Mineral Chemistry and Genesis of Emerald and Beryl Mineralization in the south Eastern Desert of Egypt | ||||
| Egyptian Journal of Chemistry | ||||
| Article 56, Volume 65, Issue 8, August 2022, Page 601-623 PDF (1.69 MB) | ||||
| Document Type: Original Article | ||||
| DOI: 10.21608/ejchem.2022.113700.5166 | ||||
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| Authors | ||||
F.M. Khaleal  1; Lentz D.R.2; Hall D.C.3
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| 1Nuclear Materials Authority, P.O. 530. El Maadi, Cairo, Egypt | ||||
| 2Department of Earth Sciences, University of New Brunswick, Fredericton, NB, Canada | ||||
| 3Microscopy and Microanalysis, University of New Brunswick, Fredericton, NB, Canada | ||||
| Abstract | ||||
| Beryl mineralization in Egypt occurs in the south Eastern Desert and Sinai, occurring in two geologic environments. In the first environment, beryl occurs in phlogopite schist next to contacts with discontinuous muscovite leucogranite and linked to cogenetic pegmatites. Their spatial distribution is a well-defined NW-SE trend district extending ~45 km long and ~9 km wide. This extensive district coincides with the major Nugrus thrust and linked strike-slip shear-zone system. Zabara-Um Addebaa district (Z-UD) resembles this type and the schist hosting emerald in the south Eastern Desert of Egypt is confined to this district. In the second geologic environment, beryl occurs within pegmatite (lenses, bodies, and veins), quartz veins, and disseminated form in alkali feldspar granite; the Homret Akarem-Homret Mukpid district (HA-HMD) resembles this type. In Z-UD, the averages of Al2O3, K2O, CaO, TiO2, V2O3, and Cr2O3, in emerald of phlogopite are higher than those of green beryl either in phlogopite or in quartz veins. It is sodium-rich beryl, as Na2O ranges between 1.74 and 1.96 wt.%. In the studied emerald and beryls, the concentrations of Cr, V, and Fe+2 control the beryl coloration (chromophore). In HA-HMD, the beryl mineralization of Homret Akarem is a whitish and pale green color, while beryl of Homret Mukpid is of pale blue color. The averages of Na2O, MgO, Al2O3, K2O, CaO, MnO, NiO, and Cs2O in Homret Akarem are higher than those of Homret Mukpid. Conversely, the averages of TiO2, V2O3, Cr2O3, and FeO of Homret Akarem are less than those of Homret Mukpid. The pale blue color of Homret Mukpid is attributed to the high content of Fe+2, Cr, and V, whereas the whitish color of Homret Akarem beryl is due to the deficiency of these elements. The genesis of beryl mineralization in Z-UD district is interpreted as a result of the interaction between highly evolved felsic magma (muscovite leucogranite and associated pegmatite) and the pre-existing mafic-ultramafic rocks embedded in mélange matrix (schists). These processes involve the addition of the elements characteristic of a highly evolved granitic assemblage (Be, F, B, P, alkalis) to the ultramafic assemblage that is quite high in Mg, Ti, Cr, Ni, and Cu. Consequently, phlogopite (K-metasomatism) formed at the expense of earlier actinolite (Mg, Ca metasomatism), which released Cr and (or) V giving the green to deep green color. The genesis of beryl mineralization in HA-HM district is attributed to metasomatism by emanation of volatiles exsolved from a deep-seated highly evolved felsic magma source. | ||||
| Keywords | ||||
| Beryl; Emerald; Mineral chemistry; Zabara; Um Addebaa; Akarem; Mukpid | ||||
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