The Sukari Gold Mine, Eastern Desert - Egypt: structural setting, mineralogy and fluid inclusion study

The Sukarl gold mine (18.8 Mt @ 2.14 g/t Au) is located 15 km west of the Red Sea coast in the southern central Eastern Desert of Egypt. The vein-type deposit is hosted in Late Neoproterozoic granite that intruded island-arc and ophiolite rock assemblages. The vein-forming process is related to overall late Pan-African shear and extension tectonics. At Sukari, bulk NE-SW strike-slip deformation was accommodated by a local flower structure and extensional faults with veins that formed initially at conditions of about 300 degreesC and 1.5-2 kbar. Gold is associated with sulfides in quartz veins and in alteration zones. Pyrite and arsenopyrite dominate the sulfide ore beside minor sphalerite, chalcopyrite and galena. Gold occurs in three distinct positions: (1) anhedral grains (GI) at the contact between As-rich zones within the arsenian pyrite; (2) randomly distributed anhedral grains (GII) and along cracks in arsenian pyrite and arsenopyrite, and (3) large gold grains (GIII) interstitial to fine-grained pyrite and arsenopyrite. Fluid inclusion studies yield minimum vein-formation temperatures and pressures between 96 and 188 degreesC, 210 and 1,890 bar, respectively, which is in the range of epi- to mesothermal hydrothermal ore deposits. The structural evolution of the area suggests a long-term, cyclic process of repeated veining and leaching followed by sealing, initiated by the intrusion of granodiorite. This cyclic process explains the mineral-ogical features and is responsible for the predicted gold reserves of the Sukari deposits. A characteristic feature of the Sukari gold mineralization is the co-precipitation of gold and arsenic in pyrite and arsenopyrite.