Mineralogical, Geochemical and Thermal Characterization of Precambrian Banded Marble, Gebel El Rokham, In Comparison with Serpentine-Related Carbonate, Eastern Desert, Egypt

The Precambrian marble is banded, composed of coarse translucent and fine grained bands. It is found as lensoidal mass intercalated with metsediments. XRD, DTA, XRF analyses and petrography reveal that, the composition of the banded marble is magnesite with minor phases of calcite, dolomite and hercynite. MgO and CaO of the coarse- and fine- grained bands are (41.8 and7.7 wt. %) and (43.6 and 3.8 wt. %) respectively. %. Fe2O3 (0.26 wt. %) and SiO2 (0.87 wt. %) of fine-grained band are slightly higher than those of coarse-grained band. The serpentine-related carbonates are composed of white and translucent grains with massive texture. The fine-grains are composed of dolomite with minor phases of lizardite, vermiculite and anthophyllite. The translucent grains are composed of dolomite and minor phase of clinochlore. The serpentinerelated carbonate has high concentrations of Cr, Ni, V, Co, Nb, Ta, La, Zr, Y and Sr. Abundances of Sr and Rb of translucent grains are higher than those of white grains of marble and serpentinerelated carbonate which confirms their association with high content of calcium content in translucent grains of both types. The purity of the magnesite of the translucent band resulted in lowering the temperature of its decomposition (589 C) as compared with the fine-grained band (622 C). The low concentration of Cr, Ni, Y and occurrence of graphitic materials indicate para origin as a result of regional metamorphism of Mg-rich carbonate or magnesite of shallow marine environment.