Preliminary Petro-Geochemical Investigation of the Ni–Cu Occurrence of W1 Ultramafic Intrusion (Wapatik) within the Lower Eastmain Greenstone Belt of the Superior Province, Eeyou–Istchee Baie-James, Northern Quebec, Canada

Milier, K; Houlé, M.G.; Saumur, Benoit M.; Dejou, B et Lulin, J.-M. (2023). « Preliminary Petro-Geochemical Investigation of the Ni–Cu Occurrence of W1 Ultramafic Intrusion (Wapatik) within the Lower Eastmain Greenstone Belt of the Superior Province, Eeyou–Istchee Baie-James, Northern Quebec, Canada », dans GAC-MAC-SGA 2023 Sudbury Meeting: Abstracts, Volume 46 (GAC-MAC-SGA, Sudbury, 24-29 mai 2023), sous la dir. de Lesher, M. p. 187.

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Résumé

The Superior Province and its greenstone belts are favourable environments for theemplacement of mafic–ultramafic intrusions prospective for Ni-Cu-(PGE) mineral-ization. However, remote areas of the Superior Province, such as the Eeyou–IstcheeBaie-James region of northern Quebec, remain underexplored. In 2021, Ni-Cu sul-phide mineralization was discovered in a previously unrecognized kilometre-scaleultramafic intrusion, referred to as “W1”, within the Lower Eastmain greenstonebelt (LEGB) of the La Grande subprovince. W1 is a folded, undifferentiated ultra-mafic sill, located on the southern flank of a regional E–W trending anticline,emplaced within the ca. 2752 Ma Kauputauch Formation. This formation corre-sponds to the first volcanic cycle of the LEGB and consists of a succession of vol-canic and volcano-sedimentary rocks that have reached greenschist to amphibolitefacies. The W1 intrusion is emplaced within sulphide-rich supracrustal rocks of theKauputauch Formation and subsequently intruded by late felsic plutons and gab-broic dykes. It is composed mainly of peridotite, with subordinate olivine pyroxeniteand pyroxenite. Small enclaves of pyroxenite are occasionally recognized within peri-dotite. Diffuse crosscutting contacts between peridotite and pyroxenite units suggestthat they were emplaced synchronously. Several styles of Ni-Cu mineralization occurwithin W1: (1) disseminated sulphide within the ultramafic rocks, (2) semi-massiveto massive sulphide at or near the contact with footwall rocks or internally withinthe intrusion, and (3) semi-massive sulphide veinlets within the metasedimentaryrocks stratigraphically below the intrusion. The semi-massive to massive sulphide isthe most common mineralization style and can be found at two locations, albeit withvery different characteristics. A first occurrence occurs within the hinge zone of thedeposit-scale fold and consists of a few horizons (0.1 to 1.15 m) of semi-massivesulphide containing ultramafic and wall rock clasts. Sulphide occurrences are anassemblage of pyrrhotite, pentlandite and chalcopyrite that grade up to 2.68% Ni,1.30% Cu, and 0.09% Co over 3.30 m. The second occurrence occurs on the limbof the fold and exhibits a classic magmatic ore profile showing, from bottom up,massive, semi-massive, net-textured, and disseminated sulphide. It occurs in the mid-dle of the ultramafic body, presumably at a contact between two subunits. The sul-phide assemblage is dominated by pyrrhotite and is relatively depleted in chalcophileelements compared to the first occurrence. Future work will consist of petrographyand whole rock geochemistry of the mineralization and ultramafic rocks of theintrusion and will provide further insight on the mineral potential of Archean ultra-mafic intrusions of Eeyou–Istchee Baie-James.

Type:	Communication, article de congrès ou colloque
Mots-clés ou Sujets:	minéraux critiques, nickel, cuivre
Unité d'appartenance:	Faculté des sciences > Département des sciences de la Terre et de l'atmosphère
Déposé par:	Benoit Saumur
Date de dépôt:	10 mars 2025 10:09
Dernière modification:	10 mars 2025 10:09
Adresse URL :	http://archipel.uqam.ca/id/eprint/18549

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