Challenge: To help select and permit an optimal mine closure strategy.

Solution: INTERA developed a groundwater flow and transport model of the Maurliden mining area to simulate the potential impacts of various mine closure options on water resources. This work was completed in support of a Pre-Feasibility Study and environmental permit application required for mine closure. The Maurliden mining area consists of polymetallic (Zn-Pb-Cu-Au-Ag), open-pit mines. Each volcanic-hosted massive sulfide deposit consists of a fractured rhyolite bedrock system overlain by approximately 10 meters of relatively more permeable glacial till. Dissolved metals are generated by the natural oxidation of highly sulfidic (~20 weight % sulfide) materials present in the waste rock dump and in the wall rock of the open pit, and these represent the two principal sources of constituents of potential concern that could impact ground and surface water through various pathways. In support of selecting the best closure strategy for the Maurliden Mine, a calibrated groundwater flow and transport model was developed and applied to predict future concentrations of dissolved metals in nearby groundwater and surface water resources over a 1,000-year period. In developing the conceptual and numerical models, INTERA characterized the hydraulic properties of the predominately fractured bedrock system through a field program that included flow logging, single-well pumping tests, and a multiple-well pumping test. Following the interpretation of flow logging and pumping tests, and after model calibration, the model was used to evaluate nine different closure options with two future climate scenarios for three constituents of potential concern. Closure options ranged from capping the waste rock dump in place and allowing the natural formation of a pit-lake, to completely filling the open pit with cemented paste backfill mixed with offsite tailings.  

Results: The modeling simulations informed Boliden’s decision on the best closure strategy to be presented in an environmental permit application to the Swedish Land and Environmental Court.