Archean: Manus Basin; Hokuroku district; Iberian pyrite belt; Skellefte district; Abitibi greenstone belt. Second, some SMS and VMS deposits are associated with submarine, mostly felsic, calderas. Demonstrating a caldera association in ancient successions can be difficult. There is a scale challenge: silicic calderas tend to be large, so a regional study is necessary to identify one. Good exposure is therefore essential, which is not always the case, and major structural complexities can hamper the recognition of potential caldera complexes in ancient successions. Moreover, there is no consensual facies model showing what a submarine caldera should look like, since such volcanoes are not particularly well studied, and there are several types. But without thick piles of pumiceous felsic volcaniclastic deposits of explosive origin, arguing for a large submarine caldera remains a challenge. The two convincing examples reviewed here come from the modern Isu-Bonin arc and the Ordovician of northern Maine. Finally, it is important to stress that several VMS deposits are not associated with felsic footwalls. Canadian examples of VMS deposits associated with mafic to intermediate footwalls include the ~300 Mt Windy Craggy deposit (BC) and the Corbet deposit (QC).