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British Columbia Mine Reclamation Symposium

Evaluation of static testing results as validation of visual classification of PAG waste rock Pollard, Dan; Finke, Niko; Bianchin, Mario


A challenge facing mines is prevention of metal leaching (ML) and acid rock drainage (ARD). These naturally occurring processes can be intensified by exposure of sulphidic geological materials to oxygen and water, frequently because of legacy practices in the handling of mine rock. To prevent any negative impacts on the environment, an essential task in the remediation of legacy mines is the identification and proper treatment of potentially acid generating (PAG) waste rock. No single test provides reliable prediction of drainage chemistry and the potential for ML/ARD. Consideration of several lines of evidence is typically necessary. Static testing of samples to determine metal content, sulphur speciation, acid and neutralization potential, and calculation of acid base accounting statistics such as net neutralizing potential (NNP) and neutralization potential ratio (NPR) is a key tool. It can provide important baseline information to assist with characterization of different material types found at a mine site. Material characterization can be complicated by variation in chemical and mineralogical content within a deposit, and by mixing with different materials during placement. If used in isolation, static testing may not adequately inform remediation requirements. Remediation efforts that involve the removal of PAG material must rely on information that is available in real time, such as visual identification of material classes and indications of chemical behavior, such as staining indicating pyrite oxidation, in addition to static testing. We examine the use of various lines of evidence to validate visual identification of PAG waste rock at a former gold mine. In addition to sulphur speciation, signatures in the relative abundance of metals, including copper and zinc, were used to validate the visual classification of PAG and non-PAG material.

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