Pyrite Microbial Attack

Microbial oxidation of pyrite is one of the most common microbial metabolisms existing in the nature. A series of biogeochemical process from the formation to oxidation of pyrite reflects the fluctuation of the REDOX reaction interface. In recent years, the study of microbial oxidation of pyrite has become a hot issue in the field of geobiology. However, most of the researches are mainly focused on the laboratory studies; the study of microbial oxidation of pyrite in natural conditions is rare.In this paper, we combined the study of geological records of microbial dissolution of pyrite with the microbial oxidation of pyrite experiments in laboratory and the microbial oxidation of sulfide minerals in modern submarine hydrothermal sediments for the first tine. All of the details such as the erosion pitting patterns on the crystal surfaces, the secondary mineral deposits, the oxidation mechanism and process, the influencing factors were described, compared and discussed. This study will help us understand the biogeochemical iron and sulfur cycles impressively. Furthermore, it is also an important clue to trace the origin and evolution of microbial metabolism.The main research contents of this study includes the study of microbial oxidation of pyrite in sediments, which refers to the ancient sedimentary rocks and the modern submarine hydrothermal sediments, and the study of microbial oxidation of pyrite experiments. The study of the ancient sedimentary rocks is focused on the petrology analyses of the samples, the characteristic pitting patterns on the pyrite crystals, the second mineral deposits and the mineralized microbial community. While, the study of the modern submarine hydrothermal sediments includes the analysis of mineral composition of sulfide minerals, the characteristic pitting patterns on the chalcopyrite and pyrite crystals, and the mineralized microbial communities on the pyrite surfaces. The study of microbial oxidation of pyrite experiments refers to the pyrite oxidation mechanism by A. ferrooxidans and A. thiooxidans, the characteristic pitting patterns on the pyrite crystals, the second mineral deposits, the changes of pH and Fe3+concentration.The results are summarized as follows:The euhedral pyrite in the sediments were formed during the burial process, and eroded by microorganisms in the earliest stage of diagenesis. And a variety of pit structures with characteristic shapes and sizes were formed during microbial oxidation of pyrite, which are generally similar to those obtained from the laboratory studies on the oxidative dissolution of pyrite by iron-oxidizing bacteria. The major mineral phases of the modern submarine hydrothermal sediments are pyrite and chalcopyrite. The sulfide minerals were extensively oxidized with characteristic dissolution pits on the surfaces, mainly polygons pits on chalcopyrite surfaces and rounded-elliptic pits on pyrite surfaces.Experiment study indicates that A. ferrooxidans eroded pyrite with the indirect contact mechanism. The concentration of Fe3+and H+were both increased significantly during the oxidation process. Pyrite were extensively oxidized with characteristic pits, which were rounded and geometric (mainly hexagon) in morphologies. The bacteria and the secondary mineral deposits were also observed in or around the pits. It is also indicated that A. thiooxidans can reinforce the bioleaching ability of A. ferrooxidans.Furthermore, bacillus-sized and-shaped microfossils communities were described, which are very likely to be fossilized sheaths produced by iron-oxidizing bacteria during pyrite oxidative process in the samples.