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Abstract

The objective of this study was to identify the trace metal/secondary mineral phase associations in a heterogeneous waste rock dump that contains carbonate bearing lithologies and a mix of metal sulfides. The identification of attenuation processes can be used to better predict the drainage chemistry from waste rock at this site and/or other sites with similar waste rock. This study also provides the opportunity to investigate metal attenuation at the largest scale of complexity and compare these observations to those made from the smaller scale tests conducted for this site and is useful for understanding scalability of the smaller scale tests. This study shows that in carbonate bearing waste rock the predominant processes that attenuate copper (Cu) and zinc (Zn) are precipitation of hydroxycarbonate and hydroxysulfate phases and sorption onto iron oxides. Arsenic (As) and molybdenum (Mo) are associated with iron oxides, although for Mo this association was observed in only a few samples. Lead (Pb) was observed in association with iron oxides. Wulfenite observed in a few samples provides an additional attenuation process for Mo and Pb. The stability of the phases and potential for remobilization of these metals can also be suggested from this study. The hydroxycarbonate/hydroxysulfate phases are the least stable phases identified and can dissolve at pH