الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
Abstract
The present thesis aims to study the geology, petrography, mineralogy, geochemistry and radioactivity of the study area. The results will be used to shed light on the radioelements distribution with special emphasize on the study of uranium potentiality in the Late Carboniferous rock units in the study area. The results based on the integration of various surface and subsurface geologic data in order to define the anomalous radiospectrometric zones in the study area, their distributions and their relations with lithology and structure.
The area under investigation occupies a part of the northeastern side of Wadi Araba at the intersection between Wadi Rod El-Bir in the eastern side and Wadi Abu Murakh in the western side. This area covers about 20.64 km2 and characterized by plain to mild topography. The plain part of the study area is dissected form eastern side by Wadi Rod El-Bir and from the western side by Wadi Abu Murakh. The top of these topographic features often flat and mostly formed of fragmented dolomitic limestone.
The Carboniferous-Permian succession in the study area is representative by upper Rod El Hamal Formation (Late Carboniferous) and Qiseib Formation (Permian-Triassic). The basal contact of upper Rod El Hamal Formation is unexposed while its upper contact of this formation is overlain by unconformity produced from the incomplete erosion of the Carboniferous-Permian or Permian-Triassic red beds of the Qiseib Formation beds.
The present work deals with the top member “V” (C – 5) of Rod El-Hamal Formation and Qiseib Formation. The studied rock units are composed of five major rock units (sandstone and shale intercalating with
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siltstone and marl and covered by dolomitic limestone), exhibiting different lithologic criteria and fossil contents. In addition, the depositional environments of the studied formations are exhibiting gradual facies progress from fluvial to shallow marine environment. The member “V” of Rod El Hamal Formation is subdivided into lower, middle and upper units depending on field observations. In addition, Qiseib Formation is subdivided into lower and upper members. The member “V” of Rod El Hamal Formation (~ 89m thick) is essentially composed of arenaceous and argillaceous rocks with some limestone horizons and microfaunal content. The lower unit (~25.5m thick) consists mainly of sandstone associated with iron oxides. It exposed in the southern side of the study area at Block II (sections B and B`) and Block III. The middle unit (~44m thick) consists mainly of argillaceous and arenaceous rocks with some carbonate. The argillaceous rocks of this unit are mainly represented by shale (47%) and marl (4%). The arenaceous rocks of this unit are mainly represented by sandstone (44%) and siltstone (4%). The carbonate is represented by dolomitic limestone (1%). Iron oxides are noticed in these rock units. The upper unit (~19.5m thick) consists of arenaceous and argillaceous rocks. The arenaceous rocks of this unit are mainly represented by sandstone (73%). The argillaceous sediments are represented by shale (27%). Iron oxides are noticed in some shale and sandstone.
Qiseib Formation consists of alternating sandstone, silt and dark shale which overlies the Rod El-Hamal Formation and located at the downthrown sides of some normal faults. It represented by some small
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ridges with an average thickness about 21m in the western side of the study area (sections D and J) and in eastern side is about 29 m (section I). The lower member of Qiseib Formation (~14.5m thick) consists mainly of arenaceous rocks intercalated with some argillaceous rocks. The arenaceous rocks are mainly represented by sandstone (87%) and siltstone (2%). The argillaceous rocks are represented by marl (6%) and claystone (5%). Iron oxides are noticed in some claystone, siltstone and sandstone of this lower member. The upper member of Qiseib Formation (~27m thick) consists of arenaceous and argillaceous rocks covered by thin beds of fragmented dolomitic limestone. The arenaceous rocks are represented by sandstone (44%) and siltstone (13%). The argillaceous rocks are represented by claystone (38%) and marl (5%). Iron oxides are noticed in some claystone, siltstone and sandstone. The microfacies analysis of the member “V” of Rod El Hamal Formation and Qiseib Formation in the area revealed the presence of six lithofacies types which indicate that these rocks were deposited under alluvial to shallow marine environments. These lithofacies include lithofacies A (pebbly sandstone) and lithofacies B (massive sandstone), lithofacies C (cross-bedded sandstone), lithofacies D (laminated sandstone), lithofacies E (siltstone) and lithofacies F (shale and claystone). The study area is characterized by strong forms of structures and was subjected to more than one tectonic event. Paleozoic rocks in the study area display high fracture density and affected by faults, joints of different trends, minor anticlines and synclines folds. Main faults have NNE-SSW (Gulf of Aqaba trend), E-W (Tythian trend) and ENE-WSW (Wadi Araba fold axis and regional Syrian Arc anticline structure) trends.
