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TitleGeochemistry of hydrothermal tourmaline from IOCG occurrences in the Great Bear magmatic zone: implications for fluid source(s) and fluid composition evolution
AuthorKelly, C J; Davis, W JORCID logo; Potter, E GORCID logo; Corriveau, LORCID logo
SourceOre Geology Reviews vol. 118, 103329, 2020 p. 1-13,
Alt SeriesNatural Resources Canada, Contribution Series 20190285
Mediapaper; on-line; digital
File formatpdf; html
ProvinceNorthwest Territories
NTS85N; 86C; 86D; 86E; 86F; 86K; 86L
AreaContact Lake; DeVries Lake
Lat/Long WENS-119.0000 -116.0000 67.0000 63.0000
Subjectseconomic geology; geochemistry; Science and Technology; Nature and Environment; mineral deposits; mineral occurrences; iron oxides; copper; gold; ore mineral genesis; mineralization; crystallization; geochemical analyses; tourmaline; tectonic evolution; hydrothermal systems; metasomatism; alteration; source rocks; fluid migration; fluid dynamics; bedrock geology; lithology; igneous rocks; intrusive rocks; mafic intrusive rocks; granitic rocks; breccias; quartz veins; isotopic studies; boron; models; electron probe analyses; major element analyses; tectonic setting; Great Bear Magmatic Zone; NICO Deposit; Southern Breccia Deposit; Hottah Terrane
Illustrationslocation maps; geoscientific sketch maps; photographs; photomicrographs; tables; ternary diagrams; geochemical plots; bar graphs; schematic models
ProgramTargeted Geoscience Initiative (TGI-5) Uranium ore systems
Released2020 01 13
AbstractTourmaline crystallized during iron oxide and alkali-calcic alteration and IOCG mineralization in the Great Bear magmatic zone, Canada. Within the samples analyzed, tourmaline occurs as small crystals in the groundmass of hydrothermal breccias (Southern Breccia and Contact Lake), or as large prismatic crystals in quartz (± ore mineralogy) veins (Contact Lake, DeVries Lake, and NICO). The tourmaline from these localities is predominantly shorlitic in composition, with minor dravitic, uvitic and feruvitic components. The boron isotopic composition ranges from -15 per mille to -5 per mille, with the majority of values between -15 per mille and -10 per mille. The lack of variation among samples supports a common fluid source across the belt for the metasomatic-hydrothermal systems. These results are isotopically similar to global magmatic and non-marine evaporitic reservoirs, and lighter than seawater and marine sedimentary rocks. The delta-11B results support a single-fluid IOCG deposit model for the systems studied, wherein metasomatic-hydrothermal fluids derived by magmatism ascend and evolve over time through fluid-rock interactions.
Summary(Plain Language Summary, not published)
Geologic reservoirs have distinct isotopic signatures which can be used to fingerprint fluid sources in ore systems if there is a way to preserve the isotopic ratio through subsequent metamorphism, deformation, or hydrothermal events. Tourmaline collected from iron oxide-copper-gold (IOCG) occurrences of the Great Bear magmatic zone (GBMZ) preserve a largely magmatic boron isotopic signature suggesting that a secondary, marine derived fluid does not significantly contribute fluids to the system as in some other global examples. This suggests that the IOCG deposits of the GBMZ formed by a single-fluid, wherein metasomatic-hydrothermal fluids driven by magmatism ascend and evolve over time through fluid-rock interactions.

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