Microbial communities in constituent layers of a geosynthetic clay-liner cover system and underlying tailings at the abandoned Cu/Zn Kam Kotia Mine (ON, Canada). KAM KOTIA 2017

Sustainable mine-waste management practices are an increasingly important aspect of metal production. Canada is home to more than 10,000 orphaned and abandoned mine sites, the legacy of which continues to impact local environments and communities. The largest liability associated with the metal-mining industry derives from acid mine drainage (AMD), caused by accelerated chemical and/or biological oxidation of sulfidic minerals within waste rock and mill tailings. AMD is characterized by acidic water, containing high concentrations of sulfate, ferrous iron, and associated metal(loid)s. The abandoned Cu/Zn Kam Kotia Mine, near Timmins, Ontario, is undergoing remediation by the Province of Ontario. Installation of a geosynthetic clay-liner (GCL) cover system was completed in 2008 to isolate acid-generating tailings from water and oxygen to mitigate sulfide oxidation. The GCL cover system is comprised of a vegetated soil cover layer, a granular protective layer (sand), a clay moisture retaining layer (clay), a GCL, granular capillary-break material (cushion sand), and a crushed waste-rock capillary-break layer, overlaying the acid-generating tailings. The goal of this study is to characterize the microbiology of the cover system and the underlying tailings to assess the performance of the cover for mitigating AMD generation. Total genomic DNA was extracted from each layer of the cover system, as well as the underlying tailings, and was analysed using a high-throughput amplicon sequencing of the 16S rRNA gene. Low relative abundances (and also viable counts) of microorganisms that catalyze transformations of iron and sulfur in the covered tailings, compared to previous studies on unreclaimed tailings, indicate that sulfide oxidation rates have decreased due to the presence of the GCL.