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The structural forms exhibited by the different exposed lithological rock units are primary (bedding, lamination, fissilility, ripple marks and cross-bedding) and secondary (faults, joints, dykes and folds) types. The obtained data from structural analyses showed that the measured bedding in the study area is found to be following ENE-SSW and E-W which dips from 26º WNW and 23º N, respectively. The bedding strike of the Blocks in the study area followed a clockwise direction when move towards the north. The Blocks have steep slopes when seen from east, south and west directions while it shows gently northward margins. Laminations are common in the study area especially in mudstone, siltstone and sandstone that usually result of slow steady deposition. Fissility is commonly observed in various shale outcrops in the study area. Ripple marks (climbing current ripple and ripple cross-lamination) detected in the study area. Cross-bedding is common in sandstone where bioturbation is slight, the thickness of cross-bed sets range from centimeters to several meters. Most of the recorded faults are of the normal and/or strike-slip type. They show pronounced, displacement and well-developed slickensides on their walls. The faults are trending essentially in the NNE-SSW, E-W, ENE-WSW and NE-SW directions. Some of fault zones occupied by sandstone dykes. The common ENE-WSW trend runs conformable with the Wadi Araba trend. NW-SE and NNE-SSW fault trends are considered younger than NE-SW, NNW-SSE, WNW-ESE and E-W fault sets.
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Some wadis are structurally controlled by fault trending as NE-SW trend. Other fault systems such as N-S, ENE-WSW and E-W have no effect on wadi courses. Folding is one of the main secondary distinct structural elements observed in the studied rock units. It is quite clear in minor scale at some exposures. The attitudes of beds show several direction of bedding which is mainly indicated to be folded toward ENE-WSW axis and dipping toward NNW and SSE which is in hormony with major Wadi Araba anticline fold. There are two fundamental types of joints; tension and shear ones. Some other types of joints may be intimately related to faulting, such as feather joints, or other pinnate fractures. The most joints trend in the E-W, WNW-ESE, NNW-SSE and N-S directions. Mineralized joints filled with
silica, epidot and iron oxide follow NNE-SSW and WNW-ESE directions. A comparing the main trends direction and the intensity of fault sets revealed that Wadi lines and joint sets show good statistical matching in some trends and no obvious relations in other. The non-obvious relation between faults and joints belongs to ENE-WSW, WNW-ESE and E-W trends and wadi courses. NNE-SSW, NE-SW trends have smaller length in proportion to the corresponding wadis. N-S, NW-SE and NNW-SSE have nearly comparable to greater length in proportion to the corresponding wadis. The composition of the studied samples was determined by using a polarizing microscope and thin sections. The investigated samples in member “V” of Rod El Hamal Formation are sandstone, shale, siltstone, marl and dolomitic limestone.
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The main framework of the sandstone are composed of quartz grains and subordinate lithic fragements (represented by chert, carbonates and claystones) set in a fine matrix of the same constituents in addition to secondary recrystallized gypsum and carbonate. The matrix is mainly composed of clay minerals and iron oxides with subordinate amounts of quartz, micas, epidote and chlorite. Iron oxides either disseminated all over the rock in irregular shaped or filled the cracks. This sandstone is mainly classified as quartz arenite and quartz wacke. Quartz grains of this sandstone were derived mainly from plutonic igneous rocks and/or high-grade metamorphic rocks because they show undulatory extinction. Some quartz grains were derived from volcanic rock sources or they recycled from older sandstone because they show unit extinction. Many quartz grains show silica overgrowths indicate that this sandstone were recycled from sedimentary rocks. The absence of feldspar in this sandstone may be related to climate and topography of the source area. This means that chemical weathering was extensive, probably because of climate and/or low relief of the source rocks. Therefore, feldspar grains have been partially altered to clays and fine muscovite mica (sericite), giving it a dirty, mottled appearance. By contrast, the quartz grains in the same slide are clear and unaltered. Most of this sandstone grains are rounded to subrouned which may be related to intense abrasion of the grains during wind transportation or during the back and forth motion of the grains along shorelines. Multiple cycles of uplift, erosion and deposition, each are accompanied by a modest gain in grain roundness.
