|Title||Iron-oxide-copper-gold ±uranium deposits in the Great Bear Magmatic Zone|
|Author||Potter, E G; Corriveau, L; Montreuil, J -F|
|Source||Geological Association of Canada-Mineralogical Association of Canada, Joint Annual Meeting, Abstracts Volume vol. 36, 2011 p. 175-176; 1 CD-ROM|
|Alt Series||Earth Sciences Sector, Contribution Series 20100423|
|Meeting||GAC/AGC - MAC/AMC - SEG - SGA; Ottawa; CA; May 25-27, 2011|
|Area||Lou Lake; Cole Lake; Fab Lake|
|Lat/Long WENS||-117.0000 -116.5000 63.7500 63.5000|
|Subjects||economic geology; mineral occurrences; mineral deposits; iron oxides; copper; gold; uranium; Great Bear Magmatic Zone|
|Program||Uranium, GEM: Geo-mapping for Energy
|Abstract||Under 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.