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TitleCharacterization of mafic and ultramafic sills in the Gerido Zone, Lacs Qamaniik region, Labrador Trough, Nunavik, Québec
AuthorBédard, M -P; Houlé, M; Huot, F
SourceQuébec Mines 2015: mines from every angle, abstracts of oral presentations and posters; Ministère de l'Énergie et des Ressources naturelles du Québec, Documents divers DV 2015-06, 2016 p. 55 Open Access logo Open Access
LinksOnline - En ligne (complete volume, volume complet, PDF, 34.2 MB)
Alt SeriesNatural Resources Canada, Contribution Series 20190405
PublisherGouvernement du Québec
MeetingQuébec Mines 2015; Québec City, QC; CA; November 23-26, 2015
Mediapaper; on-line; digital
File formatpdf
AreaLacs Qamaniik; Nunavik
Subjectseconomic geology; geochemistry; igneous and metamorphic petrology; Science and Technology; Nature and Environment
ProgramGEM2: Geo-mapping for Energy and Minerals Hudson/Ungava Core Zone
Released2015 11 01
AbstractThe mafic to ultramafic Montagnais sills of the Labrador Trough cut through almost the entire supracrustal sequence over a period of more than 280 million years. In the summer of 2015, mapping and sampling work was carried out to characterize the different types of mafic and ultramafic intrusions found to the northwest of Kuujjuaq (NTS 24K05, 24K06 and 24K12), where they were injected mainly into the Baby sedimentary for¬mations and the Hellancourt volcanics of the Koksoak Group, both of which are associated with the second volcano-sedimentary cycle.
Three types of intrusions can be defined based on field observations: mafic (MI), ultramafic (UMI) and mafic to ultramafic (MUMI). Stratigraphic tops in the study area generally face east, based primarily on features observed in the MUMI sedimentary and volcanic structures, as well as magmatic differentiation. No evidence of major folding was reported; on the other hand, some structural repetition cannot be ruled out. The MI are continuous over ~20 km and range in thick¬ness from 400 to 1,500 m. They are mainly composed of massive, fine- to medium-grained aphyric gabbro, sometimes layered. Facies with variable and pegma¬titic textures, and the appearance of bluish quartz, are more common in the uppermost section of the MI. Small concentrations of disseminated PGE-enriched sulphides (less than or equal to 5 %) are locally present. The UMI are composed of peridotites that locally exhibit poikilitic (pyroxene) texture or pyroxenitic borders. Discontinuous and relatively thin (less than or equal to 100 m), they are mainly found in the cores of the MI. They contain gabbroic enclaves of variable sizes. The MUMI form a differentiated mafic-ultramafic sequence that is continuous for at least 20 km and is ~130 m thick. The ultramafic part of the MUMI is composed of, from base to top (west to east), a gabbro unit overlain by pyroxenite and a unit of locally poikilitic peridotite. The upper part of the latter is characterized by alternating layers (centimetre- to decimetre-scale) of peridotite and pyroxene-rich peri¬dotite that gradually evolve into pyroxenite. The mafic component of the MUMI is composed primarily of gabbro with variable grain size; bluish quartz appears towards the top.
The petrographic and geochemical characterization of the Montagnais intrusions in this area has been successful in distinguishing different types of intrusions and assessing their respective potential for Ni-Cu-PGE mineralization.

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