Métallogénie du gîte d'or orogénique La Pointe au contact entre les sous-provinces de La Grande et d'Opinaca, Eeyou Istchee Baie-James, Québec

Authors: Fleury, Jean-Philippe
Advisor: Beaudoin, GeorgesGuilmette, Carl
Abstract: The La Pointe gold deposit is hosted in Archean rocks metamorphosed to amphibolite facies straddling the boundary between the La Grande and Opinaca subprovinces, in Eeyou Istchee Baie-James, Québec. The lithological assemblage comprises a tonalite of the Langelier Complex (3326 ± 4 Ma), quartz arenite from the Apple Formation, amphibolite and iron formation from the Yasinski Group, and paragneiss from the Laguiche Complex. These rocks are cut by felsic dykes (2747 ± 2 Ma), ultramafic sills and pegmatitic granite dykes. The La Pointe deposit is defined in twozones, Zone 25 and Zone 26. Zone 25 is hosted in biotite-rich paragneiss and the mineralization consists of disseminated native gold along with arsenopyrite, pyrrhotite, chalcopyrite and minor pyrite. The depositis oriented WNW-ESE (S1) and has been deformed and folded by the main regional deformation (S2). The mineralization is associated with recrystallized alterations consisting of quartz, phlogopite, dravite ± titanite, microcline, muscovite and calco-silicates veins. Native gold occurs as inclusionsin the annealed metamorphic assemblages and at the margin of arsenopyrite. The low content of gold in arsenopyrite suggests re-equilibration at peak condition during arsenopyrite recrystallization which causedgold exsolution. Zone 26 is hosted in an iron formation characterized by replacement by sulfides, consisting of pyrrhotite-arsenopyrite-löllingite-chalcopyrite. The replacement is accompanied by calcic amphibole-biotite-garnet-tourmaline ± chlorite. Native gold occurs as inclusions in peak metamorphic minerals, or at the interface between löllingite core and arsenopyrite. The La Pointe depositis interpreted as a disseminated, pre-peak metamorphismorogenic gold deposit, subsequently overprinted by later higher, amphibolite-grade, and late retrograde metamorphism. This study provide new hintson understanding hypozonal lode gold deposits with regardtothe timing of mineralizationin relationtotheir complex tectonometamorphic history.
Document Type: Mémoire de maîtrise
Issue Date: 2019
Open Access Date: 18 December 2019
Permalink: http://hdl.handle.net/20.500.11794/37593
Grantor: Université Laval
Collection:Thèses et mémoires

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