Implications of Non-Acid Metal Leaching on Mine Rock Management at a Nickel Mine in Permafrost Terrain:1 – Mine Rock Evaluation

• Main Authors: M. J. Rinker, R. V. Nicholson, M. A. Venhuis, B. Swarbrick
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Subjects: Nicholson; permafrost
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.502.9016; http://www.techtransfer.osmre.gov/NTTMainSite/Library/proceed/sudbury2003/sudbury03/130.pdf

Raglan is a nickel-copper-cobalt mine in the continuous permafrost region of Quebec. The management plan for waste rock at the mine was developed during the Environmental Assessment stage of the project and was based on acid based accounting (ABA) methods to identify acid generating and non-acid rock types with the intent to backfill the open pits and freeze the acid waste. The screening criteria were reexamined in 1999 to address nickel leaching and to develop more conservative and lower risk criteria than the ABA approach. A waste rock assessment study was initiated to focus on nickel leaching at neutral pH. The major rock types were characterized and humidity cell tests were established with regular distilled water and with pH adjusted (acetic acid to pH<7) water to determine nickel release rates from these materials. The results showed that the waste rock solids exhibited high nickel to sulphur ratios that likely reflected traces of pentlandite sulphur in contrast to the more usual pyrrhotite sulphur in similar waste rock. Nickel leaching was evident for most rock types even when the sulphur contents in the rock were as low as 0.3%. In contrast to other studies that exhibited lag times of tens of weeks to observe nickel leaching, the absence of buffering above pH values of 8 in the Raglan materials resulted in nickel leaching within a few weeks of initiating the humidity cell tests. It was found that nickel leaching at neutral pH and not acid generation was the defining criteria for waste rock that required additional management. As a result, a significant decision was made to alter the mine plans and to revise the baseline assessment of the proposed mining areas as described in a companion paper (Nicholson et al., 2003).