Li distribution in aegirine lujavrite, Ilímaussaq alkaline intrusion, South Greenland: role of cumulus and post-cumulus processes

Li was analysed by activation analysis in 363 whole-rock samples and 53 minerals from a 200 m drill core through aegirine lujavrite I, Ilímaussaq intrusion. The rocks are interpreted as cumulates and Li is dominantly located in the intercumulus material which is thought to represent the coexisting magma with 540 ppm: whole-rock contents generally range from 80–260 ppm Li and reflect variations in the amount of intercumulus material from 25–48 wt. %. The proportion of intercumulus material is lowest in the deeper parts of the drill core, in layers with a moderate density stratification resulting from showers of near-liquidus crystals and in compressed cumulates beneath a large naujaite xenolith from the roof. Intercumulus arfvedsonite with an average of 2200 ppm Li contains the bulk of Li in most samples, but nearly every sample contains Li (0–176 ppm) outside the rock-forming minerals (Li-ORFM) which was unlocated by conventional mineral separation. Li-ORFM formed during late-magmatic crystallization (a) from the final residues of intercumulus magma which crystallised as accessory Li-mica and alteration products and (b) during in situ zeolitization of arvedsonite which released Li. A later, more intense zeolitization released Li from the rocks of the drill core. Naujaite xenoliths contain 42–130 ppm Li, except where Li-metasomatised, and are associated with low Li values in adjacent lujavrites. Shearing of consolidated lujavrite allowed mobilization of the Li and its reprecipitation along narrow channels (< 10 cm). Li is not concentrated in late hydrothermal coatings.