Detection of alteration zones using ASTER imagery and geological field observations: Al Wajh area, Northwestern Arabian Shield, Saudi Arabia

Neoproterozoic rocks are exposed in the southwestern Midyan terrane, which is located in the northwestern Arabian Shield. This terrane contains ophiolitic and metavolcanic rocks and arc-related intrusions. A NW-trending sinistral fault system (Najd Fault System, NFS) affected these Neoproterozoic rocks. The integration of remote sensing techniques, such as band combinations and band ratios of ASTER images, with field observations, helped to discriminate sulfide-rich rocks and to delineate alteration zones, gossans, and quartz veins, which commonly host ore mineralization. The band ratios used were the Al-OH minerals/advanced argillic alteration and the silica and Fe2+ band ratios. ASTER images were used to discriminate different rock units and construct an alteration map of the study area. Additionally, principal component analysis and frequency filtering techniques for ASTER images were used to extract linear faults and shear zone structures. Remote sensing ASTER images helped in the discovery of ancient mines that had not been previously recorded in the study area.