Alkaline complexes are enriched in elements like REE, Nb and Be similar to the geochemistry of granitic pegmatites. However, the mineralogy and processes are different and for example Nb is found to be extremely mobile in alkaline environments. Actually, secondary Nb-minerals are often among the last minerals to form after zeolites. Many alkaline pegmatites will show a core rich in zeolites with clear replacement textures, but whether these are formed during the last bit of solidification or a much later event is not always obvious. However, it is clear that this zeolitisation is a contributing factor to the wealth of minerals in alkaline systems.
This presentation will focus on observations mainly from pegmatites in the Ilímaussaq alkaline complex in South Greenland and from the Larvik Plutonic Complex in Norway with an emphasis on rare element minerals and element mobility. However, rather than provide conclusions I wish to encourage input from the audience about how to generate a more systematic study of alkaline pegmatites and what we can learn from the work carried out on granitic pegmatites.