Mineralogical, REE-geochemical and fluid inclusion studies on some uranium occurrences, Gabal Gattar, Northeastern Desert, Egypt

Abstract

Altered granite occurrences (GII and GV) at Gabal (G.) Gattar are the most important mineralized rocks hosting U-mineralization in Egypt. This mineralized granite is affected by multi-stage hydrothermal alteration processes along brittle structures. This alteration comprises pre-ore alkali-metasomatism and ore-stage hydrothermal hematitization, silicification, kaolinitization, fluoritization, carbonatization and episyenitization. Autoradiographic examination indicates that primary uranium mineralization is present as massive or disseminated ores along tectonic fractures, interstitially in granular minerals, and as cements of breccias. Uraninite, pitchblende and coffinite are the main primary minerals, while uranophane and kasolite are the secondary ones. Galena, chalcopyrite, pyrrohtite and pyrite are the most abundant sulphides in association with uranium mineralizations. Hydrothermal alterations at the GII occurrence exhibit an increase in Ni, Cu, Zn, Pb, Mo, Nb, Rb beside HREEs and a decrease in Ba, Co, Sr, and V, while alterations at the GV occurrence show enrichment in Ni, Cu, Pb, Mo, Nb, Y, HREEs and depletion in Zn, Ba, Co, Rb, Sr, and V. Hydrothermal alteration during the late magmatic stage is also identified through the development of unusual REE patterns and fractionation of ratios like Zr/Hf and Y/Ho out of the CHARAC (Charge Radius Controlled) range. Non-chondritic Y/Ho ratio at GV is of larger value than chondritic one which may result from water-rock interaction or print from the encompassing sedimentary rocks. Fluid inclusion studies on quartz and fluorite revealed that temperatures of the mineralizing fluids range between 126 and 240℃ at pressure ≤0.5×10 8 Pa and give salinity values ranging between 1 wt% and 7.8 wt% NaCl equivalent.

Natural Radionuclide Levels and Radiological Hazards of Khour Abalea Mineralized Pegmatites, Southeastern Desert, Egypt

“…The mean U and Th levels of the examined pegmatites are considerably enriched in both U and Th mean levels 1700.91 ppm and 2881.86 ppm, respectively, as compared to the ranges and averages of Reference [38], (1-6 ppm U and 1-23 ppm Th) [39] and (3 ppm U and 8-17 ppm Th) [40]. eTh/eU ratios in igneous rocks are 3 or 4:1 [41]; however, eTh/eU ratios of the studied mineralized pegmatites have average ratios of 1.7, which is lower than the average of igneous rocks, suggesting uranium enrichment. Some radioelements' inter-relationships could clarify the geochemistry of uranium and thorium.…”

“…Radioactive equilibrium in the study area can be estimated by the equilibrium factor (P), which was suggested by Reference [45] and applied by [41][42][43]46]. If the P-factor is ≥1, uranium is being added or removed.…”

Geological, Mineralogical and Geochemical Aspects of the Granitic Rocks at Umm Nafie Area, North Eastern Desert, Egypt

“…The high HREEs content relative LREEs may clarify that LREEs could be precipitated with uranium elsewhere in the sheared granites. El Feky (2011) shows the presence of mirroring between HREEs and LREEs in Gattar granites and Hammamat sediments. Masuda et al (1987) classified the tetrad effect into two different types, M-and W-type (M-type in solid sample as residues and W-type in the interacting fluids as extract).…”

Spatial Distributions and Risk Assessment of the Natural Radionuclides in the Granitic Rocks from the Eastern Desert, Egypt

“…The accessory minerals are zircon, monazite, xenotime, fluorite, apatite, allanite and sphene. Magnetite, ilmenite, pyrite, chalcopyrite and pyrrohtite are the opaque minerals [16,21]. Uraninite, uranophane and geothite are the associated secondary minerals.…”