الفهرس 
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Abstract
Gabal Abu El-Hassan area is located between Lat. 26°50΄-27°00΄N and Long. 33°10΄-33°20΄E covering about 230 km2. The study area forms a mountainous region with rugged topographic features and high to moderate relief. The exposed Precambrian rocks generally form steep slopes against the wadis. There are three main peaks in the present area, Gabal Abu El Hassan in the south-east reaching about 1558m, Gabal Abu Samyuk in the north reaching 1572m and Gabal Abu El Hassan El Ahmer in the center reaching 1234m.
Gabal Abu El Hassan area is a part of the Egyptian Pan-African belt in the Central Eastern Desert. This area is composed of metavolcanics, serpentinites, gabbroic rocks, older granites, Dokhan volcanics, Hammamat sediments, younger granites and post granitic dykes. These rocks represent the essential rock units encountered in the study area. Field relationships showed that the granites form high elevation intrusions with clearly defined contacts. The geologic map of Gabal Abu El Hassan area shows distribution of the various rock types and their mutual field relations. Gabal Abu El Hassan is traversed by three main tributaries parallel to the major faults in the area. These tributaries drain at NE-SW to E-W direction. The southern one is Wadi Abu El Hassan, the northern, and the central are tributaries from the main wadi of Abu El Hassan. At the western side of the area, Wadi El Ghuzah is running NE - SW traversing Gabal Abu El Hassan and Gabal Abu Samyuk. The eastern side of the area is bounded by a wide plain which separates these mountains from the Red Sea Ranges from Esh El Mellahah Range.
Generally, Wadi Abu El Hassan basin occupies the basin 14 of the hydrographic units in the Eastern Desert (El-Shamy, 1988 and 1992). The basin of Wadi Abu El Hassan is of class III, which points to areas of moderate flooding probabilities and water potentialities as well. Wadi Abu El Hassan basin has a high average bifurcation ratio (7.9). This means that such basin has elongated shape that permits the passage of runoff over an extended period of time (low rate of runoff velocity), thus giving more chance for downward infiltration. The basin of Wadi Abu El Hassan possess a high number of drainage segments and consequently of high frequency values. Such conditions are favoured for surface water runoff, i.e., high rate of flow and discharge out of such basin. The basin of the study area shows high drainage density value indicating impermeable subsurface materials, sparse and/or rugged mountainous relief. These conditions favuor limited contribution of local rain fall to the groundwater. The drainage pattern in the area is southwards either to the east or to the west.
Investigating secondary dispersion of radioactive minerals in the stream sediments is considered as a tool for exploration of radioactive anomalies. The main objectives of this study are to construct a drainage map for the study area, to investigate the mineralogical composition of the stream sediments, to determine the uranium and thorium contents of the stream sediments, to compare between the mineralogical composition of stream sediments in different tributaries, to search for radioactive minerals and U-Th bearing minerals in different sizes of stream sediments, to investigate the sources of radioactivity among the different components of stream sediments, to investigate the possible roles of clay and organic matters contents in uranium adsorption and to investigate Gabal Abu El Hassan granitic rocks as a possible source rock for stream sediments.
Several analytical methods were incorporated in the present work including field work, sampling, grain size analyses, radiometric investigations using multichannel analyzer of γ-ray detector Bicron scintillation detector NaI (TI), mineralogical investigations using Heavy liquid separation, magnetic separation, microscopic investigations, X-Ray Diffraction, Environmental Scanning Electron Microscope (ESEM) and geochemical analysis using XRF technique and spectrophotometric determination of uranium and thorium. Computer software were used for data treatment and presentation including Minpet, SPSS and ArcMap.
A total number of 35 stream sediments samples were collected from the streambed sediments of three major tributaries of Gabal Abu El Hassan area. The samples were collected along the flow direction of the main wadis and near their intersection with the second order tributaries. The sampling interval was about 500m from holes having about 70cm diameter and about 50cm depth. Also, eight samples from Gabal Abu El Hassan granite were collected for characterizing this rock. The modal classification of younger granites of Gabal Abu El Hassan categorize the rock as monzogranite.
The resulted grain size distribution data showed that more than 80% of the studied samples lie in gravelly sand field and few samples are located in sandy gravel, and sand fields. The stream sediments were subjected to different mineralogical studies including heavy liquid separation, magnetic fractionation and microscopic studies in order to identify the heavy mineral contents of the sediments. About 11 minerals were identified and described including ilmenite, columbite, zircon, rutile, allanite, uranothorite, garnet, monazite, fluorite, apatite and titanite. The percentages of heavy fraction of the north tributary is higher than which in the two other tributaries. This may be explained by the presence of additional source of heavy minerals to this tributary and is likely to be the biotite granite rock unit which surrounding Gabal Abu El Hassan. This is consistent with the existence of higher amounts of some heavy mineral varieties such as uranothorite and columbite in northern tributary stream sediments than which present in the other two tributaries. from the relation between grain size and the recorded heavy minerals, it is concluded that most of the recorded heavy minerals were mainly concentrated in the 0.125- 0.063 mm size fraction.
