Radioactivity, Mineralogy and Rare Earth Elements (Ree) Geochemistry of Monzogranites and Alkali-Feldspar Granites, Wadi Hawashia, North Eastern Desert, Egypt

Abstract

The studied monzogranites and alkali-feldspar granites of W. Hawashia, North Eastern Desert of Egypt occur as small granitic mass intruding the granodiorites. The monzogranites represent the central part of the mapped area and are intruded by the alkali-feldspar granites forming a small mass or cupola at the roof of the monzogranites. The alkali-feldspar granites cut by faults trending in NNW-SSE, E-W and NNE-SSW directions and show brecciation and local silicification, hematitization, sericitization and chloritization. Petrographically, the monzogranites are essentially composed of plagioclase, quartz, alkali-feldspars and biotite. The accessory minerals are apatite and zircon. The alkali-feldspar granites are mainly composed of K-feldspars, quartz, albite and biotite, while zircon, allanite, samarskite and violet fluorite are the accessory minerals. Chondrite-normalized REE patterns show that the alkali-feldspar granites have higher REE content (∑REE= 202ppm) than the monzogranites (∑REE= 43ppm). The monzogranites have small negative Eu anomaly reflecting high contents of plagioclase, while the alkali-feldspar granites show large negative Eu anomaly suggesting highly fractionated magma characterized by the least content of plagioclase. The chemical analyses of uranium and thorium indicate that the examined alkali-feldspar granites are characterized by higher U and Th contents (averages are 73 and 119 ppm, respectively) compared with the studied monzogranites (averages are 9 and 21 ppm, respectively). Detailed microscopic investigations supported by X-ray diffraction (XRD) and Environmental Scanning Electron Microscope (ESEM) with EDX microanalyzer for the radioactive alkali-feldspar granite samples revealed the presence of uranophane as secondary uranium mineral and thorite as thorium mineral beside some U-bearing accessory minerals such as samarskite, allanite, metamict zircon and violet f luorite.