Radioactivity, geochemical characteristics, and genetic relation of some younger granite plutons: example from central Eastern Desert, Egypt

Abstract

Gabal Abu Diab and Gabal Homret Waggat younger granite masses are located in the central Eastern Desert of Egypt. They show highly alteration, uranium enrichment, and a strong enrichment in some rare metal contents (U = 22, Zr = 373, Y = 120, Nb = 30 ppm). Field study indicates that they are biotite and biotite-muscovite granite and consist essentially of quartz, plagioclase, K-feldspar, biotite, and muscovite. Petrochemical studies and tectonic discrimination diagrams reveal that Gabal Abu Diab and Gabal Homret Waggat are highly differentiated granites classified as alkali feldspar granite and granite originated from metaluminous to mildly peraluminous magma in nature formed in post-orogenic environment. Field radiometric measurements revealed the localization of the radiometric anomaly in the shear zone at Gabal Abu Diab area. Within this anomaly, the uranium content reaches up to 97 ppm, while at Gabal Homret Waggat granite, the uranium content reaches up to 50 ppm (eU). Fractional crystallization and mass balance modeling for the younger granites of Gabal Abu Diab and Gabal Homret Waggat indicate their derivation from the parent mafic magma granodiorite, through fractional crystallization of 36.77 % plagioclase (An37), 9.99 % hornblende, 3.79 % biotite, 32.98 % quartz, 6.59 % orthoclase, and 3.79 % titanomagnetite with 6.09 % residual liquid and sum R 2 = 0.566 for Gabal Abu Diab and fractional crystallization of plagioclase (An37) 37.06 %, hornblende 10.19 %, biotite 4.10 %, quartz 33.38 %, orthoclase 5.99 %, and titanomagnetite 3.70 % with 5.58 % residual liquid and sum R 2 = 0.570 for Gabal Homret Waggat. The small value sum R 2 for both Gabal Homret Waggat and Gabal Abu Diab younger granites indicates a good fit of resulting model.