الفهرس 
CHAPTER ONE: INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
Gabal (G.) Umm Salatit area is a part of the Central Eastern Desert of Egypt. It is bounded by longitudes 33° 45’ and 33° 60’ E and latitudes 25° 10’ and 25° 20’ N, covering an area of 450 km2. The present work deals with the detailed investigations of the geology, petrography, geochemistry, mineralogy and spectrometric propecting of the studied granitic rocks and trachyte dykes to identify their mode of occurrence.
Detailed field mapping of the basement rocks based on the field relations and structure observations, as well as, the petrographical studies revealed that, the chronological sequence of the rock types of G. Umm Salatit area is arranged tectonostratigraphically beginning with the ophiolitic mélange, older granitoids, younger granitoids andpost granitic dykes and veins.
The ophiolitic mélange occupies the major portion of Wadi Umm Salatit forming an elongated belt trending E-W, covering an area about 90 km². The mélange consists of ophiolitic fragments setting in highly sheared and schistose matrix consisting of metasediments (hornblende schist, actinolite schist and biotite schist). The ophiolitic fragments consist mainly of serpentinite, talc-carbonate and rare blocks of metagabbros as well as marble. The older granitoids are represented by tonalites and granodiorites.The younger granitoids are represented by biotite and muscovite granites, covering an area about 30 km2.
Geochemically,the differentiation index (D.I.) for the studied muscovite granite (80.8-95.1) is relatively high indicating that they are evolved from strongly acidic differentiated magma. Muscovite granites are high-K calc-alkaline, peraluminous syn-collision to late orogenic regime and chachterized by (1) enrichment in light rare earth elements (LREEs), (2) depletion in HREEs and (3) negative Eu-anomaly. The Nb/Ta ratio shows a positive correlation with Ti, Zr suggesting that the ratio is modified during fractional crystallization involving both major phases as well as accessory phases. However, the Nb/Ta ratio displays a negative correlation with Rb and Li. This suggests that the fractional crystallization in more evolved rocks was accompanied by fluid fractionation and the addition of mineralizing fluids.
Thirteen representative samples of the muscovite granite were analyzed for REEs and the average normalized REEs patterns of G. Umm Salatit muscovite granites display low to moderate fractionated REEs pattern , where the averages (La/Yb)n = 2.27 and have slight enrichment in the LREEs (47.4), where the averages (La/Sm)n= 1.4. It is
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concluded that G. Umm Salatit muscovite granite have moderate negative Eu anomaly (Eu/Eu*= [EuN / [(SmN). (GdN)]1/2= 0.4)] reflects the slight difference in their origin.This difference can be interpreted due to the removal of feldspars from a felsic melt by crystal fractionation or by partial melting of a rock in which feldspars is retained in the source will give rise to a negative Eu anomaly in the melt or due to the greater effect and higher oxygen activity of the melt, which is relates to volatile saturation (higher oxidation state) in case of the melt that formed the granitic melt.
The studied trachyte dykes have fall within the calc-alkalic field, continental basaltsand display a crustal contamination and or fractional crystallization (AFC) direction. The average normalized REEs patterns of G. Umm Salatit trachyte dykes display low to moderate fractionated REEs pattern, where the averages (La/Yb)n = 16.8 and have marked enrichment of the average of ΣLREEs (324.6) relative to the average of ΣHREEs (26.4) where the averages (La/Sm)n= 5.6. It is concluded that trachyte dykes in G. Umm Salatit area have moderate negative Eu anomaly (Eu/Eu*= 0.5), this may reflects the plagioclase and k-feldespar fractionation or due to the greater effect and higher oxygen activity of the melt, which is relates to volatile saturation (higher oxidation state) in case of the melt that formed the melt.
The mineralization in G. Umm salatit area can be classified into the following groups: 1) Uranium-thorium minerals(kasolite and thorite), 2) Niobium - tantalum minerals (fergusonite),3) Base metals (pyrite,galena and chromite), 4) Accessory minerals (zircon, spessartine, flourite, apatite, xenotime, spinel, magnetite, goethite) and 5) Carbonate minerals (magnesite andcalcite).
The determination of equivalent uranium, thorium ( in ppm), potassium% and dose rate (m Sv/y) radiometrically by using portable RS-230 indicates that the average of eU is 74.4 and 188.6 ppm for mineralizedsheared muscovite granites and pegmatite veins respectively.
The D - factor (chemically determined uranium/radiometrically measured uranium) of themineralizedsheared muscovite granites(fault zone) and pegmatite veins of the studied area clear that chemical uranium is more than the radiometric uranium in all samples, which reflects disequilibrium due to the addition of uranium. This means that uranium has been transported recently and has not time for decay.