PETROGENSIS AND MINERALOGICAL CHARACTERIZATION OF PEGMATITES FROM KHOUR ABALEA, SOUTH EASTERN DESERT, EGYPT

Khour Abalea in Abu Rusheid area is located at the midst part of the cataclastic rocks having U-shaped
It was formed as a result of deep strike-slip faults, some forming shear zone in some trends. Two forms of
pegmatites have been distinguished (pockets and veins) occurring within the cataclastic rocks as hosted
rocks. Petrographically, they consist of quartz, orthoclase, microcline and micas.
The identified minerals in the studied pegmatites can be grouped into primary uranium minerals
(uraninite), secondary uranium minerals (kasolite, uranophane and meta-autunite), thorium minerals
(thorite and uranothorite), the niobium-tantalum minerals (columbite, ferro-columbite, samarskite, euxenite
and fergusonite), the accessories (zircon, monazite, cassiterite, pyrite and fluorite) and mica (muscovite,
phlogopite and fluor-phlogopite) as well as the opaques (hematite and goethite).
Geochemically, the studied pegmatite (S-type) are calc–alkaline and peraluminous in nature. It is highly
fractionated possibly due to hydrothermal alterations. The REEs display clear tetrad effect of M-type
accompanied with relative enrichment of the HREE over the LREE and marked negative Eu anomaly
(Eu/Eu* =0.03 to 0.36). The calculated tetrad effect in the pegmatite demonstrates clear tendency towards
the ratios of the common isovalents such as Zr/Hf, Nb/Ta and Y/Ho. However, the tetrad effect seems not
to be mutual with the content of Na2O and Rb/Sr. The absence of coherence between tetrad effect and soda
or potassic contents may indicate insignificant role of the Na- or K-metasomatism in developing the tetrad
effect.
Detailed spectrometric survey of the study pegmatite revealed their enrichment of eU (49-306 ppm)
and eTh (76-634 ppm) and the potential anomalous radioactivity is attributed to both magmatic and
hydrothermal processes.