Occurrence of sulfate-reducing bacteria under a wide range of physico-chemical conditions in Au and Cu-Zn mine tailings

Sulfate-reducing bacteria (SRB) have been observed in mining environments, but their presence has not been linked to specific physicochemical and mine ralogical factors. The present study was undertaken to assess the presence of SRB in several Au and Cu-Zn mine tailings located near Timmins, Ont., Ca nada, and determine the factors responsible for their presence. Vegetated a nd non-vegetated mine tailings were sampled for SRB enumeration, pH, Eh, wa ter content, total carbon content and sequential chemical extraction. Resul ts first showed that SRB populations were present at all sites and that the ir distribution varied with depth. Populations were recovered from neutral pH and slightly anoxic tailings and from highly acidic (pH 2) and oxic tail ings. The total carbon content of the tailings was generally low and not re lated to the presence of vegetation. In addition, the carbon content did no t affect SRB population distribution and appeared to be more related to the type of tailings, i.e., oxidized and acidic Cu-Zn tailings contained on av erage more carbon than Au tailings. Results also indicated that the water c ontent of the tailings varied greatly with depth and was not related to the presence of SRB populations. The sequential chemical extraction showed tha t the pyrite content of the tailings was lower in Au tailings than in Cu-Zn tailings, and that some oxidized Cu-Zn sites were depleted in pyrite due t o microbial and chemical oxidation. Our results indicate that SRB could be cultured From a variety of sites and sample types, and that factors such as pH, Eh, water content and carbon content at the collection sites did not e xert control on their presence. (C) 2000 Federation of European Microbiolog ical Societies. Published by Elsevier Science B.V. All rights reserved.