Ben Dhifallah, Imen; Saumur, Benoit M.; Houlé, Michel G.; Richer, Mathieu et Augereau, Guillaume
(2025).
« Preliminary observations on the Inukshuk Ni-Cu-(PGE) deposit hosted within the Expo subsuite of the Lac Esker suite, Cape Smith belt, Nunavik, Québec », dans GAC-MAC-IAH-CNC 2025 Ottawa Meeting: Abstracts, Volume 48 (GAC-MAC-IAH-CNC, Ottawa, 11-14 mai 2025), sous la dir. de Bingham-Koslowski, Nikole.
p. 129.
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Résumé
The Inukshuk Ni-Cu-(PGE) deposit is one of numerous magmatic sulphide deposits hosted within the ca. 1882 Ma Expo ultramafic-mafic subsuite of the Lac Esker suite, Cape Smith belt, northern Québec (Nunavik). Discovered by Canadian Royalties in 2021, Inukshuk occurs along an E-W trending intrusive dyke system that also includes the Expo and the Méquillon deposits. The host intrusion is a km-scale, blade-shaped intrusive body that penetrates a sediment-rich horizon of middle Beauparlant Formation (of the ca. 1998 Ma Povungnituk Group) and terminates downward against basalts of the lower Beauparlant Formation and locally against the post-mineral Inukshuk fault. Inukshuk was affected by two phases of deformation: D1, which is responsible for offsets associated with south-verging F1 thrust faults (such as the Inukshuk fault); and D2, which folds these thrusts and produces a NW plunging, open, upright fold system expressed as an antiform at the deposit. The internal lithological facies reveal a progressive transition from a marginal gabbro at the contacts, to a pyroxenite, to a peridotite in the core. The peridotite exhibits poikilitic textures, showing variable degrees of serpentine-talc-tremolite alteration, with gradational contacts between the major lithological facies defined by modal shifts in plagioclase, pyroxene, and olivine. Later cm to m-thick dykes of biotite-gabbro crosscut most lithological facies. Mineralization consists largely of disseminated sulphides but other facies are also observed, including massive, semi-massive, nettextured, stringer, and blebby sulphides. Sulphide mineralogy is typical of orthomagmatic assemblages, consisting of variable proportions of pyrrhotite, pentlandite, and chalcopyrite. All facies are variably overprinted by deformation-induced foliation; stretched pentlandite "eyes" within a foliation defined by chalcopyrite and pyrrhotite commonly characterize massive sulphides. New observations highlight the primary orthomagmatic nature of the sulphide ores at Inukshuk (e.g. loop textures); however, Inukshuk also displays abundant evidence for subsequent sulphide mobilization that locally obliterates primary sulphide textures.
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