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By Chris Castle

The Chatham Rise is a submarine topographic feature lying off the east coast of New Zealand between the South Island and the Chatham Islands and within New Zealand?s jurisdiction. The Chatham Rise hosts economically significant deposits of rock phosphate and other potentially valuable minerals. The deposits comprise nodules lying on, or just below the surface of the seabed in shallow waters. Rock phosphate is an essential ingredient of fertilizer and can be applied directly to pasture. There is a realistic opportunity the phosphate deposits could supply New Zealand?s agricultural requirements for an estimated 30-year period at current rates of consumption.

Jan 1, 2011

By Daisuke Monoe, Kisaburo Nakata, Rika Takeuchi, Tetsuo Yamazaki, Tomoaki Oomi, Tomohiko Fukushima

There are generally two methane passes in conjunction with the seafloor natural cold seepages, as is schematically shown in Fig. 1. The first pass consists of the coupled anaerobic oxidation of methane and anaerobic sulfate reduction, as well as sulfur oxidation in the bacterial mats and immobilization thereafter in the sediment layer and on the seafloor. Through the first pass, calcium and organic carbonates are formed in biological and chemical processes from the methane (Luff and Wallmann, 2003; Luff et al., 2004). The detailed structure of the seafloor methane consumption process unit and its biological and chemical processes were introduced in Yamazaki et al. (2005). The other pass consists of direct bubbling into the water column. Through this pass, organic carbonate is formed with biological oxidation, and a small amount of the methane escapes into the atmosphere. Methane flux is supplied to these two passes through the sediment layer from the deeper structures. The structure of the methane supply process unit was introduced in Yamazaki et al. (2006).

Sep 24, 2006

By Tetsuo Yamazaki

The Kuroko-type seafloor massive sulfides (SMS) in the western Pacific have received much attention as sources for economic recovery of gold (Au), silver (Ag), copper (Cu), zinc (Zn), and lead (Pb). Since the end of the 1980s, the Kuroko-type SMS have been found in the back-arc basins and on oceanic island-arc areas. In Okinawa Trough (Halbach et al., 1989) and on the Izu-Ogasawara Arc (Iizasa et al., 1999) are the typical representatives in the Japan’s EEZ. They yield a higher concentration in Au and Ag than the SMS found in ocean ridge areas (Rona, 1985). Similar formation processes with the Kuroko ore deposits on-land in Japan have been expected and outlined by many researchers (Sillitoe, 1982; Scott, 1985). The higher Au and Ag contents have increased the chances for profitable mining operation, which is under consideration by a private company (Malnic, 2001). Information about the resource potential of the targeted Kuroko-type SMS deposit, such as the amount of SMS ore body, the inside structure, the mean metal yields, and the geographical details are necessary for a technical and economic validation analysis for the development. The Sunrise Deposit of Myojin Knoll on Izu-Ogasawara Arc in the Japan’s EEZ is selected as a target for the technical and economic validation analysis. The relatively higher amount of information on its resource potential is the reason why the deposit is selected.

Sep 24, 2006

By K. Vanstaen, K. M. Cooper, S. Ware, S. L. Boyd

Remediation and restoration of offshore marine habitats is a relatively new concept with attempts in European regions largely being instigated by requirements of various strategic directives including Article 2 of the Habitats Directive (1992), the EC Water Framework Directive (2000, Article 2 of the OSPAR Convention (1992) and the developing European Marine Strategy Directive. A field experiment to establish the practicality of various options for rehabilitating the seabed on the cessation of dredging has been successfully set-up. The purpose of this experiment is to investigate the practicality and effectiveness of gravel seeding as a potential restorative method which could be applied at marine aggregate extraction sites following cessation of dredging. Zone 2, within Area 408 (offshore Humber) was chosen as the experimental site as there is some evidence for persistence of sand which may have resulted from screening operations at this site.

Aug 24, 2006

By I. Yu. Melekestseva, V. V. Zaykov

Paleooceanic structures of the Urals fold belt contain different volcanic-hosted massive sulfide deposits of the Urals, Kuroko and Cyprus types [Prokin, Buslaev, 1999]. Small Cobearing massive sulfide deposits, as Ishkinino, Ivanovka and Dergamysh, associated with ultramafites of the Main Urals fault, are less known. Interest to them had arisen after discoveries of the modern “black smokers” associated with ultramafic rocks of the Middle-Atlantic Ridge (MAR). Ores of the Urals deposits are enriched in Co (0.3 %) and Ni (0.6 %) that are concentrated in Co-Ni-Fe-sulfides, sulfarsenides, and arsenides. Ores also contain the increased gold contents – 3–6 ppm and up to 16 ppm in those saturated with As-bearing minerals. The aim of the paper is a comparison of precious metal mineralization in ores from the Paleozoic and modern ultramafic-hosted massive sulfides.

