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TitreExploration technologies and models for IOCG and affiliated iron oxide alkali-altered deposits with case examples from the Great Bear Magmatic Zone, Canada
AuteurCorriveau, L; Montreuil, J -F; Hayward, N; Enkin, R; Davis, W; Potter, E; McMartin, I; Normandeau, P X
SourceAssociation géologique du Canada-Association minéralogique du Canada, Réunion annuelle, Programme et résumés vol. 36, 2013 p. 81-82
LiensOnline - En ligne
Séries alt.Secteur des sciences de la Terre, Contribution externe 20130011
ÉditeurAssociation géologique du Canada
RéunionGAC MAC Annual Meeting 2013; Winnipeg; CA; mai 22-24, 2013
Documentpublication en série
ProgrammeGisements polymétalliques - Zone magmatique du Grand lac de l'Ours (T.N-O.), GEM : La géocartographie de l'énergie et des minéraux
Résumé(disponible en anglais seulement)
Polymetallic, 1.87 Ga iron oxide alkali-altered (IOAA) systems and iron oxide copper-gold (IOCG) deposits in the Great Bear magmatic zone (Canada) stand upright, are tilted or gently folded, differentially exhumed, and/or transcurrent faulted, exposing the metasomatic 82 footprints of IOAA systems from upper crustal source regions to deposits. Each system exhibits similar regional space-time evolution of
metasomatic alteration, veins and breccias from least-altered precursors (plutonic, volcanic, sedimentary and metamorphic) to deposits. Once the metasomatic mineral parageneses are unified under their key chemical elements (e.g., Na, Ca-Fe, K-Fe), diagnostic metasomatic facies emerge, each with distinct chemical characteristics largely inherited from the fluids and formed under different temperature regimes. Element speciation, mobility and redistribution across the metasomatic facies and associated brecciation are of a magnitude beyond that of any other deposit type. Such activity and their intensity account for an extraordinary range of deposit types including iron oxide-apatite, specialized metal, magnetite- to hematite-group IOCG and albitite-hosted uranium deposits, with continuum to epithermal and porphyry deposits. The ideal prograde alteration sequence represents a conceptual IOAA alteration vector-to-deposit model. Though presented as unidirectional, each metasomatic facies can be permuted or repeated to adapt to transition, juxtaposition, superimposition and cyclical buildup of alteration tied to faulting, brecciation, differential exhumation, and magma emplacement. In the field or during core logging, inferences can be drawn about incoming and outgoing fluids/metals foreach alteration observed and used to highlight components of the system that remain to be discovered. Tested under the Geomapping for Energy and Minerals (GEM) program, the model has demonstrable predictive exploration capabilities in the field. Moreover, the distinctive composition of each metasomatic facies facilitates the use of discrimination diagrams and geochemical alteration profiling (e.g., molar concentration profiles) to prognosticate fertility of IOAA systems and develop exploration targets. Multivariate signatures of pathfinder and alteration-related elements also enhance effectiveness of exploration based on till geochemistry whereas chemical/physical distinctiveness of a selection of minerals (i.e. apatite, magnetite) show potential for the indicator mineral exploration method in glaciated terrain. Rock physical properties and radiometric attributes are also distinctive. Alteration mapping aided by portable gamma-ray spectrometers and magnetic-susceptibility meters, and new geophysical potential field techniques enhance rapid targeting of prospective areas at local and regional scales. Finally, in examples where IOAA systems have been entrained in orogenesis and metamorphosed to high-grade, attributes of their metamorphosed metasomatic facies remain diagnostic though some exploration methods will have to be adapted to these environments to remain efficient.
Résumé(Résumé en langage clair et simple, non publié)
La région du Grand lac de l'Ours dans les Territoires du Nord-Ouest (zone magmatique du Grand lac de l'Ours), renferme des gîtes minéraux à oxydes de fer et métaux multiples et de multiples prospects ainsi que de vastes régions encore sous explorées. Le programme Géocartographie de l'Énergie et des Minéraux (GEM) et ses collaborateurs ont documenté que les mécanismes de minéralisation peuvent conduire à l'échelle régionale à la formation d'un large éventail de gîtes affiliés à métaux de base, précieux, de haute technologie ou d'uranium. Le modèle de gîtes minéraux qui découle des recherches GEM présente des capacités prévisionnelles importantes pour l'exploration. De plus les attributs géologiques diagnostiqués ont conduit au développement de nouvelles technologies et protocoles d'exploration qui maximisent encore plus l'efficience de l'exploration pour les terrains cibales.