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UBC Theses and Dissertations

Microbiology and geochemistry of neutral pH waste rock from the Antamina mine, Peru Dockrey, John William


The microbial populations of waste rock piles and field cells producing neutral pH drainage at the Antamina mine were characterized to better understand processes which affect current and future drainage quality. Naturally weathered waste rock samples were collected and examined using a variety of high resolution imaging, geochemical, mineralogical, and microbiological techniques. Despite the relatively young age of the waste rock piles (1.5 years), populations dominated by neutrophilic sulfur oxidizers as large as 10⁸ bacteria per gram were found. An exponential relationship was found between the size of microbial communities and the contemporary sulfate loadings. These results indicate that the microbial populations rapidly grow to reach a mass which is proportional to the rate of substrate release, and then decrease as the host rocks reactivity diminishes. One sample from a field cell producing pH 6.2 drainage had a mixed population of neutrophiles and acidophiles capable of both S⁰ and Fe²⁺ oxidation. A mini-column study was conducted to determine the catalytic effect of microbiology in various rock types. No catalysis was identified in the sulfur concentrations of most mini-column series, with the exception of the one mini-column series constructed of material containing acidophilic S⁰ and Fe²⁺ oxidizing bacteria, which demonstrated strong microbial catalysis. It was also determined that concentrations of Mo as low as 10mg/l were toxic to these acidophilic bacteria, and dissolved Mo may inhibit the establishment of these geochemically important bacteria. A massive sulfide from this material was thoroughly examined using high resolution imaging techniques. Biofilms of bacteria were found upon and within a porous schwertmannite precipitate. The mixed population of neutrophilic and acidophilic bacteria and circumneutral drainage pH implies that the bacteria are living in acidic microenvironments surrounding sulfide minerals in which ferric iron leaching can take place. The large microbial populations and the close correlation between geochemistry and biology described in this study, emphasize the importance of biological processes in determining current and future drainage quality emanating from the mine waste.

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