RARE-EARTH ELEMENTS AND CRYSTAL-CHEMISTRY OF XENOTIME BEARING SEDIMENTS OF UM-BOGMA AREA, SOUTHWESTERN SINAI, EGYPT

The Exposed Paleozoic deposits in the Um Bogma area in south-western S inai contain three main subdivisions; the lower sandstone, the middle carbonate and the upper sandstone units. The upper layers of the lower sandstone and the base of the middle carbonate units contain possible resources of anomalously radioactive xenotime (YPO4). The studied two localities, namely; Um Hamd and Ramlet Hemyir are shown to contain hi gh potential of xenotime. The chrondrite-normalized REEs patterns, whe ther of bulk samples or grain size fractions bear a clear ''finger pri nt'' of xenotime. The empirical formula of xenotime is calculated to b e as follows: (Y(2.53)RE(0,38)Ca(0.04)U(0.05)) (P3.87Si0.62Al0.51)O-4 Uranium is not only confined to xenotime structure, but it is also ads orbed on clays and ferromanganese materials.