Geomicrobiology : an Interdisciplinary Science Blending Microbiology with Geology

Speaker Biography:
Dr. Gordon Southam is currently a Professor at the School of the Environment and the Sustainable Minerals Institute at the University of Queensland.

BSc & PhD in Microbiology, the University of Guelph, Canada
Assistant / Associate Professor, Northern Arizona University, USA
Canada Research Chair, Western University, Canada.
Vale-UQ Chair in Geomicrobiology, The University of Queensland, Australia
 
Abstract:

My research is centred on bacteria-mineral interactions, examining the role of microbiology in mineral weathering.

Bacterial metabolism, involving redox reactions with carbon, sulfur and metals has been important since the dawn of life on Earth. Stromatolites representing one of the classic biogenic materials found in ancient geologic systems, e.g., the 1.8 billion year old Gunflint Chert from northern Lake Superior, Canada can be found today living in Shark Bay, Western Australia.

Bioleaching and the formation of acid mine drainage represents one of the classic biogeochemical reactions, differing only on whether metals are extracted and recovered by ‘good bacteria’ or whether this process occurs in an uncontrolled manner where ‘bad bacteria’ harm natural environments. With 15% of the world’s copper production occurring through bioleaching, there is increasing interest in the transformation of mine wastes into resources.

High-grade iron ore deposits in tropical areas are capped by a hard, erosion-resistant iron duricrust that protects the friable ore below. Combining microscopy, molecular biology, cultivation and geochemical analyses on duricrust samples from Carajás, Brazil, we confirmed the critical role microorganisms play in goethite dissolution and re-precipitation leading to natural stabilisation of these duricrusts, providing a strategy to improve the stabilisation of mine waste, to protect against the inherent risks associated with tailings dam failure.

Mineral carbonation of mafic and ultramafic materials is becoming an increasingly important component in climate change mitigation strategies. Laboratory and field trials have demonstrated that microbial weathering of these materials supports the growth of bacteria, and where photosynthesis is occurring, atmospheric carbon dioxide is sequestered as biomass and as carbonate minerals.

While gold is generally considered to be inert, the biosphere can catalyze a variety of geochemical processes than can transform gold.  Microbial weathering of gold bearing minerals contributes to the mobilisation of gold, by releasing elemental gold trapped within minerals, and by solubilising gold under oxidising conditions, promoting gold complexation.  Subsequent microbial destabilisation of gold complexes can immobilise gold, completing the cycle. Secondary gold starts as colloids, producing crystalline gold, and ultimately ‘growing’ gold grains.