EXPLORATION FOR THE MINERALIZED GRANITES IN ARABO-NUBIAN SHIELD, USING ORBITAL REMOTE SENSING

Abstract: In the Arabo-Nubian Shield, many granitic rocks host mineralized alteration zones. These are large enough (several hundreds of meters across) and have distinctive characteristic reflectance spectra to be mapped with the 30 m spatial resolution Landsat Thematic Mapper (TM) images. Landsat TM data have been used for finding and mapping alteration zones associated with ore mineral deposits, in the central part of the Eastern Desert of Egypt. Digital processing of Landsat TM images for the study area generated several products ranging from natural color composites images (bands 7 – 4 – 2) to ratioing images (5/7 - 5/1 and band 4) and (5/7 – 4/5 - 3/1). The natural color composite images (bands 7-4-2) have been used in regional structural analysis and provide an excellent base map. The ratioing images (5/7-5/1 and band 4 in RGB) were used in discrimination of the different rock units in the study area. The ratioing images (5/7 - 4/5 – 3/1 in Red, Green and Blue) succeeded to distinguish between mineralized alteration zones (hosted in the granitic rocks) and non mineralized zones. Geological studies using Lansat TM images and field studies reveal that the study area is covered by ophiolitic ultramafic rocks, island arc assemlage (metavolcanic and gabbro-diorite rocks) and granitic rocks. Several alteration zones hosted in the granitic rocks were detected and characterized by ferrugination, silicification and kaolinitization. Geochemical data indicate that these alteration zones are associated with fluorite veins and enriched by Nb, Ta, Li, Be, Ce, La and Y. The fluorite veins are enriched in radioactive minerals, where uranium reaches up to 500 ppm and thorium up to 194 ppm. The contents of Ta₂O₅ reach up to 0.0065 % and Nb₂O₅ up to 0.017 % in these mineralized zones.

This demonstrates the utility of orbital remote sensing for finding unknown mineralized zones in the Eastern Desert and other arid regions.