GEOCHEMISTRY, URANIUM, THORIUM AND RARE EARTH ELEMENTS OF TRACHYTE DYKES OF UMM SALATIT MOUNTAIN AREA, CENTRAL EASTERN DESERT, EGYPT

M. M. Ghoneim, G. M. Saleh, M. D. Dawoud, M. S. Azab, M. A. Mohamed, H. A. Awad

Ghoneim M. M. et al. / News of the Ural State Mining University 3 (2018) 7-18

Umm Salatit Mountain area is a part of the Central Eastern Desert of Egypt. It is composed of ophiolitic mélange, older granitoids, biotite granites, muscovite granites and post granitic dykes and veins.
Purpose of the work. The present work deals with the detailed investigations of the geology, petrography, geochemistry and spectrometric prospecting of the studied trachyte dykes as a possible source of uranium mineralization.
Research methods. This work involves both field work (Construction of geological map with the structural features, scale 1 : 50,000, Spectrometric measurements of the different rock units using a portable gamma-ray spectrometer RS-230) and laboratory work (preparation of thin sections for petrographic studies by polarizing microscope), Atomic Emission Spectroscopy (AES), and Mass-Spectrometer with Inductively Coupled Plasma (ICPMS).
Results. Petrographically, trachyte dykes consist mainly of K-feldspar with relatively minor amount of plagioclase, iron oxides, quartz and biotite. Secondary minerals are represented by sericite, muscovite, chlorite, carbonates and epidote. Accessory minerals are represented by opaque minerals. Trachytic textures are the main characteristic feature in trachyte. Geochemically, the investigated trachyte dykes were originated from an alkali magmarich in total alkalis, and the tectonic setting is continental basalt. Trachyte dykes have steep LREEs, nearly flat HREEs and a negative Eu anomaly. The negative Eu anomaly is either due to the partitioning of Eu into feldspar during fractionation, which is an important process in developing alkalinity, or the presence of residual feldspar in the source. Another alternative explanation for the negative Eu anomaly is based on the high oxygen fugacity in the melt due to volatile saturation. In general, all trachyte samples show moderate enrichment of most large ion lithophile elements (LILE) and high field strength elements (HFSE) and depletion of P, Ti and K. The depletion of Ti and p is ascribed to fractionation of titanomagnetite and apatite. The determination of equivalent uranium, thorium (ppm), potassium % and dose rate (m Sv/y) radiometrically by using portable RS-230 indicates that the dose rate in the trachyte dykes ranges from 0.5 to 1.5 with an average of 1.2 (m Sv/y). The radiometric data of the radioelements for them show a wide variation in eU and eTh contents. The eU content ranges from 2 to 14 ppm with an average of 6.6 ppm and the eTh content ranges from 4 to 37 ppm with an average of 18.03 ppm. Both U and Th correlate similarly with other major and trace elements, reflecting their geochemical coherence during the crystallization of the magma.

Keywords: geochemistry, uranium, trachyte dykes, Egypt, Umm Salatit.

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