地理情報学と地球統計学: 概要

Geochemical Characteristics and Radioactive Elements Estimation along Trenches of Um Ara area, South Eastern Desert, Egypt

Saleh GM and Kamar MS

Um Ara area is located in the extreme south Eastern Desert of Egypt between 581400mE-584900mE and 2503000mN-2504600mN. The area comprises distinct tectono-stratigraphic units beginning with the oldest as follows: Dokhan volcanic and post-collision granitoids (monzogranite, and alkali feldspar granite), and associated with dykes and quartz veins. The granite affected by deuteric K-metasomatism (microclinization) followed by Na-metasomatism (albitization) causing zonation in this part of the pluton. The high radioactivity in the anomalous sites is structurally controlled (strong shearing, fracturing and jointing). The intensity of mineralization is especially significant along joint sets striking NNW-SSE, NNESSW and NE-SW trending. The spacing among these joints ranges from few mm up to about 5 cm. locally, the joints are filled with kaolinite and other alteration products including hematite and Mnoxides. Geochemically, Um Ara granites trenches and core samples show a relative enrichment in K2O compositions due to plagioclase destruction and formation of muscovite/sericitization.

Um Ara granites trenches and core samples have variable total REEs contents 117.41 to 308.28 and 256.51 to 397.22 ppm respectively. ΣLREEs in trenches and core samples range from 108.47 to 298.41ppm and from 236.84 to 384.78 ppm respectively, whereas ΣHREEs range from 5.48 to 14.01 ppm and from 12.44 to 19.67 ppm respectively. The lowest concentration of total REEs in core samples is at 100m depth, while the highest values at 145m depth. Um Ara granites trenches, U contents vary from 154 to 506 ppm with an average of 245.7 ppm, and Th contents vary from 47 to 415 ppm with an average of 165.4 ppm. Core samples granite, U contents vary from 128 to 349 ppm with an average of 237.3 ppm, and Th contents vary from 45 to 146 ppm with an average 107.4 ppm. Visible secondary uranium mineralization is represented mainly by uranophane and β-uranophane. Uranium is also contained within a range of U-bearing accessory minerals, mainly fluorite, monazite, xenotime, allanite and zircon. The secondary processes played a main role in uranium enrichment (uranium added to these granitic sites post-magmatically). Um Ara altered granites trenches and core samples rocks are an abnormal radiation and have an extension. So, these anomalies are suitable to be a place for uranium extraction. The result is the continuous of its mining work besides leachability experiments.