PETROGENESIS OF SELECTED PEGMATITIC BODIES FROM EASTERN DESERT AND SINAI MASSIF, EGYPT | ||
| Delta Journal of Science | ||
| Article 21, Volume 29, Issue 2, December 2005, Pages 156-184 PDF (2.21 M) | ||
| Document Type: Research and Reference | ||
| DOI: 10.21608/djs.2005.158268 | ||
| Authors | ||
| Mohamed T.S. Heikal1; S.A. Awad2; I.E. Aassy3; S. E. Ammar3; E.K. Abu Zeid3 | ||
| 1Geol. Dept. Fac Sci. Tanta Univ., Tanta, Egypt | ||
| 2Geol. Dept. Fac. Sci. Ain Shams Univ., Cairo, Egypt | ||
| 3Nuclear Materials Authority, Cairo, Egypt | ||
| Abstract | ||
| Selected pegmatitic bodies of simple and complex types (unzoned and zoned) located in the Eastern Desert (ED) and Sinai Massif (SM) have been carefully studied. The simple pegmatites under consideration occur at Wadi Hawashia (northern ED), Gabal El Hudi area (southern ED) and Wadi Dahab (SM) forming irregular lenses and pods. Alkali feldspar, quartz and muscovite pockets represent the essential mineral constituents. On the other hand, the complex types of zoned nature occur at Gabal Abu Dob (central ED) and Wadi Um Shoki (SM) forming sheets and dyke-like appearance. They constitute a sequence of mineral assemblage from the contacts inward as follows: alkali feldspar ± mica pockets followed by graphic quartz and quartz megacrysts at the core. Almost all pegmatitic bodies invade granitoids with a mild contact effect (if present). Petrographically, the pegmatites are granitic (comprise alkali feldspar granite constituents as perthite, microcline perthite, quartz ± mica) and perthitic (string, patch and net types of perthite are the main mineral constituents). Allanite, zircon, apatite, cassiterite and uranophane are mostly accessories. Geochemically, almost all pegmatites have metaluminous to peraluminous nature and are characterized by their high alkali contents (up to 12 wt%) as well as low CaO contents (<1.0 wt%). Regarding to mineral chemistry, the perthite analyzed lies in the field of alkali-feldspar-rich rocks. Composition of Mg-mica (manganophyllite) is distinguished by elevated abundances of alumina, magnesia and manganese contents. Textural and mineralogical features of manganophyllite suggest late-crystalized phase with variable degrees of metasomatism of an initial source rock. It is quite clear from the field, petrographic and geochemical studies of the present pegmatites that these rocks seem to be strictly of magmatic nature in one hand and in combination with metasomatism associated with volatile input in another hand. | ||
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