Mineralogy of zirconium and niobium in calcite-nepheline-feldspar pegmatite of the ilmeny-vishnevogorsky complex (the South Urals)
Composition of minerals of the pyrochlore group, columbite-(Fe), Nb-containing rutile, zircon, baddeleyite and zirconolite has been studied in the calcite-nepheline-feldspar pegmatite (12 × 2 m in size) located in the south-west endoсontact of the Ilmenogorsky miaskite massif. There were identified two generations among the pyrochlore group minerals and for baddeleyite. Early generations of fluorcalciopyrochlore and fluornatropyrochlore have high contents of Ti and REE (TiO<sub>2</sub> 9-18 wt %, ∑REE up to 12 wt %), the early generation baddeleyite contains Nb (Nb<sub>2</sub>O<sub>5</sub> 6.2 wt %). Minerals of the later generation have been found in the ilmenite crystal inside the coarse-grained nepheline. The later pyrochlore group minerals contain low quantities of Ti, REE (TiO<sub>2</sub> 3-5 wt %, ∑REE up to 3 wt %), the later baddeleite contains Hf and Y (up to 1 wt %) and it does not contain Nb. Zirconolite has been revealed as a new mineral for the complex. It was formed in the hydrothermal stage in association with cancrinite, stronalsite and gonnardite and it has the higher contents of REE, Th and Mn in its composition.