الفهرس 
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Abstract
Mining activities generally cause a disturbance, redistribution of elements in the nearby area and an elevation in the levels of toxic pollutants. The present study is mainly concerned with petrography, mineralogy, geochemistry, environmental and health risk assessment of phosphorites as well as mining processes’ impact on the nearby wadis. These mines are the Beida, Wadi Qweih, Hamadat, Yunis and Nakheil. The study area is located in the central part of the Eastern Desert on the western side of the Red Sea where it is usually enriched mainly by phosphate mining work activities.
Ninety-four samples were collected from five mines in Quseir area which include fifty phosphate samples, twenty-eight samples of stream sediments and sixteen samples of phosphate dust. Phosphate samples were investigated using petrographical, mineralogical, geochemical and radioactive techniques, while stream sediments and phosphate dust were assessed environmentally to evaluate mining processes’ hazards.
The exposed sedimentary succession in the study area is differentiated into seven rock units; Tarif Formation, Quseir Variegated Shale, Duwi Formation, Dakhla Shale, Tarawan Chalk, Esna Shale and Thebes Formation. The Duwi (Phosphate) Formation contains several phosphatic horizons intercalated with banded shale, chert, limestone and siliceous limestone. The study area is bounded by basement rocks on the northern and western sides and by the Quaternary and Neogene deposits on the eastern side to the coastal boundary of the Red Sea.
Petrographically, ten phosphatic thin sections resulted in the recognition of the following major microfacies associations: molluscal bioclastic phosphatic grainstone and biopeloidal phosphatic grainstone are recorded in the Beida phosphorites. Siliceous phosphatic bioclastic grainstone is recorded in Wadi Qweih phosphorites. Dolomitic phosphatic bioclastic grainstone is recorded in Hamadat phosphorites. Ferrugineous bioclastic phosphatic packstone is recorded in Yunis phosphorites, and in Nakheil phosphorites ferrugineous bioclastic phosphatic grainstone is recorded.
The petrographic examination of the thin sections revealed the presence of marine vertebrates, suggesting a high-energy near-shore depositional environment and deposited in suboxic, protected-shallow basins with moderate water circulation. The peloidal phosphates including pristine and reworked pellets were formed authigenically in oxic to suboxic zones, from phosphate-rich sediments, followed by storm wave winnowing and storm-generated, shelf-parallel geostrophic currents and minor compaction. High rates of supersaturation in the pore water in the suboxic zone led to the rapid precipitation of carbonate fluorapatite (francolite), which was confirmed by XRD analysis, via an amorphous metastable precursor, which is transformed into a stable apatite by involving the uptake of fluoride from the seawater. The pristine phosphogenesis province prefers to occur near the margin of the shelf and is potentially dominated by upwelling. The existence of oysters indicates shallow marine influences and represents submarine carbonate skeletal shoals typically forming in a restricted shallow subtidal regime and suggested that these oyster banks developed in more distal environments and prograded landward during continued sea-level rise through the impact of onshore-directed storms and fair-weather waves. The progradation of oyster buildups developed behind the distal banks in shallower environments. The existence of dolomite may indicate that it is late diagenetic in origin. The Mg2+ may be leached from the overlying shales by the meteoric water and penetrated the phosphatic deposits where the dolomite is crystallized. The presence of detrital quartz indicates a high-energy near-shore depositional environment. The presence of isopachous cement fringes indicates phreatic precipitation.
The investigated minerals from X-ray diffraction analysis are classified into phosphatic minerals and non-phosphatic minerals. The detected phosphatic minerals are dahlite, francolite and hydroxylapatite, while the non-phosphatic minerals are quartz, calcite, anhydrite, gypsum, halite, ankerite, kaolinite, dolomite and pyrite. Francolite represents the main apatite minerals in peloids, whereas dahlite is the substance that provides the mineral content of organically-formed bones and teeth, which was confirmed by petrographical studies. The existence of francolite and dahlite in the Beida mine is confirmed by SEM analysis that shows the dominance of peloids and bone fragments. The presence of pyrite in Wadi Qweih and Yunis mines indicates the increasingly abundant source of iron-bound phosphate associated with terrigenous sediment input to the near-shore depositional environment along the eastern side of the study area. The existence of kaolinite only in Nakheil phosphorites in the X-ray diffraction pattern was affirmed using SEM analysis that shows kaolinite with its prominent booklet shape indicating a source region that experienced intense weathering under possibly tropical conditions where increasing rainfall favored ionic transfer and pedogenic development of kaolinite.
