Three-Dimensional Structural Analysis of Ferromanganese Nodules from the Western North Pacific Ocean Using X-ray Computed Tomography

Kentaro Nakamura,Ryo Shimomura,Daiki Terauchi,Kazutaka Yasukawa,Shiki Machida,Yasuhiro Kato,Koichiro Fujinaga

doi:10.3390/min11101100

Kentaro Nakamura, Ryo Shimomura + Show 5 more

Open Access

https://doi.org/10.3390/min11101100

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Journal: Minerals	Publication Date: Oct 7, 2021
Citations: 7	License type: CC BY 4.0

Affiliation: The University of Tokyo, Chiba Institute of Technology

Abstract

The three-dimensional layered growth structure of 934 ferromanganese nodule samples collected from dives in the Pacific Ocean around Minamitorishima Island was assessed using X-ray computed tomography (X-ray CT) to elucidate their growth history. The thickness of the layered structure measured in three orthogonal directions showed that the ferromanganese nodules grew equally in all directions regardless of shape and size. Based on differences in CT numbers, a layered structure was subdivided into sublayers I, II, III, and IV, which corresponded to petrological features. The nodules were then classified as Types I, II, III, and IV according to whether they had sublayers I, I and II, I–III, or I–IV, respectively. Correlations between the total thickness of the layers and the number of sublayers indicated that both represented the relative age of the nodules. Nodules with all these types were recovered from most of the sampling sites, and histograms of the total layer thickness at each dive site showed several peaks. These findings indicated that the initiation of nodule growth was intermittent, rather than simultaneous. Three distinct thickness peaks were found at many sites throughout the study area, suggesting that at least three nodule initiation events covering hundreds of kilometers initiated the growth of ferromanganese nodules.

Highlights

Spherical ferromanganese nodules composed of iron (Fe) and manganese (Mn) oxides and hydroxides are widely distributed on the deep seafloor [1,2,3]
These nodules are enriched in critical metals such as nickel (Ni), copper (Cu), cobalt (Co), and rare-earth elements (REEs), representing a potential resource of the metals that are crucial for hightech and green-tech products [2,4]
Total oxide layer thickness was determined by averaging the twovalues values measured the three threeaxes, axes, parameters could be measured in some measured along along the parameters could notnot be measured in some damdamaged samples

Summary

Introduction

Spherical ferromanganese nodules composed of iron (Fe) and manganese (Mn) oxides and hydroxides are widely distributed on the deep seafloor [1,2,3]. The nodules from the Minamitorishima EEZ generally consist of concentric layers, L0, L1, and L2 that are comparable to those of ferromanganese crusts in the western North Pacific, including the Minamitorishima EEZ [12]. L2 that are comparable to those of ferromanganese crusts in the western North Pacific, the three-dimensional structure of the oxide layer of 934 ferromanganese nodule samples including the Minamitorishima EEZ [12]. Sample Collection observing a large number of nodules is laborious, costly, and impractical. Ferromanganese three-dimensional structures of numerous ferromanganese nodules should provide new nodules were sampled to six pointstheeach from of X-ray the 16 dive sites (Figure 1). Oxide layer of 934 ferromanganese nodule targeted samples collected from the western. Samples were collected Nodules were collected by 16 dives using the deep-sea manned submersible

Sample

Method

Computed

Relationshipbetween betweenOxide

Contour of CT numbers representative samples sublayer

Implications for the History and Trigger of Nodule Growth

Conclusions