Search

The Nuweibi area (7.5 km2) is located towards NW Marsa Alam City, central Egyptian Nubian Shield. It constitutes ophiolite assemblages (serpentinites, metagabbros), Tuffaceous metasediments, granodiorite–tonalite, and Late Ediacaran albite granite. The present study mainly focuses on determination of the concentrations of specific elements and their interrelationships to 238U, 232Th, and 40K for the granitic rocks. The radiometric measurements have been performed using a high-purity germanium (HPGe) detector and a portable RS-230 γ-ray spectrometer in combination with chemical analysis using ICP-MS. The radionuclide values measured with a ground gamma-ray detector are more than twice those recorded using both HPGe spectroscopic and chemical analysis methods. On the other hand, the chemical data given by many correlations between U, Th, and K as well as selected major, trace, and rare earth elements suggest the occurrence of the magmatic process followed by Na-metasomatic albitization in albite granite. This process caused redistribution and remobilization of U, as follows the facts that eTh/eU exceeds 3 and the average eTh/eU ratio of albite granites exceeds the Clark's value (3.5). On the other hand, the higher eTh contents of the albite granites reflect additional contribution from Th-bearing minerals, and in most sampling sites the 232Th/226Ra activity ratios are higher than the natural equilibrium ratio, 1.1, indicating possible enrichment process of these radionuclides as a result of alkali metasomatism. [ABSTRACT FROM AUTHOR]

The present study focuses on the distribution of natural radionuclides and the determination of radioelement favorability in the Nugrus mylonite rock. The radionuclide contents were measured with a NaI(Tl) detector. The concentrations of U, Th, Ra (in terms of eU), and K in the mylonite studied range from 27 to 247 ppm, from 96 to 377 ppm, from 11 to 166 ppm, and from 1.14 to 3.12%, with the averages of 100 ppm, 201 ppm, 55 ppm, and 2.1%, respectively. The interelement relationships indicate that the radioelement distribution is not only magmatic but also hydrothermal. Variations of migration parameters for uranium indicate fluctuations in physicochemical conditions that lead to U accumulation and leaching processes, which are confirmed by increments and decrements in uranium concentrations. The examined samples demonstrate disequilibrium, with eU/Ra (eU) ranging from 1.32 to 3.26, with an average of 1.95, which suggests uranium addition. Uranium, thorium, and potassium favorability indices of the investigated mylonite rocks indicate moderate favorability of these rocks for uranium and thorium and high favorability for potassium. The F-parameter illustrates the presence of different stages of alterations. Mineralogical investigation indicates the presence of such radioactive minerals as thorite and Uranothorite, of Nb–Ta minerals (columbite and ishikawite), and of zircon and xenotime. [ABSTRACT FROM AUTHOR]

Ferrugination, sericitization, desulfitization, chloritization, and kaolinitization of hydrothermal origin are the main wall rock alterations occurring within the NNW shear zones at Abu Rusheid area. The secondary uranium minerals occur as hair-like radiated spots and thin micaceous flakes with canary and yellow color, which are deposited along the small cracks and microfractures of altered gneiss and lamprophyre dyke and coat surfaces of hematitized rock. The radiometric measurements proved that the uranium content increases from sericitized gneiss (average 317.9 ppm) to ferruginated gneiss (average 863.1 ppm) and then to altered lamprophyre dyke (average 1352.7 ppm). The latter is the most radioactive zone along the NNW shear zones and is considered as a good trap for the uranium leached from the host rock due to the high ability of iron oxides and clays to adsorb radioactive elements from their solutions. Therefore, the present work focuses on the uranium leaching from Abu Rusheid area using sulfuric acid. The effect of sulfuric acid concentration, liquid/solid ratio, contact time, and leaching temperature on the leaching efficiency has been investigated. The data obtained show that about 74.0% of uranium can be leached successfully under the following conditions: sulfuric acid concentration 4 M, liquid/solid ratio 10 mL/g, room temperature, 6.0 h. The leaching kinetics is well interpreted with shrinking core model with control by diffusion through a porous product layer. The diffusion-controlled process is characterized by the activation energy of 6.3 kJ mol–1. [ABSTRACT FROM AUTHOR]

Abu Rusheid area is a part of the Arabo-Nubian basement exposures and is located in the southern Eastern Desert of Egypt, 95 km southwest of Marsa Alam City on the Red Sea coast. The Precambrian basement rocks include (a) ophiolitic metagabbros, (b) ophiolitic mélange, (c) mylonitic rocks, and (d) granites which were later intruded by lamprophyre dikes, pegmatite, and quartz veins. Geochemical studies revealed that both the mica schist and mylonite are mainly arkoses to greywacke in composition and confined to the passive margin tectonic setting. Chondrite-normalized REE patterns illustrate enrichment in HREEs in mica schist relative to LREEs, and there is a balance between them in mylonite. The minerals that have been identified in both mica schist and mylonite are soddyite, uranophane, kasolite, metazeunerite, thorite, uranothorite, and zinnwaldite. These mineralizations are related to shear zones and mainly coincide with the Najd fault (left lateral strike-slip) shear system. Field spectrometric measurements revealed that the average eU is 219 ppm and eTh is 451 ppm along trenches, whereas along channel samples the average eU is 64 ppm and eTh is 271 ppm. [ABSTRACT FROM AUTHOR]

Hydrometallurgical processing of micaceous bands concentrate for recovering U and Th using sulfuric acid agitation leaching was studied. This concentrate assays 4.1% ZrO2, 3.8% Nb2O5, 1.2% RE2O3, 2.8% ThO2, and 0.55% U3O8. The corresponding minerals of these elements include zircon, ferrocolumbite, fergusonite, uranothorite, autunite, and uranophane. About 96% of Th and 94% of U were dissolved under optimum leaching conditions: 30% H2SO4, 1/3 S/L ratio, 4 h leaching time, and 85°C leaching temperature. Di(2-ethylhexyl) hydrogen phosphate (HDEHP) in kerosene was used for U extraction with 90.9% efficiency and its separation from Th in the presence of 0.3 M EDTA solution. Th was then selectively precipitated from the raffinate solution as Th peroxide. [ABSTRACT FROM AUTHOR]