Mapping gold-bearing massive sulfide deposits in the Neoproterozoic Allaqi Suture, southeast Egypt with Landsat TM and SIR-C/ X SAR images

Meta-volcanic sequences in the Neoproterozoic AmbianNubian Shield host auriferous massive sulfide deposits with su$ace 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)-CIX-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 517-511-314*5/4 band-ratio Landsat TM image shows the Umm Garaiat alteration zone as sugary white; this appears red in the 517-415-311 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 glt gold. Density slicing using 517 and 311 Landsat TM band-ratios effectively maps clay and iron alteration. The 517 density slicing Landsat TM image suggests that the Umm Garaiat alteration zone is dominated by clay minemls. The 311 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-CIX-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.