Saleh, and 5 co-authors (2019) reported that rare-earth elements associated with granitic pegmatites at Gabal El Fereyid area are exposed in the south Eastern Desert of Egypt. The study area is occupied by tonalite and monzogranites, the latter is intruded by pegmatites with a distinctive distribution of economically important mineralization. The studied pegmatitic bodies occur as veins that are ranging in size from few meters to 25 meters long and their width usually less than 7 meters; although small pockets are present. The latter display zoning structure (concentric layering) consisting of feldspar-rich zones enveloping pockets of mica (mainly muscovite) and all zoning internal quartz core. Field work using gamma spectroscopy measurements over these pegmatites shows that some bodies are radiometrically anomalous, especially the muscovite-rich zones. The mineralogy and geochemistry (trace and rare earth elements contents) of the radioactive zones in such pegmatites were achieved.
Mineral characterization of the highly radioactive zones shows enrichment in thorite, uranothorite, ishikawaite, samarskite and fergusonite minerals. The spectrometric measurements of the studied pegmatites show that they possess the highest content of radioelements as well. They show enrichment in large ion lithophile elements (LILE; Pb, Rb, Sr) and high field strength elements (HFSE; Y, Zr, Th, U, Nb) and depletion in K, P and Ti. The studied granitic pegmatites indicate moderate to large negative Eu anomaly and show clear M-type tetrad effect of REE.
The "REE tetrad effect" can appear as four distinct anomalies spanning elements, La-Ce-Pr-Nd, (Pm)-Sm-Eu-Gd, Gd-Tb- Dy-Ho and Er-Tm-Yb-Lu, when plotted in series as normalized REE concentrations. The tetrad effect appears in meteorites (Inoue et al., 2009) and various types of terrestrial rocks (Masuda et al., 1987;Masuda and Akagi, 1989;Akagi et al., 1993;Lee et al., 1994 Lee et al., 2010a Lee et al., 2013 Bau, 1996 Bau, 1999 Irber, 1999; Jahn et al., 2001; Monecke et al., 2002 Monecke et al., 2007 Monecke et al., 2011 Takahashi et al., 2002; Wu et al., 2004; Liu and Zhang, 2005; Veksler et al., 2005; DukTin and Keppler, 2015). Researchers interpret the "tetrad effect" in highly evolved granitic rocks either as forming within the magma-fluid system or as inherited from an external fluid influencing the system during or after magma emplacement (Bau and Dulski, 1995; Jahn et al., 2001; Monecke et al., 2002; Wu et al., 2004) and others.
The tetrad effect appears in meteorites (Inoue et al., 2009) and various types of terrestrial rocks (Masuda et al., 1987; Masuda and Akagi, 1989; Akagi et al., 1993; Lee et al., 1994 Lee et al., 2010a Lee et al., 2013 Bau, 1996 Bau,1999 Irber, 1999; Jahn et al., 2001; Monecke et al., 2002 Monecke et al., 2007 Monecke et al., 2011 Takahashi et al., 2002; Wu et al., 2004; Liu and Zhang, 2005; Veksler et al., 2005; DukTin and Keppler, 2015). Researchers interpret the tetrad effect in highly evolved granitic rocks either as forming within the magma- fluid system or as inherited from an external fluid influencing the system during or after magma emplacement (Bau and Dulski, 1995; Jahn et al., 2001; Monecke et al., 2002; Wu et al., 2004). Liu and Zhang (2005) alternatively proposed that pegmatitic magmas or parent materials acquired the signature from interaction with an external fluid prior to their emplacement.
In this interpretation, the tetrad effect ultimately results from differential REE partitioning during separation of the aqueous phase from a silicate melt. However, Monecke et al. (2002) reported that mineral precipitates from the hydrothermal fluids showed an M-type REE tetrad effect. This indicates that the REE tetrad effect represents a secondary phenomenon related to fluid-rock interaction rather than a process intrinsic to magma evolution.
The mineralogical and geochemical signature of investigated pegmatites represents a NYF-type (Niobium–Yttrium–Fluorine family), whereas the enrichment of rare element is an indication of high degrees of fractional crystallization of a suite of volatile-rich magmas. Uranium and thorium mineralization in the studied pegmatite are related to magmatic (syngenetic) origin with hydrothermal (epigenetic) input. The magmatic mineralization is evidenced by occurrence of thorite and zircon, whereas the hydrothermal activity is represented by alteration of feldspars and formation of pyrite and iron oxides associated with the radioactive minerals. The high levels of radioactivity and rare earth elements mineralization in the studied granitic pegmatite bodies make them a target to exploration and to enlarge the potentiality of the highly mineralized localities.
An approach was made to study the radioactive pegmatites to determine their compositional characteristics and assessing their mineralization potentials at El Fereyid area in the South Eastern Desert of Egypt. Economically important uranium and rare earth elements mineralization were recorded in the pegmatite bodies intruding monzogranites.
These pegmatites occur as veins, pockets, dykes and irregular bodies.
Petrographic studies of the pegmatites and their enclosing granitic rocks shows similar mineral composition mainly of perthite, quartz and less abundant plagioclase with minor accessory phases of micas.
Mineralogically, the studied pegmatites are characterized by abundance of radioactive minerals, radioelements-bearing accessory minerals and rare earth elements.
Geochemically, they are clearly enriched in Zr, U, Th, Nb, F and REE compared to the host granite. They are considered as a promising ore material for their rare earth elements mineralization which contain mainly Zr, Ta, Y, U, Th, Zn, Nb, Rb, Hf, and REE. The overall geochemical signatures of El Fereyid pegmatites show high fractionation, and high level of rare earth elements mineralization potential. The main potentiality of the study area is in U and Th, whereas Nb, Y, Zr and REE are of secondary importance. The high levels of radioactivity and rare earth elements mineralization in some pegmatite bodies make them a target to enlarge the potentiality of the
highly mineralized localities.
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