Aug 24, 2006

By Charles L. Morgan

"In 2012 the International Seabed Authority (ISA) established nine “Areas of Particular Environmental Interest” (APEIs) for consideration as future Marine Protected Areas to help preserve the biodiversity of life on the seabed within the Clarion-Clipperton Zone (CCZ) between Baja California, Mexico, and the Hawaiian Islands. The CCZ is believed to have a high potential for future seabed mining operations. Areas under active exploration contracts in the CCZ, plus the areas currently reserved by the ISA for exploration by developing nations, comprise about 1.9 million km2 of seabed area. The currently designated APEIs consist of more than 1.4 million km2 of seabed. Each APEI includes a central primary conservation area of 200 X 200 km, surrounded by 100-km buffer areas on all sides. The 100-km buffers are intended as a very conservative spacing between the primary conservation area and potential mining activities in adjacent seabed. The selection of these nine 400 X 400 km APEIs, has been criticized as possibly not including sufficient representative habitat similar enough to the potential mining areas (identified currently as the exploration contract and reserved areas administered by the ISA within the region) to ensure protection of the biodiversity that might be impacted by mining.An area to the east of the existing exploration contracts and reserved areas is known to have substantial mineral deposits; it is very similar to the adjacent exploration contract areas in its geology, environmental setting, polymetallic nodule abundance and nodule metal content. Because it is located in the northeastern extreme of the CCZ, this area is also likely to have relatively high densities of benthic life, compared with benthic communities further westward within the CCZ. Many options for the designation of this APEI are possible, but the area designation must accommodate the boundaries of the Exclusive Economic Zones of Mexico and France.This paper discusses why the selected region in the eastern extreme of the CCZ is a good candidate for designation as a new APEI.Keywords: polymetallic nodules, Marine Protected Areas, Clarion-Clipperton Zone, Areas of Particular Environmental Interest"

Jan 1, 2017

By Ian J. Graham, Cornel E. J. de Ronde

New Zealand lies astride a convergent plate boundary that extends north-eastwards from the Taupo Volcanic Zone (TVZ) to Tonga. This boundary is marked by the Kermadec arc, c. 1200 km of which falls within New Zealand’s EEZ, and which is host to numerous volcanic edifices both on the arc and in a zone immediately behind the arc to the west. In 1999, thirteen volcanic centres in the southern 260 km of the arc were surveyed for their hydrothermal plumes with seven of them discharging vent fluids into the surrounding ocean. Three of the seven volcanic centres have had mineralised rocks recovered from them during dredging and submersible operations, namely Brothers, Rumble II West and Clark. Presentday plume data combined with mineralogical evidence indicate that the vent sites at Rumble II West and Clark are waning, although the presence of Cu-rich sulphides in samples recovered from Rumble II West suggest there may be a massive sulphide (Cu-Zn-Pb-Ba ± Au) deposit located within the caldera. Brothers volcanic centre is host to the largest polymetallic mineral deposit discovered along the Kermadec arc and has numerous, up to 7 m tall chimneys within a c. 600 x 200 m area located on its NW caldera wall. Geochemical data indicate that concentrations of base metals are variable and depend critically on sample type. When combined with mineralogical and plume data, this indicates addition of a magmatic fluid component to the vent fluids.

Aug 24, 2006

By Jonguk Kim

Texture and geochemical composition of hydrogenous ferromanganese crust from relatively adjacent three seamounts (OSM2 at 157°35'E, 13°55'N, Lomilik at 161°37'E, 11°42'N and Lemkein at 165°05'E, 9°18'N) near the Marshall Islands in the western Pacific (Figure 1) were investigated in order to elucidate their growth history. These seamounts, located in different latitudes, are along a line that is parallel with the direction of Pacific plate movement. Thick crusts commonly have three or four distinct layers (Figure 2): (1) layer 1, uppermost layer, is black, dense, and has a botryoidal, columnar, or laminated texture; (2) layer 2, overlain by layer 1, is Fe-stained, porous to vuggy and filled with sediment; (3) layer 3, phosphatized layer, is black, massive, dense, and impregnated by CFA, (4) layer 4 shows parallel to undulatory laminated texture and cut by CFA-filled veins. Layer 1 and 2, unphosphatized young layer, are observed in crust samples collected from all seamounts. However, lower part of the crust shows different textures in different seamounts. Both layer 3 and 4 are found in thick crust from OSM2 but layer 4 is absent in crust samples from Lemkein and Lomilik. All the uppermost layers (layer 1) from three seamounts have similar textural and geochemical characteristics. Layer 2 is overlain by layer 1, is porous, partly Fe-stained, and sediment-infilled. In previous studies, layers 1 and 2 have grown in different oceanic environment. Textural and geochemical properties show that layer 1 has grown under relatively higher bottom water activity and lower productive environment than layer 2. Carbonate and detrital materials in layer 1 are not abundant compared to layer 2. Layer 2 can be assumed to have grown under equatorial high productivity zone (EHPZ) while layer 1 has started to grow when the seamount left from the EHPZ.

