Mapping hydrothermal alteration zones using ASTER images in the Arabian–Nubian Shield: A case study of the northwestern Allaqi District, South Eastern Desert, Egypt

Abstract

In order to map and differentiate ore-bearing hydrothermal alteration zones at the northwestern part of Allaqi-Heiani, we use a combined method of the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) image processing, field relationship, mineralogical features, and rock chemical compositions. Hydrothermal alteration zones are identified on the basis of Advanced Spaceborne Thermal Emission and Reflection Radiometer data. Propylitic, phyllic, argillic, and silicification zones are recorded in different types of igneous and metamorphic rocks typically with chromite, goethite, ilmenite, galena and gold. Crosta and CEN techniques using ASTER are successfully applied to highlight the hydrothermal alteration zones and the structural elements represented by lithologic contacts and faults/fracture zones. Combining data of lineaments, alteration zones and ore mineralogy studied after obtaining a consequence of each map allowed predicting and mapping areas of probable high mineral resources. According to petrographic and remote sensing studies, types of alteration include sericitization, chloritization, epidotization, kaolinitization, carbonatization and silicification. The results of remote sensing in the study area are confirmed by X-ray diffraction (XRD), petrography, and SEM. In the studied district, there are ophiolitic ultramafic rocks,island-arc assemblage of metasediments, volcaniclastics and metagabbro-diorite, syntectonic graniteand dykes. Accordingly, to the present study can identify the most potential areas of mineralization taking us into consideration the overlapping of high lineament density areas with abundant alterations.