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TitreThe gold content of VMS deposits: Key features and controlling parameters, with implications for exploration in the Appalachian orogen
AuteurMercier-Langevin, P; Dubé, B; Hannington, M; Bécu, V
SourceAssociation géologique du Canada-Association minéralogique du Canada, Réunion annuelle, Programme et résumés vol. 35, 2012 p. 91
LiensOnline - En ligne
Séries alt.Secteur des sciences de la Terre, Contribution externe 20130555
RéunionThe Geological Association of Canada (GAC) and the Mineralogical Association of Canada (MAC)Joint Annual Meeting; St. John's, NL; CA; mai 27-29, 2012
Documentpublication en série
Lat/Long OENS-56.5000 -56.0000 50.0000 49.7500
Sujetsgisements minéraux; assemblages de minéraux; minéralisation; or; gîtes volcanogènes; sulfures; déformation; métamorphisme; altération; altération hydrothermale; roches volcaniques; roches ignées; géologie économique
ProgrammeÉtude des gîtes de sulfures massifs volcaniques, Initiative géoscientifique ciblée (IGC-4)
Résumé(disponible en anglais seulement)
VMS deposits contain variable amounts of gold, both in terms of average grade and total contents. The analysis of gold grades and tonnages of 513 VMS deposits of all ages worldwide revealed that a large proportion of deposits are characterized by a relatively low gold grade (<2 g/t). The geometric mean and geometric standard deviation appear to be the simplest metric for identifying subclasses of VMS deposits based on gold grade. The geometric mean gold grade is 0.76 g/t; the geometric standard deviation is +2.70 g/t Au. Deposits with more than 3.46 g/t Au (geometric mean plus one geometric standard deviation) are considered auriferous. The geometric mean gold content is 4.7 t Au, with a geometric standard deviation of +26.3 t Au. Deposits containing 31 t Au or more are considered to be anomalous in terms of gold content, irrespective of the gold grade. Deposits with more than 3.46 g/t Au and 31 t Au are considered gold-rich VMS. A large proportion of the total gold hosted in VMS worldwide is found in a relatively small number of such deposits. The identification of these truly anomalous systems helps shed light on the geological parameters that control unusual enrichment of gold in VMS. At the district scale, the gold-rich deposits occupy a stratigraphic position and volcanic setting that commonly differs from other deposits of the district possibly due to a step change in the geodynamic and magmatic evolution of local volcanic complexes. The gold-rich VMS are commonly associated with transitional to calc-alkaline intermediate to felsic volcanic rocks, which may reflect a particularly fertile geodynamic setting and/or timing (e.g., early arc rifting). At the deposit scale, uncommon alteration assemblages (e.g., advanced argillic) and trace element signatures are present, suggesting a direct magmatic input in some systems. There are over 30 VMS deposits and occurrences for which tonnage is known in the Appalachian orogen of Newfoundland, including about 10 deposits that have reported gold grades. These VMS deposits are hosted in distinct arc and back-arc sequences, and those hosted in the Baie Verte oceanic tract, including Rambler-Ming, are enriched in gold relative to the deposits of the Annieopsquotch and Penobscot sequences. Similar trends are developed in the Bathurst Camp with the VMS deposits of the California Lake Group being on average slightly richer than the VMS deposits of the Tetagouche Group. This suggests that some specific rock sequences of the Appalachian orogen are more prospective than others to host gold-rich and auriferous VMS deposits.