Reconnaissance studies of four pegmatite populations in the Northwest Territories

Abstract

The Aylmer Lake and Torp Lake pegmatite fields in the Slave Province of the Canadian Shield are composed primarily of beryl type and beryl-columbite-phosphate subtype pegmatites, with a portion of each field attaining the characteristics of the complex-spodumene type. The Chantrey Inlet and Foxe pegmatites in the Rae Province are of the beryl-columbite and beryl-columbite-phosphate subtypes. Detailed study of the Aylmer Lake field documents the distribution of at least 227 pegmatites and 18 granitic plutons. Parts of the Aylmer Lake field (Reid and Nebbish lakes) display regional mineralogical and geochemical zoning of pegmatite groups about parental granites. Series containing spodumene-bearing dykes display the best potential for economic Be and Li mineralization. Most pegmatites of the Torp Lake field are geochemically simple. Some dykes, however, are complex, and one intrusion is rich in spodumene, lepidolite, albite (cleavelandite), and elbaite. Pegmatites may be regionally zoned about a two-mica granite. The potential for pegmatites with substantial Be and Li is considered good. The Chantrey Inlet field contains abundant pegmatites and evolved granites. Fractionated pegmatites contain columbite-tantalite and Li, Fe, Mn phosphate minerals. Pegmatite-granite relations are complex and patterns of regional zonation of pegmatite series are not apparent. The Foxe field contains small leucogranitic sheets and a series of beryl-bearing pegmatites, including the PLEX pegmatite. This pegmatite contains columbite-tantalite, spessartine-rich garnet, beryl, and schorl and the degrees of rare alkali fractionation are typical of the beryl-columbite subtype. This field has minor potential for pegmatites enriched in Nb,Ta-oxides.

The Classification of Granitic Pegmatites Revisited

“…Although present in virtually all pegmatite bodies of this subtype, and commonly in substantial proportions, abundances of the minerals of Be and Nb-Ta are widely variable and their ratio may become very steep. Beryl very strongly dominates over Nb-Ta-bearing minerals in the CAT group in southeastern Manitoba (Černý et al 1981) and in the Lamoureux Lake pegmatites at Yellowknife (Meintzer 1987, Wise 1987, whereas the Plex pegmatite, Baffi n Island (Tomascak et al 1994) and the YITT-B group, southeastern Manitoba (Anderson et al 1998) are rich in Nb and Ta phases, but contain mere traces of beryl (cf. Černý 1992).…”