When the historic Copper Mountain Mine in south-western British Columbia restarted mining in 2010, waste rock and low grade ore (LGO) had to be segregated based on their acid rock drainage (ARD) potential, using operational monitoring of blast hole cuttings. Subsequent testing of waste rock and LGO blast fines showed that rock initially classified as potentially acid-generating (PAG) was expected to behave as non-PAG in stockpiles.
SRK evaluated the influence of rock type and age of the rock on ARD potential in several blast rock size fractions ranging from -2 mm to +25 mm. Samples were analysed by size fraction for parameters used to classify their ARD potential (sulphide sulphur and total inorganic carbon).
Bulk rock classified as PAG was found to be predominantly non-PAG in the 2 mm fraction; an observation attributable to the occurrence of carbonate as fracture fillings rather than a matrix component. Differences due to rock type and rock age did not significantly change the outcome.
These findings, in conjunction with the observed lack of ARD at the Copper Mountain Mine, despite historical mining spanning more than a century, resulted in the recommendation to the owner and regulator that geochemical segregation was not needed. Segregation is no longer required resulting in substantial reduction of costs for managing current and future waste rock and LGO. The ARD Management Plan for the mine was revised to include provisions for ongoing evaluation of the finding and re-imposing segregation based on alert and trigger levels.
This study demonstrated the value of a systematic rock ARD monitoring program implemented at start-up. The monitoring program was developed from a sound understanding of site-specific factors including deposit geology, climate, mining method, waste mineralogy and reactivity, and waste storage.
