Gold in Ivory Coast

The Afema gold district in SE Côte d'Ivoire is controlled by regional NE-trending shear zones within a Paleoproterozoic (Birimian) volcanosedimentary sequence affected by low-grade metamorphism (chlorite geothermometry: 200-400°C). The post-metamorphic mineralization is in mylonitic quartz-muscovite-carbonate veins (locally cryptocrystalline graphite) parallel to the regional schistosity in meta-arenite and consists of pyrite, arsenian pyrite, arsenopyrite, and minor amounts of chalcopyrite, sphalerite, tetrahedrite, tennantite. Gold occurs as blebs and invisible in arsenian pyrite and arsenopyrite. Arsenopyrite geothermometry gives temperatures of 300-360°C. The hydrothermal system is chemically characterized by elevated As and Au, and depletion in Na (feldspar destruction). Ar-Ar dating on vein muscovite gave plateau ages of 1840 ±17  Ma and 1833 ±16 Ma; a Re-Os errorchron has an age of 1.9 ±0.1 Ga. Nd isotope analyses are in progress.