National Conferences

Abstract

Recent subdivision of the Grenville Province into Northwestern, Central and Southeastern tectonic zones provides a convenient basis for describing the tectonic affiliation of the contained mineral deposits.The Northwestern zone consists of reworked foreland lithologies southeast of the Grenville Front. Major deposits of metamorphosed Superior-type iron formations are present in metamorphosed Kaniapiscau Supergroup equivalents, exposed at lower metamorphic grades in the Labrador trough. Occurrences of volcanogenic massive sulphides (Abitibi Group equivalents), NiCu, quartzite-hosted UAu, and alkaline intrusion-hosted REE's are of only mineralogical importance.The Central zone contains polydeformed gneisses that have been intruded by three ages of anorogenic anorthosite massifs (circa 1.64, 1.36, and 1.14 Ga) and associated charnockite/magnerite complexes. Major magmatic Ti-Fe (Lac Allard) and large, low-grade NiCu (McNickel) deposits are associated with the younger anorthosite suite. Magmatic NiCu also occurs in differentiated metapyroxenite/metaperidotite of uncertain age. Pegmatites are widespread but not commercially important.The Southeastern zone consists of the rocks of the Central Metasedimentary Belt (CMB) and Central Granulite Terrane (CGT) as well as rocks of the relatively unmetamorphosed Wakeham Supergroup. Initial deposition of volcanic and carbonate rocks occurred in the CMB between 1.28 and 1.24 Ga and was followed by deposition of the Flinton Group ∼1.15 Ga. The rocks are overprinted by the Elzeviran and Ottawan orogenies ∼1.25 and 1.08 Ga respectively. Volcanogenic ZnPbAgAu deposits and SEDEX marble-hosted Zn deposits occur widely in the layered rocks of the Central Metasedimentary Belt (deposition ∼1.28 Ga). Small massive sulphide and shale hosted base metal occurrences and both oxide and sulphide iron formations are widespread near volcanic lithologies but are generally small or very low-grade. Syngenetic-magmatic deposits include subeconomic FeTi and NiCu deposits that are syntectonic with respect to the Ottawan orogeny but others may be as old as Elzeviran. Small magnetite-rich skarn deposits are widespread, with 2 major past-producing deposits, and are related to magmatic events accompanying the Elzeviran orogeny. Gold and gold sulphosalt occurrences in Grenville volcanic and carbonate lithologies and Flinton Group rocks of various types are not well constrained in age. Some are spatially associated with older Elzeviran intrusions and have been genetically related to them, others exhibit metamorphic textures but cut younger Flinton group rocks while others appear to be completely post-metamorphic. Extensive pegmatitic and related skarn and carbonate vein U ± Mo ± REE occurrences may relate either to metamorphic or intrusive processes related to the Ottawan orogeny.In the CGT, FeTi and NiCu occurrences associated with the younger anorogenic anorthosite massifs are similar to occurrences in the Central zone. Large fluorite-bearing magnetite iron deposits associated with alaskitic gneisses are interpreted as similar to the Swedish Kiruna-type deposits.Following stabilization of the Grenville craton, rifting associated with the opening of Iapetus in the latest Proterozoic-Cambrian and again in the Cretaceous resulted in the regional intrusion of alkaline complexes which included large Nb-and REE-rich carbonatite intrusions. In the Cretaceous, rift-related faults became the sites of small fluorite-barite-galenastrontianite deposits over a wide area in the Elzevir and Frontenac terranes and in the Charlevoix-Saguenay area of the Central Zone.