Transpressional zones in ophiolitic mélange terranes: Potential exploration targets for gold in the South Eastern Desert, Egypt

Gold-bearing quartz ± carbonate veins at the El-Anbat mine area, in the South Eastern Desert of Egypt, are associated with pervasively silicified, highly sheared ophiolitic and island arc rocks. Structural analysis of the shear fabrics along the ore zones indicate that geometry of the mineralized quartz veins and alteration patterns are controlled by the regional, NNW-trending zone of transpression, known as the Wadi Kharit-Wadi Hodein shear system, which is related to the 655-540. Ma, Najd strike-slip fault system in the Eastern Desert of Egypt. Microscopic and electron microprobe studies reveal that gold is chemically bound in As-pyrite, arsenopyrite, and gersdorffite, while free-milling gold is rarely observed in the quartz veins and silicified host rocks. Hydrothermal alteration could have liberated additional traces of gold from early pyrrhotite disseminated in listvenite. Geochemical studies reveal that shear zones associated with lenticular masses of porphyritic granite in the middle of the transpression zone are heavily mineralized (ppm levels) compared with other parts of the alteration zone. Where no granite is observed, low-grade zones (ppb levels) of gold mineralization occur in the highly deformed serpentinite and metavolcaniclastic rocks. Mass balance calculations suggest that hydrothermal fluids infiltrated under brittle-ductile shear conditions led to addition of Au, As, Cu, Rb, and Sb, concurrent with silicification, carbonatization and sericitization of the host rocks. Dispersion of gold and associated pathfinder elements is reported in altered rocks beyond the lode zone, indicating the potential for extensive, low-grade zones outside the already known El-Anbat mine location.