JpGU-AGU Joint Meeting 2020

Presentation information

[J] Oral

M (Multidisciplinary and Interdisciplinary) » M-ZZ Others

[M-ZZ57] Marine Manganese Minerals: Science, Engineering and Application

convener:Akira Usui(Marine Core Research Center, Kochi University), Yoshio Takahashi(Department of Earth and Planetary Science, Graduate School of Science, The University of Tokyo), Katsuhiko Suzuki(Submarine Resources Research Center, Japan Agency for Marine-Earth Science and Technology), Takashi Ito(Faculty of Education, Ibaraki University)

[MZZ57-01] On-site experiment of hydrogenetic ferromanganese oxide precipitation and absorption for 12-15 years

*Akira Usui1, Hikair Hino1, Suzushima Suzushima1, Naotaka Tomioka2, Teruhiko Kashiwabara2, Kyoko Yamaoka3, Michinari Sunamura4 (1.Marine Core Research Center, Kochi University, 2.Japan Agency of Earth and Marine Science a Technology, 3.Geological Survey of Japan, AIST, 4.Earth and Planetary Sciences, University of Tokyo)

Keywords:marine manganese minerals, manganese crusts, marine minerals

The redox-sensitive metals Mn and Fe are thought as terrestrial and volcanic origin and of variable composition and property due to forming environments, but details of oxidation and growing processes are yet known or still hypothetic. Here we report our first successful on-site and long-term experiment of Fe-Mn mineral precipitation and metal absorption, which clearly ascertained a modern on-going deposition of the hydrogenetic oxide materials from normal sea waters at 1000-5000m depths. We were able to use well-controlled deep-sea platforms (manned and unmanned vehicles) for installation and analyses near sea beds, and high-resolution analytical apparatus. The results indicated a substantial ultra-slow but continuous growth of hydrogenetic Fe-Mn minerals when both Mn and Fe are supplied into the bottom waters. All the installed artificial plates have yielded spread-out particles of coccoid-like to irregular shapes of a few-μm diameter with the maximum some 100-1000 individual particles per cm2 and per year after 12-15 year exposure. The mineralogical, chemical and structural properties are similar to natural precipitates from modern hydrogenetic ferromanganese crusts, from pelagic brown-clay sediments, suspended particles from hydrothermal vents, or from cultivated bacterial MNDB, SG-1.

The on-site precipitation experiment and in-laboratory analysis of precipitation and absorption are those of the direct and simple methods to understand the processes and mechanism. Experiment and observation were carried out in terrestrial environments, soils, hot springs, dessert varnish, meadows, and described from VNS chimneys, though no experiments have been done on the deep-sea floors yet. Such an experiments must prove the morphology and composition of initial products, timing and environment of deposition, and accumulation of useful metallic elements.

The on-site absorption experiments were carried out at the same site for the same time, using artificial Na-buserite (phyllomanganate) chrystals within a membrane-filtered chamber, and variety of metallic elements were absorbed or ion-exchanged. This results indicated metal accumulation take place in a normal deep-sea water after long-time exposure of a Mn oxide mineral.

Considering the global geochemical cycles of Mn and Fe in oceans, the origin and paths of transportation, mechanism of oxidation, and deposition must be understood. The model suggests reconsideration on chemical forms of Mn and Fe in normal sea waters with varying redox potential at the depths. The results ascertained the proposed model of modern continuous precipitation when both Mn and Fe are supplied to ambient underlying waters. The particulate is thus the smallest unique constituent of ferromanganese crust and nodule deposit of the Neogene to modern age at full water depths of oxic deep-sea environments at all oceans. Hydrogenetic particulate, Fe-Mn oxide forms the piled ferromanganese crusts and nodules at a wide-range of depths including OMZ.