Geochemistry and mineralizations of the Wadi Ghadir younger granites and associated pegmatites, South Eastern Desert, Egypt

Abstract

The study area is covered by quartz diorites, monzogranites, and pegmatites. Geochemically, the monzogranites and pegmatites have peraluminous to slightly metaluminous calc-alkaline to alkaline affinity, emplaced in volcanic arc setting and crystallized under moderate water-vapor pressure (3–5 kb) and temperature of 800–850 °C for monzogranites and 700–750 °C for pegmatites. The monzogranites reveal small to moderate negative Eu anomaly (Eu/Eu* = 0.62 to 1.0) and averages Eu/Sm = 0.168 and light rare earth elements (LREEs)/heavy rare earth elements (HREEs) = 48.78. The pegmatites reveal moderate to large negative Eu anomaly (Eu/Eu* = 2.39 to 2.96) patterns and have averages Eu/Sm = 0.075 and LREEs/HREEs = 32.22. The monzogranites are altered along two fracture zones exhibiting propylitic, silicification and record high radioactive measurements. These alterations cause enrichment in SiO2, Fe2O3 t, Ni, Y, V, Co, Th, and REEs except Er and depletion in Al2O3, TiO2, CaO, MgO, Na2O, K2O, P2O5, Cu, Zn, Cr, Zr, Rb, Ba, Pb, Sr, Nb, Ga, Hf, Cs, Li, Sn, Be, Sc, U, and Ta. The normalized chondrite pattern denotes moderate REEs fractionation and shows a narrow range fractionation of HREEs in both fresh, altered monzogranites and pegmatites. The studied fresh and altered monzogranites do not show tetrad effect, while the pegmatites show tetrad effect. The average eU content in fresh monzogranites is 5.55 parts per million (ppm), and the average U content is 5.03 ppm, whereas the average eTh content is 18.93 ppm, and the average Th content is 20.90 ppm. The average eU content in pegmatites is 14.76 ppm, and the average U content is 4.75 ppm, whereas the average eTh content is 57.02 ppm, and the average Th content is 15.30 ppm. The eU and eTh in the alteration zones reach up to 16.50 and 296.20 ppm, respectively. These high radioactivities are attributed to the presence of thorite, bastnasite, fluorite, and columbite.