Abstract
Platinum-group elements are strategically important metals1. Finding new deposits is becoming increasingly difficult owing to our limited understanding of the processes that affect their mobility in surface environments2. Microorganisms have been shown to promote the mobility of metals around ore deposits3. Here we show that microorganisms influence the mobility of platinum-group elements in mineral grains collected from Brazil, Australia and Colombia. Scanning electron microscopy showed biofilms covering the platinum-group mineral grains. The biofilms contained abundant platinum-group element nanoparticles and microcrystalline aggregates, and were dominated by Proteobacteria, many of which were closely related to known metal-resistant species. Some platinum-group mineral grains contained carbon, nitrogen, sulfur, selenium and iodine, suggesting the grains may be biogenic in origin. Molecular analyses show that Brazilian platinum–palladium grains hosted specific bacterial communities, which were different in composition from communities associated with gold grains, or communities in surrounding soils and sediments. Nano-phase metallic platinum accumulated when a metallophillic bacterium was incubated with a percolating platinum-containing medium, suggesting that biofilms can cause the precipitation of mobile platinum complexes. We conclude that biofilms are capable of forming or transforming platinum-group mineral grains, and may play an important role for platinum-group element dispersion and re-concentration in surface environments.
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Acknowledgements
We acknowledge the Australian Research Council (DP1093238 to F.R.). We thank T. Reith, the Pope family (Barry, Marnie and Michael), R. Wolfe and R. Morley for their enthusiastic field support; A. R. Cabral and B. Lehmann are thanked for providing motivation and initial field support; we also thank L. Green and A. Basak (Adelaide Microscopy) for support using the FIB-SEM and J. Young (Flinders Analytical) for support with the SP-ICP-MS. Published with permission of the Director of Mines, Tasmania.
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F.R. conceived and led the project. C.M.Z., S.S.S., B.E., R.B., G.S. C.T., M.K., T.O., A.S.B. and J.B. contributed samples, experimental and analytical data. F.R. wrote the paper and all co-authors contributed by commenting on and revising it.
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Reith, F., Zammit, C., Shar, S. et al. Biological role in the transformation of platinum-group mineral grains. Nature Geosci 9, 294–298 (2016). https://doi.org/10.1038/ngeo2679
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DOI: https://doi.org/10.1038/ngeo2679
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