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Compositional variation in chromite from the Eastern Desert, Egypt

Published online by Cambridge University Press:  05 July 2018

Ali A. Khudeir ,
Mervet A. El Haddad  and
Bernard E. Leake
Ali A. Khudeir
Affiliation:
Department of Geology, University of Assiut, Assiut, Egypt
Mervet A. El Haddad
Affiliation:
Department of Geology, University of Assiut, Assiut, Egypt
Bernard E. Leake
Affiliation:
Department of Geology and Applied Geology, University of Glasgow, G12 8QQ, U.K.
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Abstract

Electron microprobe analyses of chromite ores from Baramiya, Seifein, Siwigat, Ashayer, Um Salatit and Ras Shait, Egypt, reveal two compositional groups. The unaltered chromites from Baramiya and Seifein have high Al and low Cr contents [Cr/(Cr + Al) = 0.56] whereas the remainder have low Al and high Cr contents [Cr/(Cr + Al) = 0.73]. Such bimodality characterises Alpine-type peridotites. The second group probably crystallised at higher T and lower P than the first group and has a composition characteristic of a type III alpine-type peridotite, i.e. of arc or possibly ocean plateau origin but not of mid-ocean ridge origin. The crystallisation setting of the first group is less certain but not inconsistent with the same environment as the second group so that considering the likely higher pressure of crystallisation of the first group overall favours plutonic crystallisation in the roots of an arc for both groups.

Rim, patchy and fracture alteration of the chromite occurred possibly partly of late magmatic (deuteric) origin but mainly connected with fluid movements, serpentinisation and tectonism. The final composition of the resultant ferritchromite is variable and depends largely on the original chromite composition; the composition of the ferritchromite developed in highly cataclased chromites deviates markedly from that of the original chromite presumably due to unmixing and migration.

Keywords

chromiteferritchromiteEastern DesertEgypt
Type
Research Article
Information
Mineralogical Magazine , Volume 56 , Issue 385 , December 1992 , pp. 567 - 574
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1992

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