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TitreMagnetite in hydrothermal alteration associated to IOCG systems in the Great Bear Magmatic Zone, Canada
AuteurDe Toni, A F; Corriveau, L; Montreuil, J -F
SourceAssociation géologique du Canada-Association minéralogique du Canada, Réunion annuelle, Programme et résumés vol. 35, 2012 p. 1
Séries alt.Secteur des sciences de la Terre, Contribution externe 20120053
RéunionThe Geological Association of Canada (GAC) and the Mineralogical Association of Canada (MAC)Joint Annual Meeting; St. John's, NL; CA; mai 27-29, 2012
Documentpublication en série
ProvinceTerritoires du Nord-Ouest
SNRC85N; 86C; 86D; 86E; 86F; 86K; 86L
Lat/Long OENS-119.0000 -116.0000 67.0000 63.0000
Sujetsgîtes minéralogiques; minéralisation; minerais de fer; oxydes de fer; or; cuivre; magnetite; altération hydrothermale; altération; gisements minéraux hydrothermaux; Zone de Great Bear Magmatic ; géologie économique
ProgrammeGisements polymétalliques - Zone magmatique du Grand lac de l'Ours (T.N-O.), GEM : La géocartographie de l'énergie et des minéraux
LiensOnline - En ligne
Résumé(disponible en anglais seulement)
Magnetite is a minor to major constituent of veins, breccias and incipient to intense alteration in iron oxide-copper gold systems of the Great Bear magmatic zone, Northwest Territories. Prevalence of magnetite in most of the known IOCG systems makes it a key mineral to understand and monitor their evolution and development. Multiple magnetite paragenesis associated with numerous textures are observed in these magmatic/hydrothermal systems. The macroscopic and microscopic observation of magnetite-bearing paragenesis is used to understand the processes that have generated the spectrum of textures observed. Mineral assemblages and associated textures can be used as exploration vectors to mineralized zones so distinctions between different paragenesis are essential in the comprehension of IOCG systems. To show the numerous aspects that can exhibit magnetite-associated alteration, a protocol for regional to megascopic description of replacements, veins and breccias has been developed to facilitate the description of these rocks in the field and subsequently on stained and unstained rock slabs and thin sections.
Prevailing paragenesis consists of 1) magnetite (Fe alteration), 2) amphibole-magnetite ± apatite ± albite (high temperature Ca-Fe±Na alteration), 3) K-feldspar-magnetite ± biotite or biotite-magnetite(high temperature K-Fe alteration), with common overprint by hematite. Magnetite replacement is preferentially formed around phenocrysts, within vesicules, in groundmass, or replaces fragments in breccias. These habits suggest that magnetite replacement forms where fluids circulate through porous and permeable rocks and/or minerals. In bedded or layered rocks, magnetite alteration can form selective stratabound replacements of specific horizons. Magnetite also crystallize as breccia cement or fill veins. High temperature K-Fe alteration crystallizes magnetite with K-feldspar in felsic and intermediate igneous rocks, and biotite in siliciclastic sedimentary rocks and mafic rocks. In potassic-altered porphyritic volcanic rocks, K-feldspar first replaces the groundmass and then the phenocrysts with increasing alteration intensity whereas biotite replaces selectively pre-existing amphiboles. Replacements and veins of transitional high temperature Ca-K-Fe and subsequent high temperature K-Fe alteration are commonly followed by the mineralization stage, in which a wide variety of metal can be concentrated (e.g. Cu, Au, Ag, Bi, Co, etc.). Each type of paragenesis and textures exert a control on the aspect that will take subsequent alteration. As an example, amphibole-magnetite veins preferentially cross-cut albitized zone at the expense of the unaltered volcanic rocks. Ultimately, the main objective of the project is to produce an atlas of alteration associated to IOCG that will provide exploration tools and a framework for geologists during the exploration of under-explored terranes.