| Author(s) | Omar, A. Sherbini and Talal, M. Qhadi |
| Affiliation | Department of Mineral Resources andRocks, Faculty of Earth Sciences, King Abdulaziz University, Jeddah, Kingdom of Saudi Arabia |
| Title | Origin of the Rare-metal-bearing Peraluminous Albite Granite of the Umm Al Suqian Pluton, Asir Region, Kingdom of Saudi Arabia |
| Source | Journal of King Saud University. Science. Volume 17, No 1. (2005/1425) |
| Abstract | The Umm Al Suqian albite granite, in the southern Asir region, Kingdom of Saudi Arabia, is a late Proterozoic post-collisional peraluminous granite that hosts greisens and disseminated rare metal-bearing minerals. It was emplaced at shallow crustal levels into a metasedimentary and dioritic rock. The rocks of the Umm Al Suqian albite granite pluton consist of four petrographic facies: i) quartz-pegmatite, ii) a mixed layer of conglomerate, quartz-diorite xenoliths in albite granite, and iii) greisenized zone and iv) albite granite. Mineralization consists of small veins and lenses of fluorite and dessiminated minerals such as ixiolite, monazite and bastanesite. Field observations strongly suggest a comagmatic origin of the albite granite, greisens and the associated mineralization. Geochemical data indicate that the albite granite is enriched in SiO2-, Na2O-, F-, Rb-, Nb-, Sn-, and depleted in MgO-, CaO-, and TiO2 and can be termed specialized felsic granite. It is characterized by low K/Rb ratios (49 - 16), high Rb/Sr ratios (76 - 8) and less fractionated REE patterns. The albite granites show geochemical variation indicating their generation by extensive fractional crystallization of major phases such as feldspars and biotite. Subsequent fluorine complexing is assumed to have scoured and transported the HFSE as soluble components. Fractional crystallization of the evolving F-rich peraluminous granitic magma was accompanied, particularly at later stages by fluid fractionation, which plays an important role in the genesis of the greisenized rocks and the associated mineralizations. The parent magma of this granite pluton was formed by dehydration melting of lower crustal rocks. The melting was related to crustal thickening associated with continental collision at the end of the Pan-African orogeny. |
