During Dive 408 of Shinkai 2000 on the flank of the Kaikata Seamount located on the volcanic front of the Izu-Ogasawara (Bonin) Arc, possibly recent hydrothermal manganese deposits were observed on sandy volcanic sediments at water depths of between 800 and 1200 m. The deposits cover almost the entire surface sediment across the manganese belt on the northwestern flank on the seamount on a scale of kilometers. The occurrence of the deposits, seafloor morphology and temperature of the sediments, together with previous shipboard results, lead to a possible model for the formation of the manganese deposits: A low-temperature hydrothermal solution ascends through fractures or faults in the volcanic substrate into permeable volcanic sands and precipitates manganate minerals which cement several centimeters of surface sand as hardpan. More intense and probably intermittent discharge of hydrothermal solution follows and forms many typical ridge-like vents and mounds on the seafloor. Subsequently, pure dense manganate layers developed beneath the semi-consolidated volcanic sandstone and act as a cap to the ascending fluids. The proposed mechanism may be the dominant type of low-temperature hydrothermal mineralization in submarine island-arc volcanoes and rifts. Similar hydrothermal manganese deopsits most probably occur in other active areas of the modern seafloors and in inactive island arcs.

From 1983 until 1989 NOAA-NCEI compiled the NOAA-MMS Marine Minerals Geochemical Database from journal articles, technical reports and unpublished sources from other institutions. At the time it was the most extended data compilation on ferromanganese deposits world wide. Initially published in a proprietary format incompatible with present day standards it was jointly decided by AWI and NOAA to transcribe this legacy data into PANGAEA. This transfer is augmented by a careful checking of the original sources when available and the encoding of ancillary information (sample description, method of analysis...) not present in the NOAA-MMS database.

Supplement to: Usui, Akira; Nishimura, Akira (1992): Submersible observations of hydrothermal manganese deposits on the Kaikata Seamount, Izu-Ogasawara (Bonin) Arc. Marine Geology, 106(3-4), 203-216