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TitleFluorapatite in till as an indicator mineral for iron oxide alkali-alteration systems, Great Bear magmatic zone, Northwest Territories, Canada
AuthorNormandeau, P X; McMartin, IORCID logo; Corriveau, LORCID logo; Harlov, D E; Paquette, J
SourceMargins through time, GAC-MAC 2016, Abstracts-Résumés; by Geological Association of Canada-Mineralogical Association of Canada / Association géologique du Canada-Association minéralogique du Canada; Geological Association of Canada-Mineralogical Association of Canada, Joint Annual Meeting, Abstracts Volume vol. 39, 2016 p. 70
LinksOnline - En ligne (PDF, 1.3 MB)
Alt SeriesEarth Sciences Sector, Contribution Series 20150464
PublisherGeological Association of Canada
MeetingGAC-MAC 2016; Whitehorse; CA; June 1-3, 2016
Mediaon-line; digital
File formatpdf
ProvinceNorthwest Territories
Subjectsgeochemistry; mineral assemblages; iron oxides; alteration; tills; mineral zoning; Great Bear magmatic zone
ProgramTargeted Geoscience Initiative (TGI-4) Uranium Ore Systems
ProgramGEM: Geo-mapping for Energy and Minerals Iron-oxide Copper-gold (IOCG) / Multiple Metals - Great Bear Lake (NWT)
AbstractFluorapatite-amphibole-magnetite assemblages are a signature alteration product in iron oxide alkali-alteration systems (IOAA) that can host iron oxide-copper-gold (IOCG) deposits. Major and trace element compositional zonation of fluorapatite (Ca5(PO4)3F) within such ore systems is distinct from other settings and can indicate the presence of these ore systems in bedrock or surficial sediments. As part of the Geological Survey of Canada's GEM-1 IOCG-Great Bear Project, fluorapatite recovered in the high-density (specific gravity >3.2) and mid-density (specific gravity 3.0-3.2) fractions of till and disaggregated bedrock samples from the Great Bear magmatic zone (GBMZ) and IOCG deposits within were examined to evaluate the mineral's usefulness as an indicator mineral. The chemistry of fluorapatite was determined through EMPA and LA-ICP-MS in addition to SEM and cathodoluminescence (CL) characterization. Within IOAA systems, REE-rich fluorapatite forms during high temperature sodic-calcic-iron and calcic-iron metasomatism. As temperature declines and the fluid chemistry evolves, localized REE leaching within fluorapatite leads to irregular zonation and formation of secondary REE-bearing minerals. Inclusions of monazite and allanite are found in the fluorapatite from the GBMZ samples with allanite being the dominant REE-bearing phase where late, low temperature calcic alteration is evident. A blue CL response in fluorapatite grains reflects low Mn and high REE content and is common in fluorapatite from the GBMZ IOCG systems. This blue CL response was observed in 30 to 50 % of fluorapatite grains in 3 till samples down-ice of the Sue Dianne IOCG deposit and contrasts with the more common Mn-activated green to yellow CL responses of fluorapatite in till throughout the GBMZ. Grains with blue CL fluorapatite response occasionally display small orange and red CL spots that reflect the presence of calcite in polymineralic fluorapatite-calcite grains, and are indicative of calcic alteration within IOAA metasomatism. Zoning in the green to yellow CL response, metasomatic dissolution pits and REE-rich mineral inclusions can discriminate the regionally present GBMZ fluorapatite from those in the neighboring Wopmay metamorphic zone and Slave Craton. The 0.25 to 2 mm size range is adequate both for CL and SEM characterization of grains in bedrock and till samples. In till samples, metasomatic fluorapatite grains derived from IOAA systems can be mixed with fluorapatite from less altered host rocks of the GBMZ, therefore characterization of at least 50 grains per till sample is recommended to be able to detect the presence of the IOAA-derived fluorapatite.
Summary(Plain Language Summary, not published)
This study examines the composition and nature of the mineral apatite which can help to trace mineralized rocks of iron oxide copper-gold (IOCG) deposits in the unconsolidated glacial sediments left during the last glaciation in the Great Bear Lake area. The work will help provide the geoscience knowledge required to develop effective mineral exploration methods in formerly glaciated terrain. It is part a graduate research project from McGill University, conducted first under the Geo-mapping for Energy and Minerals (GEM-1) Program and continued as part of the Targeted Geoscience Initiative 4.

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