Sandstone fabric is either randomly distributed (isotropic) or oriented (parallel alignment of elongate or disk-shaped grains). Oriented
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fabric indicates that sand grains were deposited by strong, directionally constant currents. The long axes of fluvial sand grains are commonly aligned parallel to the direction of current flow. Sandstone is texturally immature or submature. Immature sandstone is particularly characteristic of alluvial fans, turbidite sands, and fluvial overbank sands. Submature sandstone deposited in a various environments and particularly common in fluvial channels and turbidites. Shale is sandy, slightly calcareous and ferruginous. This indicates that marine environment influenced the flood plain. Sand sized fraction in shale is almost entirely quartzose. The cements in shale are made up mainly of iron oxides and minor calcite. Iron oxide is either concentrated in irregular patches or along layers parallel to the bedding. Secondary idiomorphic gypsum crystals are commonly observed in the upper unit. Siltstone is slightly or moderately sandy, calcareous, ferruginous and gypseous, which indicates a tidal flat sedimentation. The cements in siltstones are made up of iron oxides, calcite and, rarely, cryptocrystalline silica. Iron oxides are remarkably present as patches, globules or laminations. Calcitic cements are more common where they occasionally corrode the quartz grains at their peripheries. Secondary gypsum crystals were observed in the rock groundmass. Marl is moderately calcareous, ferruginous and gypseous which, indicates tidal flat sedimentation. The cements in marl made up of iron oxides, calcite and cryptocrystalline silica. Iron oxides in marl are present in the form of patches or laminations.
Dolomitic limestone is less commonly recorded in the upper beds of middle and upper units. It is argillaceous, ferruginous, fossiliferous, rarely sandy and represented by packstone and grainestone. Some of the fossil shells are filled by recrystallized calcite while the other are leached
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producing moldic porosity. These are occasionally lined with cryptocrystalline silica or iron oxides. Silica in the dolomitic limestone is usually observed replacing the shell fragments, filling the fossil cavities and/or replacing some parts of the matrix. Iron oxide is dominant as irregular patches or concentrated along layers parallel to the bedding. The microfacies analysis of member “V” of Rod El Hamal Formation indicates the presence of different types of carbonate fossils that played an important role in iron oxide precipitation and rock diagensis. X-ray diffraction analysis (XRD) illustrate that the common non radioactive minerals present in the studied samples are (in descending order) bavenite, analcime, joesmithite, quartz, sanidine-high, anhydrite, dolomite and some halite, chalcothallite, goethite, kaolinite, brushite, sazhinite-(La), umangite, jerrygibbsite, majorite and bustamite. The main identified radioactive mineral in the studied samples is demesmaekerite although some widenmannite and carlosbarbosaite are rarely present. Some of these minerals are associated with other and more or less mixed with quartz and other silicate minerals. The non-radioactive minerals recorded by SEM are grossular, sekaninaite, kumtyubeite and titanium meanwhile the radioactive minerals are represented by nioboaeschynite-(Y), zircon, zirconolite-3O and kasolite.
