Abstract
A unique, highly radioactive variety of fluorite mineral has been recorded in the uranium occurrence of El-Missikat sheared granite pluton. In this occurrence, the uranium assumes different forms, including its presence as discrete, visible, secondary minerals, rare uraninite and its association with the jasperoid and silica veinlets. However, in some other parts of the sheared zone, the uranium was found to be solely incorporated with fluorite crystals, filling veinlets and fractures without any other manifestation. This paper focuses on the relevant mineralogical and geochemical characteristics of this unique fluorite variety. In addition to an investigation with binocular and polarizing microscopes, the separated fluorite grains were analyzed using an environmental scanning electron microscope (ESEM) and a field-emission scanning electron microscope. In addition to this, some fluorite crystals were subjected to electron microprobe analyses. While the fluorite accounted for as much as 20 % of the sheared granite samples studied, it was found to range from 82 to 96 % in the different size fractions of the separated heavy mineral content. In some parts of the separated fluorite crystals, uranium in quantities of up to 2200 ppm was found to be heterogeneously distributed in the fluorite lattice, regardless of its coloration.
Highlights
Several uranium occurrences have been discovered within or near the peripheries of some younger granitic plutons in the Eastern Desert of Egypt (Fig. 1)
The uranium mineralization in the El-Missikat occurrence is associated with jasperoid veins found along the faults and fractures that are mainly filled with silica in typical shear zones (Bakhit, 1978; Abu Dief, 1985; Hussein et al, 1986; Abu Dief et al, 1997 & Raslan, 2004)
Radioactive fluorite-bearing granite was recorded in the jasperoid veins of the highly sheared granite of the El-Missikat pluton, but without any visible secondary uranium minerals
Summary
Several uranium occurrences have been discovered within or near the peripheries of some younger granitic plutons in the Eastern Desert of Egypt (Fig. 1). In his study of the highly sheared granites of Wadi Belih in the Gattar pluton, Raslan (1996) ascertained that the granites rich in secondary uranium minerals are usually rich in fluorite with a deep-blue to violet colour (Raslan, 1996). Apart from these mineralized silicious veins, visible deepblue to violet fluorite crystals were recorded in other parts of El-Missikat, highly sheared mineralized granite that are very strongly radioactive, but without any visible uranium mineralization (Fig. 3A).
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