MIS46-01

Room:A05

Time:May 27 09:30-09:45

Marine manganese deposits: Status, subjects, and perspectives.
USUI, Akira1∗
1

Kochi University

Marine manganese deposits, for example, crusts and nodules, occur mainly on the deep floors below the depth about 1000
meters. The deposits are notes as probable metallic ores for some useful metal elements. The distribution patterns, mechanism offormation and deposition, are recently intensively studied around the Japanese Islands in the Northwestern Pacific ocean. In thispaper, the history of geoscientific study and resource exploration will be reviewed, in various aspects of geology, geochemistry,mineralogy, microbiology, and paleoceanography. The most important scopes of study on marine manganese deposits are, 1)chemical and mineralogical forms of manganese minerals, 2) mode and processes of deposition of useful metallic elements, 3)
relationship of deposition of manganese oxides to marine geology, hydrological condiitons, 4) characterization as nano material,5) microbial effects on the deposition of manganese minerals, 6) correlation with terrestrial manganese and iron/manganese oxide
deposits. A systematic joint scientific programs should be reactivated to veil the real occurrence of the deposits, using modern
high-tech vehicle, sonsors, analysis apparatus of fine, fast, and high-resolution. In the paper, recent results will be overviewed
based on our cruises and analysis with joint collaboration with domestic and international institutions
Keywords: marine manganese deposit, manganese nodule, manganese crust, Northwest Pacific, seamount, geoscience

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MIS46-02

Room:A05

Time:May 27 09:45-10:00

Geochemistry of ferromanganese crust: recent scientific results
SUZUKI, Katsuhiko1∗ ; GOTO, Kosuke T.2 ; NOZAKI, Tatsuo1 ; KASHIWABARA, Teruhiko1 ; IIJIMA, Koichi1 ;USUI, Akira31

JAMSTEC, 2 GSJ, AIST, 3 Dept, Natural Science, Kochi Univ.

Ferromanganese crusts (Fe-Mn crusts) are a kind of marine chemical sediment composed of iron and manganese oxides
occurring on the surface of seamounts and oceanic plateaus at depths from 400 to 4000 meters below sea level (mbsl) (Hein etal., 2000). Fe-Mn crusts possess especially high concentrations of rare metals such as cobalt, tellurium, and rare earth elements,and are expected as submarine mineral resources. Occurrence, chemical compositions and growth patterns of Fe-Mn crusts are
locally variable, and their genesis, growth rates and enrichment processes of elements are required to evaluate Fe-Mn crusts as
mineral resources. Therefore, we have been conducting scientific research on genesis of Fe-Mn crusts.
The depositional ages of sublayers in a Fe-Mn crust sample have been determined by the Be-10 isotope system and ultrafinescale magnetostratigraphy (Oda et al., 2011). Though these methods can provide precise age data of the young part of Fe-Mn
crusts (up to 10 million years), development of the method to determine the age of the whole layers is required. Klemm et al.
(2005) applied osmium (Os) isotope stratigraphy in which the Os isotopic composition of each Fe-Mn crust layer is measured
and matched to the well-known marine Os isotope evolution of the past 80 Ma. We analyzed the Os isotope of the Fe-Mn crusts
collected from the Takuyo-Daigo, Ryusei and MC10 (Micronesia) seamounts. The obtained results indicate that the Fe-Mn
crusts from Takuyo-Daigo and Ryusei seamonts have the growth rate of approximately 3 mm/million years in the past 15 million
years. Also, it is proposed that, though the Fe-Mn crust from MC10 seamount is likely to have grrown continuously, those fromthe Takuyo-Daigo seamount encountered significant changes in growth rates, possibly a growth hiatus, between ca. 15 and 30
million years ago.
We have revealed through speciation of elements by synchrotron X-ray that element concentration in Fe-Mn crusts are wellconstrained by mode of adsorption on iron (ferrihydrite) and manganese oxides (MnO2) (Kashiwabara et al., 2008, 2011, 2013,2014). As for homologous tungsten and molybdenum, for example, Fe-Mn crusts are distinctly more enriched with tungsten
than molybdenum. Kashiwabara et al. (2013) conducted EXFS analyses and proposed its mechanism based on the chemical
speciation data as follows: Tungsten forms an inner-sphere complex both on iron and manganese oxides, while molybdenum
forms an inner-sphere complex on iron oxide and forms an outer-sphere complex on manganese oxide. Such difference in modeof adsorption leads to difference in concentrations of tungsten and molybdenum in Fe-Mn crusts. On the other hand, tungsten
abundance of seawater is suggested to be low due to removal of tungsten in seawater driven by its adsorption on Fe-Mn crusts
and other Fe-Mn oxides on the seafloor.
Keywords: ferromanganese crust, seamount, osmium isotope stratigraphy dating, rare metal, coordination complex