The investigated heavy mineral fractions of the separated silt sizes revealed existence of the same heavy mineral assemblage of sand size including U-Th bearing heavy minerals namely, zircon, monazite and allanite. These minerals constitute the major source of radioactivity in the silt fractions of Gabal Abu El Hassan stream sediments. The zircon grain in the silt size fraction shows enrichment in Fe and Ca relative to zircon of the sand size fraction. The monazite grain of the silt size fraction shows enrichment in Th, Fe and Ca relative to monazite of the sand size fraction. Similarly, allanite of the silt size show relatively more REE contents.
Trace elements concentrations in the studied stream sediments are relatively enriched in Zr, Ba, Y, Nb, Zn V, Rb, U and Th. The enrichment of barium in the sediments suggests that the area is most probably affected by high intensive hydrothermal solutions. On the other hand, some base metals such as Cr, Ni and Cu are depleted in the concerned sediments, presumably due to the absence of the basic rocks in studied area. A remarkable depletion in Pb is also noticed and attributed to the lack of lead-bearing minerals.
Uranium contents in the stream sediments from the study area ranges between 4 and 28 with an average of 13.68 ppm, whereas Th contents ranges between 14 and 80 with an average of 46 ppm. The average Th/U ratio is 3.36 which is slightly lower than that of the upper continental crust of 3.8. This may indicates an insignificant mobility of uranium and also suggests that uranium and thorium are mainly accommodated in accessory mineral phases of the stream sediments.
Correlation matrix demonstrates significant binary relations between some trace elements. Rb has negative correlation with all trace and heavy metals since it exists mainly in feldspars, whereas heavy metals are accommodated mainly in accessory minerals. Rb also shows positive correlation with Sr reflecting their association in K-feldspars. Sr and Ba in the stream sediments from study area have correlation coefficient = +0.91. Heavy metals seem to have strong positive correlations with each other reflecting their association in different varieties of accessory minerals. For example, the strong positive correlations between Cr and Ni and between Y and Nb. The strong positive correlation between Zn and Pb reflects their existence in similar minerals probably sulfides and their alteration products.
Conversely, uranium and thorium have no significant relations with trace and heavy metals. This is a good indication that uranium and thorium are mainly present together in a radioactive accessory minerals such as uranothorite. On the other hand, the radioelements bearing minerals such as zircon, monazite and allanite play a minor role in this regards. The coherence between U and Th and the well known low mobility of thorium in secondary environment indicate that uranium is partially stable in the accessory minerals and not leached away.
Distribution maps for the trace elements Cu, Zn, Zr, Pb, Rb, Y, Sr, V and Nb suggest a general enrichment trend at the upstream of Wadi El Ghozah and the downstream of Wadi Abu El Hassan El Ahmar. Whereas, Ni and Cr present in the study stream sediment as a dispersed spotty concentrations increasing downstream of the three wadies.
Equivalent uranium of the southern tributary ranges from 2 to 9 with an average of 5.57 ppm, while in the central tributary it ranges from 2 to 10 with an average of 4.69 ppm. At the northern tributary the uranium content ranges from 2 to 15 with an average of 7.08 ppm. On the other hand, no significant change is noticed in radium contents in the three tributaries. It can be concluded that the northern tributary has the highest radioactivity compared to the central and southern tributary. Also, it is clear that the whole three tributaries show uranium enrichment reflecting a source of radioactive minerals from nearby granitic rocks of the area. There is a remarkable matching between mineralogical composition of stream sediments and their radioelements contents. The radioactivity of these sediments from northern tributary are higher than the two other tributaries which is consistent with the high percentage of heavy minerals fractions in this tributary and also occurrence of uranothorite as confirmed by SEM and EDX analyses.
The radioelement distribution maps demonstrate the concentrations of eU, eTh, and K in the sediments of the three tributaries. The distribution map of eU indicates higher values in the stream sediments of northern tributary compared to the central and southern tributaries. The northern tributary lies between two different granitic source rocks; namely, biotite granite to the north and Gabal Abu El Hassan monzogranite to the south. Conversely, the central tributary shows the lowest eU values, this tributary seems to have its sediments from Gabal Abu El Hassan monzogranite as a main source.
The distribution map of eTh is a further indication for the relative high radioactivity in the northern tributary. eTh values are higher in this tributary with average of 17.2 ppm. In central tributary, the average is 11.7 ppm, whereas in south tributary is 13.4 ppm.
This study suggests minor roles of clay and organic matters in uranium and thorium adsorption in the stream sediments of the study area, an expected situation in such an arid area with limited rainfall.
When this ratio is disturbed, it indicates either depletion or enrichment of uranium. The eU against eTh variation diagram of the studied stream sediment shows strong positive correlation indicating a coherence between the two elements. This result explains the low effects of alteration processes on eU, and suggests the existence of these radioelements in accessory minerals delivered from the nearby granitic rocks. This concept is supported by the strong negative correlation between eU and eTh/eU Fig. (VII.6.a).
when comparing the distribution of radioelements within the three tributaries it can be concluded that, biotite granite has a higher contribution for uranium and thorium enrichment in the stream sediments of the study area compared to Gabal Abu El Hassan monzogranite. Therefore, it is recommended to perform a detailed ground radiometric study for the biotite granite.