U-Pb dating of niobium minerals from the pyrochlore group (Ilmeny-Vishnevogorsky carbonatite-miaskite complex, South Urals)

The article covers the U-Pb dating of minerals belonging to the pyrochlore group from the rare-metal ore deposits of Ilmeny-Vishnevogorsky carbonatite-miaskite complex (South Urals). Individual pyrochlore crystals were dated through a new technique of in-situ U-Pb dating using SHRIMP-II, which was developed at VSEGEI (St.Petersburg). The U-Pb dating of high-uranium pyrochlore (more than 2.5 wt % UO2) was carried out employing laser ablation and ICP-MS. The U-Pb systems of studied pyrochlore samples indicate a multi-stage formation of rare-metal niobium mineralisation. The earliest age of ore formation (378 ± 4.9 ma) is yielded by the U-Pb systems of U-bearing pyrochlores from the carbonatites of the Potanino deposit. This period of ore formation is probably associated with the final stages in the crystallisation of the alkaline-carbonatite magmatic system. The next periods of ore formation (230 ± 1.5 Ma) are widely manifested in the Vishnevogorsky and later in the Potanino deposit (217.2 ± 1.9 Ma), which is probably associated with the remobilisation and redeposition of alkaline-carbonatite and rare-metal substances at the post-collision stage in the evolution of Ural carbonatite complexes.