Variations in the composition of pyrochlore group minerals in ongonites and zwitters of the Verkhneurmiysky massif (Russian Far East)
Alekseev V. I., Marin Yu. B.
Zapiski RMO (Proceedings of the Russian Mineralogical Society). 2018. V. 147. N 2. P. 65-79
https://doi.org/10.30695/zrmo/2018.1472.04
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Language: Russian
Abstract
For minerals of the pyrochlore group in ongonites and zwitters of Verkhneurmiysky granite massif (in Badzhalsky district of Russian Far East) are characterized their composition, genesis and consequence of the pyrochlore formation. For the first time, for this Far East region, there were revealed three rare species of this mineral: pyrochhore-I and pyrochlore-II in ongonites, and pyrochlore-III in zwitters. Pyrochlore-I is probably a new mineral species of the pyrochlore group—the bismuth-bearing «oxyferropyrochlore». Pyrochlore-II is the uranium- and iron-bearing hydrokenopyrochlore; pyrochlore-III corresponds to the lead- and iron-bearing hydrokenopyrochlore. All three pyrochlore species were formed by metasomatic replacement of the earlier accessory minerals: niobium-bearing wolframite, samarskite, ishikawaite, wolframoixiolite, scheelite, and fergusonite. These new Far East pyrochlores are characterised by extremely high contents of tantalum, tungsten, and iron. Variations of their compositions are connected with isomorphic substitutions of Nb, Ta, W in the position В and exchange of U, Pb, Bi, Fe in the position A. While transition from the late-magmatic stage to the greisens one in the mineral-forming process, the contents of tantalum, bismuth, and thorium in pyrochlore were decreasing, with increasing mineral-forming significance of niobium, tungsten, uranium, yttrium, lead, and water, as following: Ta, Nb, Bi, Fe, Th, As, P, Ca, Ti→ Nb, Ta, W, U, Fe, HREE, Sc, Mn, Na, H2O → Nb, Pb, W, Fe, Y, H2O.
Key words: pyrochlore group, bismuth-bearing oxyferropyrochlore, uranium-bearing hydrokenopyrochlore, lead-bearing hydrokenopyrochlore, ongonites, zwitters, Verkhneurmiysky granite massif, the Russian Far East.
