Ta-Nb mineralization in the alkaline rocks of the Eastern Azov Area (Ukraine)

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Marco E. Ciriotti
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Ta-Nb mineralization in the alkaline rocks of the Eastern Azov Area (Ukraine)

Messaggio da Marco E. Ciriotti » lun 08 ott, 2018 11:06

Referenza:
▪ Kryvdik, S.G., Sharygin, V.V., Dubyna, O.V., Morgun, V.G., Tomurko, L.L. (2018): Ta-Nb mineralization in the alkaline rocks of the Eastern Azov Area (Ukraine). Mineralogical Journal, 40(3), 39-64 (in russo con abstract in inglese).

Abstract:
New results of investigation of Nb and Ta mineralization in the magmatic and metasomatic rocks of the Eastern Azov area are presented. The pyrochlore super group minerals in the biotite-aegirine dike microfoyaite, agpaitic phonolites and mariupolites of the Oktyabrsky massif are investigated. In addition to "usual" pyrochlores typical of mariupolites of the Oktyabrsky massif the relatively high-tantalum (13.2 % Ta2O5) pyrochlore with high content of ZrO2 (up to 6.7 %) is identified in microfoyaites. The minerals of pyrochlore super group contain a high concentration of rare earth elements (up to 19 % REE2O3) and variable concentration of U and Th. In the agpaitic phonolites two types of minerals of pyrochlore group are distinguished: 1) Ta-rich (up to 23.8 % Ta2O5) and high-Zr (11.6 % ZrO2); 2) REE-rich (up to 31 % REE2O3) varieties. The first type is distinguished by high content of Zr (as for pyrochlore) as well as by high content of Ta. Pyrochlore in gneiss-like mariupolites is characterized by high content of sodium (10.05—10.85 % Na2O), rare earths (12—18 % REE2O3) and uranium (7.3—12.86 % UO2) in contrast to mariupolite ones. In the alkaline metasomatites (fenites) from the Dmytrivka and Khlibodarivka quarries and Kalmytska ravine (the tributary of the Kalmius River) the pyrochlore group minerals are the main Nb-Ta-hosted minerals, while columbite and fergusonite-(Y) play a subordinate role. Pyrochlore is most predominant among the pyrochlore group minerals. Low or moderate content of Ta, REEY, Zr, U, Th, Pb is typical for minerals of pyrochlore group, but varieties with high concentration (%) of these elements occur there comparatively often: Ta2O5 (to 13—24), REE2O3 (up to 13—30), Y2O3 (up to 7—15), ZrO2 (up to 12), UO2 (up to 14), ThO2 (up to 10), PbO (up to 15—33). Varieties with increased or high REE content (19 %) and low or moderate Ta, Th and U content prevail among minerals of pyrochlore group in the alkaline metasomatites (fenites) of the Dmytrivka quarry. Species with high Pb content (up to 29 % PbO) and separate grains with high content of SrO and BaO, ThO2 are also found in some samples. The predominance of pyrochlore group minerals over other niobates is explained by high alkalinity of the hosted rocks. Columbite is quite rare in metasomatites of the Dmytrivka and Khlibodarivka quarries. Fergusonite-(Y) is also quite rare mineral, and it was analyzed as small inclusions in astrophyllite, ilmenite and perraultite only in alkaline metasomatites of the Dmytrivka quarry. A significant portion of Nb is isomorphically included in titanium and titanium-containing silicates and oxides (%): ilmenite (up to 6), rutile (up to 10.7), pseudorutile (up to 13), baotite (up to 7—18), zirconolite-(Y) (up to 8), kupletskite (up to 5—8).
Marco E. Ciriotti

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