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TitleA Paleoproterozoic Andean-type iron oxide copper-gold environment, the Great Bear magmatic zone, Northwest Canada
AuthorOotes, L; Snyder, D BORCID logo; Davis, WORCID logo; Acosta-Góngora, P; Corriveau, LORCID logo; Mumin, A H; Gleeson, S A; Samson, I M; Montreuil, J F; Potter, EORCID logo; Jackson, V A
SourceOre Geology Reviews vol. 81, pt. 1, 2016 p. 123-139, Open Access logo Open Access
Alt SeriesEarth Sciences Sector, Contribution Series 20150397
PublisherElsevier BV
Mediapaper; on-line; digital
File formatpdf
ProvinceNorthwest Territories
NTS86L; 86K; 86C; 86D; 86E; 86F
AreaGreat Bear Lake
Lat/Long WENS-120.0000 -116.0000 67.0000 63.0000
Subjectstectonics; mineralogy; metallic minerals; geochemistry; iron oxides; gold; copper; apatite; magmatism; Hottah terrane
Illustrationslocation maps; tables; photographs; diagrams; graphs; plots
ProgramTargeted Geoscience Initiative (TGI-4) Intrusion/Porphyry Ore Systems
Released2017 03 01
AbstractIron oxide copper-gold (IOCG) and associated iron-oxide apatite (IOA) styles of metallic mineralization are recognized throughout the Paleoproterozoic Great Bear magmatic zone of the northwest Canadian Shield. The Great Bear magmatic zone was constructed between ca. 1876 and 1855 Ma on top of the older Hottah terrane, which preserves continental arc magmatism that began around ca. 2.0 to 1.97 Ga and continued between ca. 1.93 and 1.89 Ga. The Great Bear represents the final stages of ca. 150 million years of intermittent and pulsed magmatism related to an evolving continental orogenic belt. The preserved geology supports a dramatic geodynamic change in the subduction zone process at ca. 1875 Ma, a key driving mechanism for magma and metal mobilization, and was rapidly followed by a large-scale introduction of felsic-intermediate plutons. The overall tectonic setting is partially constrained from new and previously published geochemical data that show that the volcanic and plutonic rocks are high-K calc-alkaline to shoshonitic in nature (e.g., high K2O, Th/Yb, and Ce/P205). They also have suprasubduction-zone geochemical signatures, including primitive mantle normalized positive Th and negative Nb, P, and Ti anomalies. The data support the primary melts were derived from a GLOSS-modified mantle wedge. Three-dimensional rendering of geophysical datasets suggest that two (of four) preserved surfaces within the upper mantle lithosphere, at 70 to 120 km depths, represent frozen, subducted oceanic slabs, and likely were the drivers for the bulk of Hottah and Great Bear arc magmatism. The older slab is northwest-striking and dips 12° to 15° northeast, whereas the younger is deeper and north-striking, dipping 13° east. The geometry of the surfaces are comparable with 4D modeling, where a subduction zone is temporarily shut down due to plateau collision, and then steps oceanward and re-initiates; there is no need for polarity reversal of the subduction system. This new geometry and the related inferences about process should be the focus of future research in the region, but for the time-being it can be stated that these subduction and collisional processes were the first order control on lithospheric evolution, and therefore metallic mineralization. Overall, the Great Bear magmatic zone IOCG and related mineralization is not comparable to other Proterozoic IOCG belts, such as those in Australia. However, the complexity of mineralization styles, the spatial-temporal relationship between IOA and IOCG mineralization, the suprasubduction zone environment, and a major change in tectonic regime are features similar to Andean-type IOCG mineralization, as well as Cordilleran alkali porphyry Cu-Au deposits. This further establishes the linkages between subduction zone processes and IOCG formation, as well as relationships in the IOCG-porphyry deposit continuum model.
Summary(Plain Language Summary, not published)
This NRCan contribution of the Targeted Geoscience Initiative program is part of a series of scientific papers submitted for a special issue on polymetallic iron oxide deposits of Missouri and the Northwest Territories organized by USGS and Geological Survey of Canada scientists. The paper uses the regional geoscience outcomes of the former Geomapping for Energy and Minerals program in the Great Bear Lake region. The research was conducted in collaboration with the Northwest Territories Geoscience Office, private sector exploration companies (Fortune Minerals Ltd), the Tlicho community of Gamètì, and academia. Geochemical and geophysical observations provide new geochronological and deep structural information about the geological history, distinguishing for the first time two separate major geological events. Polymetallic iron oxide deposits are still associated with second (Great Bear) event, but are now recognized to derive directly from geological conditions created by the earlier (Hottah) event.

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