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TitleAlteration facies linkages among iron oxide copper-gold, iron oxide-apatite, and affiliated deposits in the Great Bear Magmatic Zone, Northwest Territories, Canada
AuthorCorriveau, LORCID logo; Montreuil, J F; Potter, E GORCID logo
SourceEconomic geology and the bulletin of the Society of Economic Geologists vol. 111, no. 8, 2016 p. 2045-2072,
Alt SeriesEarth Sciences Sector, Contribution Series 20140270
PublisherSociety of Economic Geologists
Mediapaper; on-line; digital
File formatpdf
ProvinceNorthwest Territories
NTS86C; 86D; 86L; 86K; 86E; 86F
AreaGreat Bear Lake
Lat/Long WENS-120.0000 -116.0000 67.0000 63.0000
Subjectsstructural geology; tectonics; iron; gold; copper; base metals; metamorphism, prograde; albitites; skarns; magmatism
Illustrationslocation maps; tables; bar graphs; geological sketch maps; photographs; photomicrographs; diagrams
ProgramTargeted Geoscience Initiative (TGI-4) Uranium Ore Systems
Released2016 11 16
AbstractHigh-temperature metasomatism driven by ascent of voluminous, saline fluid columns in the upper crust plays a major role in the genesis of iron oxide-alkali alteration ore systems but fundamental questions remain on genetic linkages among iron oxide copper-gold (IOCG), iron oxide-apatite (IOA), albitite-hosted uranium, and skarn deposits that they produce. Excellent surface exposures of such systems in the Great Bear magmatic zone of northernwestern Canada record the depth to paleosurface, prograde evolution of iron oxide-alkali alteration facies, and mineralization. Across the belt, albitite corridors that are tens of kilometers in length record the earliest reactions between highly saline fluids and host rocks along fault zones and subvolcanic intrusions. Pervasive albitization partitioned metals from the host rocks into the ascending fluid column, leaving behind structurally weakened corridors of porous albitite. These corridors were cut, replaced, and overprinted by amphibole- and magnetite-bearing, calcic-iron alteration assemblages. In extreme cases, the discharge of calcium, iron, and specialized metals formed iron oxide-apatite deposits (±vanadium ± rare earth elements) while recharging the outgoing fluids in sodium, potassium, and base and precious metals. As temperatures declined and fluid chemistry evolved through fluid-rock reactions, the formation of potassic-iron alteration assemblages, breccias, and sulfides resulted in magnetite- and hematite-group IOCG mineralization. Within carbonate units, skarns formed prior to, are replaced by, and evolved to calcic-iron alteration facies. Skarns can locally host base metal mineralization. Tectonically uplifted albitite breccias replaced by potassic-iron alteration assemblages became a preferential host for uranium mineralization. The results of this study also illustrate that permutations and cyclical build-up of alteration products can arise from a combination of faulting, differential uplift, and renewed magmatism. Framed within an alteration-facies deposit model, alteration zones and mineral occurrences play a pivotal role in predicting the mineral potential of iron oxide and alkali-altered systems at district to deposit scales.
Summary(Plain Language Summary, not published)
The Targeted Geoscience Initiative (TGI-4) is a collaborative federal geoscience program that provides industry with the next generation of geoscience knowledge and innovative techniques to better detect buried mineral deposits, thereby reducing some of the risks of exploration. Iron oxides and alkali-altered mineral systems stand out worldwide as hosting the most diverse suites of potential economic metals (precious, base and specialised metals, including those needed for green energy, high technology and nuclear energy). These systems include among others iron oxide copper-gold (IOCG) deposits. This paper synthesises the extreme mineralogical and chemical transformations undergone by precursor rocks at district to deposit scale due to their interaction with mineralizing fluids. To each set of attributes corresponds a distinct alteration facies and associated deposit type. The proposed model change exploration paradigms for IOCG and affiliated deposits.

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