U-MINERALS AND REE DISTRIBUTION, PARAGENESIS AND PROVENANCE, UM BOGMA FORMATION SOUTHWESTERN SINAI, EGYPT

The lower Carboniferous sediments at SW Sinai comprises four stratigraghic formations from bottom:
Um Bogma, El Hashash, Magharet El Maiah and Abu Zarab formations. The uranium bearing sediments
are mainly confined and associated with Um Bogma Formation. The stratigraphic sections exposed at the
six localities, (Talet Selim, Nasib, Abu Thor, Allouga, Abu Hamata and El Sahu), were studied in detail.
These are exposed within a low basinal shaped area that was affected by several fault sets comprising
strike-slip and step faults. These faults commonly trending (NW, NE, N-S and E-W) created a mosaic of
faulted blocks within and outside the studied area, which to some degree helped the localization of the U-
minerals.
The sedimentary rocks of the Um Bogma Formation comprise the sedimentary facies: gibbsite bearing
sediments, shales, ferruginous siltstone, marl, dolostone, claystone and (Mn-Fe) ore. These sedimentary
facies are well developed in the central parts of the studied area (Allouga and Abu Thor). The siltstone,
shale and claystone are the main sedimentary facies hosting the U-minerals especially in the lower member
of Um Bogma Formation.
The U-minerals found within these facies comprise U-oxides, U-silicates, and Uranyl-Oxyhydroxides, -
silicates, -phosphates, arsenates, -vanadate-, -molybadate-, -carbonates and-sulphate complexes. The uranyl
phosphate (phurcalite) [Ca2(UO2)3(PO4)2(OH)4].4H2O, was first detected in the study area. The U-minerals
association indicated formation under low temperature (<100oc) oxidizing conditions with pH range 6-7.5
and high evaporation rate for the precipitation of the uranyl sulphate complexes.
The REE patterns of the above sedimentary facies suggest a provenance of recycled old sediments with
contributions from plutonic component. These sediments were deposited in an active continental margin.