PAN-AFRICAN GRANITOID ROCKS HOSTING JASPEROID VEINS, MASSAK BIRAYKE AREA, NORTH EASTERN DESERT, EGYPT: RADIOACTIVITY AND MINERALOGY

The studied granitic rocks are mainly distinguished into granodiorites and syenogranites based on their
field relationship and petrography. The syenogranites are unconformably overlain by Nubian sandstones
from the west. They exhibit an extensive alteration nearby the jasperoid veins such as ferrugination,
sericitization, kaolinization, silicification and black manganese dendritic staining. The mineralized reddish
brown jasperoid veins intrude the syenogranites and are mostly observed at the highly fractured parts.
Some of these jasperoid veins stained with black and reddish brown Mn and Fe oxides associated with
bright yellow color of secondary uranium minerals.
The radiometric measurements show that the granodiorites and syenogranites exhibits moderate uranium
and thorium contents. They display 6 ppm eU and 15 ppm eTh in average for the first and 19 ppm eU and
30 ppm eTh for the later. Unlike, the jasperoid veins attains highest values (eU=250 ppm, eTh=72 ppm)
in average. The enrichment of U in the jasperoid veins is probably because of mobilization of U from the
syenogranite. Detailed microscopic examinations, X-ray diffraction (XRD) and Environmental Scanning
Electron Microscope (ESEM) with EDX microanalysis revealed that the presence of secondary uranium
minerals as carnotite and uranophane as well as U-bearing accessory minerals such as betafite, samarskite,
zircon and violet fluorite are responsible for radioactivity.