Between 1970 and 1990 approximately 180 million tons of very low grade copper and molybdenum were mined @ 30,000 tpd from an open pit mine, processed by floatation to produce a concentrate and the tailings deposited in a cross valley tailings impoundment constructed by the centerline method. Approximately 200 million tons of waste rock had been generated during open pit mining. Both the waste rock and tailings contained both sulphides and calcite and while they were not acid generating, oxidation of the sulphides in circum neutral to alkali conditions resulted in the leaching of molybdenum. The mine closed in 1989 and a closure plan was required.
Dr. Robertson was the project principal for SRK who were retained to do the mine waste and tailings characterization, contaminated leaching studies, and develop appropriate remediation and control measures and an overall closure plan. Site investigation measures included drilling, sampling and testing for both waste material geochemical characterization, acid generation and leaching studies; contaminant plume investigations and characterization, site hydrology determination, assessment of the stability of all structures and identification and evaluation of remediation construction materials. Design activities included the modelling of all surface flows and contaminant leaching, including long term leaching, the evaluation and design of alternative control measures including covers, resloping, relocation, collection and treatment of contaminated water, downstream environmental impacts assessments. Extensive detailed closure plans and reports were prepared and there was extensive participation in meetings and negotiations with all levels of the Provincial Regulations Authorities.
Brenda Mines Ltd
Mine Closure Planning