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| Titel |
Columbite and fergusonite from rare metal granitoids, Central Eastern Desert of Egypt |
| VerfasserIn |
Mabrouk Sami, Theodoros Ntaflos, Awaad F. Ahmed, Haroun A. Mohamed, Esam S. Farahat |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250137534
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| Publikation (Nr.) |
 EGU/EGU2017-280.pdf |
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| Zusammenfassung |
| The Central Eastern Desert (CED) of Egypt, as a part of the Arabian Nubian Shield (ANS)
belt, hosts more than 14 rare metal granitoids plutons. The garnet bearing muscovite granite
(GBMG) from Gabal Abu-Diab and alkali-feldspar granite (AFG) from Gabal El-Ineigi were
selected to study their rare metal mineralization. The GBMG and AFG are a metaluminous to
weakly peraluminous consists of quartz, K-feldspar, plagioclase and muscovite in both types
with subordinate amounts of garnet in GBMG and biotite + fluorite in AFG. Columbite,
zircon, thorite, rutile, ilmenite and monazite are the common accessories in both types, while
fergusonite are exclusively encountered in AFG. Both granitoids are highly fractionated
calc-alkaline characterized by high Rb, Nb, Y, U and many other HFSE contents,
and extremely low Sr and Ba. Texturally, the columbite and fergusonite crystals
occur as homogeneous disseminated grains between the major minerals phases
and as inclusion in protolithonite, zircon and fluorite. In few cases, they have a
well-developed normal and oscillatory zoning pattern, suggesting their primary magmatic
crystallization. Compositional variation (results of electron microprobe analyses) of
columbite and fergusonite from these granitoids is evaluated. Columbites from AFG are
mostly represented by Ta rich columbite-(Fe) with average chemical composition of
Nb2O5 (88 wt. %), Ta2O5 (up to 31 wt. %), FeO (17 wt. %) and MnO (5 wt. %).
While columbites from GBMG, are classified as Ta poor columbite-(Mn) and are
chemically consists of Nb2O5 (73 wt. %), Ta2O5 (6 wt. %), FeO (9 wt. %) and
MnO (12 wt. %). Fergusonite-(Y) occur as homogenous crystals with an average
concentration of Nb2O5 (44 wt. %), Y2O3 (24 wt. %), Ta2O5 (2.3 wt. %), UO2 (2.1 wt.
%) and ThO2 (1.2 wt. %). The ΣREE2O3 dominated by HREE (Yb2O3, Er2O3,
Dy2O3, Gd2O3, Lu2O3 and Tm2O3), ranges from 15.3 to 16.6 wt. % and Ce2O3
(up to 3.3 wt. %). The Metamictized fergusonite contain ubiquitous subordinate
amounts of U and Th that could be formed due to the hydrothermal effect. During the
late magmatic fractionation stage, the progressive decrease in temperature led to
gradually ceasing the solubility of rare metal complexes in magma followed by
sequentially crystallization of rare metal minerals including columbite and fergusonite. |
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