The platinum-group mineralogy (PGM) of the chromitite from Gebel Lawi, in the southeastern desert has been investigated. The most abundant base metal sulfides (BMS) associated with the Lawi chromite are pentlandite, millerite and heazlewoodite. The major platinum-group minerals identified were as follows: laurite (IrOsRu)S2, osmian iridium (Oslr), hollingworthite (RhAsS), tellurian arsenopalladinite (PdTeSbAs), potarite (PdHg) besides cuprian palladian gold (CuPdAu), a Pd-Sb-Hg and HgTe phases. Laurite and osmian iridium occur preferentially in chromite. Os-Ir commonly forms composite PGM with laurite. Hollingworthite and tellurian arsenopalladinite are included within serpentine and, close to the base-metal sulfides, the cuprian palladian gold shares boundaries with chromite. Potaritc together with the Pd-Sb-Hg and HgTe phases are embedded in serpentine. Palladium is the most abundant PGE in the Gebel Lawi chromite.A paragenetic sequence of PGM formation is described. Textural evidence indicates that Os-, Ir-and Ru-bearing PGM formed early and were followed by Rh-and Pd-bearing PGM. The concentration ofai1 five PGE could be magmatic, but much of the PGE mineralogy except for laurite and osmian iridium in the center of chromite grains, has been modified by subsequent processes. At later stages, the environment became Te-, Sb-, As-and Hg-rich, which finally led to the formation of low-temperature alteration minerals.The chromite deposits of Egypt are commonly hosted in ophiolitic rocks. The ophiolites of the Eastern Desert form part of an extensive tectonic melange which resulted from the complete dismemberment and total disruption of their original stratigraphy (Petters 1991). The melange is characterized by the presence of a significant proportion of serpentinites either as matrix or as variably sized blocks, in addition to other ophiolitic fragments, deep-sea sediments and calcalkaline volcanics. Other components such as granitic rocks, carbonate rocks, quartzites and mudstone attest to the characteristic heterogeneity of the melange which constitute mappable litho-stratigraphic entities. The melange is commonly formed of thrust sheets or slices which were incorporated within allochtonous belts of metasediments (Hassan and Hashad 1990).The Gebel Lawi (or the Lawi mountain, a geographic name) forms a part of the Ghadir area (Fig. 1). The latter is a large ophiolitic melange with proximal and distal facies. The former consists of rolled and fragmented rock-debris of highly variable sizes in a sheared matrix of scaly and schistose mudstones, abundantly serpentinized peridotite blocks, some of which are surrounded by sheaths of schistose talc-carbonate rock produced by squeezing and rolling of the blocks besides other rock debris including volcanic material, greywackes, quartzites, chert, granite and amphibolites. The distal facies is a low-grade pelitic schist with pockets and lenses of highly schistose talc-carbonate rock.A genetic model (Fig. 2) for the Ghadir ophiolitic melange was given by Elbayoumi (1984) inv...
This paper investigates the distribution of four natural radioisotopes 238U, 226Ra, 232Th and 40K in one hundred twenty-five granitic samples covering sixteen mountainous areas situated at the northern, central and southern parts of the Eastern Desert of Egypt (EDE). The concentrations of the examined radioisotopes in the collected samples were recognized utilizing a HPGe detector based gamma spectrometry. The average concentrations of these radioisotopes were higher when compared with the worldwide reference values. The radiation risk indicators including the radium equivalent activity index (Raeq), external and internal hazard indicators (Hex and Hin), external and internal level indicators (Iα and Iγ), absorbed dose rate (ADR), annual effective dose rate (AEDR), annual gonadal dosage equivalent (AGDE), and excess lifetime cancer risk (ELCR), associated with these radioisotopes have been calculated and compared with their recommended global values and safety limits. These indicators showed that the granites from most studied areas exceeded the universal standards pointing to the difficulty of using them as building materials. This study together with future investigations will serve to develop an essential database for future environmental monitoring surveys.
The naturally occurring radionuclides (radium-226, thorium-232, potassium-40 and radon-222) were investigated in the alkaline rocks of Abu Khuruq Ring, southern Eastern Desert, Egypt. A high-resolution germanium detector was used for the detection of 40K, 232Th, and 226Ra (Canberra, GR4020 model) while 222Rn concentration was measured by the Alpha-Guard Saphymo GmbH system, model PQ 2000 (AG). Major and rare earth elements (REEs) were assessed using the inductively coupled plasma mass spectrometry and atomic emission spectrometry techniques. Positive correlations were observed between REEs, indicating symmetrical chemical properties and their overall presence in the parent material—also, a positive correlation was observed between effective radium content and radon concentrations pointing to the strong linear dependency between both contents in the studied rocks. The average values of activity concentration of 40K, 232Th, 226Ra, and 222Rn were less than the suggested level by a factor of 1.38%, 3.16%, 2.09%, and 1.16%, respectively. Significant variations were found among the radiological hazards parameters, e.g., the mean value of the annual effective dose (0.55 mSv y−1) was more than the global reference value (0.41 mSv y−1) by a factor of 1.34. The calculated average value of the gamma index was 0.90, and that of the alpha index was 0.37. Hex, Hin and Raeq showed fewer average values than the standard values of unity and 370 Bq kg−1, respectively.
In this paper, a thorough radio- and chem-ecological evaluation of ElSibai-Abu ElTiyur granites located within Egypt’s crystalline basement rocks was conducted for risk and dose assessments. Twenty granitic samples from the study area’s various lithological units were analyzed using high-resolution γ-ray spectrometry to determine the natural radioisotopes (U-238, Th-232, and K-40) concentrations. The average concentrations of U-238, Th-232, and K-40 were 38.72, 38.23, and 860.71 Bq/kg, respectively, exceeding the GAV (global average value) documented by UNSCEAR (Scientific Committee on the Effects of Atomic Radiation, Vienna, Austria). The radiological parameters and indices judging the usage of ElSibai-Abu ElTiyur granites in homes were computed. The obtained results showed that ElSibai-Abu ElTiyur granites are safe to be used by inhabitants as superficial building materials, as per the globally accepted values and the recommended safety limits approved by UNSEAR, WHO (World Health Organization, Geneva, Switzerland), ICRP (International Commission on Radiological Protection, Ottawa, ON, Canada), and EC (European Commission, Luxembourg). Further, the samples were subjected to ICP-MS (inductively coupled plasma mass spectrometry) analysis for quantifying radionuclide variations with chemical composition. Geochemically based on the ICP-MS results, the studied granites proved to be highly evolved A-type granites. They span the metaluminous to peralkaline fields. The REE patterns are characterized by the enrichment of the light rare earths (LREE) over the heavy ones (HREE) where (La/Yb)n = 5.2, (Gd/Yb)n = 1.63 with pronounced negative Eu-anomalies (Eu/Eu*)n = 0.49. The albite granite exhibits the highest concentrations of Ga, Nb, Ta, U, and Y, and REE (Gd, Dy, Ho, Yb) than the Na-metasomatic granites. Finally, the obtained data serve as a valuable future database for finding out the compatibility of the geochemical data with the natural radioactivity levels of granites.
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