Micromorphological, Mineralogical And Geochemical Characteristics Of The Si-Fe-Mn Oxides From The PACMANUS Hydrothermal Field, Eastern Manus Basin

The Si, Fe and Mn rich hydrothermal oxides are very common in modern seafloor hydrothermal systems. Although studies on hydrothermal oxides have been made by many researchers, most all these samples were collected from basaltic or andesitic volcanic rock bearing areas. While detailed reports about hydrothermal oxides sampling from dacite bearing areas are less. In this paper, we present data on the micromorphological, mineralogical and geochemical characteristics of the Si-Fe-Mn hydrothermal oxides from the PACMANUS hydrothermal field which is characterized by hydrothermal activity occurring in a dacite bearing area. We also show images of unique micro-textures that could be of microbial origin and may be of interest in studies on the reaction between microbe and metal of the seafloor hydrothermal system.Samples are poorly crystallized with a few of birnessite, todorokite, nontronite, goethite and opal-A. Under scanning electron microscope, lamellar crystals of nontronite is found forming honeycomb fabric, others distributing in the surface of the hollow pipes. Nontronite is the product of precipitating from low temperature hydrothermal fluid and microbes may act as a factor of affecting its formation. Also the remains of microorganic, filamentous, distorted and flaky materials, helical materials, hollow pipes and flaky material with high content of carbon are observed under scanning electron microscope, which all of them manifest microbes have participated the formation of the Si-Fe-Mn oxides.Two kinds of nucleuses are observed under electronic probe and are characterized by multi-layer texture. Combinning the electronic probe analisis results and the scanning electron microscope finding, we think the forming of the Si-Mn nucleus has a close relationship with the microbes whereas the Si nucleus is inorganic origin.The formation of the Si-Fe-Mn oxides are resulted from the hydrothermal fluids of rich in Si, Fe and Mn mixing with the oxidizing seawater leading to the co-precipitation of Si, Fe and Mn. Some microbes have joined in the oxides's formation and have be a part of the oxides.