The chemical analysis of the low radioactive samples (LRS) and moderately radioactive samples (MRS) in the study area indicate that they are mainly altered and suffered from many stages of diagenesis. These samples are characterized by a wide variation in their composition with major elements. The chemical data do not show great difference between the mean compositions of the sandstone and shale. This fact reflects that
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both rock types having a common source and suffered from variable energy depositional agents. Shale is characterized by the dominance of SiO2 and this could be attributed to their silty/sandy nature. The studied samples are characterized by marked dominance of kaolinite and rarity of illite, K-feldspars and micas. Fe2O3 and TiO2 in LRS is low as compared with the corresponding values reported for MRS. This result may be related to the presence of detrital rutile and ilmenite in MRS which were mechanically transported and brought later to the site of deposition. The studied samples contain low concentrations of MgO, K2O, Na2O and that related to their high mobility during weathering processes. The relatively higher values of CaO may relate to secondary calcitization processes after weathering processes. The studied LRS affected by secondary calcitization more than MRS. Cr, Ni and V are mutually fractionated during weathering. The means of these elements in MRS are higher than those reported for LRS. Accordingly, it is believed that Cr, Ni and V were variably concentrated by weathering processes. Ba is mainly associated with Fe-oxides, especially in LMS and it hosted in kaolinite rather than in illite. MRS are enriched by Zr, Y and Nb relative to LRS, these indicate that MRS are enriched in felsic rocks relative LRS. The geochemical classifications revealed that most of the studied samples are mostly plotted around wacke and some around quartz arenite and lithicarenite.
The normalized pattern for the studied samples indicates that the content of SiO2, Al2O3 and Ga in source rocks did not change during weathering, diagenesis and mineralization. TiO2, K2O, Na2O, P2O5, Cr,
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Ni, Cu, Zr, Rb, Y, Ba, Sr, V, and Nb are more enriched in MRS relative to the LRS. In addition, the calcitiaztion and dolomitization are the main causes of decreasing the radiometric mineralization in the rocks of the study area. The recorded CIA values for the studied samples suggested that the source rocks were mainly having feldspars and/or mafic minerals and subjected to moderately chemical weathering. In addition, the proportions of clay minerales to primary plagioclases increase with increasing chemical weathering. The studied samples are generally slightly enriched in immobile elements, such as Al and Ti, because these elements can survive throughout intensive chemical weathering and diagenesis. The studied samples revealed that they were inherited mainly from predominately granitic to mixed basaltic granitic rocks and plotted in both the arid and semiarid climate fields. Values of the index of compositional variation show that the studied samples are considered to be moderately mature to immature and are products of moderately chemical weathering. Ba, Al2O3, TiO2 and CaO contents in the studied samples suggest accumulation in marine-water environment. On the other, the recorded values for Ga, Rb, Zr, Cr, Ni, MgO and Fe2O3 are in accordance with fresh-water deposition. In addition, the relation between K2O/Al2O3 and MgO/Al2O3 revealed that most of the studied samples plotted in the marine-water field and some in non-marine water field. This may indicated that these sediments were deposited under marine conditions followed by fresh water. The low concentrations of the trace elements Ni and Cr can be attributed to the abundance of felsic components in the source area and the moderately chemical weathering of felsic and intermediate igneous.
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The investigated samples seem to be related to oceanic island arc provenance and active continental margin. It can be believed that a part of the area was formed under humid conditions during the early part of Carboniferous period while the rest originated under semiarid conditions after the uplifting and changing in climate during the later part of Carboniferous period. The geo-accumulation indices revealed that the environment is moderately-polluted with respect to Zr and Nb, moderately to strongly polluted with respect to Y and strongly to very strongly polluted with respect to Pb. The concentrations of the major and trace elements in the investigated samples have been normalized to the mean values of the Upper Continental Crust (UCC). These results indicate that the presence of relatively high mobility and strong leaching during weathering processes. The range and mean of the total gamma ray activity and radioelements concentrations in the Rod El Hamal Formation are higher than those of Qisieb Formation. Several radiometric anomalies have been recorded for the first time in Rod El Hamal Formation especially in shale, siltstone, marl and sandstone. The mean of the total radioactivity of these anomalies ranges between 37 to 76 ppm. The measured values of the total gamma ray activity, 238U, 232Th, and 40K through marl, shale and siltstone are generally higher than the sandstone and dolomite limestone.
