Integration of geophysical and geological data for delimitation of mineralized zones in Um Naggat area, Central Eastern Desert, Egypt

摘要

An integrated approach for geophysical, geological and mineralogical data was followed for Um Naggat area, Central Eastern Desert, Egypt, in order to delineate its mineralized zones. The albitized granites are well-defined on the Th- and U-channel images, by their anomalous shapes, reaching 150ppm and 90ppm respectively, beside low K content.Interpretations of the aeromagnetic maps delineated four regional structural trends oriented due NNW, NW, ENE and E–W directions. They are identified as strike-slip faults, which coincide well with field observations, where NW-trending faults cut and displace right laterally ENE-trending older ones. The interaction between these two strike-slip fault systems confining the albite granite is easily identified on the regional data presenting longer wavelength anomalies, implying deep-seated structures. They could represent potential pathways for migration of enriched mineralized fluids. Geochemically, albite granites of peraluminous characteristics that had suffered extensive post-magmatic metasomatic reworking, resulted into development of (Zr, Hf, Nb, Ta, U, Th, Sn) and albite-enriched and greisenized granite body of about 600m thick, and more than 3km in strike length. The albite granite is characterized by sharp increase in average rare metal content: Zr (830ppm), Hf (51ppm), Nb (340ppm), Ta (44ppm), and U (90ppm). Thorite, uranothorite, uraninite and zircon are the main uranium-bearing minerals of magmatic origin within the enclosing granite. However, with respect to Zr, Nb, and Ta, the albitized granite can be categorized as rare metal granite. The integration of airborne geophysical (magnetic and γ-ray spectrometric), geological, geochemical and mineralogical data succeeded in assigning the albite granite of Um Naggat pluton as a mineralized zone. This zone is characterized by its high thorium and uranium of hydrothermal origin as indicated by its low Th/U ratio, with rare metals mineralization controlled by two main structural trends in the NW- and ENE-directions.