Geochemically, the phosphorites are analyzed for the following major oxides: SiO2, Al2O3, CaO, MgO, P2O5, Fe2O3, Na2O, K2O, F, Cl, SO3 and L.O.I., trace elements: As, Ba, Cd, Co, Cr, Cu, Mn, Ni, Pb, Rb, Sr, Ti, V, Y, Zn and Zr and rare earth elements: La, Th and U. P2O5 concentration in the phosphorites of the five mines is considered an indicator of reducing environment with organic matter or the presence of phosphate minerals as shown in the diffraction analysis. The phosphorites in the Beida and Wadi Qweih mines are medium-grade ore and in Hamadat, Yunis and Nakheil mines are high-grade ore. The moderate trend of the CaO/P2O5 indicates the contribution of phosphate is due to precipitation and not by detrital input. P2O5 exhibits a negative correlation with the terrestrial components (SiO2, Al2O3 and Ti) indicating that these phosphorites are mainly precipitated from the seawater rather than derived from detrital terrestrial input. The significant positive correlation between P2O5 and U in the different mines is attributed to the substitution of U for Ca in the apatite structure, and U may be accommodated in the carbonaceous matter associated with phosphate. Also, the significant positive correlation between P2O5 and F is due to the precipitation of the phosphorus and fluorine at the same pH of 7-7.8 and the F substitutes PO4 in the crystal lattice of apatite and forms the francolite. Moreover, the low concentrations of fluorine may be attributed to the substitution of F by CO32- where the highly carbonate deposits were supported by X-ray diffraction through the presence of ankerite mineral in the Beida and Hamadat mines. The positive correlations between P2O5 and Cr, V and As suggest their association with the francolite structure. Whereas the negative correlation between P2O5 and Cd indicates a common substitution in the francolite structure. The high values of CaO may be due to the presence of phosphate minerals and calcareous material, that were presented in the petrographical studies as micrite matrix material and sparite cement. The positive correlation between P2O5 and Fe2O3 in Yunis and Nakheil mines is confirmed by the petrographical studies, which revealed the presence of iron oxides staining and patches. The significant positive and positive correlations between Na2O and Cl are confirmed by X-ray diffraction, where halite was detected and may be attributed to the presence of Na in carbonate fluorapatite due to the substitution process between Ca and Na in apatite.
The positive correlation between P2O5, Ba and Sr in phosphorites rather than with CaO suggests that Ba and Sr are associated within the apatite structure. The high Sr/Ba values in the different mines reflect their genesis by normal marine sedimentation. According to redox-sensitive elements, the moderate to high V and Cr contents of the studied phosphorites are probably due to their formation under oxic marine conditions. The average ratios of V/Cr of the studied phosphorites indicated that the deposition took place under oxic conditions in the Beida, Wadi Qweih, Hamadat and Yunis mines, while the phosphorites of Nakheil mine were deposited under suboxic conditions. V/Ni values indicate that the phosphorites of the Beida, Wadi Qweih and Yunis mines were deposited under suboxic conditions, while Hamadat and Nakheil phosphorites were deposited under anoxic conditions. Overall, the V/Ni ratio in the phosphatic samples for the study region indicated that these phosphatic rocks were deposited in a reducing environment. V/(V+Ni) and V/(V+Cr) ratios of phosphorites in the different mines indicated strongly reducing conditions of the depositional environment. Low concentrations of Rb and Ti may be attributed to being excluded from apatites. The high concentrations of Y in all phosphorites have been attributed to the activity of organic matters, which are derived from marine plankton and resulted from enhanced uptake from seawater and/or pore-water during redox cycling and diagenesis. The positive correlation between P2O5 and Zn in the Beida, Wadi Qweih and Nakheil mines is attributed to its attraction to the apatite mineral assemblage, which is typical of the organic matter commonly associated with marine phosphorites. Zr is recorded in low concentrations, which confirms the low detrital inputs during the phosphorite deposition.
