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TitleNi-Cu-(PGE) deposits in the Raglan area, Cape Smith Belt, New Québec
AuthorLesher, C M
SourceMineral deposits of Canada: a synthesis of major deposit-types, district metallogeny, the evolution of geological provinces, and exploration methods; by Goodfellow, W D (ed.); Geological Association of Canada, Mineral Deposits Division, Special Publication no. 5, 2007 p. 351-386
Alt SeriesNatural Resources Canada, Contribution Series 20170066
PublisherGeological Association of Canada, Mineral Deposits Division (St. John's, NL, Canada)
Mediapaper; DVD; digital
RelatedThis publication is contained in Goodfellow, W D; (2007). Mineral deposits of Canada: a synthesis of major deposit-types, district metallogeny, the evolution of geological provinces, and exploration methods, Geological Association of Canada, Mineral Deposits Division, Special Publication no. 5
File formatpdf
NTS35G/09; 35G/16; 35H/11; 35H/12; 35H/13; 35H/14
AreaRaglan; Cape Smith; Ungava Peninsula; Cross Lake; Raglan Lake
Lat/Long WENS -74.5000 -73.0000 62.0000 61.5000
Subjectseconomic geology; tectonics; metallic minerals; geochemistry; mineral occurrences; mineral deposits; mineral potential; mineral exploration; mineralization; base metals; nickel; copper; platinum; igneous rocks; ultramafic rocks; peridotites; gabbros; tectonostratigraphic zones; deformation; metamorphism; mineral deposits genesis; Chukotat Group; Povungnituk Group; Cape Smith Belt; Cross Lake Member; Katinniq Member; platinum group elements; Precambrian; Proterozoic
Illustrationssketch maps; photographs; stratigraphic sections; graphs; tables; cross-sections
ProgramConsolidating Canada's Geoscience Knowledge
ProgramTargeted Geoscience Initiative (TGI-3), 2005-2010
AbstractNickel-Cu-(PGE) mineralization in the Raglan area occurs within a series of thick (50-200 m) mafic-ultramafic complexes that outcrop discontinuously along the contact between the Proterozoic Chukotat and Povungnituk groups in the east-central part of the Cape Smith Belt of the Ungava Peninsula between Cross Lake and Raglan Lake. All of the ores, host rocks, and country rocks have been regionally metamorphosed to lower greenschist facies, but igneous and volcanic structures and textures are extremely well preserved.

The ultramafic complexes appear to comprise two principal facies assemblages: conduit facies assemblages, which are laterally more restricted and composed primarily of peridotite, and channelized sheet facies assemblages, which comprise a laterally restricted conduit facies composed primarily of peridotite flanked by laterally extensive sheet facies composed of massive gabbro or differentiated peridotite-gabbro. Mineralization occurs exclusively within conduit facies of both assemblages, but the largest deposits occur within the larger conduit facies assemblages. Conduit facies in both assemblage types are relatively massive and undifferentiated, composed primarily of olivine mesocumulate with lesser olivine orthocumulate, thin lower margins of fine-grained pyroxene-porphyritic rock, and thin upper margins of fine-grained pyroxene-porphyritic rock capped by aphyric or microspinifex-textured basalt or basalt breccia. Many units exhibit columnar jointing in their upper and lower parts and polyhedral jointing in their uppermost parts. The lateral margins are interfingered with adjacent sediments and basalts and flanked in some areas by blocky and fluidal peperites. Footwall rocks (sulphidic graphitic semipelites, gabbros, and local basalts) have been eroded thermomechanically, forming larger broader V-shaped first-order embayments in the footwall rocks and superimposed smaller highly irregular (often re-entrant) second-order embayments that localize the Ni-Cu-PGE mineralization. Sediments underlying conduit facies are strongly hornfelsed (recrystallized, bleached, spotted), especially beneath ore-localizing embayments, but sediments and basalts overlying conduit facies, and underlying and overlying sheet facies are only very rarely and very locally contact metamorphosed. The ultramafic complexes have been previously interpreted as feeder sills and lava ponds, but many may represent deeply erosive lava conduits, some may represent invasive (downward burrowing) lava flows, and one may represent a feeder conduit.

The olivine mesocumulate rocks contain up to 40% MgO and rarely preserved relict olivine ranges Fo85-88, but they appear to have formed from magmas originally containing 17 to 19% MgO and Fo87-89. The high MgO and olivine contents suggest that they are petrogenetically related to olivine-phyric basalts in the lower Chukotat Group, but they are variably enriched in highly incompatible lithophile elements (Th-U-LREE) relative to moderately incompatible lithophile elements (Zr-MREE-Ti-Y-HREE) and depleted in Nb-Ta relative to Th compared to Chukotat basalts, consistent with variable degrees of local contamination by Povungnituk Group semipelites.

The Ni-Cu-PGE ores are texturally quite variable, ranging from massive and semimassive through net- and reverse net-textured, and disseminated ores at or near the bases of the complexes (Type I ores) to patchy and uniformly disseminated ores within the ultramafic complexes (Type II ores). Type I ores are localized within second-order embayments within the footwall rocks, which in some cases form linear-trending belts of differing ore tenor. Ore tenors (metals in 100% sulphides) range 4-17% Ni, 1-9% Cu, 3-25 ppm Pd, 1-6 ppm Pd, and 0.1-4 ppm Au, consistent with equilibration with a parental komatiitic basaltic (Chukotat) magma at magma:sulphide ratios (R factors) in the range 300 to 1100, followed by minor fractional crystallization of monosulphide solid solution and local tectonic/metamorphic modification. Sulphur isotope compositions are primarily 4 to 5 per mil, within the range of and consistent with derivation of the majority of the S from sulphides in the footwall semipelites. The ore zones in some areas appear to define multiple trends of differing ore tenor, as observed in other deposits of this type. The ores are interpreted to have formed by thermomechanical erosion of the sulphidic graphitic semipelites at an early stage in the emplacement of the host ultramafic units.