الفهرس 
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Abstract
The present study deals with thorium mineralization and its relation to uranium migration in some localities, south western Sinai, Egypt. Three areas were selected for this purpose namely Khaboba, Ras Milan and Sharm El Sheikh.
Khaboba area is delineated by the following co-ordinates; Longitudes 33˚14’ 30” - 33˚ 45’ 00”E and Latitudes 28˚ 50’00” - 29˚ 3’ 20” N.
Ras Milan area lies between latitudes 27o 57’ 15” – 28o 00’ N and longitude 33o 55’ 34” E.
Sharm El Sheikh studied area lies between latitudes 27o 47’ 00’’ - 28o 05’ 00” N and longitudes 34o 08’ 44” E.
The field observations and the petrographical investigations declare the following:
Khaboba area is covered by metamorphic rocks, basal conglomerate and Sarabit El Khadim Formation.
The metamorphic rocks are represented by biotite schist. It is the oldest rock unit in the studied area characterized by its grey to dark grey color and well-developed schistosity. Petrographically, it is composed essentially of quartz, biotite and iron oxides.
The basal conglomerate unit rests directly on the weathered biotite schist. It ranges in thickness from10 to 120cm. It is not continually outcrops all over the study area. It is composed of rounded to sub-angular quartz particles, quartz grains with fragments of igneous rocks. Petrographically, it is composed of
sub-rounded to sub-angular quartz grains (70 %), K-feldspars with biotite and muscovite inclusions and lithic fragments of igneous rocks.
Sarabit El-Khadim Formation is of Cambro-Ordovician age and formed essentially of alternating sandstone and siltstone. It attains considerable thickness about 10 meters. Petrographically it is described as greywacke and composed essentially of badly sorted sand-sized quartz grains.
Ras Milan area is covered by highly weathered alkaline granites, basal conglomerates. Araba and Naqus Formations unconformably overlie the basement rocks.
Alkaline granites are fractured and jointed as a result of faults movements. Petrographically, it is composed mainly of quartz, potash feldspars, plagioclases, riebeckite and biotite with zircon and opaques as accessories minerals.
Basal conglomerate rests on the granitic rocks. It has thickness ranging from 20 up to 70 cm with discontinuous extension. It is made up of Chert, qz pebbles and sand sized grains embedded in kaolinitic matrix. and highly affected by solutions. Petrographically, it is composed mainly of chert, quartz pebbles (Polly crystalline quartz), granules and sand size grains embedded in kaolinitic matrix.
The Nubian clastics are mainly Cambro-Ordovician sandstones of Araba and Naqus Formations. Petrographically; the studied sandstones of Araba Formation are composed mainly of quartz
arenites (quartz up to 92.8%) and sublithic quartz arenite (quartz up to 64%). Naqus Formation is composed
of subrounded grains of quartz (about 200 micron), well sorted, and cemented by iron oxides. The pores are filled by clay minerals, gypsum, iron oxides and debris.
Sharm El Sheikh area:
Based on the field observations and petrographical investigations, younger granites cover the most part of the studied area and represented by syenogranite. Under the microscope the main framework contains essential minerals as potash feldspar, plagioclases, quartz, biotite and hornblende. Apatite and zircon are the accessories.
The aplites occur as dykes associated with the syenogranite and always possess sharp contacts with their hosts. Petrographically, these rocks are composed of potash feldspar, quartz, plagioclases, riebeckite and arfvedsonite as essential minerals. Zircon is the main accessory mineral.
The geochemical studies:
The results of chemical analyses for granitic rocks in the three localities revealed the following:
According to De La Roche et al. (1980), samples of alkaline granites collected from Ras Milan and those collected from aplite dyke are plotted within the alkaline field while younger granite samples collected from Sharm Elsheikh are located within the syenogranite field.
The alkaline granite rocks have per-alkaline affinities with alkaline suites and they are of truly anorogenic rifting tectonic environment.
The aplite rocks have per-alkaline affinities with alkaline suites and they are of post-orogenic tectonic environment.
The syenogranite rocks have calc-alkaline affinities with metaluminous to peraluminous suites and they are of syn-collision tectonic environment.
The radiometric studies:
In Khaboba area, according to the ground survey; the biotite schist and the Sarabit El Khadim Formation exhibit normal level of radioactivity while the highest values are recorded in the basal conglomerate especially Th (1100 ppm) and uranium ( 22 ppm).
Radioactive equilibrium-disequilibrium state for the different rock units using (Uc/eU) in Khaboba area is summarized as following:
Biotite schist and Sandstone show positive disequilibrium; It means uranium is enriched in these rocks, while Conglomerate shows negative disequilibrium; It means uranium is removed from the rock.
In Ras Milan area, The ground survey of uranium and thorium indicate that the highest anomalies are related to the basal conglomerate with (eU up to 38 ppm) and (eTh up to 1700 ppm).
Radioactive equilibrium-disequilibrium state for the different rock units in Ras Milan area revealed that alkaline granites and Conglomerate show negative disequilibrium with Uc/eU less than 1; It means uranium is removed from these rocks, while
Sandstone shows positive disequilibrium with Uc/eU value more than 1. It means uranium is enriched in the rock.
In Sharm El Sheikh area, the radiometric ground survey reveals that the highest uranium and thorium concentrations are associated with aplite dykes with (eU up to15.6 ppm) and (eTh up to52.5 ppm).
Radioactive equilibrium-disequilibrium state for the different rock units show positive disequilibrium in both syenogranite and aplites with Uc/eU value more than 1. It means uranium is enriched in these rocks
Mineralogical studies:
The mineralogical studies of the anomalous representative samples of the separated heavy fractions indicated that the high radioactivity is due to the presence of thorium minerals as well as heavy minerals as cassiterite and iron oxides and associated with zircon, monazite, xenotime, rutile and barite.
Based on the binocular microscope investigations and Scanning Electron microscope examinations as well as X-ray diffraction analyses, these thorium-uranium minerals are mainly thorite (Th,U)SiO4 and thorianite (Th,U)O2.
In Khaboba area; thorite, thorianite, hematite, metamict zircon, monazite associated with zircon and rutile are well defined, while in Ras Milan area; thorite, cassiterite, hematite, less radioactive zircon, xenotime, monazite and barite are the main separated minerals and in Sharm Elsheikh area; ilmenite and zircon were recognized.