干旱区生态环境知识资源中心

Meta-volcanic sequences in the Neoproterozoic Arabian-Nubian Shield host auriferous massive sulfide deposits with surface expression in the form of clay and iron alteration zones. These are large enough (few 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) together with Shuttle imaging Radar (SIR)-C/X-Synthetic Aperture Radar (SAR) images are used for finding and mapping the alteration zones in the western part of the east-trending Allaqi suture in the Southeastern Desert of Egypt. The 5/7-5/1-3/4*5/4 band-ratio Landsat (TM) image shows the Umm Garaiat alteration zone as sugary M hire; this appears red in the 5/7-4/5-3/1 band-ratio Landsat (TM) image. Geological and geochemical data indicate that the Umm Garaiat alteration zone is the surface expression of a massive sulfide deposit that contains up to 12 g/t gold. Density slicing using 5/7 and 3/1 Landsat (TM) band-ratios effectively maps clay and iron alteration. The 5/7 density slicing Landsat (TM) image suggests that the Umm Garaiat alteration zone is dominated by clay minerals. The 3/1 density slicing Landsat (TM) image shows little evidence for FeO minerals associated with the Umm Garaiat alteration zone. Analysis of Landsat (TM) images with supervised classification techniques using the Umm Garaiat alteration zone as the training site helped identify previously unknown alteration zones at Wadi Marahiq. Interpretation of Chh-Lhh-Lhv SIR-C/X-SAR images helped in understanding the lithological and structural controls on massive sulfide deposits in the study area. This demonstrates the utility of orbital remote sensing for finding ore deposits in arid regions.