Li in minerals from the Ilimaussaq alkaline intrusion, South Greenland

Abstract

Li was analysed by instrumental neutron activation analysis and Cerenkov counting in 120 mineral samples (30 species) from the Ilfmaussaq alkaline intrusion, South Greenland. More than 0.23 wt.% Li (0.5 wt.% Li2O) is found in polylithionite, neptunite, riebeckite, Na-cookeite, ephesite, arfvedsonite, gerasimovskite and astro­phyllite. Arfvedsonite (200-2500 ppm Li) carries the bulk of Li in most of the highly alkaline rocks. Li-Mg and Li-F relations indicate that the distribution of Li is con­trolled by the structure of minerals, their absolute contents of Mg and F and the fractionation stage within the intrusion. Li is probably linked with Fin the fluid state and this linkage continues into crystallising phases where Li occupies sites which also accommodate Mg. Li/Mg and Li/F ratios of Ilfmaussaq rocks and minerals are higher than in equivalent materials from the Lovozero intrusion (Kola, Russia). The Li­Mg-Fe2+ geochemical association at Ilfmaussaq (Fe2+>>Mg) and Lovozero (Fe2+>Mg) contrasts with the commercially important Li-rich but Mg-Fe2+-poor association found in certain granite pegmatites and greisenised granites.