On the petrogenesis and evolution of U-rich granite: insights from mineral chemistry studies of Gattar granite, North Ea
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ORIGINAL PAPER
On the petrogenesis and evolution of U-rich granite: insights from mineral chemistry studies of Gattar granite, North Eastern Desert, Egypt Mahmoud Hany Shalaby & Ehab Korany Abu Zeid & Nasser Mourad Mahdy
Received: 8 January 2014 / Accepted: 14 May 2014 # Saudi Society for Geosciences 2014
Abstract In Egypt, the younger granites are essentially undeformed and emplaced at shallow levels with typical A-type chemical characteristics. Petrogenesis of A-type granites in Egypt may be more intricate, especially where magmatic fluids and hydrothermal solutions are concerned. Moreover, these post-orogenic granites are attracting increased economic interest because some plutons like Gattar granite are associated with high concentrations of ore metals such U and Mo, and most of such U-rich granites have common features of localization of the U-mineralization within the alteration zones along sheared and fractured parts of the granites and intimate fluorite association. Our study demonstrated that the feldspars formed in a temperature below 700 °C and at a shallow depth, the temperature of transformation of zircon is high between 400 and 700 °C and shifted to less than 600 °C by an increasing F content in final differentiation products. Muscovite of Gattar granite is late to post-magmatic and formed in a temperature between 300 and 400 °C by hydrolysis of K-feldspars, and chlorite originated in nearly 300 °C on the average estimation. The chemical compositions of apatite reported that the apatite classified as fluoro-apatite with average F contents 3.56 % reflecting either primary magma conditions or subsequent metamorphism in the presence of relatively high F fluids. Pitchblende appeared in average 230 °C, and secondary uranium minerals emerged in average 150 °C. It is markedly noticeable that there is temperature gradation from very high temperature alteration near to solidification of granitic magma to very low alteration that represents prevalence of secondary uranium deposits. Our findings articulated the role of H2O- and F-bearing fluids in alteration
M. H. Shalaby : E. K. Abu Zeid : N. M. Mahdy (*) Nuclear Materials Authority, P.O.530, El-Maadi, Cairo, Egypt e-mail: [email protected]
of essential and accessory minerals and transformation of uranium element from solution and fluids into the crystal lattice of zircon as U+4 in an early stage event. Perhaps, the cause of this gradation is the evolution of U-rich granitic magma into residual fluids through magmatic differentiation and, afterwards, hydrothermal solutions through fluid-rock interaction. Keywords Granite . Petrogenesis . Uranium . Fluorite . Evolution
Introduction Granites are among the most controversial rocks of the Earth’s continental crust. They have been enigmatic for a long time along the history of geology and still they are in present days. Granite geology, like the other problems related to the origin and evolution of the Earth, had its proper dark ages, where all kinds of conjectures and speculations prevailed. Today
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