Genetic link between uranium mineralization and the emplacement of limited intrusion adjacent to alkaline granites, Abu Hamr area, north Eastern Desert, Egypt

Abstract

The recorded uranium mineralization is genetically related to the U content and structural setting of syenogranitic dyke that occurs near alkaline granites, Abu Hamr area, north Eastern Desert of Egypt. The associated abnormal level of radioactivity exhibits maximum equivalent uranium (eU) of 155.6 parts per million (ppm) with an average of 54 ppm while the maximum of eTh reaches up to 235 ppm with average content of 120 ppm. The nearby alkaline granites of Gabal Abu Hamr show a normal distribution of eU and eTh resembling that of normal granites (4 ppm eU and 8 ppm eTh). Radioactive anomalies can be interpreted as successive concentrations of U-Th, which are related to magmatic processes of syn-shearing syenogranite dyke formation followed by hydrothermal redistribution during the emplacement, and then supergene enrichment. Testing of uranium equilibrium has revealed major chemical U addition to both the syenogranitic dyke and, to less extent, the alkaline granites. The rare-earth element (REE) patterns display pronounced enrichment of light REEs and heavy REEs of the syenogranitic dyke in contrast to the alkaline granites, which might have attributed to the subsequent hydrothermal circulation. The studied dyke is also characterized by well-developed U, Th, and Pb enrichments. Post-magmatic hydrothermal activity is evident from the presence of dark violet fluorite with inclusion of U and Th minerals, in addition to the presence of zircon crystals with overgrowth, xenocrystic cores, REE replacements, and spatially inclusions of allanite-(Ce) with irregularly distributed patchy overgrowths of U and Th.