Abstract
Operating mines commonly manage geological materials and define materials as geochemically suitable for construction use based on their acid rock drainage potential, which can result in a binary classification based on well-defined criteria such as neutralization potential ratio. However, trace element leaching can occur over a continuum so that criteria for “metal” leaching potential depend on many site-specific factors such as mineralogical and chemical characteristics, pH and Eh conditions, material physical characteristics, local climatic conditions, and proximity to receiving environment, and therefore cannot be generic. This paper presents some concepts for development of metal leaching criteria for construction materials at mining operations based on statistical evaluation of trace element occurrences, linkage to elemental deportment in reactive minerals, and expected pH of weathering environments. Trace elements that occur in association with readily soluble mineral phases or sulphides, which will release metals following oxidation, have higher potential for metal leaching in comparison to weathering-resistant mineralogical forms with low solubility such as silicates. For trace elements released from sulphide oxidation, metal leaching potential is also dependent on sulphide deportment. Trace element mobility is commonly dependent on pH of weathering environments, with elements speciating as cations showing higher mobility under relatively lower pH conditions and those speciating as oxyanion species (e.g., arsenic and selenium) showing greater leaching under alkaline conditions. The degree to which the latter elements leach is controlled by their mineralogical hosts and overall solid phase enrichment. The concepts will be discussed using a case study of a construction project at the Kerr-Sulphurets-Mitchell (KSM) Project in British Columbia, Canada.