QUANTIFYING THE EFFECT OF LOCALIZED DEPRESSURIZATION ON A DEEP UNDERGROUND OREBODY AT THE McARTHUR RIVER MINE THROUGH CROSS HOLE HYDRAULIC TESTING AND GROUNDWATER MODELLING

摘要

The McArthur River mine in northern Saskatchewan is the largest single producer of uranium in the world. Most of the ore is extracted by raisebore mining methods at depths of 530 to 600 m below ground surface where pore pressures in the fractured host sandstone are on the order of 5 MPa. Currently, ground freezing is used to isolate the ore from ground-water sources. Localized depressurizing of the freeze drifts is being considered to increase their ground-stability. Cross-hole flow and shut-in tests in eight NQ-size coreholes were conducted in the basement rock that is adjacent to a fault contact with the overlying 500 m thick sandstone unit. The hydrogeologic parameters of basement rock in the vicinity of a freezing drift were obtained. A 15% to 25% reduction of pore pressure over a 25 m distance was observed within a three-hour test period. A detailed three-dimensional groundwater flow model was constructed to replicate the pore pressure measured in the coreholes. The pore pressure distribution simulated from the model provides the hydrogeologic input for geotechnical engineers to evaluate ground-stability and assess whether additional active depressurizing should be conducted.