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 Aspyrite,
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. |
