Uranium mineralizations of Wadi Sikait mylonites, Southeastern Desert, Egypt

摘要

This article deals with mineralizations and spectrometric study as well as geology and geochemistry of the late Pan-African cataclastic rocks (mylonites) of Wadi Sikait area. The area is composed of metagabbros, ophiolitic mélange, metasediments, mylonitic rocks, porphyritic biotite granites, leucogranites and lamprophyre dykes. The mineralogical study of the mylonitic samples revealed the presence of uranothorite, thorite, boltwoodite and niobium minerals (ferroclombite, ishikawaite), REEs bearing minerals (monazite, xenotime) and accessory minerals (zircon, pyrite, galena, fluorite, apatite). Geochemically, the mylonitic rocks are enriched in incompatible elements and HFS elements (Nb, Zr and Y) and emplaced in greisen field. The melt of mylonitic rocks were originated from pelites (clay-rich sources). The present study shows that the geochemical characteristics of the mylonitic rocks could be used as exploration guides for U, Th, Nb, Zr and Ga rich sites in similar occurrences in the northern part of the Pan- African belt of Egypt. The mylonitization process led to changes in shape and size of minerals and accompanied with change in chemical compositions of the original rock. It could be related to role of the fluid, heating and metasomatic processes. Detailed spectrometric study reveals the eU/eTh ratio varies directly with eU concentration and randomly with eTh, indicating that the radioelement concentration is governed by post magmatic redistribution. The origin of these secondary minerals is mainly related to alteration of primary minerals by the action of oxidizing fluids, mobilization of uranium and then redeposition in other forms. Redistribution by circulating meteoric water might have taken place.