COMPOSITIONAL FEATURES AND GENESIS OF STEENSTRUPINE FROM IGNEOUS ROCKS OF THE LOVOZERO ALKALINE MASSIFS, KOLA PENINSULA

Abstract

Steenstrupine from igneous rocks (foyaites and lujaurites) of the Lovozero alkaline massif was studied for the first time. Unlike the early magmatic steenstrupine of the Ilimaussaq massif, the Lovozero steenstrupine is a late mineral, which crystallizes in the interstices of rock-forming mineral grains. Compared to steenstrupine from pegmatites, the Lovozero magmatic steenstrupine has an elevated Ti content and variable Na content and Fe/Mn and Si/P ratios. The distinct correlation between Th and P indicates isomorphic substitution Si 4+ + Th4+ = P5+ + REE 3+. Thorosteenstrupine was found in eudialyte lujaurite. The minerals of the steenstrupine-(Ce)-thorosteenstrupine series from the Lovozero, Khibina, and Ilimaussaq ultra-alkaline pegmatites were studied for comparison.