Environmental impact of mine exploitation: An early predictive methodology based on ore mineralogy and contaminant speciation

摘要

Mining wastes containing sulfide minerals can generate contaminated waters as acid mine drainage (AMD) and contaminated neutral drainage (CND). It occurs when such minerals are exposed to oxygen and water. Nowadays, mineralogical work is parsimonious, independently, and differentially done according to the needs of the department (exploration, geotechnics, metallurgy and environment), at different stages in the mine development process. Moreover, environmental impact assessments (EIA) are realized late in the process and rarely contain pertinent mineralogical characterization on ores and piloting wastes. Contaminant-bearing minerals are often not detected at the early stages of life mining cycle and environmental problems could occur at the production or mine closure steps. This work proposes to implement a reliable methodology, based on mineralogical characterization of the ore at the exploration stages, which is useful for each stage of the mine projects and limit the surprising environmental or metallurgical issues. Three polymetallic sulfide ores and seven gold deposits from various origins around the world were studied. Crushed ore samples representing feed ore of advanced projects and of production mines were used to validate the methodology with realistic cases. The mineralogical methodology consisted in chemical assays and XRD, optical microscopy, SEM and EPMA were done. Five of the ores were also submitted to geochemical tests to compare mineralogical prediction results with their experimental leaching behavior. Major, minor, and trace minerals were identified, quantified, and the bearing-minerals were searched for the polluting elements (and valuables). The main conclusion is that detailed mineralogical work can save redundant work, time and money, and allows detecting the problems at the beginning of mining developments, improving mine waste management and mine closure planning.