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An investigation into the construction, excavation, and geochemical history of a waste rock dump and implications for long-term water quality at the Island Copper Mine, Port Hardy, British Columbia

University of British Columbia

The Island Copper Mine, near Port Hardy, British Columbia, is currently in the process of closure. As part of its closure plans, the mine excavated a waste rock dump (the Northwest Dump) and disposed of it into the open pit. The open pit was flooded with seawater from Rupert Inlet and will become chemically meromictic once a freshwater cap becomes established on top of the seawater. The decision to excavate the waste rock dump and place it into the open pit was made because the dump was generating acid rock drainage. The excavation of the dump provided a unique opportunity to examine the interior of a waste rock pile that had been weathering for over ten years. This thesis examined three main questions: 1) was local groundwater contaminated by the acid rock drainage coming from the Northwest Dump?, 2) has excavation of the dump led to improvements in the quality of the local groundwater and nearby Francis Lake, and 3) will the material from the Northwest Dump have a noticeable effect on water quality in the flooded pit, specifically the freshwater cap? To answer these questions, samples were collected from various parts of the dump and subjected to numerous analyses. Samples were characterized in terms of particle size, mineralogy, and chemical composition. Since the rock in this dump had been weathering for so long, it contained large amounts of reaction products. Before meaningful results could be obtained from kinetic prediction tests, these reaction products had to be removed, otherwise the kinetic tests would have had to continue for many months. Shake flask tests were used to determine what type of solution would be most efficient at removing the reaction products from the samples. When the best solution was determined, the samples underwent a batch leach to remove the reaction products. After the samples came out of the batch leach, they were subjected to both static and kinetic prediction tests. These tests were used to characterize the samples in terms of their acid-generating and acid-consuming ability and to determine their oxidation, neutralization, and leaching rates. As a result of this testwork, the following conclusions were made: 1) based on the batch leach tests, significant levels of sulphate and metals would be produced by this material when it was first rinsed (either by precipitation or by seawater during flooding), 2) the static prediction tests indicated that nearly all of the dump material tested had a high potential to generate acid, 3) the kinetic tests indicated that all but three of the samples tested would be acidic from the time they were first exposed, (three of the samples remained neutral throughout kinetic testing with correspondingly low levels of sulphide oxidation and metal leaching), 4) local groundwater has been contaminated and acid rock drainage from the Northwest Dump is probably the primary source of this contamination, 5) excavation of the dump has not yet led to any noticeable improvements in the quality of the local groundwater or Francis Lake, and 6) the material from the dump could have a noticeable impact on the water quality in the flooded pit, specifically the freshwater cap (copper concentrations especially are likely to exceed the water quality guidelines of the Water Management Pond discharge permit within five years).

Thesis/Dissertation

application/pdf

2009-03-07

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http://hdl.handle.net/2429/5717

Mining Engineering

University of British Columbia

UBCV

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