Tuesday, April 26, 2016
Confluence Ballroom Foyer (The Westin Denver Downtown)
The colonization and weathering of sulfide minerals by Fe- and S-oxidizing bacteria in aerobic waste rock at a sub-Arctic, mine-waste research site is counterbalanced by the extreme climate. Experimental waste rock piles were constructed to examine the mine's closure design of a double layer cover composed of a low sulfide waste rock and low permeability till atop the higher sulfide waste rock. Leachate from these experiments indicated variable pH and SO4 concentrations because of sulfide content and a temperature-moderating influence by the till. The thermal moderation below the till provided a more stable environment for the production of acid, growth of acidophilic Fe- and S-oxidizing bacteria, and enhanced weathering during wet up; however, the production of acid rock drainage was limited after saturation and freezing of the fine-grained matrix. Examination of sulfide weathering in the closure design indicated a strong SO4 signal above the till and less oxidation and no difference in S speciation below the till. Examination of the bacterial communities indicated the prevalence of Pseudomonas, Rhodanobacter, Sideroxydans, and Thiobacillus in the waste rock. Pseudomonas were dominant in the drier and more extreme environment of the freeze-thaw zone above the till, and Thiobacillus were dominant in the wetter/frozen environment below the till. A decreasing trend in Thiobacillus from the exterior to the interior and an opposing trend in Acidithiobacillus suggest more extensive sulfide oxidation and acid generation occurred deeper in the interior of the waste rock prior to onset of frozen conditions. Although the presence of the till layer in the cover may have initially moderated temperature variations and enhanced initial weathering in the underlying waste rock, it also increased water retention and led to a continually frozen waste rock. The heterogeneity of microbial populations and geochemical environments was still apparent in this moderated but frozen environment.
Jeff Langman, University of Idaho, Moscow, ID
Harish Veeramani, University of Glasgow, Glasgow, Scotland
David Blowes, University of Waterloo, Waterloo, ON, Canada
David Wilson, University of Waterloo, Waterloo, ON, Canada
Leslie Smith, University of British Columbia, Vancouver, BC, Canada
David Sego, University of Alberta, Edmonton, AB, Canada
Richard Amos, Carelton University, Ottawa, ON, Canada
Steven Holland, University of Waterloo, Waterloo, ON, Canada
