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Acid Mine Drainage (AMD) is characterized by high metal concentrations and an extremely low pH, primarily generated by the microbial oxidation of iron sulfides from mine tailings. Research on the microbial AMD community has largely focused on Bacteria, while little information is known about the Archaeal and Eukaryote members or the seasonal patterns within the communities. Here I examined the Bacterial, Archaeal, and eukaryotic AMD seasonal microbial community, using direct sequencing techniques on AMD samples from the Copper Cliff Tailings AMD site in Sudbury, Ontario, Canada. I found large variation in the community profile and species composition between sampling times of both the Bacterial and Eukaryote communities, suggesting a dynamic community, both between and within seasons. Bacterial diversity was highest during the winter, with Acidithiobacillus dominating, while during the summer, Acidiphilium was the dominant genus. The winter Eukaryote community was dominated by classes of algae and fungi, while the majority of summer sequencing could not be classified to the class level. Few reads were obtained for the Archaeal domain, with low and similar biodiversity between seasons. Overall, the AMD community variation and abundance were found to largely correlate with drainage water and seasonal temperature.

In general, tailings dams are expected to seep. Anomalous seepage, especially when induced by internal erosion, is a major concern for owners and operators. The long established techniques for monitoring water seepage provide sparse information which may not be sufficient to detect and map the seepage path. Hence, there exists a great need for non-invasive techniques that would be sensitive to changing seepage conditions. The non-invasive nature of the techniques is particularly important because drilling and other penetrating (invasive) investigation methods are normally avoided. / Non-invasive techniques such as self-potential and high-resolution resistivity have been significantly improved in the past decade and have been successfully used for water retention dam investigation and monitoring. The main difficulty in the use of these techniques in monitoring sulfide rich tailings dams is the presence of electrochemical potentials that renders the interpretation of the acquired self-potential data difficult. / Numerical modelling is one of the latest methods in interpreting self-potential anomalies induced by liquid flow. But, in order to model streaming potentials several parameters need to be measured or estimated; (1) the hydraulic driving force and the hydraulic conductivity are required to solve for the hydraulic pressure distribution; (2) the cross-coupling conductivity distribution is needed to calculate the conduction current source parameter; and (3) the resistivity distribution is needed to determine the resulting potential distribution. / The zeta-potential and the resistivity of three pyrite rich tailings from the Abitibi region in Quebec were measured over the pH range 2 to 5 in different KCl aqueous solutions for the purpose of estimating the magnitude of electrokinetic effect induced by mine water seepage and the electrical resistivity variation induced by particle migration. The experimental and theoretical results obtained in the present study are pertinent to the interpretation of self-potential data. The zeta-potential was found to vary from -27 to -2 mV and the resistivity of the tailings was found to increase when fine particles are eroded.

Over a century of mining activities and smelting in the area of Sudbury, Ontario, Canada have resulted in the contamination of the local soils with metal(loid) bearing particulates. Minor and trace elements associated with these phases are released during their weathering. This release is therefore strongly dependent on the mineralogical and chemical character of the metal(loid) bearing phases. The metal(loid)s are then subject to transport before being attenuated through their incorporation into secondary phases. Elevated concentrations of metal(loid)s in silica rich alteration layers has recently been described for altered surfaces at the solid-water and solid-atmospheric interfaces in tailings, and in the vicinity of smelters, respectively. To determine if similar coatings occur in soils, samples were taken from areas around three major smelting centers in the area. Coated grains were extracted from these samples and individually mounted to be analysed. Particulate matter (representing primary metal(loid)-bearing phases) and coatings (secondary metal(loid)-bearing phases) were analysed using scanning electron microscopy, Raman spectroscopy, Laser-Ablation Inductively-coupled plasma mass spectroscopy, Micro-X-ray fluorescence, and X-ray photoelectron spectroscopy. The particulates were divided into three main groups: smelter-derived particles, sulfides, and nickel-oxides. Smelter derived particles contained the most elevated concentrations of metal(loid)s in their sulfide inclusions and metal(loid)-rich rims. The mobility of metal(loid)s in the identified mineral phases found within particulates mirrored the transport observed in the soil column; Zn>Cu>Ni>Pb. Once mobilized, these elements are subject to transport before being attenuated by secondary phases. Micro-coatings were found to be composed of hematite, schwertmannite, ferrihydrite, silica, and jarosite group minerals. Coatings are distinguished on the basis of their atomic Si:Fe ratios: FeOx coatings have Si:Fe <1, Si–FeOx coatings have Si:Fe between 1-10, and SiOx coatings iv have Si:Fe>10. Iron-rich coatings (FeOx) and silica-rich coatings (SiOx) have lower trace-metal concentrations than Fe-SiOx coatings. Micrometer-thick coatings are predominantly composed of hematite, schwertmannite, ferrihydrite and (amorphous) silica and contain elevated metal(loid) concentrations in the form of metal(loid)-rich phosphate minerals (mainly minerals of the jarosite group). A general model is developed that describes the formation of mineral coatings in acid soils and their important role in the uptake and retention of metal(loids). Here, micrometer-thick Fe-silica coatings form through adsorption, co-precipitation and dehydration processes involving amorphous silica and iron hydroxides. Metal(loid)-bearing phases nucleate within a gel-type matrix and are subsequently preserved during dehydration and solidification. Aluminum-rich surfaces form on mineral grains once the pH has been raised sufficiently high (pH~5-6) so as to lead to the complete removal of sulfate-bearing phases. The implications of this model are widespread in terms of the attenuation of metal(loid)s in acid soils and their retention or subsequent remobilization in recovered soils with near neutral pH.

The existence of small-scale gold mining in Nova Scotia between 1868 and 1942 has resulted in many high arsenic (As) tailings areas in the province, some of which are near rural/urban areas and are used for recreational activities such as dirt bike racing and all-terrain vehicle (ATV) riding. Because of the natural association of As with gold ore in the Meguma Terrane, processing of ore has resulted in As-rich mine waste that contains up to 2500 times more As than the Canadian soil quality guideline of 12 mg/kg. These high As concentrations in combination with the recreational use of these sites creates a risk of human exposure. The objective of this work was to investigate the effects of different cover options that might be used to mitigate the risk of human exposure. Four tailings samples were selected to represent the geochemical variability from two tailings areas: Montague gold mines and Goldenville. These samples were characterized and subjected to 29 weeks of column testing, in which each sample was leached with three different input solutions including synthetic rainwater (to simulate uncovered tailings exposed to natural acid rain), synthetic rainwater equilibrated with calcium carbonate (to simulate rainwater percolation through a crushed limestone cover), and a dilute organic acid solution (to simulate a vegetative cover). Results of acid base accounting (ABA) tests indicate that samples have the potential to generate acid in the future (ratio of neutralization potential to acid potential is less than 2), though surface water at the sites is currently circum-neutral. Acidic paste pH values (2.9) from a sample of As-rich hardpan indicate that a small volume of tailings at Montague are currently generating acid. Results of column testing indicate that the cover types simulated by the input solutions had less of an effect on the out-flowing leachate chemistry than did the small volume of secondary As phases in each sample (scorodite, yukonite, hydrous ferric arsenate and hydrous ferric oxides). For the majority of sample types, columns leached with an organic acid solution reported higher leachate As concentrations than were reported from columns leached with either the rainwater or carbonate-rainwater solutions. / Thesis (Master, Geological Sciences & Geological Engineering) -- Queen's University, 2010-10-27 14:26:06.13

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