Journal of the Korean Society of Mineral and Energy Resources Engineers ISSN:2288-0291(Print) 2288-2790(Online) 한국자원공학회지

Within the Mayo Kebbi Prefecture, southwestern part of Chad, numerous gold-bearing hydrothermal quartz vein deposits occur. The Gouin gold mine is a typical example among these deposits. Gold-sulfide mineralization of the mine occurs in a single stage of massive quartz veins which filled fractures in fault shear zones in Precambrian greenstones. Ore mineralogy is relatively simple, consisting of sphalerite (1.47~1.96 atom. % Fe), pyrite, chalcopyrite, covellite, galena, altaite and electrum. Electrums (75.47~90.91 atom. % Au) occurs as both free gold infilling the fracture of quartz and gold intergrown with chalcopyrite. Compared with electrums from other Archean mesothermal gold vein deposits, electrums from the Gouin mine area are typically gold-rich. The gold-rich nature of electrums, the absence of Ag-Sb (-As) sulfosalt mineral, and the massive appearance and simple mineralogy of veins indicate that gold mineralization at Gouin is correlated with Archean mesothermal gold deposits in the world. Fluid inclusion data show that main gold-sulfide mineralization was formed from H2O-NaCl fluids with relatively low salinities (1.91 to 14.97 wt. % equiv. NaCl) at temperatures between 129o and 361oC. Evidence of initial fluid boiling may indicate up to 640 bars assuming lithostatic loads. Gold deposition was probably a result of decreasing sulfur activity accompanying boiling caused by sulfide precipitation and/or H2S loss.