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TitreGeology of the banded iron formation-hosted Meadowbank gold deposit, Nunavut, Canada
AuteurJanvier, V; Castonguay, S; Mercier-Langevin, P; Dubé, B; Malo, M; McNicoll, V; Pehrsson, S; De Chavigny, B; Côté-Mantha, O
SourceL'Association géologique du Canada-L'Association minéralogique du Canada, Réunion annuelle conjointe, Recueil des résumés vol. 37, 2014 p. 127
LiensOnline - En Ligne
Séries alt.Secteur des sciences de la Terre, Contribution externe 20130597
RéunionGAC-MAC Joint annual meeting; Fredericton; CA; mai 21-23, 2014
Documentpublication en série
SNRC56D/13NW; 56E/04SW; 66A/16NE; 66H/01SE
Lat/Long OENS-96.2500 -95.7500 65.0833 64.9167
SujetsArchéen; formations ferrifères; gîtes minéralogiques; assemblages de minéraux; minéralisation; or; géologie du substratum rocheux; interpretations structurelles; caractéristiques structurales; failles; plis; lithologie; roches volcaniques; roches plutoniques; roches ignées; quartzites; roches volcaniques felsiques; roches ultramafiques; déformation; Groupe de Woodburn Lake ; géologie structurale; géologie économique; Précambrien; Protérozoïque
ProgrammeÉtude des gîtes d'or, Initiative géoscientifique ciblée (IGC-4)
Résumé(disponible en anglais seulement)
The Meadowbank banded iron formation (BIF)-hosted world-class gold deposit is hosted in the polydeformed and metamorphosed ca. 2711 Ma Pipedream-Third Portage volcanic sequence of the Woodburn Lake Group that comprises several similar BIFs, of the most significant of which being the East BIF, the Central-BIF and the West-BIF. Despite their similarity, only the Central BIF contains economical gold mineralization. The deposit host succession consists of greenschist to amphibolite grade intermediate volcaniclastic rocks, BIFs, intermediate to felsic volcaniclastic rocks, mafic and ultramafic rocks, and quartzite. The pronounced negative Nb, Ta and Ti anomalies of the intermediate and intermediate to felsic units indicate an arc-like affinity. Notwithstanding cryptic and strongly overprinted Archean tectonism, four phases of Trans- Hudsonian (Proterozoic) deformation, have been recognized in the Meadowbank deposit area: isoclinal F1 folds and early shear zones, strongly overprinted by coplanar N-trending isoclinal F2 folds and associated D2 shear zones that cut the stratigraphy and mineralized zones. Shallowly to moderately-inclined, open to tight, chevron-style F3 folds and open to closed SW-plunging F4 folds further affect the deposit, resulting in a complex polyphase geometry. The bulk of the gold at Meadowbank is hosted in iron-formation occurring at or near the contact with sheared ultramafic rocks and is associated with pyrrhotite ± pyrite and traces of chalcopyrite and arsenopyrite. Gold-rich quartz-pyrrhotite ± pyrite veins are locally present in intermediate to felsic volcaniclastic rocks intercalated with BIFs. The ore-associated mineral assemblages include grunerite/cummingtonite and chlorite in BIF layers, whereas sericite ± chlorite and carbonates dominate in altered volcaniclastic rocks. The metamorphic grade increases southward along the deposit, where biotite, Fe-Mg amphibole and garnet occur in variable proportion. Crosscutting relationships suggest that the bulk of the gold was introduced prior to D2, preferentially along the sheared contact between BIFs and ultramafic rocks, and was later locally remobilized during D2. Deposit- and regional-scale lithogeochemistry and new U-Pb zircon ages indicate that the Meadowbank deposit is located at the boundary between two distinct lithological assemblages (2711 Ma and 2717 Ma) separated by long-lived shear zones that potentially have controlled gold deposition and distribution. The study demonstrates that integrated structural analysis, lithogeochemistry and geochronology are essential aspects to understand BIF-hosted gold deposits in order to develop better genetic and exploration models.