Mineralogy and radioactivity of pegmatites from South Wadi Khuda area, Eastern Desert, Egypt

Abstract

Radioactive minerals in pegmatites associated with granitic rocks are commonly encountered in the south of the Wadi Khuda area and found as dyke-like and small bodies. They are observed within garnet-muscovite granites near the contact with older granitoids. Field surveys indicated that the studied pegmatites vary in dimensions ranging from 2 to 10 m in width and from 10 to 500 m in length. They are composed mainly of intergrowth of milky quartz, reddish-pink K-feldspar and plagioclase together with small pockets of muscovite.Field radiometric measurements indicated that radioactivity in pegmatites is more than twice that of their enclosing country rocks. Radionuclide measurements revealed that the average contents of U and Th increase gradually from rocks of dioritic to granodioritic composition (1.5×10 -6 U and 4.3×10 -6 Th) and increase significantly in biotite granites (5.8×10 -6 U and 15.2×10 -6 Th) but drastically decrease in muscovite granites (2.2×10 -6 U and 5.6×10 -6 Th). The average contents of U and Th of anomalous pegmatites are 95.3×10 -6 and 116.9×10 -6 , respectively, indicating their uraniferous nature. In the south of the Wadi Khuda area, pegmatites are low in average Th/U (1.4) and high in average U/K (35.6), which suggests that uranium concentrating processes did not affect the pegmatites, indicating poor source-rocks.Mineralogical investigations of the studied pegmatites revealed the presence of secondary uranium minerals (kasolite and autunite), in addition to zircon, thorite, apatite, garnet and biotite. Primary and secondary radioactive mineralizations indicated that the mineralization is not only magmatic, but also post-magmatic. Electron microprobe analyses showed distinct cryptic chemical zoning within thorite where UO 2 decreases from core to rim. This feature in thorite is sporadic, suggesting non-uniform redistributions of UO 2 within thorite during magmatic processes.

Shear-Related Gold Ores in the Wadi Hodein Shear Belt, South Eastern Desert of Egypt: Analysis of Remote Sensing, Field and Structural Data

“…These rocks intrude Wadi Khuda gneisses (Figure S2d) and the eastern parts of Wadi Rahaba-Gabal Abu Dahr ophiolitic mélange and intruded by late to post-tectonic biotite and muscovite granites (Figure S2e). Their contacts with Wadi Khuda gneisses are characterized by the strongly foliated diorite and amphibolite [46,47]. The gabbro-diorite complex forms variable degrees of deformation, from massive to strongly sheared or foliated.…”

“…The granitic rocks of Gabal El Maarafay and Gabal Al Farayid include monzogranite, granodiorite, and tonalite and are locally foliated [48]. At Wadi Khuda, leucogranite forms small stocklike and dikelike bodies intruding on the core of the Khuda gneisses and the granite pluton [46]. The ophiolitic rocks of Wadi Arais are cut by monzogranite and syenogranite of the Gabal El-Nukeiba and Gabal Handusa.…”

U–Pb geochronology, REE and trace element geochemistry of zircon from El Fereyid monzogranite, south Eastern Desert, Egypt

“…The monzogranite rocks are hosting late magmatic pegmatites occurring as pockets and veins (Abd El-Naby and Saleh, 2003;Raslan et al, 2010aRaslan et al, , 2010bSaleh et al, 2018;Dawoud et al, 2018). Pegmatites are often very coarse-grained and are reddish to buff-colored.…”

Mineralogical, fluid inclusion and radiometric studies on Wadi El-Dob pegmatites, northern Eastern Desert, Egypt.

“…From economic and metallogenic point of views, the boundary zone between the central and southern portions of the Eastern Desert is the most important zone, where huge pegmatite fields are extending around Migif-Hafafit terrain (Khaleal et al, 2022). NYF-pegmatites are recorded at Kadabora (Saleh, 2007), Ras Baroud (Raslan et al, 2010a;Fawzy et al, 2020), Wadi Khuda (Raslan et al, 2010b), Abu Rusheid Ali, 2011), andGabal El Faliq (Abu Elatta, 2019).…”