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TitreBreccias as markers of tectono-hydrothermal evolution of iron oxide-bearing hydrothermal systems in the Great Bear Magmatic Zone
AuteurMontreuil, J -F; Corriveau, L; Ootes, L; Jackson, V; Gélinas, L -P
Source38th annual Yellowknife Geoscience Forum, asbstracts of talks and posters; par Palmer, E; Northwest Territories Geoscience Office, Yellowknife Geoscience Forum Abstracts Volume 2010, 2010 p. 85-86 (Accès ouvert)
LiensOnline - En ligne
Séries alt.Secteur des sciences de la Terre, Contribution externe 20100245
Réunion38th annual Yellowknife Geoscience Forum; Yellowknife, NWT; CA; Novembre 16-18, 2010
Documentpublication en série
ProvinceTerritoires du Nord-Ouest
Lat/Long OENS-120.0000 -118.0000 66.0000 65.0000
Sujetsgisements minéraux hydrothermaux; altération hydrothermale; brèches; minerais de fer; oxydes de fer; 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
Résumé(disponible en anglais seulement)
Breccias represent key markers of tectono-hydrothermal evolution of iron oxide copper-gold (IOCG) systems, acting as fluid and magma conduits, strain accommodation zones and preferential environments for leaching and/or trapping of metals. As such they provide a record of fluids, alteration and mineralization evolution, and timing relationships between magma, fluids and deformation involved in IOCG systems. Summer 2010 Geomapping for Energy and Minerals program fieldwork led to the identification of three new hydrothermal systems hosting extensive iron oxide breccias (south of the NICO deposit, east of Hottah Lake, East of Grouard Lake) and recognized new breccias within two others (west of Terra Mine and southwest of Cole Lake). Two systems evolve from magnetite to hematite-K-feldspar/sericite alteration, are spatially associated with unconformities and fault zones, record syntectonic to post-tectonic development and have plurikilometric potassic alteration haloes.
The system south of the NICO deposit is a magnetite-to-hematite group U-Th-sulphides-bearing IOCG system emplaced along a large deformation corridor trending 120° within Treasure Lake Group and overlying Faber Group volcanic rocks. Brecciation was initiated in brittle-ductile conditions and is coeval with magmatic (altered, boudinaged to fragmented porphyry dykes) and hydrothermal (magnetite, silicification/hematization and potassic alteration) activity. A 2 km long and still open to the west U-Th-sulphides mineralizing event (mean Ueq anomalies around 300 ppm) is coeval with brecciation. Tardi-tectonic magnetite veins and subsequent hematite veins record a shift to brittle conditions during which brecciation was mainly done by hydraulic fracturation and accompanied by emplacement of widespread tourmaline breccias and porphyry dykes (quartz-feldspar porphyries). Our observations show that the rhyolite was already emplaced during the first brecciation and that strain partitioning occurs between massive and competent rhyolite and the stratified, altered and more ductile Treasure Lake Group metasiltstone, focussing much of the brittle-ductile deformation in the altered metasedimentary rocks and then the brittle deformation in both units.
The system east of Hottah Lake comprises extensive hematite breccias that grades locally to zones of magnetite and/or amphibole alteration and veining below an unconformity between volcanic rocks and overlying Conjuror Bay Formation. Volcanic rocks were impacted by multiple stages of pervasive and penetrative K alteration and silicification. Magnetite alteration occurs in the eastern part of the system. Multiple generations of syntectonic alteration (quartz-hematite, biotite-sericite, phyllic) are coeval with a large brecciation event. The tectono-hydothermal breccias locally show preferred clast orientations and protomylonitic foliation, recording brittle-ductile conditions during this tectono-hydrothermal event. These breccias are found within large corridors parallel to the dominant vein and foliation trend. A tardi- to post-tectonic, intense and spectacular specular hematite alteration crosscut the foliation in the syntectonic breccias and itself formed numerous crackle breccias, recording more brittle conditions at this later stage.
A third system, east of Grouard Lake system, consists of decametre-wide deformation and breccia corridor with locally extensive magnetite and magnetite-amphibole alteration. It is also spatially associated with a fault zone (that crosscut the older volcanic Labine Group) and has developed below an unconformity with felsic volcanic rocks of the Sloan Group. The latter appears to have acted as an impermeable cap.