الفهرس 
Synopsis of the Precambrian Rocks in the Nubian Shield
GEOLOGIC SETUP & STRUCTURALOnly 14 pages are availabe for public view
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Abstract
Gabel Nuweibi represents the landmark and the main target of the present study area, which constitutes the Nuweibi Albite Granite (NAG), the main focus of the present study, which is characterized by rare metals enrichment and tin mineralization. Regarding the field aspects, it has sharp intrusive contacts with almost country rocks, marked by a thin strip of contact aureole of hornfels against the tuffaceous metasediments. Petrographically, the albite granite is composed of albite (An8-10), quartz, mica and K-feldspar (microcline) as main constituents. The accessory minerals are zircon, topaz, garnet, iron oxide, apatite, and Nb-Ta-Sn ore minerals. On the basis of geochemical data, the studied albite granite is enriched in Na2O, HESEs, Ta, Nb similar to granites within extensional regime and depleted in MgO, CaO, Fe2O3, TiO2, Ba, Sr, rare earth elements and radioelements (U, Th). The geochemical signature of the present albite granite indicate peraluminous domain of alkaline affinities. Geodynamic modeling reveals that the rocks were generated as a result of partial melting and fractionation of lower crust basaltic magma and tonalitic melts giving rise to A1-subtype granite. Subsequently, they were emplaced within intra-plate environment at the later phase of Pan African Orogeny. Moreover, the fractional crystallization and reworking of plagioclase-rich affected alkali metasomatism after extraction of alkali feldspar granite melts. Regarding the radiometric and geochemistry of radioactive elements of 238U, 232Th and 40K in the NAG and granodiorites, the measurements are provided by γ-ray spectroscopic analysis, including portable RS-230 model hand-detector and High Purity Germanium (HPGe) spectrometry. Chemical analysis using ICP-MS have been carried out to determine the concentrations of major oxides and trace elements including U, Th (ppm) and 40K % for the studied rocks. With respect to the field spectrometric measurements, the average radionuclide concentrations for point samples of eU, eTh (ppm) and K% were 8.45, 33.89 and 4.71 respectively for NAG and 2.55, 6.35 and 1.95 respectively for granodiorites. Gamma ray HPGe detector indicates that the average specific activities of 226Ra, 232Th and 40K were 42.62 ± 2.63, 71.61 ± 3.5 and 816.74 ± 34.74 Bq/kg for NAG, respectively and 11.65 ± IX 0.78, 11.95 ± 0.78 and 289.42 ± 13.02 Bq/kg for granodiorites. Regarding the chemical laboratory analysis for U, Th (ppm) and K%, the average concentrations were 4.39, 23.83 and 1.62 for NAG, respectively and 1.43, 3.13 and 1.19 for granodiorites. The obtained chemical and radiometric concentrations of U, Th and K% and their ratios were used in combination with their relevant diagrams to delineate the distribution, magmatic processes and geochemical behavior of the studied radionuclides. The radiometric and chemical data of the studied radionuclides in NAG confirmed that the redistribution of the radionuclides was formed later by hydrothermal Na-metasomatic albitization. With respect of the possible radiological risk factors with the help of internationally approved health hazard indices. The study aimed to dose rate evaluating in the area within and surrounding Nuweibi mining area. Gamma spectrometric measurements were performed using a HPGe detector for the NAG and granodiorites. Statistical depicting groups, summary statistics were used for statistical evaluations. Radium equivalent activity (Raeq), external and internal hazard indices (Hex, Hin), absorbed gamma dose rate (D) and annual effective dose rate (AEDRin, AEDRout) were also calculated. Almost all the values of the radiation hazard indices in the studied samples were under the health hazard limits.