Ta-Nb MINERALIZATION IN ALKALINE ROCKS OF THE AZOV AND MIDDLE DNIEPER REGIONS

Abstract

The results of niobium minerals investigation in alkaline rocks of the Azov and Middle Dnieper regions are presented. In the mariupolites of the Oktiabrskyi massif, natro- and calciopyrochlore have been ana-lyzed. Natropyrochlore differs from most published analyzes by high Na (10.05–10.85 % Na2O), REE (12–18 % REE2O3) and U (7.3–12.86 % UO2) and low Ta content. In the dike microfoyaites of this massif investigated calciopyrochlore varies in the content of Ta2O5, Na2O, ZrO2. In agpaitic phonolites among the minerals of the pyrochlore group two types were found: (1) rich in Ta (up to 23.8 % Ta2O5) and Zr (11.6 % ZrO2) natropyrochlore; (2) enriched in REE fluorceriopyrochlore (up to 31 % REE2O3) with a high content of U3O8 (up to 9.05 %). Minerals of the pyrochlore group from foyaites of Malotersianskyi massif have a negligible distribution and are represented by fluorocalciopyrochlore. In alkaline metasomatites of Dmytrivka among minerals of the pyrochlore group, the varie-ties prevail with increased or high content of REE and low or moderate – Ta, Th and U. In some samples, plumbopyrochlore (32.8 % PbO) and niobate with high Y content (up to 15 % Y2O3), probable yttriumpyrochlore, are presented too. The peculiarity of the pyrochlore group minerals in the carbonatites and fenites of Khlibo-darivskyi quarry is the high ThO2 content (up to 9.9 %), REE2O3 (9 %) at low UO2 (0.22 %) and Ta2O5.