Mineral associations of late processes in the calcite-nepheline-feldspar pegmatite (Ilmenogorsky miaskite massif)

The features of the composition of minerals formed during the albitization and cancrinitization of rocks in the calcite-nepheline-feldspar pegmatite vein (southwestern endocontact of the Ilmenogorsky miaskite massif) are studied. Albite formed together with annite, pyrite, strontianite, barite, and fluorapatite. Annite revealed a low content of TiО2 and MgО (up to 1.0 wt. %) and a high content of Fe (31.2-41.4 wt. %). Fluorapatite is characterized by an increased amount of rare earths, ∑ REE = 2.9-4.8 wt. %, and an increase in the content of SrО to the edge of the grain, up to 5.4 wt. %. The content of BaО increases from 0.6-1.0 to 2-7 wt. % in the composition of orthoclase at the border with albite. The development of late fluorite-calcite formations with the sulfide-rare-earth mineralization is associated with the processes of the cancrinitization of nepheline.