La demonstrates a positive correlation with P2O5 in the Beida, Wadi Qweih, Yunis and Nakheil mines and a weak negative correlation in Hamadat mine, which reveals the adsorption mechanism of REE to the apatite lattice. The low Th content reflects very little, if any, detrital input during phosphorite formation. The high positive correlation between U and P2O5 indicated the important role of phosphate in the fixation of U6+ as uranyl ion (UO2)2+. Thus, the secondary uranium minerals such as phosphuranylite {Ca (UO2) (PO4)2(OH)2 6H2O} may be precipitated. The relatively elevated U/Th ratio in the different mines confirms a very little detrital input during phosphorite formation due to low Th content. Regarding the geochemistry of the Mardin-Mazidag Phosphate deposit based on P2O5 - U - F interrelations, the values of the studied phosphorites in the five mines are higher in Um values than Ucalc, which indicates the post-depositional enrichment of uranium. The D-factor (Uc/eU) ratio in the different mines used in determining the equilibrium state of the phosphorites under study showed that all samples contained more chemically analyzed Uc than radiometrically equivalent 238U, which reflected the non-equilibrium state characterized by the addition of 238U in the study area.
Environmentally, stream sediments of the selected three wadis were used for grain size analysis to investigate the physico-chemical properties and obtain the relation between the analyzed heavy metals and these parameters. The pollution indices used in this research are Enrichment Factor (EF), Geo-accumulation (Igeo), Improved Nemerow’s Pollution Index (Pn), Pollution Load Index (PLI) and Potential Ecological Risk Index (PERI). Obvious accumulation of stream sediments PTEs was detected in three wadis in the Beida, Qift-Quseir road and Wadi Qweih. EF values in the three wadis show extremely high, very high and significant enrichment for As and Cd, while it shows moderate enrichment, no enrichment and rare significant enrichment for other metals. Igeo values for As exhibit moderately contaminated and moderately to heavily contaminated sediments in the three wadis, while values for Cd show a wide range of contamination from moderately contaminated, moderately to heavily contaminated, heavily contaminated and heavily to extremely contaminated sediments. Other metals values indicated uncontaminated to moderately contaminated sediments, except for Cr which recorded moderately contaminated sediments in some samples. Pn values in the Beida and Wadi Qweih stream sediments indicated extremely contaminated sediments for all samples, while in Qift-Quseir road Pn values exhibit variable classes ranging between moderately contaminated, moderately to heavily contaminated, heavily contaminated and heavily to extremely contaminated sediments. PLI values for the three wadis samples indicated a range of contamination from moderately polluted to strongly polluted where Cd and As demonstrate the great contribution in these values. PERI values demonstrate very high ecological risk levels in the Beida and Wadi Qweih sediments, while in Qift-Quseir road, PERI values recorded a wide range of ecological risks between moderate ecological risk, considerable ecological risk and very high ecological risk where Cd and As demonstrate almost the whole contribution in these values.
The correlation matrix revealed that most of the heavy metals are positively correlated with each other, indicating their association with each other and their influence by clay content % content due to adsorption.
The investigation of the heavy metal contamination of phosphate dust revealed that Igeo values for As show a wide range of contamination and values for Cd recorded extremely contaminated dust in the three mines. Other metals exhibit uncontaminated to moderately contaminated samples. Pn values in the three mines show extremely contaminated pattern. PLI values in Hamadat and Yunis dust show moderately to strongly polluted pattern, where Cd and As demonstrate the greatest contribution to these values. PERI values demonstrate very high ecological risk in the three mines where Cd demonstrates the greatest contribution with moderate contribution of As.
The external and internal radiation hazards susceptibility by mine workers due to the measured activity concentrations of the examined natural radionuclides were assessed. Raeq, Hex, Dex, AEDex, AEDinh, AEDing, AEDt and ELCR were performed. The values of Raeq of the three mines dust are higher than the safe maximum value and Hamadat dust has the highest level of risk. Regarding Hex, values are higher than unity and they can be considered considerable values and Hamadat has the highest level of hazard. Dex values are higher than those of the worldwide average and the highest dose rate is recorded in Hamadat mine dust. The AEDex values are higher than those of the worldwide average for external outdoor exposures where the highest value of annual effective dose is obtained in Hamadat dust. The highest values for AEDinh and AEDing were detected in Hamadat dust. ELCR values are extremely higher than those of the world average indicating the high probability of developing cancer, where Hamadat dust recorded the highest values.
The values of these parameters exceed the acceptable limits which represent a considerable health risk for the mine workers and this area is not radiologically safe.