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TitleIron-oxide-copper-gold ±uranium deposits in the Great Bear Magmatic Zone
AuthorPotter, E G; Corriveau, L; Montreuil, J -F
SourceGeological Association of Canada-Mineralogical Association of Canada, Joint Annual Meeting, Abstracts Volume vol. 36, 2011 p. 175-176; 1 CD-ROM
Year2011
Alt SeriesEarth Sciences Sector, Contribution Series 20100423
MeetingGAC/AGC - MAC/AMC - SEG - SGA; Ottawa; CA; May 25-27, 2011
Documentserial
Lang.English
Mediapaper; CD-ROM
ProvinceNorthwest Territories
NTS85N/10
AreaLou Lake; Cole Lake; Fab Lake
Lat/Long WENS-117.0000 -116.5000 63.7500 63.5000
Subjectseconomic geology; mineral occurrences; mineral deposits; iron oxides; copper; gold; uranium; Great Bear Magmatic Zone
ProgramUranium, GEM: Geo-mapping for Energy and Minerals
AbstractUnder the Northern Uranium for Canada project (GEM-Energy Program), the nature of uranium in iron oxide copper-gold (IOCG) systems is being investigated using examples from the Great Bear magmatic zone (GBmz). Hypotheses being addressed include: Can uranium and thorium serve as vectors to multiple-metal endowments in IOCG systems? What is the potential for IOCG systems to contain recoverable energy resources? How can we maximise geological vectoring to ore with geochemical information from hand-held gamma-ray spectrometers? Fieldwork focused on known IOCG alteration systems with anomalous uranium (U) and thorium (Th) showings at Lou, Cole
and Fab lakes. At Lou Lake, two U-Th-bearing breccias were discovered west and south of the NICO deposit. The more significant discovery consists of a 2 km long, northwest-southeast trending, U-Th-arsenopyrite breccia corridor (eU = 0.01-1%, eTh =0.2%). This corridor comprises syn- to post-tectonic hydrothermal iron oxide (magnetite to hematite) breccias and U-Th-arsenopyrite ± molybdenite anomalies within either sodic-, potassic- or silica-altered metasedimentary rocks. This new corridor is spatially distinct from the NICO ore zone (which does not contain U), corresponds to the inferred apical part of the ideal IOCG system, and may have been a pathway for both incoming and outgoing fluids that formed the NICO deposit. At Fab Lake, several new Th and one U anomalies were discovered and the timing amongst the various generations of porphyries and IOCG alteration better constrained. On the northeast and northwest shoreline, several Th-bearing amphibole-magnetite veins brecciate feldspar porphyry and are sharply cross-cut by younger, two-feldspar porphyry dykes. Although both porphyries contain late biotite alteration, the two-feldspar porphyry dykes lack the amphibole-magnetite-K feldspar assemblage and subsequent brecciation characteristic of the older porphyry. Variable Th enrichment in these brecciated zones (Th/U = ~4-10) records decoupling of U and Th during formation and may be a vector to ore.
Discovery of the significant U-bearing zone near the NICO deposit was predicted by the IOCG alteration to brecciation and mineralization model developed by the project. Predictions were made by analysis of regional metallogenetic and geological data compiled by the Geological Survey of Canada and Northwest Territories Geoscience Office. Follow-up field studies in 2010 provided further constraints on the structural, magmatic and hydrothermal events which led to documentation of the IOCGporphyry continuum in the GBmz. These results also highlight the potential of the GBmz to host undiscovered IOCG-type ore deposits.
GEOSCAN ID287858