Ta-Nb mineralization in rare-metal pegmatite from north-western frame of Lypniazhka granite-migmatite structure

S.I. Kurуlo 1, 3
Е-mail: kurylo.sergiy@gmail.com, https://orcid.org/0000-0003-4466-6851
N.M. Lуzhachenko 2
Е-mail: lyzhachenko@gmail.com, https://orcid.org/0000-0001-8598-0551
S.M. Bondarenko 3
https://orcid.org/0000-0001-7948-3583
V.O. Syomka 3
https://orcid.org/0000-0001-5202-4045
O.V. Hrinchenko 4
https://orcid.org/0000-0003-3030-1720
1 Earth Science Institute, Slovak Academy of Sciences
2 State Institution «The Institute of Environmental Geochemistry of National Academy of Science of Ukraine»
3 M.P. Semenenko Institute Geochemistry, Mineralogy and Ore Formation of the National Academy of Science of Ukraine
4 Taras Shevchenko National University of Kyiv, Institute of Geology

Language: Ukrainian
Geochemistry and ore formation 2020, 41: 32-41
https://doi.org/10.15407/gof.2020.41.032

The three type of rare-metal pegmatites are know in Stankuvatske ore field (Ingul megablock, the Ukraianian Shield), such as: Li-bearing, Bi-As-U and Ta-Nb pegmatites. For the first time Ta-Nb mineralisation from Ta-Nb bearing albite-K-Feldspar rare metal pegmatite have been described. Investigated pegmatite is located on the Norh-West frame of the Lypnazky granitemigmatite massive among hosted amphibolites. Rare-metal pegmatite doesn’t have obvious zonality and consist of alkaline feldspar, biotite, muscovite, dark to black colour quartz, blue-greenish apatite, nigerite, gachnite, tourmaline, monazite. The primary ferrocolumbite and Nb-rutile-II have undergone strong hydrothermal alteration. Thus primary rutile-II decomposed with formation of skeletal intergrowths of secondary cassiterite and rutile-III with a much lower volume of Nb and Ta under the influence of hydrothermal fluid. Primary homogenous Nb-rutile-I (Nb2O5+Ta2O5 from 33,5 to 42,9 wt.%) exsolved a fine trellis-like pattern and lamellar of Nb-pure rutile-III, cassiterite and Mn-rich ilmenite. The Nb-rutile-II is occurred in tabular grains with unclear internal zonation. Primary ferrcolumbite breakdown to Ti-ixiolite and Nb-rutile-III. Primary oscillatory zonality is transformed into irregularly patchy and veinlety. Recrystallized ferrotantalite is secondary and uncommon mineral. Ferrocolumbite contains 2.93 to 4.74 wt.%TiO2, and titanian ixiolite 7,33-10,76 wt.%. The (Ti,Nb)>Ta mineral assemblages, and compositional trend of columbite with very low Ta/(Ta+Nb) and Mn/ (Mn+Fe) imply a general low level of fractionation in comparison with typical beryl-columbite rare-metal pegmatites.

Keywords: ferrocolumbite, tantalite, titanian ixiolite, rutile, ilmenite, cassiterite, nigerite, exsolution, rare-metal granite pegmatite, Ingul Domen, Ukrainian Shield.

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