Geochemical and remote sensing exploration of mineralized zones in A-type granites, Central Eastern Desert, Egypt: Origin and concentration of rare metals
Abstract
Neoproterozoic granites from the Umm Naggat and Homrit Waggat areas, Cen-tral Eastern Desert (CED),Egypt, form part of the Nubian Shield and on the basis of textural and chemical characteristics, resemble highly fractionated rare metal-bearing A-type granites. Decorrelation Stretch (DS) and Band Rationing (BR) techniques of Sentinel-2 and Landsat-9 remote sensing data were successfully used in the spectral identification of lithological units, and particularly mineralized zones in A-type granites. Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) were successfully processed and analyzed to discriminate the spatial and spectral extent of the hydrothermal mineralized alteration zones related to the rare metal-bearing granitic plutons. Structural features associated with hydrothermal alteration minerals may control the distribution of rare earth element (REEs) and rare metal mineraliza-tion, which have been successfully identified by Sentinel-1enhanced Soble directional filter images, using automatic lineament extraction techniques. The predominant structural feature directions in rare metal-bearing granitic plutons are N-S and NW-SE trending. These plutons mainly comprise biotite granites, syenogranites and alkali feldspar granites. Rock-forming minerals are quartz, K-feldspar (Or94-99), plagioclase (An0-7) and biotite, with subordinate chlo-rite, muscovite and fluorite.. Zircon, Fe-Ti oxides, rutile, apatite, epidote, titanite, columbite and thorite are the main accessory phases. The investigated granitoids are enriched in Rb, Nb, Y, Ta, Hf, Ga, Zr and rare earth elements (REE = 170-558 ppm) in contrast to low contents of CaO, MgO, Sr, and pronounced negative Eu anomalies (Eu/Eu* = 0.01-0.29), similar to post-collisional rare-metal bearing A-type granites. Based on mineral and whole-rock chemistry, these A-type granites crystallized from highly fractionated I-type tonalite-granodiorite magma, followed by extensive fractional crystallization in the upper crust during lithospheric delamination. Rare-metal minerals of both magmatic and hydrothermal origin such as zircon, rutile, xenotime, thorite, cerite-(Ce), parasite, uranothorite, columbite, ishikawaite and bastnaesite are mainly disseminated. Integration of the enhanced images and geochemical analysis data are promising in discriminating lithological units and potential areas enriched with rare metals in the study areas.
Full text here: 10.5281/ZENODO.7562685
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