The field measurements revealed that the thorium display higher values than the uranium values (reach up thirteen times). This fact indicates that uranium were leached from the studied rock samples. This variable distribution may be related to the high mobility of uranium
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relative to thorium during transportation and deposition of the host rocks. In addition, the thorium has more uniform dispersion value than uranium. This means that thorium is more stable than uranium under the prevailing physicochemical controls. So the measurement of the subsurface radioactivity (especially uranium) was carried out along the Wadis between Blocks. The studied rocks that display high radioactivity are characterized by strong alterations (hematitiztion, kaolinitization and some manganese dendrites). The distribution of uranium and thorium mineralization is mainly confined to the altered shale and siltstone with scarce cases in marl and sandstone. The activity ratio of 232Th/238U in MRS indicates that the two elements are slightly accompanied each other in the different rock types. This means that the sandstone, siltstone, marl and shale in MRS were subjected to intense alterations due to thorium migration-in. The correlation between radioelements indicates that individual results for any one of the radionuclide concentrations in each pair are a good predictor for the individual values of the other. The behavior of 238U and 232Th with the major and trace elements indicate a heterogenerous distribution of these elements in the studied samples. The relation between 238U and 40K with most trace elements in LRS indicates a homogeneous distribution. The relation between thorium with most trace elements in MRS indicates a homogeneous distribution. The variation of uranium versus thorium in LRS shows relatively very weak correlation that could be originated from the high mobility of U relative to Th. In the MRS the relation between uranium versus thorium increases, which indicates that the high enrichment of U and the remarkable increase of Th could be attributed to hydrothermal processes.
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The relation between uranium versus Th/U in the LRS and MRS indicates that uranium has been redistributed within the studied MRS relative to LRS, while thorium remained relatively fixed. The normalized pattern for the studied samples indicate that eU content of this element in the source rocks did not show more change during the weathering, diagenesis and mineralization. K % is moderately enriched in MRS relative to LRS. In addition, the enrichment factor of eTh is the highest among the other radioactive elements and it is the most enriched in the studied MRS. The radioelements in the studied sample has been freshly (recently) deposited, hence the level of radioactivity is lower than would be expected for the amount of radioelements present. Therefore, it is clear to mention that the state of positive disequilibrium dominates in the rocks of the study area. Surface spectrometric contour maps show the presence of one main radiometric anomaly, nearly in the north central part of the selected area. The surface spectrometric contour maps for total γ-ray intensity and (eTh) show clear correspondence. This fact indicates that thorium are mainly responsible for the high radioactivity spots in the study area and the enrichment of eTh is the highest among the other radioactive elements. The spectrometric contour map for eU/eTh ratio displays concentration of uranium in the northern part of the selected study area. High values of radon concentrations occur in three main fields in the selected area. These fields indicate the presence of three parts of the subsurface radioactive anomaly in the area, which are structurally controlled. The dimension of the subsurface radioactive anomalies can be calculated directly from radon concentrations-topographic map (NW-SE direction).
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Comparing the surface spectrometric contour maps and concentration map of radon show anomalies in subsurface at some stations. These high subsurface measurements in radon concentrations did not show any reflection at surface. This fact refers to the presence of subsurface radioactive sources that mainly reflect the presence of subsurface radioactive mineralization. The track density in cylindrical chamber is decreased by increasing the height of the detector from the bottom of the cylindrical chamber. This indicates that, the diffusion of radon changed with the height of the detectors in the chamber. The radon concentration in the detector within the cylindrical chamber explains the presence of three expected sources of radium in this location. The relation between radon concentration and the height of the detector (CR-39) in the cylindrical chamber revealed the presence of expected sources of radium at depth 22.59m (exploratory drilling is proposed in this site), the flux density for soil =467.8 x 10-6 and the flux density for air =46.78 x 10-6. Type of the bedrocks, prospect source minerals of radon, structural elements and radioelements distribution were the main mechanisms responsible for the strong radon surface anomalies over deep sources