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TitleEvidence for a Neoarchean to earliest-Paleoproterozoic mantle metasomatic event prior to formation of the Mesoproterozoic-age Strange Lake REE deposit, Newfoundland and Labrador, and Quebec, Canada
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LicencePlease note the adoption of the Open Government Licence - Canada supersedes any previous licences.
AuthorMohammadi, N; Corrigan, D; Sappin, A -AORCID logo; Rayner, NORCID logo
SourceGeological Survey of Canada, Scientific Presentation 143, 2022, 23 pages, https://doi.org/10.4095/330866 Open Access logo Open Access
Image
Year2022
PublisherNatural Resources Canada
Documentserial
Lang.English
Mediadigital; on-line
File formatpdf
ProvinceNewfoundland and Labrador; Quebec
NTS24A; 24B; 24G; 24H
AreaStrange Lake
Lat/Long WENS -68.0000 -64.0000 58.0000 56.0000
Subjectsgeochemistry; mantle; metasomatic deposits; rare earths; Archean; Churchill Province; Strange Lake REE deposit; Core Zone; Proterozoic; Precambrian
Illustrationsphotographs; location maps; schematic diagrams; plots; photomicrographs
ProgramTargeted Geoscience Initiative (TGI-6) Ore systems
Released2022 10 12
AbstractA complete suite of bulk major- and trace-elements measurements combined with macroscopic/microscopic observations and mineralogy guided by scanning electron microscope-energy dispersive spectrometry (SEM-EDS) analyses were applied on Nekuashu (2.55 Ga) and Pelland (2.32 Ga) intrusions in northern Canada, near the Strange Lake rare earth elements (REE) deposit, to evaluate their magmatic evolution and possible relations to the Mesoproterozoic Strange Lake Peralkaline Complex (SLPC). These Neoarchean to earliest-Paleoproterozoic intrusions, part of the Core Zone in southeastern Churchill Province, comprise mainly hypersolvus suites, including hornblendite, gabbro, monzogabbro/monzodiorite, monzonite, syenite/augite-syenite, granodiorite, and mafic diabase/dyke. However, the linkage of the suites and their petrogenesis are poorly understood. Geochemical evidence suggests a combination of 'intra-crustal multi-stage differentiation', mainly controlled by fractional crystallization (to generate mafic to felsic suites), and 'accumulation' (to form hornblendite suite) was involved in the evolution history of this system. Our model proposes that hornblendite and mafic to felsic intrusive rocks of both intrusions share a similar basaltic parent magma, generated from melting of a hydrous metasomatized mantle source that triggered an initial REE and incompatible element enrichment that prepared the ground for the subsequent enrichment in the SLPC. Geochemical signature of the hornblendite suite is consistent with a cumulate origin and its formation during the early stages of the magma evolution, however, the remaining suites were mainly controlled by 'continued fractional crystallization' processes, producing more evolved suites: gabbronorite/hornblende-gabbro ? monzogabbro/monzodiorite ? monzonite ? syenite/augite-syenite. In this proposed model, the hydrous mantle-derived basaltic magma was partly solidified to form the mafic suites (gabbronorite/hornblende-gabbro) by early-stage plagioclase-pyroxene-amphibole fractionation in the deep crust while settling of the early crystallized hornblende (+pyroxene) led to the formation of the hornblendite cumulates. The subsequent fractionation of plagioclase, pyroxene, and amphibole from the residual melt produced the more intermediate suites of monzogabbro/monzodiorite. The evolved magma ascended upward into the shallow crust to form monzonite by K-feldspar fractionation. The residual melt then intruded at shallower depth to form syenite/augite-syenite with abundant microcline crystals. The granodiorite suite was probably generated from lower crustal melts associated with the mafic end members. Later mafic diabase/dykes were likely generated by further partial melting of the same source at depth that were injected into the other suites.
Summary(Plain Language Summary, not published)
This study examined two plutonic complexes in northern Canada (Nekuashu and Pelland intrusions) and their possible association with the well-known Strange Lake deposit, one of the richest rare-metal deposits in the world. Combined chemical and geochronological data demonstrated that Nekuashu and Pelland intrusions generated from partial melting of a hydrous metasomatized mantle source that triggered an initial rare earth elements (REE) and incompatible element enrichment that prepared the ground for the subsequent enrichment in the Strange Lake deposit. We also demonstrated that these two intrusions themselves have potential for additional REE exploration in that region.
GEOSCAN ID330866

 
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