The present work deals with the dykes of Wadi El Akhdar area in southern Sinai which is located between lat. 28˚42′-28˚55′ N and long. 33˚40′-33˚53′ E and covers an area of about 700km 2 . The area is characterized by basement rocks unconformably covered by Phanerozoic sedimentary rocks in the northeastern portion. Field surveys indicated that the studied dykes traverse most rocks in Wadi El Akhdar area except the quartz-syenite and Phanerozoic sedimentary rocks. The different rock units of the area under consideration are traversed by various types of post-granitic dykes. Frequently, many of dykes have curved outcrops, running in remarkable parallelism with each other and vary in inclination from steep inclined to vertical, 0.5 to 20m in thickness and between 0.1 to 6km in length. Different types of dykes are distinguished; acidic (granophyers, rhyolites, porphyritic rhyodacites and dacites), intermediate (andesites) and basic (dolerites and basalts). The relative ages assigned from relationship between dykes are given as follows: The acidic dykes were intruded first, followed eventually by two periods of a variety of dykes. Photogeological studies of the dyke lineaments showed that the studied area is affected by the following trends of dyke lineations; NNE, NE and NW directions. The N35˚W and N25˚E sets are the most dominant dyke trends, while the less dominant trends are E-W, N15˚W and N56˚W. The trends ENE and NW of dyke swarms are consistent with the main trends of dyke swarms in the Precambrian rocks of Egypt. The regional trends of dyke swarms are strongly consistent with the regional trends of fractures including faults and joints, i.e. dykes are structurally controlled. Radiometric measurements of dykes indicated that, the acidic dykes are relatively more enriched in eU (av. =22.3 ppm) than other types of dykes (av.=3.30 ppm) in intermediate dykes and (av.=2.10 ppm) in basic dykes. On the other hand, the acidic dykes contain most eTh contents. Their average content of eTh is 25.70 ppm whereas it is 8.94 ppm in intermediate dykes, and 4.10 ppm in basic ones. The eU contents in acidic dykes may be due to their accessory minerals (i.e. apatite, zircon and sphene).
The present study gives a trial to enhancement the management of Lake Nasser (LN) sediments and presents a demonstration of the sediments assessment process through focusing mainly on the sedimentological, minerlogical and radiometric characteristics of LN and the adjacent beach sediments. The study revealed that the increasing of sediments accumulation rate at LN cause many challenges and problems which change the morphological features and formation of the flood plains and inner islands. The occurrence of sediment accumulations and heavy mineral placers in LN onshore sediments is known but no systematic attempts has so far been made to management and explore these heavy minerals. The detailed mineralogical and γ-spectrometric studies for Lake Nasser sediments revealed that the grain size distribution in bottom samples dominant by sandy-silty clay in contrast of silty clayey sand and clayey silty sand in the eastern and western banks, respectively. Heavy fraction in the bottom sediments of LN and the adjacent beach indicates relatively low concentrations of the economic heavy minerals (magnetite, hematite, ilmenite, leucoxene, rutile, zircon, garnet and monazite) that varies between 0.61% and 1.22% for LN offshore sediments and ranged between 1.40% and 1.73% for the eastern beach samples where the western beach samples record 1.30% and 1.73%. It follows that their industrial exploitation is not economically profitable, in spite of previous exploratory studies in the survey zone. The radiometric analysis of all samples showed weak level of radioactivity. Lake Nasser bottom samples showed higher radiometric measurement relative to the adjacent beach samples. This may be attributed to the occurrence of monazite in the LN fine sediments that reach up to 0.0039% and also the presence of some metamict zircon. The proposed solution for lake sedimentation problems is to prevent eroded particles from entering the lake in the first place by mechanical dredgers. Utilization of economic minerals occurrence in LN can be facilitated by dredging mud into the lake banks. The mud fertility of the reclaimed landin the area. This process also stops sand dunes progression especially in the western bank. tween lat. 21.8 and 24.0° N and Long. 31.3 and 33.1°E, covering area of about 6,600 Km 2 with total storage of about 162 billion m 3 at water level 182 m (Avakyan and Iakovleva, 1998). It provided a water source of new populations (about 1.0 and 1.2 million people in Egypt and Sudan, respectively).
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