South Bay Mine Mill Site Area Closure

Most of the infrastructure associated with the closed mining operations was removed, while acid-producing waste rock was used to develop a useable grade over the undulating surface of bedrock for mining operations. In addition, acid rock drainage (ARD) and metal leaching were present at the Mill Site area due to concentrate spills and ore handling stockpiles. This created a limited availability of local soil and topsoil for mine reclamation.

Our team began with a desktop evaluation to develop recommendations for a suitable liner material for the low permeability cover, followed by a geophysical survey to delineate areas of elevated conductivity response attributed to impacts by base metal concentrates. Our field staff completed a test pit/trench investigation to delineate the perimeter of the ARD-producing material and, to determine if it is potentially acid-producing, collect samples for metals and static acid-based accounting (ABA) testing. To address the limited availability of local soil and topsoil, we completed a material sourcing investigation to locate suitable quantities of for the construction impermeable cover.

The selected closure design involved regrading to divert surface runoff, removal of ARD-producing material from the beach and an area north of the west drainage, consolidation of ARD-producing material into the main Mill Site area, and capping of the material with a low permeability composite cover consisting of a bitumen linear, drainage composite and soil cover. We prepared a detailed design report, engineering drawings and technical specifications for closure of the Mill Site area. Our environmental staff also guided the Ministry through permit applications for three aggregate pits to provide sufficient cover soil, as well as presenting and sourcing a local topsoil alternative for the project.

The cost-effective closure design for the Mill Site area minimized the area requiring capping, incorporating a relatively maintenance-free and robust impermeable cover while prioritizing locally sourced soil materials.