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Dense Field of Ferromanganese Nodules Found in Japanese Exclusive Economic Zone around Minamitorishima Island - Clue to comprehensive understanding of genesis of oxide mineral resources -:Professor Yasuhiro Kato, Department of Systems Innovation, and other researchers.

A research group led by the Japan Agency for Marine-Earth Science and Technology (JAMSTEC: Asahiko Taira, President), The university of Tokyo (Makoto Gonokami, President) and Chiba Institute of Technology (Kazuhito Komiya, President) found a dense field of ferromanganese nodules at a depth of 5,500 m- 5,800 m on seafloor from southern to eastern part of the Japanese Exclusive Economic Zone (EEZ) around Minamitorishima Island during research cruises in May-June 2010 and April 2016. It is the largest scale ever identified in the zone, while a smaller scale of distribution with cobalt-rich ferromanganese crusts has already been known to exist on the slope of seamounts.

It is also noted that a multi-narrow beam echo sounder system played a significant role in detecting these ferromanganese nodules in the area. After the cruise in 2010, a high-intensity reflection by the system confirmed existence of ferromanganese nodules during dives by a submersible by Shinkai 6500, followed by identification of the expanse of dense fields of the ferromanganese nodules in 2016. It demonstrated that the multi-narrow beam echo sounder system is an effective and less costly method in grasping the distribution of ferromanganese nodules.

Moreover, it became clear that 1) chemical composition of these ferromanganese nodules in Minamitorishima is common with that of ferromanganese crusts, containing metals of economic interest such as cobalt, nickel, copper and molybdenum and 2) the area of distribution of the ferromanganese nodules overlaps extensively with that of REY-rich mud. While the genesis of ferromanganese nodules, ferromanganese crusts and REY-rich mud has been usually discussed separately, it suggests that ferromanganese nodules could be a clue to understand them in a comprehensive manner. Collected samples will be further analyzed to elucidate genesis of these three types of oxide mineral resources around Japan.

The above results were published in Geochemical Journal issued by the Geochemical Society of Japan on August 26, 2016 (JST).



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