Gold Metallogeny of the Egyptian South Eastern Desert

Abstract

The South Eastern Desert, is the northern part of the Nubian Shield, characterized by abundant ophiolites, extensive high strain zones, and a multilayered structural architecture. Gold mineralisation is related to discrete occurrences of mesothermal quartz ± carbonate veins (< 100 m-long), cutting dismembered ophiolites and schistose metasedimentary-metavolcanic rocks. Though generally controlled by shear/fault zones, the mineralized quartz veins display a spatial association with granitoid-gabbroid intrusions exhibiting signs of forceful emplacement into the country rocks. In the areas where no intrusions are exposed, rhyolite and dacite dykes or granophyre sills appear to cut the structural trend in the host rocks and control the mineralized quartz veins. K-metasomatism is conspicuously associated with gold lodes, despite the variability of the host lithologies. Most of the mineralization is related to visible free-milling gold/electrum inclusions persistent in arsenopyrite or along pyrite fractures and grain boundaries, with subordinate invisible gold in As-pyrite. The mineralogy, fluid inclusions and stable isotope characteristics of several deposits in the region prove to reveal similar mineralization styles, ore fluids and isotope signatures, suggesting inherent similarities in the deposition process, fluid source and likely in the gold introduction related timing. Overheating by thrusting and concomitant calc-alkaline magmatism, along with metamorphic dehydration and devolatization promoted the circulation of hydrothermal fluids in a metallogenically fertile, mafic crust and deposited gold in accretionary and transpressional structures.