Efflorescences
and Valley Fill Quaternary Uranium Deposits,
SouthWestern Sinai, Egypt
Omar A. Hegab, Ibrahim E. ElAassey1,
Abdalla A. Abd ElMonem1 , Ibrahim F. ElFayoumi
and Nasser L. ElAgami1
Geology Dept., Fac. Sciences, Mansoura Univ., 1Nuclear Materials Auth., Cairo,
Egypt |
Several surficial Quaternary U occurrences are
associated with the Cu and Fe minerals in SW Sinai. Two main types are identified:
Pleistocene uraniferous channel fill conglomerate, and Recent efflorescence encrustation
off the roof of ancient tunnels. The principal U minerals in the Pleistocene conglomerate
are uranophane, betauranophane, phosphuranylite, zippeite and both detrital and authigenic
apatite, associated with atacamite. paratacamite and turquoise Cu minerals. The secondary
U minerals bassetite and meta-autunite are found associated with chalcanthite, langite,
turquoise. atacamite, szomolonkite, goethite, hematite, jarosite, gypsum, alunite,
alunogen, as the Recent encrustation and stalactitic masses off the roof of the ancient
tunnels. In both these U mineralizations, the U decay series is out of equilibrium
as the chemical content always higher than its radiometric measurements. The U host
sediments (shales) are significantly depleted of SiO2, Al2O3, K2O
and Rb concentrations and significantly enriched in P2O5, MnO, Fe2O3,
Zr, Y, Sr, Nb, Pb, Cu, and V concentrations relative to NASC. There is no significant
difference in Tb, Ni, Cr, CaO and MgO concentration relative to NASC.
The major processes governing the formation of surficial U-deposits are dissolution of U
from its sources by circulating meteoric and groundwaters, precipitation of carbonates and
sulfate minerals releases U and enhances its concentration in solution. Uranium is fixed
from solution by sorption onto clays and hydroxides of Al and Fe, as well as by cations
and anions in solution. Evaporation is responsible for the occurrence of thin films,
encrustation, fissure fillings and rosettes of colored secondary U-minerals.
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