Younger Granites and Associated Pegmatites of Gabal El Fereyid – Wadi Rahaba Area, South Eastern Desert, Egypt: Geological and Geochemical Characteristics

Abstract

Lithologically, the rock types of G. El Fereyid-W. Rahaba area are dominantly granites associated with pegmatites. The granitic rocks comprise tonalite and monzogranite with (minor acidic dykes), quartz and pegmatites occur as a vein type (granitic and perthitic pegmatites) hosted within the monzogranite. Structural analysis shows the presence of a prominent set of folds with axes striking WNW to NW and a less prominent set with pronounced ENE and NNW trends. Petrochemical studies and tectonic discrimination diagrams for the monzogranite reveal that it is classified as post orogenic granites (POG). Geochemically, monzogranite shows enrichment (peaks) of large ion lithophile elements (LILE; Pb, Rb, Ba, Sr) and high field strength elements (HFSE; Y, Zr, Nd,) and depletion (troughs) of K, P and Ti. Pegmatite shows enrichment (peaks) of large ion lithophile elements (LILE; Pb, Rb, Sr) and high field strength elements (HFSE; Y, Zr, Th, U, Nb) and depletion (troughs) of K, P and Ti. They exhibit high K-calc alkaline magma and peraluminous characteristics and considered as post orogenic granites (POG). The monzogranite reveal small to moderate negative Eu anomaly, while the pegmatites reveal moderate to large negative Eu anomaly. The pegmatite displays clear W-type tetrad effect of the REE while, the studied monzogranite do not show tetrad effect.

U–Pb geochronology, REE and trace element geochemistry of zircon from El Fereyid monzogranite, south Eastern Desert, Egypt

“…The pegmatite veins occur as irregular bodies varying in width from 0.5 to 1 m to over 5 m. They are mainly composed of quartz, K-feldspar, muscovite, and biotite megacrysts. Pegmatites contain higher radioactive element concentrations, especially in U and Th, as compared to other varieties of rocks in the study area due to the presence of radioactive minerals as thorite, uranothorite, samarskite, ishikawaite and are enriched by accessories such as zircon and monazite (Saleh et al, 2018;Dawoud et al, 2018). The rare earth elements concentration in pegmatite is less than that of monzogranite due to magmatic fractionation and absence of monazite (Dawoud et al, 2018).…”

“…The grains were polished to approximately half of their thickness. To select surface spots for age dating, we used optical (transmitted and re- (Middlemost, 1994) with plotted data for El Fereyid granites (Dawoud et al, 2018).…”

“…The monzogranite rocks are hosting late magmatic pegmatites occurring as pockets and veins (Abd El-Naby and Saleh, 2003;Raslan et al, 2010aRaslan et al, , 2010bSaleh et al, 2018;Dawoud et al, 2018). Pegmatites are often very coarse-grained and are reddish to buff-colored.…”

“…The bulk rock sample of El Fereyid monzogranite is enriched in large ion lithophile elements (Ba, Rb, and Sr), high field strength elements (Y, Zr, Nb, and REE), and depleted in Ca, Mg, K, P, and Ti. Monzogranite can be attributed as calc-alkaline series, has peraluminous characteristics and represents I-type granite (Dawoud et al, 2018). Monzogranite in El Fereid is plotted in the granite compositional field based on the TAS diagram (Cox et al, 1979 andMiddlemost, 1994) (Fig.…”

“…The concentration of LREE in monzogranite range from 130 to 220 ppm, while HREE range from 15 to 27 ppm. REE spectra demonstrate enrichment of LREE and low content of HREE with moderate negative Eu-anomaly (Eu/Eu* = 0.38-0.67) due to the presence of some accessory minerals like monazite, apatite, zircon (Dawoud et al, 2018).…”