We have observed and sampled the ferromanganese crusts using dredge, drills manned submersible, and ROVs, jointly with JAMSTEC, GSJ, and JOGMEC since 2009. The mode of occurrence, chemical and mineralogical properties, growth history and basement geology have been studied over the Takuyo-Daigo seamount located within the Japanese EEZ and about 300nm away from the Japanese licensed area for Co-rich Fe-Mn crusts. During more than 10 cruises and 30 ROV dives, we found continuous and constant growth at a wide range of water depths between 800 and 5500 meters including OMZ over the top to the lower flank of the seamount. Chronology data of formation of the crusts by means of radioactive nuclides, paleontological and paleomagnetic method demonstrates again basically continuous growth since the Early-Middle Miocene to the present. We found a strong water-depth control of surface modern precipitate and common tendency of decrease of the ratios, Co/Mn and Mn/Fe with a water depth in the area, probably controlled by redox condition of sea waters. A microstratigraphic correlation of the crusts again also reveals the secular desreasing variation of Co/Mn and Mn/Fe towards older layers within the crusts. The controlling oceanographic and geological parameters are still open to question.
Our geological characterization partly guarantees extending areas of abundant (thick=long aged) ore deposits. Thus geological and mineralogical properties and growth history in space and time is helpful in indicating prime areas for abundant and high-grade ore deposits. These geological information is useful for economic estimation, mining and environmental consideration, if supported by well-combined geological and oceanographic knowledge on and above the seafloors.In this study, we browse our recent results of geological studies of dating, misrostratigraphy, seafloor observation, in-situ precipitation experiment, acid-insoluble stratigraphy, and so on.