Auriferous shear zones in the central Allaqi-Heiani belt: Orogenic gold in post-accretionary structures, SE Egypt

The East-West Gondwana collision (0.75-0.5 Ga), by oblique convergence, was likely accompanied by high hydrothermal fluid flux and dispersed orogenic gold in the Arabian-Nubian Shield. Gold-bearing quartz veins along steep-dipping shear zones bordering or cutting through the ophiolitic and island arc rocks in the central Allaqi-Heiani belt in Wadi Defeit area deserved the interest of ancient miners. Field and remote sensing data revealed the structural and lithological controls of gold-bearing quartz veins, providing means of exploration for new targets in the larger Wadi Allaqi environ. The auriferous shear zones are attributed to D3 (a non-coaxial continuation of early NE-SW compression regime), and D4 (slip reactivation by E-W compression and transcurrent deformation). Microscopic investigations of quartz veins reveal the association of gold blebs and specks with fissure-filling galena-spahlerite-tetrahedrite assemblage and deformed Fe-As-sulfides (pyrite and arsenopyrite). As a gold-only province with abundant, variably deformed and carbonated metabasic rocks, metamorphic devolatilization is suggested to explain the discrete gold occurrences by fluid focusing in complex shear intersections. The available fluid inclusion data affirm the low salinity aqueous-carbonic composition of the ore fluids and mesothermal conditions of ore deposition, consistent with metamorphic devolatilization. Structures related to late ductile deformation in the post-accretionary stages of the evolution of the shield are, therefore, considered high priority zones for future exploration programs.