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MIS46-03

Room:A05

Time:May 27 10:00-10:15

Sr isotope composition of marine manganese deposits
ITO, Takashi1∗
1

Faculty of Education, Ibaraki University

Fluctuations of seawater Sr isotope ratio have been actively reconstructed since the 1980s. The seawater Sr isotope curves areused widely as a tool of dating (Sr isotopic stratigraphy) and as a tracer to evaluate surficial circulation of materials in the Earth’ssurface.
Futa et al. (1988) attempted to apply the Sr isotope stratigraphy to two Pacific manganese crusts and Ingram et al. (1990) applies the two-step sequential extraction method to leach original seawater Sr. Hein et al. (1992) observed fine-scale compositionsin texture and chemistry of a Pacific manganese crust based on Sr isotopic ages. On the other hand, VonderHaar et al. (1995)
assessed Sr isotopic dating for a manganese crust to conduct various leaching procedures. As the result, they pointed out thepossibility of replacement of original Sr by later stage seawater Sr after growth. After that, Sr isotopic stratigraphy has not been
actively applied as the dating method for marine manganese deposits.
In this study, various leaching procedures were tested to obtain basic data for Sr isotopic composition in marine manganesedeposits. It was concluded that the two-step sequential extraction using acetic acid was the best way to minimize the effect of Srfrom detrital silicates within manganese deposits.

Keywords: manganese deposits, manganese crusts, manganese nodules, strontium, isotope, growth rate

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MIS46-04

Room:A05

Time:May 27 10:15-10:30

Paleomagnetic study on the ferromanganese crusts recovered from northewest Pacific
NOGUCHI, Atushi1∗ ; YAMAMOTO, Yuhji2 ; NISHI, Keisuke3 ; USUI, Akira4
1Graduate School Of Integrated Arts and Sciences, 2 Center for Advanced Marine Core Research, Kochi University, 3 Kochi
University, 4 Geology Dept., Kochi Univ.
We have conducted paleomagnetic measurements on the ferromanganese crusts recovered from five different locations in thenorthwest Pacific. The analyses were made on a series of the thin slices (0.5-1.0 mm in thickness) cut perpendicular to thegrowth layers of the crusts, from surface to the interior. We recognized 2-8 polarity reversals in the crusts, and the most surficial
layers were commonly characterized by normal polarities. Assuming that these layers were grown constantly in Brunhes normal
polarity chron (0-0.78 Ma), growth rates were estimated as 2.1-5.0 mm/Ma. These rates are consistent with those estimated by
the 10 Be/9 Be method except for one location.
Keywords: ferromanganese crust, paleomagnetic polarity, growth rate

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MIS46-05

Room:A05

Time:May 27 10:30-10:45

Distribution of Co-rich ferromanganese crusts and evolution of the seamounts in the NW
pacific
OKAMOTO, Nobuyuki1∗
1

Japan Oil, Gas and Metals National CorporationMarine hydrogenetic ferromanganese crusts are known as potential mineral deposits for cobalt, nickel, platinum, rare earths
and other metals of emerging economic interest.
The crusts show particularly high concentrations of rare metals for high-technology and green technology and usually coverstable rock outcrops in large areas of crests and slopes of seamounts where pelagic sedimentation is generally low or often
lacking, thus the Northwest (NW) pacific seamount provinces are most promising sites for future deep-sea mining.
The ferromanganese crusts have been studied in this area by a number of scientific researchers from several countries.
Japan Oil, Gas and Metals National Corporation (JOGMEC) commenced survey cruises for the crusts in 1987. In 2014,
JOGMEC also obtained an exclusive license from the International Seabed Authority for the crusts in the high sea of NW pacific.
The area located approximately 600 km offshore of south-east of Minami-tori-shima island in the EEZ of Japan.
However, our scientific knowledge for understanding the origin, nature, environments and economic potentiality is still limited.
The patterns of distribution, resource potential and the relationship to geological parameters were found to be characterized
by the potentiality for the ferromanganese crusts little by little. In this presentation, the relationship between crust abundanceand diversity in the geological evolution of the seamounts in the NW pacific is discussed on the basis of bathymetric, geological,
geophysical and environmental data.

Keywords: cobalt-rich, ferromanganese crust, northwest pacific, seamount

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