Prediction and reality : static analyses versus actual rock weathering in waste dumps at Island Copper Mine, Port Hardy, B.C.

• Main Authors: Lister, Diane, Poling, G. W. (George Wesley), Horne, Ian A., Li, Michael Guoqing
• Language: English
• Published: 2009
• Online Access: http://hdl.handle.net/2429/11063

Island Copper Mine (ICM), owned by BMP Minerals Canada Ltd. is one of Canada's largest open pit low-grade copper mines and is located at the north end of Vancouver Island, British Columbia. Acid rock drainage (ARD) was first detected in the open pit area in 1982, and from the on-land waste rock dumps in 1985. All drainage from the mine area is directed to a water management pond for recycling in the concentrator and discharge when all provincial effluent standards are met. Island Copper is a calc-alkaline copper-molybdenum-gold porphyry deposit. Rock units have been both metasomatically (contact metamorphism) and hydrothermally altered. Minerals relevant to ARD-generating potential include pyrite, feldspar minerals, calcite, sericite and pyrophyllite. Data analysis of 214 acid-base accounting (ABA) results indicate that most ICM waste rock has a net neutralization potential (NNP) of less than +20 kg H₂SO₄/tonne, and an acid consuming to acid producing (ACPAPP) ratio of less than 3:1. Detailed study of eight weathered samples from ICM waste rock dumps indicate that type and intensity of alteration coupled with total sulphur content may be the primary ARD controls at the site. Two of the six samples (both weakly altered volcanic) predicted by ABA analysis to generate net acidity have yet to do so despite up to 12 years of weathering on the waste rock dumps.