Geology and geochemistry of ferromanganese nodules in the Japanese Exclusive Economic Zone around Minamitorishima Island

Abstract

moteness is an obstacle to mining operations. However, large Fe-Mn nodules have also been found to be densely distributed on a seamount in the eastern part of the Japanese Exclusive Economic Zone (EEZ) around Minamitorishima (Marcus) Island, Japan, where their resource potential is more promising because they are located closer to the main islands of Japan than the CCZ. Thus, further exploration in the EEZ can be expected, along with future development followed by the self-sufficiency and the stabilization of the market for critical metals. In this report, we describe results of a geological survey using the submersible SHINKAI 6500 and a multiple narrow-beam echo sounder system during cruise YK10-05 of R/V Yokosuka. We also present the results of chemical analyses to define geochemical features for representative Fe-Mn nodules and adjacent Fe-Mn crusts.

Visualisation method for the broad distribution of seafloor ferromanganese deposits

“…As a next step, we aimed to verify whether the histogram analysis of backscatter intensity is a robust approach for data collected using the different MBESs across different regions and during different observation periods. We therefore re-interpret previous data (Machida et al 2016) collected during the cruise YK10-05 of R/V Yokosuka (YK10-05SiteA and YK10-05SiteB). The representative area was selected from the YK10-05SiteB data (Figure 4), which covered the variance in the backscatter data and included ground-truth observations using the SHINKAI 6500 (dive Nos.…”

“…Indeed, certain applications using a deep-towed side scan sonar (Lee and Kim 2004;Wiedicke and Weber 1996) demonstrate highresolution mapping results for nodule fields at once only covering an area of several hundreds of square metres. In contrast, some previous investigations using vessel-equipped MBES identified variations of distributions over an area of tens or hundreds of square kilometres of lava (Hirano et al 2006(Hirano et al , 2013(Hirano et al , 2016 or nodules (Chakraborty and Kodagali 2004;Chunhui et al 2015;Machida et al 2016) based on backscatter intensity levels. Therefore, vesselequipped MBES can provide a more economical exploration for vast areas than that provided by underwater apparatuses.…”

“…These data were obtained with an identical MBES for each of the four cruises of R/V Mirai (MR14-E02, MR15-E01 Legs 2 and 3 and MR15-02) in 2014 and 2015 ( Figures S2-S5, supplementary material). We also reprocessed previous cruise data (Machida et al 2016), which were obtained during a cruise YK10-05 of R/V Yokosuka in 2010, to verify analytical reproducibility for the different MBESs and cruise periods. Data coverage is mainly in the central and eastern region of the Japanese EEZ around Minamitorishima Island ( Figure S6, supplementary material).…”

“…Histogram, diagrams and map of backscatter intensity, together with photographs for ground-truthing to verify our analysis. The presented backscatter intensity data (YK10-05SiteB) were previously obtained during the cruise YK10-05 of R/V Yokosuka (Machida et al 2016). The range of the map is indicated by a white box in Figure S6 (supplementary material).…”

Preface: Front edge of submarine mineral resources research in Japan (Part 2)

“…They also estimate the reserve of Fe-Mn crusts around the Takuyo Daigo Seamount based on some assumptions. A dense field of spherical ferromanganese (Fe-Mn) nodules with 5-10 cm in diameter was found approximately 300 km east of the Minamitorishima Island in the western North Pacific (Machida et al, 2016). They report that high acoustic reflectivity observed by the onboard acoustic system is related to this dense occurrence of the nodules.…”