The La Pointe gold deposit, a disseminated orogenic gold deposit at the boundary between the La Grande and Opinaca subprovinces, Eeyou Istchee Baie-James, Québec, Canada

Abstract

The La Pointe gold deposit is hosted by Neoarchean rocks metamorphosed to the amphibolite facies, straddling the boundary between the La Grande and Opinaca subprovinces, in Eeyou Istchee Baie-James (Québec, Canada). The deposit consists of two zones, Zone 25 and Zone 26, which are oriented WNW-ESE (S1) and have been deformed and folded by the main regional deformation (S2). Zone 25 is hosted by biotite-rich paragneiss of the Laguiche Complex (2710–2671 Ma) and the mineralization consists of disseminated native gold along with arsenopyrite, pyrrhotite, chalcopyrite and minor pyrite. The mineralization is associated with recrystallized alteration consisting of quartz, phlogopite, dravite ± titanite, microcline, muscovite and calc-silicate veins. Native gold occurs as inclusions in the metamorphically annealed alteration assemblages and at the margin of arsenopyrite. The low content of gold in arsenopyrite suggests re-equilibration at peak conditions during arsenopyrite recrystallization (325–531 °C) which expelled and crystallized native gold. Zone 26 is hosted in a grunerite-altered BIF of the Yasinski Group (2751–2725 Ma) and is characterized by disseminated pyrrhotite-arsenopyrite-löllingite-chalcopyrite in calcic amphibole-biotite-garnet-tourmaline ± chlorite host rocks. Native gold occurs as inclusions in peak metamorphic minerals (hedenbergite, garnet), or at the contacts between löllingite cores and arsenopyrite rims. The La Pointe deposit is interpreted as pre-peak metamorphic, disseminated orogenic gold deposit, subsequently overprinted by higher, amphibolite-grade, and late retrograde metamorphism.