The impact of the presence of acidophilic iron-oxidizing bacteria in south waste rock dump has been investigated over a period of two years at la Mine Doyon. During this period of time, samples were collected from various locations within the dump. The waste rocks are made for a significant part of sericite schists and their friability is such that pyrite grains are extensively exposed to chemical weathering and microbiological oxidation.

The sampling of the south dump was done during the drilling of bore hole #1 by removing drill cuttings over the whole height of the dump; water samples were collected from the different bore holes (#1, #2, #3, #4 and #6) by pumping, and microorganisms were "trapped" with especially designed devices in underground water. The results showed that:

1- Thiobacillus ferrooxidans type bacteria are widely distributed within the dump, in underground and seepage water, everywhere iron sulfides are exposed; Thiabacillus thiooxidans and T. thioparus are also present wherever oxygen supply is not limiting. Leptospirillum ferrooxidans, another iron-oxidizing bacterium, has been isolated from a "mild" non-freezing area in the dump. Iron oxidizing activity is particularly important in sections of the dump where bacterial growth temperature is optimal, where pH lies between 2,0 and 3,5 and where porosity permits aeration. Energy source (Fe²⁺, S^2-), water (running and intersitial) and carbon source (CO₂) are abundant through the waste rocks. Fe²⁺ is continuously supplied to bacterial metabolic reactions during chemical oxidation of pyrite by Fe³⁺.

2- The fairly high temperature inside the dump does not prevent bacterial colonization and activity, it provides a selective pressure for the thermophilic microorganisms to develop and carry over the oxidizing activity of the mesophilic bacteria.

3- We confirmed, for the first time in the field, that T. ferrooxidans, along with some other unidentified strains, is able to oxidize sulfur and sulfides to sulfuric acid in an anoxic environment under 30 m of rocks. This anaerobic biological respiration uses ferric ions as electron acceptors.

Last Modified: 2003-11-26		Important Notices

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