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This paper presents mineralogical, chemical and morphological information on the oxyhydroxides from …


Biology Articles » Geobiology » Microbial and hydrothermal aspects of ferric oxyhydroxides and ferrosic hydroxides: the example of Franklin Seamount, Western Woodlark Basin, Papua New Guinea » Method of investigation

Method of investigation
- Microbial and hydrothermal aspects of ferric oxyhydroxides and ferrosic hydroxides: the example of Franklin Seamount, Western Woodlark Basin, Papua New Guinea

The samples for this study were collected by submersible and consist essentially of amorphous iron oxyhydroxides. Once on board the ship, the raw wet samples were placed into plastic containers or bags and the material was not dried until it was being prepared for laboratory study a few months later. Nothing was done to preserve possible organic remains in the samples so observed textures attributed to such are fossils.

The air-dried samples were first examined by light microscopy. This was followed by examination by scanning electron microscope (SEM) with an attached energy dispersive spectrometer (EDS). The SEM was operated at 15 to 25 kV with magnifications of 1000 to 12,000. Carbon coating of many of the samples considerably improved the quality of the images. A transmission electron microscope (TEM) equipped with an EDS was used to examine individual grains at higher magnifications of 10,000 to 200,000 at 200 kV. Grains were also characterized by selected area electron diffraction (SAED).

The observations were interpreted with reference to phase relations in the low temperature portion of the Fe–Si–O–H system. A model of the hydrothermal system at Franklin Seamount was constructed by calculating the expected thermodynamic mineral equilibria for an actively venting amorphous iron oxyhydroxide chimney within an oxygenated seawater environment using the measured composition of a vent fluid obtained during the SUPACLARK cruise (Table 1). The thermodynamic database is discussed separately. The SUPCRT92 program[19] was used to calculate expected changes in thermodynamic parameters at conditions other than 25°C and 1 bar. In addition, the kinetics of iron precipitation within this environment was estimated as a guide to ascertaining the relative roles of hydrothermal vs. biotic processes.


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