Hîrtopanu, Paulina

Hungarian

Hîrtopanu Paulina

Andersen J. C.

Fairhurst R. J.

Ludusan N.

Jakab Gy.

University of Szeged

54 Acta Mineralogica-Petrographica, Abstract Series, Szeged, Vol. 7, 2012 Joint 5th Mineral Sciences in the Carpathians Conference and 3rd Central-European Mineralogical Conference 20–21 April, 2012, University of Miskolc, Miskolc, Hungary Nb, Ta, Ti, REE(Y), Zr, Sn, Th, U OXIDES FROM GRADISTEA DE MUNTE RARE  ELEMENT MINERALS OCCURRENCE, SEBES MTS., ROMANIA  HIRTOPANU, P.1*, ANDERSEN, J.C.2, FAIRHURST, R.J.2, LUDUSAN, N.3 & JAKAB, Gy.4 1 University of Bucharest, Romania; 2 University of Exeter, Camborne School of Mine, UK; 3 1 Decembrie 1918 Uni-versity, Alba Iulia, Romania; 4 I.G. Mineral, Gheorgheni, Romania; * E-mail: paulinahirtopanu@hotmail.com  The Gradistea de Munte (GM) rare element minerals occurrence is situated in the north of the Sebes Mts., Southern Carpathians, in the upper course of the Orastie River. Geologically-structurally the GM area consists of the amphibolite facies rocks of the Upper Proterozoic Sebes-Lotru Series of the Getic Crystalline. The most important host rock of the mineralization is a quartz-microcline-albite gneiss/“granite”. Sometimes the rocks being formed only from microcline, albite, some phlogopite/biotite and accessory rare minerals, quartz is missing. Cyrtolite/zircon and magnetite are always present as ore/mineral components of the rock. The rare earth element mineralization is represented by carbon-ates, oxides, silicates and phosphates, in veinletes and nests of mm to cm size grains. The REE oxides in GM belong to 7 groups: pyrochlore, fergusonite, colum-bite, “ilmeno-struverite”, baddeleyite, cassiterite and thorianite-uraninite. 1. Pyrochlore group has 3 sub-groups. A. Pyrochlore subgroup with the major B-site cations (Nb + Ta) > Ti and Nb > Ta, comprises pyro-chlore, yttropyrochlore-(Y), uranpyrochlore, plum-bopyrochlore and thoriopyrochlore, defined by the cations residing in A-site. The GM pyrochlore has (Ca,Fe,U,Th) > 20% in A-site, Nb2O5 ≈ 50% and Ta2O5 ≈ 2–10%. Yttropyrochlore-(Y) contains beside domi-nant Y (≈  15–20 wt% Y2O3) in A site some oxides of Ce, Nd, Dy, Gd, Yb (≈  10 wt%). The Nb2O5 content varies between 40–50 and Ta2O5 between 1–2 wt%. It always contains some UO2 and ThO2, thus metamictisa-tion being very common. In addition, yttropyrochlore-(Y) has some SiO2 content, common in metamictic and late stage hydrated pyrochlores. Yttropyrochlore-(Y) is the best widespread term of pyrochlore. Plumbopyro-chlore has (Pb,Ca,U) > 20% in A site, Nb2O5 = 46.5 and Ta2O5 = 18.5 wt%. Uranpyroclore has UO2 domi-nance in A site (= 13–25%) with some Ln2O3 ≈ 4, Ca + Ba ≈  10, Y2O3 = 1.5–6 and ThO2 = 2 wt%. Its Nb2O5 content varies between 30–50 and Ta2O5 between 10–15 wt%. It is omnipresent as few mm to cm size grains in all types of rocks/ores from GM. In transmitted light it is light red, yellow orange, red. It contains some ZrO2 (≈ 2 wt%), being associated with cyrtolite. Like yttropy-rochlore, it has high SiO2 content (7–10 wt%). The GM thoriopyrochlore is Th dominant with some Y, and Fe in A site. The ThO2 content is very high, around 40 %wt. It contains OH and clorine (≈  0.6 