News from the seabed – Geological characteristics and resource potential of deep-sea mineral resources

Adsorption behavior of rare earth elements on silica gel modified with diglycol amic acid

Potential risks of supply shortages for critical metals including rare-earth elements and yttrium (REY) have spurred great interest in commercial mining of deep-sea mineral resources. Deep-sea mud containing over 5,000 ppm total REY content was discovered in the western North Pacific Ocean near Minamitorishima Island, Japan, in 2013. This REY-rich mud has great potential as a rare-earth metal resource because of the enormous amount available and its advantageous mineralogical features. Here, we estimated the resource amount in REY-rich mud with Geographical Information System software and established a mineral processing procedure to greatly enhance its economic value. The resource amount was estimated to be 1.2 Mt of rare-earth oxide for the most promising area (105 km2 × 0–10 mbsf), which accounts for 62, 47, 32, and 56 years of annual global demand for Y, Eu, Tb, and Dy, respectively. Moreover, using a hydrocyclone separator enabled us to recover selectively biogenic calcium phosphate grains, which have high REY content (up to 22,000 ppm) and constitute the coarser domain in the grain-size distribution. The enormous resource amount and the effectiveness of the mineral processing are strong indicators that this new REY resource could be exploited in the near future.

The tremendous potential of deep-sea mud as a source of rare-earth elements

Deep-sea sediments contain high concentrations of rare earth element (REE) which have been regarded as a huge potential resource. Understanding the marine REE cycle is important to reveal the mechanism of REE enrichment. In order to determine the geochemistry characteristics and migration processes of REE, seawater, porewater and sediment samples were systematically collected from the western Pacific for REE analysis. The results show a relatively flat REE pattern and the HREE (Heavy REE) enrichment in surface and deep seawater respectively. The HREE enrichment distribution patterns, low concentrations of Mn and Fe and negative Ce anomaly occur in the porewater, and high Mn/Al ratios and low U concentrations were observed in sediment, indicating oxic condition. LREE (Light REE) and MREE (Middle REE) enrichment in upper layer and depletion of MREE in deeper layer were shown in porewater profile. This study suggests that porewater flux in the western Pacific basin is a minor source of REEs to seawater, and abundant REEs are enriched in sediments, which is mainly caused by the extensive oxic condition, low sedimentation rate and strong adsorption capacity of sediments. Hence, the removal of REEs of porewater may result in widespread REE-rich sediments in the western Pacific basin.

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Rare earth element geochemistry characteristics of seawater and porewater from deep sea in western Pacific

### REE-minerals

Monazite, xenotime, and allanite are REE1-minerals sensu stricto because lanthanides (La…Lu) and yttrium are critical constituents in them Apatite does not require REE, but because it contains substantial REE in many rocks, it is included in this review All four minerals also host unusually high radionuclide concentrations, notably Th and U, forming the basis of their utility as geochronometers

This quartet of accessory minerals is playing an increasingly important role in petrochronology because they provide ways to link robust spot ages to petrogenetic ( P–T ) conditions so can lend petrogenetic context to chronology based on other minerals Part I of this review assembles the basic requisites prior to integrative petrochronologic analysis Individual characteristics of the four REE-minerals are addressed first, ie, their crystal chemistry and stability relations Thermobarometers and trace element geochemistry used for tracing petrogenesis are discussed next, and finally their chronology is summarized Part II presents case studies to highlight the specific strengths of REE-minerals used to resolve the dynamics of a broad range of processes, from diagenetic to magmatic conditions Finally, a brief section at the end outlines a few of the current challenges and promising perspectives for future work

To introduce the four REE-minerals in style, let us recall the origins of their names The three phosphates have well respected Greek grandparents, and allanite has solid Scottish roots, yet of all four of them show idiosyncracies in etymology or type material

Apatite had long puzzled naturalists, as it shows great chemical and physical variability and can resemble other minerals Once properly identified, Abraham Gottlieb Werner named it apatite His reasoning referred to the Greek root ἀπατὰω and giving the precise Latin translation: decipio  Taken literally, both mean “I deceive” or “I mislead”, which sounds like an apt confession from this mineral for having fooled …

Petrochronology Based on REE-Minerals: Monazite, Allanite, Xenotime, Apatite

We have conducted geochemical and mineralogical investigations of the rare earth and yttrium (REY)-rich mud from the Minami-Torishima area in the Pacific in order to clarify the concentration of REY and their host-phase in the mud. X-ray diffraction analysis shows that the mud is mainly composed of phillipsite, fluorapatite, quartz, albite, illite and montmorillonite. Whole-rock CaO, P2O5 and total REY contents of the mud are positively correlated. Relative abundance of apatite is also positively correlated to P2O5 and total REY contents. These correlations suggest that apatite is the main host of the P2O5 and REY in the mud. We make in situ compositional analyses of constituent minerals in the REY mud. The results show that the apatite is abundant in REY (9300–32,000 ppm) and is characterized by a negative Ce anomaly and enrichment in heavy rare-earth elements. This abundance and composition of REY of the mud is similar those of fish debris apatites. In contrast, phillipsite is less abundant in REY (60–170 ppm). Therefore we conclude that the main REY host phase of the mud is apatite.

