Geomechanical behaviour of fine- and coarse-grained copper tailings from Brazilian IOCG deposits

Iron oxide copper–gold (IOCG) deposits are unique because of the hydrothermal events responsible for their formation in the Archean Age. Such events affect the nature of the tailings resulting from copper ore extraction, as different deposits yield host rocks of varying characteristics. The present research evaluates the geomechanical behaviour of fine and coarse-grained copper tailings derived from two Brazilian mines located in IOCG deposits, focusing on a thorough mineralogical characterization of the tailings. For this purpose, drained and undrained triaxial tests were conducted on both tailings, considering three degrees of compaction and confining pressures ranging from 50 to 400 kPa. The results were evaluated in light of Critical State Soil Mechanics. They revealed distinctions in the overall geomechanical response between the fine and coarse-grained tailings because of grading and mineralogy differences. Despite being non-plastic, both tailings exhibited distinct behaviours related to the Critical State parameters and presented transitional responses. While transitional behaviour has previously been reported in both clayey and sandy soils, this is the first published case where fine-grained and coarse-grained copper tailings have demonstrated such a response.