The present work deals with the mineralogical and geochemical investigations of radioactive minerals and rare
earth elements associated with granitic pegmatites at Gabal El Fereyid area 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 25m long and their width usually less than 7 m; 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 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. |
