Abstract
This study documents the geochemical evolution of rare-metal mineralized granitic pegmatite of Ras Al-Baroud using mineral chemistry and whole rock chemistry. Pegmatite occurs as sheet-like bodies, pockets along the edges of the Ras Al-Baroud post-collisional granite, or within fault zones. Pegmatites at the outer margins of Ras Al-Baroud granites show gradational boundaries. In a few outcrops, the Ras Al-Baroud pegmatites are affected by intense metasomatic-hydrothermal alteration resulting in albitization and greisenization: especially close to the contact with the host rocks. Nb-Ta oxides are the most important rare metals in the Ras Al-Baroud pegmatite and are represented mainly by columbite and less amount of tantalite. They are commonly zoned, exhibiting a wide range of chemical compositions and are characterized by partial digestion and late-stage overgrowth due to the effecting of magmatic and hydrothermal processes in the granite-pegmatite system. Ras Al-Baroud pegmatite is considered to mainly crystallize late from a pegmatite-forming melt that resulted from a combination of magmatic and hydrothermal processes. Extended fractional crystallization in Ras Al-Baroud granites eventually produced saturated, late-magmatic magmatic fluids. These fluids migrated towards the apex of the magma chamber, reacting with still-hot but subsolidus granite and becoming increasingly focused into distinct channels and veins. This upward and outward mode of fluid migration led to pegmatites with gradational boundaries.