A high‐resolution chemical and structural study of framboidal pyrite formed within a low‐temperature bacterial biofilm |
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| Authors: | L C W MACLEAN T TYLISZCZAK P U P A GILBERT D ZHOU T J PRAY T C ONSTOTT G SOUTHAM |
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| Institution: | 1. Department of Earth Sciences, The University of Western Ontario, London, ON, Canada N6A 5B7;2. Present address: Environment Group, Mining & Mineral Sciences Laboratories, Natural Resources Canada, 555 Booth Street, O Hawa, Ontario Canada, K1A OG1.;3. Lawrence Berkeley National Laboratory, Chemical Sciences Division, Advanced Light Source, Berkeley, CA 94720, USA;4. Department of Physics, University of Wisconsin‐Madison, Madison, WI 53706, USA;5. Department of Geosciences, Princeton University, Princeton, NJ 08544, USA |
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| Abstract: | A novel, anaerobically grown microbial biofilm, scraped from the inner surface of a borehole, 1474 m below land surface within a South African, Witwatersrand gold mine, contains framboidal pyrite. Water flowing from the borehole had a temperature of 30.9 °C, a pH of 7.4, and an Eh of –50 mV. Examination of the biofilm using X‐ray diffraction, field emission gun scanning electron microscope equipped for energy dispersive X‐ray microanalysis demonstrated that the framboids formed within a matrix of bacteria and biopolymers. Focused ion beam sectioning of framboids followed by NEXAFS measurements using both scanning transmission X‐ray microscopy and X‐ray photoelectron emission microscopy revealed that the pyrite crystals grew within an organic carbon matrix consisting of exopolysaccharides and possibly extracellular DNA, which is intuitively important in sulfide mineral diagenesis. Growth of individual pyrite crystals within the framboid occurred inside organic templates confirms the association between framboidal pyrite and organic materials in low‐temperature diagenetic environments and the important role of microenvironments in biofilms in regulating geochemical cycles. |
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