Mineralogy and Trace Elements Geochemistry of Pegmatite Body at the Northern Periphery of Gabal Ras Baroud, Central Eastern Desert, Egypt

Abstract

Ras Baroud area has several rock units arranged from the oldest to the youngest as: older granites, younger granites, pegmatites, dykes and quartz veins. Yo u nger granite of Ras Baroud is exposed as small semirounded isolated mass, which is medium to coarse grained and pink to reddish pink in color. This granite is dissected with several types of dykes ranging from basic to acidic ones. Pegmatite body is encountered at the peripheral parts of this granite. It is compositionally zoned, being composed of massive milky quartz in the core and pink color blocky K-feldspars with subordinate nest like aggregates of yellowish white mica the outer rim. Ras Baroud granite is composed mainly of K-feldspars, plagioclase quartz and micas (biotite and muscovite) associated with zircon, titanite, and opaque as accessory minerals. On the other hand, the secondary minerals are represented by sericite and chlorite. The pegmatite bodies at the northern periphery of Gabal Ras Baroud consist essentially of orthoclase, quartz, plagioclase and mica (muscovite and biotite). The accessory minerals include zircon, allanite, fluorite and opaques. Compared to the parent granitic pluton, the pegmatite body has higher concentrations of Zr, Rb, Y, Ba, Pb, Nb and lower Cu, Sr concentrations. It is important to notice that the variation in the concentration of trace elements in the studied pegmatite samples may be due to the difference in the mineralogical composition of these samples. Uranium content in pegmatite body ranges from 10 ppm to 235 ppm with an average 84 but the thorium content range from 1 ppm to 309 ppm with an average 95. Pegmatite body of Ras Baroud has several important rare-metal bearing minerals include; samarskite-Y, columbite, cassiterite, zircon, fluorite and rutile in addition to some opaque minerals as magnetite and ilmenite.