Characteristic of gold mineralization associated with granites at Hamash old gold mine, South Eastern Desert, Egypt

Well-known controversy over the genesis of orogenic gold mineralization in granites has been a subject of research worldwide. Hamash gold mine is considered one of the pharaohs mines in the South Eastern Desert of Egypt, where gold mineralization is hosted by granites. In this study, we utilized field, ore microscopy, and geochemical data to determine the genesis of granites and the associated gold deposits. We found that the granites, intruded into island-arc metavolcanics and metavolcanoclastic assemblages, are characterized by variable major and trace elements, calc-alkaline, and I-type granitoids that reflect a fractional crystallization. Their trace and rare earth elements reflect magma that is related to subduction tectonic setting. The gold mineralization is confined to quartz veins that cut through granitic rocks, extend in NW-SE and N-S directions, and are formed during shear-extensional tectonics. The gold is found with sulfides in quartz veins and wallrock alteration. Silicification and sericitization are the most hydrothermal alteration zones associated the ore formation, comprise an inner quartz-sericite-carbonate-chlorite-sulfide assemblage. The results of chemical analysis reveal an increase of SiO2, Fe2O3, S, and L.O.I. concentrations and moderate depletion in K2O, Na2O, and LILE suggesting that they were affected by mineral replacement reactions and sulfidation in the altered wallrocks close to Au-quartz veins. The gold is represented by tiny inclusions, with minor chalcopyrite, galena, and arsenopyrite that mainly fill the microfracture in quartz and pyrite grains. Furthermore, a general model of gold mineralization suggests that the gold was contemporaneously formed during syn-orogenic stage, transpressional deformation assigned to D2 deformation, and subduction-related thermal processes followed by gold-bearing fluids that fill the fractures, forming veins.