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

Numerous gold-bearing hydrothermal quartz vein deposits occur in the Birimian greenstone belts of west Africa. The Kanyankaw gold mine at Ghana 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 Proterozoic Birimian greenstones. Ore mineralogy is relatively simple, consisting of pyite, sphalerite, chalcopyrite, galena, electrum and limonite. Electrums (86.5~93.0 atom. % Au) occur as gold both in limonite matrix and associated with galena. Compared with electrums from other Archean mesothermal gold vein deposits, electrums from the Kanyankaw mine area are 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 Kanyankaw is correlated with Archean mesothermal gold deposits in the world. Fluid inclusion data show that main gold-sulfide mineralization was formed from H2O-CO2-NaCl fluids with relatively low salinities (1.4 to 10.9 wt. % equiv. NaCl) at temperatures between 211o and 462oC. Evidence of initial fluid boiling may indicate up to 130 bars assuming lithostatic loads. Gold deposition was probably a result of decreasing sulfur activity accompanying boiling caused by sulfide precipitation and/or H2S loss. The d34S values of sulfide minerals(0.5 to 6.5‰) reveals igneous origin. Meanwhile, the measured and calculated O-H isotope compositions of ore fluids (d18O = 5.6 to 6.0‰; dD = -13 to -36‰) may indicate that mesothermal gold mineralization at the Kanyankaw mine overlap the general ore fluid composition from Archean mesothermal gold deposits.