الفهرس 
introduction
geologic settingOnly 14 pages are availabe for public view
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Abstract
The post-tectonic Phanerozoic trachyte rocks of W. Al-Owayrishah and its surrounding study areas crop out in the form of sheets and dykes that mostly striking and dipping in a concordant way with the primary and secondary structures of the enclosing host rocks. The trachyte rocks may be related to the rifting event that produced monogenetic volcanoes of basaltic rocks and/or alkaline felsic rocks. The trachytic dykes have patterns of significantly increasing grain size consistent with their formation in a subvolcanic complex.
Tectonic mélange, the oldest rock type in the area, comprises trench-fill metasedimentary rocks, which enclosing variably sized blocks and fragments of many rock types especially metavolcanics, serpentinites and rarely metagabbros.
Suture zone molasse-type Hammamat sedimentary rocks of the study area comprise a thick succession of red purple to greenish-grey colour consists of intercalated siltstones, mudstones, polymictic conglomerates and rarely greywackes. The pebbles of conglomerates are of different rock types (Polymictic) suggesting that the environment of deposition was unstable and some of these conglomerates were deposited in iron-rich and other in iron-poor environments. Some conglomerates were deposited in situ or at least transported for a short distance, while others experienced relatively longer transport. Some conglomerates were deposited before the Docking Stage and significant deformation, while others were deposited after stabilization but before the intrusion of collision-related granites (on the evidence of the complete absence of granite pebbles in the conglomerates).
The collision-related granites are mainly crop out in the central and western parts of the study area and are mainly represented by monzo- to syenogranites.
Petrographic studies of the trachyte rocks revealed the presence of secondary radioactive minerals mainly represented by autunite and uranophane which are always associated with iron-oxy hydroxides and/or clay minerals and carbonates. Ratios of radioactive minerals are essentially controlled by the distribution of amygdales and phyenocrysts of trachytes.
The studied trachytes are of alkaline nature with potassic affinities due to the predominance of potash feldspar. They were developed along within-plate setting and generated in an extensional intra-plate rift-related environment. They were derived from the same magma source by fractionation processes of low titanium and high potassium magma.
The maximum value of eU associated with trachytes is 209.9 ppm at W. Al-Owayrishah with an average content 21.2 ppm. The main sources of uranium anomalies in the study area are trachytes themselves, superheated solutions and hydrothermal solutions. The anomalies are controlled by the presence of low permeability of the country rocks in contact (siltstones), as well as the presence of iron oxy-hydroxides alteration as assistant agent for uranium adsorption, accumulation and fixation.
Secondary uranium minerals such as uranophane and uranium-bearing minerals such as samarskite, zircon and fluorite, as well as thorite and thorium-bearing minerals such as monazite, allanite and thorium-REEs silicates were identified using X-ray diffraction techniques and Environmental Scanning-Electron Microscope.