Evaluating mineralogical, geochemical and microbial relationships within sulfur-bearing mine wastes; a multianalytical and multivariate statistical approach

Abstract

Mine tailings harbour a dense population of extremophiles that play key roles in metal and mineral transformations. While microbially mediated mineral oxidation and reduction within sulfurbearing mine waste has been widely reported, linkages and statistical significance between environmental parameters and geochemical and mineralogical compositions with microbial community diversity has not yet been documented. A combined geochemistry, mineralogy, and genomics approach has been used in this study to better understand the biogeochemical processes occurring within a gradient of tailings dam materials both at surface and down a depth profile. Complex microbial diversity patterns across sample types, environmental conditions, spatial locations, and geochemical and mineralogical compositions, are addressed using multivariate statistical analysis. Additionally, scanning electron microscopy (SEM) and transmission electron micrscopy (TEM) are used to analyze the compositional and morphological features of microbemineral assemblages. A total of 40 sulfur-bearing tailings samples have been collected aseptically from five constructed tailing dam structures, in Sudbury, Ontario. Samples have been grouped into three zones including oxidized, transition, and unoxidized, which are distinguished by pH, munsell colour and mineralogical composition. Oxidized material is composed of silicates and ironhydroxides (goethite) and iron-hydroxy sulfate minerals (jarosite, schwertmannite), with contact pH ranging from 2.6 - 4.5. Material from the unoxidized zone consists mainly of silicates and sulfides (pyrite, pyrrhotite, chalcopyrite and greigite), with a higher contact pH ranging from 4.14 - 5.71. Transitional material is dominantly composed of silicates, but contains both sulfides and secondary iron and sulfate minerals, with pH ranging from 3.6 - 5.31. Microbial community composition and structures are often attributed to their surrounding geochemical environments. However, no significant correlations are observed between total metal content and microbial community compositions across the analyzed samples. However, community compositions and structures exhibit significant changes based on the contact pH ranges and mineralogical iv compositions of the analyzed tailings material. Oxidized, transition, and unoxidized material exhibit similar taxa, however, relative abundance of taxa exhibits extensive variability across the identified zones. Key indicator species are statistically tested across the three alteration zones, with microorganisms whose metabolic functions underpin iron and/or S oxidation and/or reduction identified as microorganisms characterizing alteration zones. Microbial-mineral assemblages analyzed at the nano-scale exhibit minerals that were not identified by routine whole sample analysis (XRD), thereby indicating the importance of performing both SEM and TEM to fully understand microbial-mineral interactions. The microbial-mineral relationships observed in this study both at the micro- and nano-meter scale have resulted in furthering understanding of biogeochemical processes occurring within the analyzed sulfur-bearing tailings material.