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TitleThe IOCG alteration to brecciation and mineralization zoning model - a vector to mineralization tested in the Great Bear Magmatic Zone, NWT
AuthorCorriveau, LORCID logo; Montreuil, J -F
SourceGeological Association of Canada-Mineralogical Association of Canada, Joint Annual Meeting, Abstracts Volume vol. 36, 2011 p. 44-45; 1 CD-ROM
Alt SeriesEarth Sciences Sector, Contribution Series 20120008
MeetingGAC/AGC - MAC/AMC - SEG - SGA; Ottawa; CA; May 25-27, 2011
Mediapaper; CD-ROM
ProvinceNorthwest Territories
AreaLou Lake; Cole Lake; Fab Lake
Lat/Long WENS-117.0000 -116.5000 63.7500 63.5000
Subjectseconomic geology; alteration; mineral occurrences; mineral deposits; iron oxides; copper; gold; uranium; Great Bear Magmatic Zone
ProgramGEM: Geo-mapping for Energy and Minerals Uranium
AbstractA conceptual alteration to brecciation and mineralization zoning model that frames the development of iron oxide-apatite, magnetite- and hematite-group iron oxide copper-gold (IOCG) and associated skarn deposits is proving to be a powerful predictive tool for mineral exploration and regional mapping in under-explored and under-mapped terrains. Under the Geomapping for Energy and Minerals (GEM) program, the systematics of alteration and evolution of brecciation were used in the significantly under-explored Great Bear magmatic zone (NWT) to 1) recognize new IOCG systems, 2) validate the model and continuity with other deposit types at known showings and past-producing mines, 3) infer maturity and potential fertility of identified systems, and 4) vector towards mineralization.
One of the case studies centres on the 31 Mt Au-Co-Bi-Cu NICO deposit. Here, magnetite-group IOCG ore is associated with a cyclical build-up of high-temperature calcic-iron and potassiciron (magnetite) alteration below an unconformity (stages 2 and 3 of the model). The extensive early sodic alteration that provides nutrients for IOCG systems (stage 1) and the low temperature potassic-iron (hematite) alteration, plus uranium/REE mineralization and silicification that should have formed through the cyclical outflow of remaining fluids and elements (stages 5 and 6) had not been observed. Systematic alteration mapping away from the deposit led to the discovery of a 2 by 0.5 km structural breccia corridor with syn- to post-tectonic hydrothermal iron oxide (magnetite to hematite) replacement-style alteration, breccias and veins, and U-Th-arsenopyrite±molybdenite anomalies within sodic-, potassic- or silica-altered metasedimentary rocks. This system records cyclical build up of alteration stages 5 and 6 within albitite (stage 1). Strain partitioning between the overlying massive rhyolite and the steeply-dipping, stratified and more ductile metasedimentary rocks focuses much of the brittle-ductile deformation in the altered metasedimentary rocks. This led to preferential brecciation of the competent albite-altered units and focussed fluid flow upward towards the unconformity. The U-Th mineralizing event with arsenopyrite and traces of molybdenite occurs at ductile-to-brittle and magnetite-to-hematite transitions coevally with syn- to post-tectonic emplacement of porphyry dykes and brecciation. Late-tectonic magnetite veins and post-tectonic hematite veins record the shift to brittle conditions during which brecciation was mainly accomplished by hydraulic fracturing and accompanied by the emplacement of tourmaline breccias and porphyry dykes.
Syn- to post-tectonic development of hydrothermal alteration at the magnetite to hematite transition, structurally controlled (faults, breccias and/or unconformities) alteration and mineralization and regional-scale alteration are attributes of many other hydrothermal systems of the Great Bear magmatic zone.

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