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Magmatic and hydrothermal evolution of highly-fractionated rare-metal granites at Gabal Nuweibi, Eastern Desert, Egypt

Moussa, Hilmy E. and Asimow, Paul D. and Azer, Mokhles K. and Abou El Maaty, Moustafa A. and Akarish, Adel I. M. and Yanni, Nagy N. and Mubarak, Heba S. and Wilner, M. J. and Elsagheer, Mustafa A. (2021) Magmatic and hydrothermal evolution of highly-fractionated rare-metal granites at Gabal Nuweibi, Eastern Desert, Egypt. Lithos, 400-401 . Art. No. 106405. ISSN 0024-4937. doi:10.1016/j.lithos.2021.106405.

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The Nuweibi intrusion was emplaced during the final tectono-magmatic stage of Arabian-Nubian Shield development (ANS). Two cogenetic phases of intrusion can be recognized in the field: the early phase is represented by porphyritic albite granite and the final phase by non-porphyritic albite granite. Mineralogically, both phases are essentially composed of albite, quartz, and K-feldspars with subordinate muscovite. Accessory minerals include fluorite, zircon, Nb Ta oxides, cassiterite, beryl, topaz, and garnet. Geochemically, the Nuweibi intrusion consists of extensively fractionated rare-metal granite with low contents of TiO₂, FeO_t, CaO, MgO, P₂O₅, Sr, and Ba in contrast to elevated concentrations of alkalis, Rb, Nb, Ta, and Hf. Their peraluminous (molar Al₂O₃/[CaO + Na₂O + K₂O] = 1.06–1.15) and low-P (P₂O₅ < 0.008 wt%) character identify them as highly fractionated I-type granites. The primary magma of the Nuweibi intrusion was most likely generated by partial melting of the juvenile crust of the ANS. We document numerous lines of evidence that the Nuweibi albite granite was formed by extensive fractional crystallization followed by interaction with magmatically-derived, F-rich hydrothermal solutions. The REE patterns of the Nuweibi albite granite show marked negative Eu anomalies (Eu/Eu⁎ = 0.01–0.15) as well as prominent M-type tetrad effects (TE_(1,3) = 1.332–3.536), typically seen in highly differentiated granites and attributed to exchange with hydrothermal fluid. Anomalous ratios of isovalent “twin” elements such as Nb/Ta, Zr/Hf, and Y/Ho likewise indicate exchange with hydrothermal fluid. The primary rare-metal accessory minerals are restricted to the Mn-rich part of the columbite-tantalite series; this manganoan trend is characteristic of highly fractionated granites. Likewise, the presence of wodginite, a Sn-bearing mineral, is a unique fingerprint of highly evolved rare-metal granites. Late-stage hydrothermal overprint of the primary rare-metal mineralization is preserved by rims of fluorcalciomicrolite partly replacing columbite-(Mn) and tantalite-(Mn). Accumulation of residual volatile-rich melt and exsolved fluids in the upper part of the magma chamber produced stockscheider pegmatite, greisen, and quartz veins that cut the peripheries of the Nuweibi intrusion and the surrounding country rocks.

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Asimow, Paul D.0000-0001-6025-8925
Azer, Mokhles K.0000-0002-3711-8630
Additional Information:© 2021 Elsevier B.V. Received 11 May 2021, Revised 28 July 2021, Accepted 29 July 2021, Available online 5 August 2021. We acknowledge the National Research Centre, Egypt for supporting this study as a part of the internal project (No. 12010306) of studies of the rare-metal bearing granites in the Eastern Desert of Egypt. PDA is support by the US NSF through award 1947616. The authors highly appreciate thoughtful reviews by the two anonymous reviewers. In addition, the authors are also indebted to the editor (Prof. Michael Roden) for his efforts and numerous helpful comments. The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Funding AgencyGrant Number
National Research Centre (Egypt)12010306
Subject Keywords:Arabian-Nubian Shield; Nuweibi intrusion; Rare-metal granite; Nb-Ta oxides; tetrad effect
Record Number:CaltechAUTHORS:20210826-203101985
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Official Citation:Hilmy E. Moussa, Paul D. Asimow, Mokhles K. Azer, Moustafa A. Abou El Maaty, Adel I.M. Akarish, Nagy N. Yanni, Heba S. Mubarak, M.J. Wilner, Mustafa A. Elsagheer, Magmatic and hydrothermal evolution of highly-fractionated rare-metal granites at Gabal Nuweibi, Eastern Desert, Egypt, Lithos, Volumes 400–401, 2021, 106405, ISSN 0024-4937,
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:110586
Deposited By: Tony Diaz
Deposited On:26 Aug 2021 20:43
Last Modified:26 Aug 2021 20:43

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