ASTER mapping and geochemical analysis of chromitite bodies in the Abu Dahr ophiolites, South Eastern Desert, Egypt

The Neoproterozoic Abu Dahr ophiolitic massif (~ 280 km²) in the South Eastern Desert of Egypt is one of the largest ophiolitic nappes in Egypt. Since in the early twentieth century, this nappe was the main source for chromitite, along with, magnesite, and asbestos (chrysotile and tremolite). In this study, we investigate the efficiency of using the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) imagery data in mapping the different rock units and chromitite bodies of the Abu Dahr nappe. The image processing techniques used encompassing decorrelation stretching, principal component analysis (PCA), minimum noise fraction (MNF), and band ratio (BR). The obtained results are verified by field work and microscopic investigations. The chemistry of chromite by using electron probe microanalysis (EPMA) technique indicates Cr-rich and Al-poor composition consistent with Cr-spinel in weakly metamorphosed fore-arc ultramafites formed in a low Al supra-subduction zone environment. The results reveal the efficiency of the ASTER data in mapping the chromitite bodies in metamorphosed ophiolitic nappes.