U-Th-REE behavior during alteration of granitic rocks : evidence from west-Nuweiba area, southern Sinai, Egypt

الملخص EN

Younger granite outcrops at Wadi El-Saada and Wadi Wateir areas located in the southwest of Nuweiba City, are classified into monzo- and syenogranites varieties.

These granites have high relief and are dissected by numerous shear zones.

At Wadi El-Saada, two shear zones striking NNE-SSW and NNWSSE and cutting the mozogranites are recognized in the southeastern corner of the area mapped.

Alteration products, such as hematitization, kaolinization and manganese mineralization are observed.

Uranothorite, monazite, allanite and U-Th-REE-bearing minerals can also be identified.

The shear zone of the Wadi Wateir area strikes NE-SW with V-shape.

Intensive alteration, as hematitization and kaolinization of the syenogranitc rocks within this shear zone, is recorded together with secondary uranium minerals as uranophane and beta-uranophane.

The U-Th-REE-bearing minerals within these altered sheared zones are highly affected by hot hydrothermal solutions, which has resulted in the liberation of U, Th and REE.

Secondary and accessory minerals, such as chlorite, serecite, monazite, zircon and allanite are recorded.

The geochemistry of major elements indicates that the granites originated from peraluminous magma and evolved in a within-plate tectonic regime.

The REE geochemistry studies indicates enrichment of LREE relative to HREEs.

This may have attributed to the presence of monazite and allanite.

Also, there is a close relation between the presence of U-minerals and REE concentration and the alteration of granitic rocks.