Acid-generating Potential of Mine Wastes from the Perkoa Polymetallic Zinc Deposit in Central-western Burkina Faso

Perkoa polymetallic zinc deposit, formed in a context of massive volcanogenic sulphides, generated large volumes of potentially reactive wastes during its exploitation due to the predominance of sulphide minerals. The aim of this study is to assess the acid-generating potential, i.e. the potential to generate acid mine drainage (AMD), of these wastes. To this end, four representative samples of these wastes were collected in a targeted manner at the Perkoa mine site, including waste rock, mine tailings and crusher waste. The analyses focused on determining the mineralogy by X-ray diffraction, the physico-chemical parameters (pH, electrical conductivity), the sulphur and carbon contents, and the acidity and neutralization potentials. The results reveal, with the exception of waste rock, acidic pH values (< 5), high electrical conductivity (> 500 µS/cm) and high sulphide content, mainly pyrite, sphalerite and pyrrhotite. The acid potential (AP) shows high values between 5 and 1000 kg CaCO3/t. On the other hand, the neutralization potential (NP) is low, with NPR (NP/AP) ratios below 1 and negative NNP (NP-AP) values in the range of -1300 to -5 kg CaCO3/t. These results show that these wastes would not be able to neutralise any acid that might be generated as a result of their oxidation. The most reactive acidogenic minerals are pyrite and pyrrhotite. Acid-producing mineral species are represented by silicates such as actinolite, microcline and chlorite. In summary, these results confirm a high risk of AMD development from mine wastes.