The Effect of Mine Dewatering and Peatland Form on the Pattern of Surface Recharge Around the Victor Diamond Mine, James Bay Lowlands

English Abstract:

The Victor diamond mine requires substantial aquifer dewatering and depressurization of the limestone bedrock to keep the mine pit dry. Located in the James Bay Lowland, the dewatering has affected the pattern and rate of surface recharge through the peatlands that cover >90% of the area. The area is typified with domed bogs and fen water tracks; the fens act as the conveyors of water and connect with active stream. The surface recharge rate in the modelled watershed was simulated using HYDRUS 3D for the period of Jan 2005 to Dec 2012 (dewatering began Jan 2007), with two periods of two and six years in steady and unsteady state, respectively. The model was calibrated by using the daily water level in 20 observation wells, as well as observed total surface outflow and recharge of mine process water into the central quarry. The flow domain is 106 km² and extends to a depth of 300 m with 13 layers. The results shows that in pre-mining and mining conditions about 50,000 m3/day of water recharged through the surface mostly through the bogs that are the inter-fluvial areas between water tracks; the shallow peat along the fen water tracks conveyed most of this water out of the system as horizontal shallow surface and sub-surface flow. At the end of the simulated period for the mining condition (Dec 2012) when the dewatering rate approached 86,000 m3/day, ~ 25% of this water was derived from a 2-3 km radius around the mine. The model suggests recharge here was intensified because of a locally thinner or absent low permeability claystone layer (elsewhere ~50 m below the surface, separating upper and lower bedrock aquifers) and a thinner marine sediment layer. Simulation revealed that surface outflow along the fen water-tracks and dewatering of the mine are the two main components that control the surface recharge rates across the domain.