Rare Metal Mineralization (Zr, U, Th, REE) Associated to El Seboah Acidic Peralkaline Rocks, South Western Desert of Egypt: Recovery Technique
El Seboah acidic mass represent one of peralkaline volcanic activity phenomena in the South Western Desert of Egypt. The mass covering an area about 0.25 km2 and consists of peralkaline granites (slightly and highly altered) intruded in Nubian sandstones and cutted by peralkaline rhyolite dyke which runs in NNE-SSW trend. Petrographical study indicated that, slightly altered peralkaline granite consists of quartz, aegirine, cryptocrystalline silica, potash feldspar perthites and alkali amphibole. The accessories are opaques and zircon while carbonate, hematite and secondary uranium minerals are secondary products. Iron oxides being heterogeneous in intensity and distribution in highly altered peralkaline granite. The original textural characteristics for highly altered peralkaline granite under the ferrugination process obliterated and essential minerals affected by different degrees. Also new mineral formed as subsolidus albite clots, eudialyte mineral and REE composite grains. Peralkaline rhyolite dyke characterized by spherulititc texture, fine - to medium-grained greenish color and composed mainly of radiated aegirine-augite, quartz, anorthoclase and opaques. Extreme enrichments in rare metals such as (Zr, Nb, U and Th, REEs and Y) characterize these peralkaline acidic rocks. The highest concentrations ( Zr up to > 1%, 0.1% Nb, 0.5% total REEs, Y up to 0 .49%, eU up to 54 ppm and eTh up to 685 ppm). The rare metals bearing minerals are zircon (a single crystals and composite grains), thorite, uranothorite, bastnaesite and amorphous secondary uranium. The chondrite normalized pattern in slightly, highly altered peralkaline granites and peralkaline rhyolite indicated that, higher LREEs enriched pattern, alterations of granites took place under open system and these rocks evolved from magma of lithospheric rifting, Slightly enriched LREEs pattern in peralkaline rhyolite dyke, due to the presence of aegirine-augite mineral. Strong negative △Eu < 1 indicated that the nature of residual peralkaline melts: (a) it was extremely rich in fluorine, H2O, and thus very low viscosity, despite its low temperature (<650oC); (b) it was strong depleted in feldspar - compatible elements, as indicated by strong negative Eu anomalies; and (c) it had abundances of HFSE cations. Redistribution of elements took place by post magmatic hydrothermal solutions. Negative △Ce < 1 anomaly, means that the alteration fluids were oxic for altered granite (open system) and slightly oxic for emplaced peralkaline rhyolite. Extraction of ΣREEs +Y from sample of highly altered peralkaline granite applied. The leaching efficiency exceeding 80%.
Peralkaline Granites, Thorite, Amorphous Secondary Uranium, Compatible Elements, Lithospheric Rifting
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