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TitreAlteration mapping in IOCG systems: Fab Lake case study
AuteurPotter, E G; Montreuil, J -F; Corriveau, L
SourceL'Association géologique du Canada-L'Association minéralogique du Canada, Réunion annuelle conjointe, Recueil des résumés vol. 35, 2012 p. 110; 1 CD-ROM
LiensOnline - En ligne
Séries alt.Secteur des sciences de la Terre, Contribution externe 20120013
RéunionGeological Association of Canada - Mineralogical Association of Canada joint annual conference; St. John's; CA; mai 27-29, 2012
Documentpublication en série
Mediapapier; en ligne; numérique; CD-ROM
ProvinceTerritoires du Nord-Ouest
Lat/Long OENS-117.0000 -116.5000 46.2500 46.0000
Sujetsgisements minéraux; gîtes minéralogiques; oxydes de fer; cuivre; or; minéralisation; altération; altération hydrothermale; gisements minéraux hydrothermaux; Zone de Great Bear Magmatic ; géologie économique
ProgrammeUranium, GEM : La géocartographie de l'énergie et des minéraux
Résumé(disponible en anglais seulement)
Building on a lengthy heritage of mineral exploration and production of vein-type uranium and silver deposits, the Great Bear magmatic zone (GBmz) is now known to have a very high potential for undiscovered magnetite- and hematite-group iron oxide copper-gold (IOCG) deposits and affiliated iron oxide-apatite and albite-hosted uranium systems. Detailed mapping of the Fab Lake hydrothermal system was undertaken, east of the community of Gamètì, NT, to test the applicability of an alteration to brecciation and mineralization evolution model developed under the GEM IOCG/Multiple Metals project. The Fab system was selected due to its relative simplicity, numerous mineral showings, ease of accessibility and restricted spatial extent. Alteration was mapped by systematically documenting alteration type, style, mineral paragenesis, breccias, cross-cutting relationships and determination of K (%), eTh (ppm) and eU (ppm) concentrations and volumetric magnetic susceptibility.
The alteration footprint of the Fab IOCG system has now been defined over an area of almost 10 by 5 km, with the long axis trending in a southeast-northwest direction. Within this area, field mapping identified seven alteration assemblages: 1) high temperature albite and albiteamphibole± magnetite; 2) amphibole-magnetite±apatite and amphibolemagnetite- K-feldspar; 3) K-feldspar; 4) K-feldspar-magnetite±hematite; 5) chlorite; 6) hematite; and 7) low temperature epidote-K-feldspar-quartz. These alteration assemblages are manifested by the development of incipient to pervasive alteration, veins, hydrothermal breccias and transient to intense, texture-preserving and texture-destructive replacements of the host rocks. All of the historic mineral showings (U-Cu) fall within zones characterized by intense, texture destructive alteration comprising multiple episodes of high temperature albite/albite-amphibole (Na and Na-Ca-Fe) and amphibole-magnetite±apatite/amphibole-magnetite-K-feldspar (Ca-Fe and Ca-Fe-K) overprinted by K-feldspar-magnetite±biotite (K-Fe) assemblages.
The conceptual alteration to brecciation and mineralization model is key to understanding the alteration assemblages documented in the Fab IOCG system. These assemblages record the build-up of a magnetitegroup IOCG system: early high-temperature Na/Na-Ca-Fe and Ca-Fe/Ca- Fe-K alteration, overprinted by high temperature K-Fe alterations and incipient to well-developed hydrothermal breccias. As field observations indicate that lower-temperature K-Fe alteration associated with hematitegroup IOCG systems is only weakly developed, the Fab Lake region is most prospective for magnetite-group types of IOCG mineralization. While petrographic studies are planned to complement field observations, these initial field observations clearly document the ability of the alteration to brecciation and mineralization zoning model to overcome the inherent complexity of these hydrothermal systems and provide field evaluations of their maturity and fertility.