title: Characterizing geochemical reactions in unsaturated mine waste-rock piles using gaseous O2, CO2, 12CO2, and 13CO2.
abstract: In situ determinations of geochemical reaction rates in mine waste-rock piles remain a challenge. Depth-profiles of field O2 and CO2 pore-gas concentrations, delta13C(CO2) values, and moisture contents were used to characterize and quantify geochemical reaction rates in two waste-rock piles at the Key Lake Uranium Mine in northern Saskatchewan, Canada. Traditionally, the presence of O2 concentrations less than atmospheric in waste-rock piles has been attributed to mineral oxidation. This study showed that the interpretation of O2 and CO2 concentration profiles alone could not be used to identify the depths of dominant geochemical reactions in the piles and could lead to erroneous estimates of reaction rates. Modeling of the delta13C(CO2) depth profiles clearly showed that the gas concentration profiles present in the piles were the result of the oxidation of organic matter present below the piles, a mechanism not previously reported in the literature. Based on these findings, the rates of reactions in the organic zone were determined. The oxidation of organic matter at the base of waste-rock piles should be considered in future mine-waste pore-gas studies, in addition to sulfide oxidation and carbonate buffering.
authors.affiliation: Department of Geological Sciences, University of Saskatchewan, 114 Science Place, Saskatoon, Saskatchewan, Canada S7N 5E2.
authors.forename: Tyler K
authors.initials: TK
authors.lastname: Birkham
authors.forename: M Jim
authors.initials: MJ
authors.lastname: Hendry
authors.forename: L I
authors.initials: LI
authors.lastname: Wassenaar
authors.forename: Carl A
authors.initials: CA
authors.lastname: Mendoza
authors.forename: Eung Seok
authors.initials: ES
authors.lastname: Lee
mesh_terms: D002245:Carbon Dioxide / Q000032:analysis*; D002247:Carbon Isotopes; D004784:Environmental Monitoring; D055593:Geological Phenomena; D005844:Geology; D006863:Hydrogen-Ion Concentration; D008906:Mining; D010084:Oxidation-Reduction; D010100:Oxygen / Q000032:analysis*; D012037:Refuse Disposal
chemical_list: D002247:Carbon Isotopes; D002245:Carbon Dioxide; D010100:Oxygen