Depressurising an Underground Ore Body at the McArthur River Mine in Northern Saskatchewan, Canada

Pre-mining depressurising of a deep ore body at the McArthur River mine in northern Saskatchewan was considered to decrease the risk associated with mining near 5 MPa water pressure and increasing the amount of ore that can be extracted. Based on a limited amount of field data, a three-dimensional finite element ground-water flow model was developed to predict the amount of water that would have to be pumped from surface wells or extracted with underground drainholes to meet this goal and the associated magnitude and extent of drawdown that would propagate to the surface over the life of the operation and its impact on surface-water resources. In addition, the results from the preliminary model were used to design a prototype depressurising well and a 30-day pumping test. Because of the predicted large volume of water that would have to be discharged, another still on-going investigation has been conducted to assess the effectiveness of localized depressurisation in improving mine tunnel stability in conjunction with ground freezing and cementaceous grouting.