https://www.onlinelibrary.wiley.com/doi/pdf/10.1111/rge.12026

Geochemical Characteristics of Apatite in Heavy REE-rich Deep-Sea Mud from Minami-Torishima Area, Southeastern Japan

Ferromanganese crusts in the Pacific Ocean are potential economic resources of cobalt, nickel and platinum. Previous shipboard geological and geophysical exploration has been directed towards innovation in effective methods of mapping the abundance and grade of manganese nodules on the seafloor for evaluation and mine site selection. However, any simple techniques have not been valid for complicated and variable nature of the crusts and topography. This study attempts to establish a distribution pattern of ferromanganese deposits on a Micronesian seamount using conventional narrow-beam and SSS mapping, dredge sampling Cand TV/camera monitoring with a geological interpretation. We tried to correlate acoustic remote sensing data with the surface geology, and decipher the regional-scale distribution of crusts in relation to large-scale mass wasting that took place in the early Miocene or before. The general distribution pattern of crusts over the surface of the seamount indicates that only about 40% of the a...

Geophysical and Geological Exploration of Cobalt-rich Ferromanganese Crusts: An Attempt of Small-Scale Mapping on a Micronesian Seamount

Cobalt-rich hydrogenetic ferromanganese crusts in the Pacific seamounts are potential mineral resources for Co, Ni, Pt and REEs. The Northwest (NW) Pacific, in particular, is one of the most promising areas for the ferromanganese crusts. During the six cruises of the Japanese research vessel Hakurei Maru No.2 over the seamounts of the Marshall Islands in 1996, 1998 and 2002, and the Federated States of Micronesia (FSM) in 1997, 1998 and 2005, the patterns of distribution, resource potential and the relationship to geological parameters were found to be characterized by the potentiality for the ferromanganese crusts. In this article, the relationship between crust abundance and diversity in the geological evolution of the seamounts is discussed on the basis of bathymetric, geological, geophysical and environmental data.

Regional Distribution of Co-Rich Ferromanganese Crusts and Evolution of the Seamounts in the Northwestern Pacific

In Japan, the Basic Act on Ocean Policy provided a basic outline of matter regarding the ocean and was promulgated in July 2007. Following on from the Act, the Cabinet introduced the “Basic Plan on Ocean Policy”, to promote measures concerning the ocean both in general and in detail. In particular, this legislation clearly defines the plan for the commercialization of seafloor polymetallic sulphides that had not yet done so. After that, the Ministry of Economy, Trade and Industry (METI) introduced a roadmap for commercializing the sulphides based on the Basic Plan. Based on the roadmap, JOGMEC started the survey program for seafloor polymetallic sulphides in the EEZ of Japan, and launched its R&D program on the mining system and the processing and metallurgical technologies, as well as an environmental impact assessment (EIA) in 2008. Regarding R&D of the mining system, JOGMEC and certain Japanese mining and machinery companies have developed two types of state of the art, small-scale seabed excavating and collecting tools. Sea trials using their tools have been conducted in hydrothermal fields at a depth of 1600m in the Okinawa trough at the EEZ of Japan since 2012. From late August to late September of 2017, the world's first ore-lifting pilot test for polymetallic sulphides was conducted with great success under the sea near Okinawa Island.

Current Status of Japan's Activities for Deep-Sea Commercial Mining Campaign

There are several types of mineral resources under or on the deep-sea bed. Manganese Nodules, Cobalt-rich Manganese Crusts, and Sea-floor Massive Sulfides (SMS) are well known future metal resources in the deep-sea. Although, there have been a lot of activities to study those resources as scientific interests as well as a business point of view, any deep-sea mineral resources has not been developed yet.

Nobuyuki Okamoto

Papers

Geochemical Characteristics of Apatite in Heavy REE-rich Deep-Sea Mud from Minami-Torishima Area, Southeastern Japan

Geophysical and Geological Exploration of Cobalt-rich Ferromanganese Crusts: An Attempt of Small-Scale Mapping on a Micronesian Seamount

Regional Distribution of Co-Rich Ferromanganese Crusts and Evolution of the Seamounts in the Northwestern Pacific

Current Status of Japan's Activities for Deep-Sea Commercial Mining Campaign

Sea-Floor Massive Sulfide Mining – Its Possibility and Difficulties to Emerge as a Future Business