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Geochemical Characteristics of the Granitic Rocks at Magal Gebriel Area, South Eastern Desert, Egypt |
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PP: 83-96 |
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doi:10.18576/jrna/090113
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Author(s) |
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Gehan B. El Shaib,
Adel H. El Afandy,
Nasser M. Moghazy,
Atef El-Taher,
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Abstract |
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| The study area comprises volcano sedimentary succession (metasediment and metavolcanics) intruded by granitoid rocks. The younger granites occupy central, northeastern and northwestern parts of the area, they form moderate to high outcrops and have sharp intrusive contacts with the surrounding metavolcanics. These rocks are highly jointed and affected by hydrothermal alterations, especially along faults and shear zones. The studied syeno- and alklifeldspar granites were investigated by polarized microscopes, analyzed for trace and rare earth element by X-ray fuoresence, ICP-ES and ICP-MS techniques. Petrographically, Syeno- and alkli feldspar granites are mainly composed of quartz, alkali feldspar, plagioclase, biotite and muscovite as essential minerals, fluorite, zircon, allanite, titanite, monazite, uranophane and iron oxides as accessories. The present study focus on the geochemical characteristics investigation of syeno- and alkali feldspar granites at Magal Gebriel area to detect their suitability for radionuclides and other mineralization. All samples of the alkali feldspar and syenogranite samples have La/Y ratios ˂1, suggesting the prevailing of acidic conditions in the depositional environment. REEs mobility are mainly controlled by the pH conditions of the media, therefore, the migration out of REEs is higher in the alkali feldspar granite relative to syenogranites. Ce anomalies in the most alkali feldspar and syenogranite samples (˂ 1) and have negative Eu anomalies, indicating its formation under reducing conditions by hypogene hydrothermal fluids, having temperature >200ºC, low pH, and relatively high ƒO2. The nonchondritic values of isovalents, illustrating the dual impact of hydrothermal solution and water on the alteration processes of these rocks. Late alteration processes lead to increments and decrements in some elements and formation of new minerals. The conjugate M-W tetrad effect in the alkali feldspar granite emphasize the alteration processes and may clarify the presence of gold mineralization. |
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