Geochemical constraints and uranium potential of the younger granitic rocks in El Maghrbia area, Central Eastern Desert, Egypt

摘要

The present work deals with the mineralogy,geochemical behavior and uranium potentiality of the monzogranites of El Maghrbia area,which comprise G.El Maghrbia and G.El Eredyia and situated in the central Eastern Desert of Egypt.G.El-Erediya monzogranites represents a promising area for uranium mineralizations.These granites have shear zone filled with red and black silica veins containing many radioactive anomalies with visible yellow secondary uranium minerals.The shear zone is highly affected by different degrees of alterations such as silicification,kaolinitization,sassuritization and ferrugination.Monzogranites of El-Erediya area possess higher values of their radioactivity than in El Maghrbia monzogranites in which eU and eTh,reaches up to 792.3 and 66.81 ppm,whilst average content of eU and eTh in El Maghrabia granites are 3.86 and 8.55 ppm,respectively owing to the presence of radioactive minerals such as uraninite,uranothorite,uranophane,kasolite,betafite,zircon and monazite.Intensive geochemical analyses indicated that,the studied monzogranites are distinctly anomalous in U,where the average U is more than 620-fold the Upper Continental Crust(UCC),marked enrichment(> tenfold) of the elements Cd,Mo,Pb,Bi,Nb and W.The Th/U ratio decreases from 2.8,as a chondritic value,to 0.0023 for the studied granites,proposing extreme fractionation towards an extensive secondary migration-in of U.The Zr and Hf are depleted in the studied granites relative to the UCC,whereas Nb and Ta are strongly enriched.The content of Y is about sixfold enriched which reflects relative enhancement of the HREE during the alteration processes.Uranium correlates with Fe_(2)O_(3),suggesting a possible association between uranium and ferrugination.Thus,the occurrences of uranium are epigenetic by remobilization from the host rock to the sheared zones,probably through metasomatic process where U-Fe-Mg replaced the feldspars in an oxidized condition.The high levels of radioactivity in the rocks being studied it them a priority for discovery and expanding the potentiality of the highly mineralized localities.