wt%) in Y site. It is associated with thorite and thorogummite. B. Microlite subgroup (TaB ≥ NbB, Nb + Ta > 2Ti) com-prise the uranmicrolite, with Nb2O5 ≈ 30, Ta2O5 ≈ 48.5, UO2 ≈ 14.6 wt%, thormicrolite with Nb2O5 ≈ 19, Ta2O5 ≈ 25, ThO2 ≈ 48 wt%, and yttromicrolite with Nb2O5 ≈ 22, Ta2O3 ≈ 25 wt%, having U, Th, respec-tively Y in A site > 20%. C. Betafite subgroup, B = 2TiB ≥ (Nb + Ta)B, in GM is represented by the occur-rence of betafite (U > 20% in A site) and yttrobetafite-(Y) (Y > 20% in A site). The last one occurs as big grains of up to 1 cm. The chemical composition of yt-trobetafite-(Y) varies: TiO2 = 27–30, Y2O3 = 15–22, Nb2O5 = 22–27, Ta2O5 = 7–19, ThO2 = 5–10, UO2 = 4–6 wt%. Some yttrobetafite-(Y) grains have a very Ta-rich composition: Ta2O5 = 31.2, Y2O3 = 28.8, TiO2 = 36.0 wt% and they do not contain Nb2O5. Composi-tional zoning was visible from yttrobetafite-(Y) inside to Ta-yttrobetafite-(Y) outside in a grain. 2. The fer-gusonite group contains the fergusonite-(Y) with Nb2O5 = 45–58, Y2O3 = 25–35, Yb2O3 + Gd2O3 + Dy2O3 ≈ 4.5 wt% and very little Ta2O5, with maximum 5 wt% UO2 and ThO2 content. The grains of ferguso-nite-(Y) are zoned with formanite-(Y), which has Y2O3 = 34.6, Ta2O5 = 48.2 wt% and little CaO, FeO and ThO2. Another grain has Y2O3 = 36.15, Ta2O3 = 45.72, Ce2O3 = 5.17 and CaO = 4.43 wt% composition. The same grain could be built up from many phases, corre-sponding to yttropyrochlore-(Y), yttromicrolite-(Y), formanite-(Y) showing the Ta increase. 3. Ferrocolum-bite has: FeO = 16.2, MnO = 3.03, Nb2O5 = 72.8, Ta2O5 = 4.2, TiO2 = 3.5 wt% and manganocolumbite has Nb2O5 = 76.28, MnO = 10.93, FeO = 0.44, TiO2 = 0.8 wt%. Some grains have high UO2 content of up to 8.4 wt%. The composition of some grains are (Y2O3 + FeO + MnO) > 20 wt%, high Nb2O5 (> 65 wt%) some Ta2O5 and no TiO2 which could belong to yttrocolum-bite. 4. “Ilmenorutile” has: TiO2 = 49.5–52.5, Nb2O5 = 21.8–26.5, Ta2O5 = 7.7–13.31, FeO = 9.4–12.03 wt%, showing a solid solution with “struverite”. 5. Baddeleyite appears to be one of the oldest minerals, older than cyrtolite and its presence indicates that the first mineralized solutions were subsaturated in silica. Its composition shows only ZrO2 with some ThO2 and very little HfO2. 6. Cassiterite appears as big cm grains in hydrothermal veinlets and has little U, Th and Fe in its composition. 7. Uraninite and thorianite, usually form solid solutions with the composition UO2 = 49.1, ThO2 = 48.0 wt%. Separately, uraninite has composi-tion: UO2 ≈ 96.6 wt% with little ThO2, Y2O3, PbO, FeO, and thorianite has ThO2 = 96.3, PbO = 3.27, FeO = 0.23, SiO2 = 0.16 wt%. Generally, the content of Nb + Ta in all rare minerals is higher than that of Y + REE, and the Y content is much higher than Ce. Also, the Th content is much higher than U. The zirconium has the highest content.  

Nb, Ta, Ti, ree (y) Zr, Sn, Th, U oxides from gradistea de munte rare element minerals occurrence, Sebes Mts., Romania

http://acta.bibl.u-szeged.hu/32996/1/mineralogica_as_007_054.pdf

Nb, Ta, Ti, ree (y) Zr, Sn, Th, U oxides from gradistea de munte rare element minerals occurrence, Sebes Mts., Romania

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