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UBC Theses and Dissertations

Application of molybdenum (and zinc) stable isotopes to trace geochemical attenuation in mine waste Skierszkan, Elliott Karl

Abstract

Mining activities generate tremendous quantities of waste rock and tailings that must be carefully managed to prevent contamination of water resources by metal-leaching. Proper environmental management of mine drainage requires a detailed understanding of the mechanisms that control the mobility of metals in mine waste. This thesis applied stable-isotope analyses of molybdenum (Mo) and zinc (Zn) to constrain the geochemical attenuation processes controlling transport of these metals in mine waste. The key outcomes of this work are: (1) the establishment of a robust protocol for determining high-precision Mo isotope ratios in mine-waste samples using double-spike multi-collector inductively coupled plasma mass-spectrometry; (2) the demonstration that mine drainage at field sites becomes enriched in heavy Mo isotopes because Mo attenuation preferentially removes light isotopes; the predominant Mo attenuation mechanisms considered being sorption onto (oxyhydr)oxides and precipitation of molybdate minerals; (3) the demonstration that mine drainage becomes depleted in heavy Zn isotopes under alkaline pH conditions because of preferential removal of heavy Zn isotopes during Zn adsorption and/or precipitation of secondary minerals; and (4) the determination of new Mo isotopic fractionation factors for the precipitation of powellite (CaMoO₄) and wulfenite (PbMoO₄)—important sinks of Mo in mine waste environments. Overall, this thesis demonstrates that metal stable isotope analyses are an informative new tool now available to trace the processes that control metal transport in the environment. Further improvements in the quantification of metal removal using stable isotopic analyses should become possible with ongoing research into the causes of metal stable isotope fractionation.

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