Hydrothermal evolution of granitoid-hosted gold mineralization in gidami area: An example for orogenic-gold deposits in Egypt

Three types of fluid inclusions are recognized at the core and rim of the auriferous quartz vein as follows: 1) Two phases aqueous (H2O-NaCl ± KCl), 2) Two phases aqueous (H2ONaCl ± MgCl2), and 3) Three phases aqueous-carbonic (H2O-NaCl-CO2±CH4) fluid inclusions. Isochores intersection from fluid inclusions data outlines that, the Gidami gold deposits are of the mesothermal type formed at temperatures range between (270-300 °C), and pressure (750-850 bar) corresponds to a depth around 3 km (assuming pure lithostatic pressure). The ore-bearing fluids are supposed to be sourced mainly by fluids of metamorphic and meteoric origin. However, criteria of partial mixing with water of magmatic signatures has been proposed during fluid evolution. The transportation of gold was in form of bisulphide compounds in moderately reduced, neutral to weakly alkaline environment and then the precipitation occurred as a result of changing in Eh and pH conditions.