Origin and tectonic environment of silicified ultramylonite in Abu Rusheid, Southeastern Desert, Egypt: geochemical aspects and spectrometric prospecting

The Abu Rusheid area, situated in the southern part of Egyptian Eastern Desert within the Northern Arabian-Nubian Shield (ANS), approximately 90 km southwest of Marsa Alam City along the Red Sea coast, is the focus of this study. The research delves into recent geological and geochemical examinations of silicified ultramylonite in Abu Rusheid to unravel the processes of ancient weathering, paleoclimatology, as well as the sources and origins of the old sediments. The cataclastic rocks comprising protomylonite, mylonite, ultramylonite, and silicified ultramylonite with transitional interfaces are the primary varieties investigated. Plagioclase and quartz are the predominant constituents under microscopic examination, accompanied by smaller crystals of microcline and biotite, along with accessory minerals such as corundum, allanite, zircon, fluorite, and opaque minerals. Scanning electron microscopy (Prisma E) and EDX analysis of the heavy minerals associated with the studied silicified ultramylonite rocks revealed the presence of various minerals including secondary radioactive minerals like kasolite and uranothorite, Nb-Ta minerals such as ferrocolumbite, yttrocolumbite, and others, accessory minerals like monazite and xenotime, as well as precious metals like gold and argentite, and base metals such as bismite, molybdenite, and arsenopyrite. Additionally, Te-bearing minerals like tellurite and volynskite were identified for the first time in the study. Geochemically, the silicified ultramylonite samples are classified within the litharenite to subarkose fields, characterized by lower concentrations of Sr (av. 17 ppm) and Ba (av. 58 ppm), and higher concentrations of Th (av. 69 ppm), U (av. 40 ppm), Zr (av. 1952 ppm), and Nb (av. 344 ppm). The enrichment of LREEs (av. 130 ppm) over HREEs (av. 84 ppm) is attributed to the presence of monazite and zircon. Notably, Abu Rusheid silicified ultramylonite exhibits a higher thorium content compared to uranium, attributed to uranium mobilization processes.