Mineralogy and geochemistry of the Sikait U-Au-bearing lamprophyre dyke, South Eastern Desert, Egypt
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ORIGINAL PAPER
Mineralogy and geochemistry of the Sikait U-Au-bearing lamprophyre dyke, South Eastern Desert, Egypt Amira Mohammed El Tohamy 1 Received: 20 September 2018 / Accepted: 27 February 2019 # Saudi Society for Geosciences 2019
Abstract A 150-m-long mineralized lamprophyre dyke intrudes mylonite-mélange at the eastern side of Wadi Sikait and granite at its western side. Its petrographic, mineral, and geochemical characteristics were investigated in order to determine its genetic history as well as the petrogensis of the hosted mineralizations. Rocks of the Sikait lamprophyre dyke have a porphyritic and, less commonly, aphanitic texture. They consist of REEs-U-Th- and Nb, Ta-bearing minerals in addition to Au and native nickel, zircon, and fluorite. The ratios of LREEs to each of the HREEs, MREEs, and HFSE are relatively high. The U and Th contents in the part of the dyke existing in granite are slightly high than those in that hosted by the mylonite-mélange. The Sikait lamprophyre dyke has a calc-alkaline affinity and metaluminous to peraluminous. Its parent melts were derived from a mantle metasomatised by carbonatitic fluids. The protolith was subjected to slight to moderate partial melting in shallow to intermediate depths. During the emplacement of the dyke, U was released from its mineral precursors, transported, and redeposited under favorable condition. Its concentration in the part of the dyke hosted by granite was increased by the action of young surficial processes. On the other hand, Au was derived from the ophiolitic metagabbros and serpentinites that over thursted on the mylonites. It was precipitated from mesothermal and epithermal solutions. The Sikait dyke was affected by several alteration processes; the most common of which is hematitization and metasomatic carbonatization. Keywords Egypt . Eastern Desert . Sikait . Lamprophyre dyke . Uranium . REEs . Gold
Introduction The term lamprophyre was first introduced by Gumbel Von (1874) for small-volume, mantle-derived rocks composed of mafic phenocrysts enclosed by a matrix of smaller mafic and felsic minerals with distinct panidiomorphic to porphyritic textures (Fitton and Upton 1987; Müller and Groves 1995; Rock 1987, 1991). They are mostly hypabyssal (dykes, sills, or pipes), volatile (H2O, CO2) rich, sodic to potassic igneous rocks. Lamprophyres are considered to be the products of a low degree of partial melting of enriched subcontinental lithospheric mantle sources (e.g., Müller and Groves 1995; Rock Editorial handling: Federico Lucci Electronic supplementary material The online version of this article (https://doi.org/10.1007/s12517-019-4394-0) contains supplementary material, which is available to authorized users. * Amira Mohammed El Tohamy [email protected] 1
Nuclear Materials Authority, P.O.Box:530, El-Maadi, Cairo, Egypt
1987). Therefore, their geochemical characteristics are closely related to the enrichment of these sources throughout the evolution of the lithosphere in a dynamic system. Rock (1991), Le Maitre (19
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