Jan 1, 2003

By Kira Mizell, James Hein

"INTRODUCTIONThe majority of studies on the genesis of ferromanganese crusts focus on the adsorption and accumulation of metals, and therefore cations, especially those of economic interest. From these studies, a first-order electrochemical model has been proposed based on the zero point of charge of the manganese and iron oxides at typical seawater pH, which assumes that positively charged ions will bind to the negatively charged manganese oxide phase and neutral and negatively charged ions will bind to the slightly positively charged iron oxide phase (e.g. Koschinsky and Halbach,1995; Hein et al., 2013). While the theory behind this model is sound, and it has been consistent for many elements, other elements may not follow the model (Koschinsky and Hein, 2003), and thus requires additional investigation and validation. As a new approach to understanding element accumulation in ferromanganese crusts and to test the proposed electrochemical model, this study investigates the surface chemistry of the halogens, which occur as negatively charged ions in seawater and have high and consistent concentrations in seawater.ResultsBulk Halogen ConcentrationsTo determine the distribution of halogens in ferromanganese crusts, an initial dataset of 24 FeMn crusts (24 bulk and 19 layer samples) from throughout the global ocean, including the Arctic and the Southern Oceans, has been analyzed for chlorine and fluorine content using ion-selective electrode. Although both Cl and F are conservative in seawater, their content in crusts shows striking variability (Cl: 326 - 13310 ppm; F: 146 – 1048 ppm for non-phosphatized crusts) and has no obvious geographic relationship to ocean basin and no correlation with water depth, latitude, or longitude. We plan to have bromine concentration data to present at the time of this conference."

Jan 1, 2017

By Timothy F. McConachy

Magmatic-hydrothermal activity in the South-West Pacific and SE Asian island arcs during the Tertiary has created a premier copper-gold province with numerous, commercially attractive base and precious metal deposits. This activity continues to the present day, especially in submarine sectors of those arcs where modern technologies enable direct observation of ore-forming processes in action. Until recently, however, the volcanic island arcs of Indonesia escaped such attention. The Indonesia-Australia Survey for Submarine Hydrothermal Activity (IASSHA), involved three cruises with KR Baruna Jaya VIII, focused particularly on the Sangihe arc; Tomini Bay, Sulawesi, including the vicinity of isolated Colo volcano; and the Sunda Strait including the neighborhood of Krakatau volcano. IASSHA 2001 and 2003 cruises studied the arc and behind-arc sectors of the Sangihe volcanic island chain extending northwards from Quaternary volcanoes on the northeastern tip of Sulawesi, near Manado, to the Kawio Islands near the border with the Philippines (Fig. 1). This chain lies above a west-dipping Wadati-Benioff seismic zone whose subduction trench is obscured by accreted sediments and mélange, forming the Talaud-Mayu ridge. West of the main active chain and extending northwards from Manado there is a subparallel ridge (The Manado Line) surmounted by a number of high (>2000 m) seamounts of uncertain age.

Jan 1, 2005

By Mark Vardy, Kasia-Leigh Chidlow, Tim Minshull, Jeorg Bialas, Sven Peterson, Bramley Murton, Alba Gil

Since the discovery of the first black smoker on the East Pacific Rise in 1977 (Francheteau, et al., 1979), the hydrothermal vents, now called seafloor massive sulphides (SMS) deposits, have generated great interest in the geological community, especially regarding their formation and composition. SMS deposits are areas of hard substratum, with high base metal and sulphides content, that form through hydrothermal circulation and are commonly found at hydrothermal vent sites. The high base metal (Fe, Cu, Zn, Pb), sulphur-rich mineral content has interested mining companies, due to their potentially high economic value. Currently, the known SMS deposits do not have the same dimensions as the massive sulphides (MS) found on land (covering just 10s to 100s m2) and pose significant mining challenges (being located in water depths between 800 m and 6000 m), meaning that they do not appear to be economically exploitable at present. However, these deep-sea mineral resources could be important targets in the near future, particularly with our ever-increasing demand for base metals. A key aim of the European Union-funded Blue Mining project is to develop techniques to robustly quantify SMS deposits dimensions (both surface expression and subsurface extent) and therefore assessing the suitability of SMS deposits for future economically viable and environmentally clean deep-sea mining operations.

Jan 1, 2017

By Ulrich Schwarz-Schampera

Submarine hydrothermal vents and associated mineralization on the Tonga arc have been identified in the summit calderas of two shallow-water volcanoes. The highest temperature vents (up to 270°C) occur at water depths between 430 and 540 meters below sea level (mbsl) near the summit of one volcano at 24°S (volcano 19). Clusters of large barite, anhydrite, and sulfide chimneys on the summit cone are vigorously discharging clear hydrothermal fluids with temperatures on the seawater boiling curve. There is abundant evidence of phase separation and associated gold and base metal precipitates. Pyrite, marcasite, wurtzite-sphalerite, tennantite, and chalcopyrite line the interiors of the highest temperature vents. Acid-sulfate alteration of basalts and basaltic andesites is evidenced by intense silicification and the presence of abundant alunite. One volcano at 21°S (volcano 1) has a chain of explosion craters on the flank of a neovolcanic scoria cone and associated massive pyrite, barite and native sulfur deposits at a water depth of 210 mbsl. Intergrowths of pyrite and enargite are associated with intensely argillic altered basaltic andesites. The reported alteration and Au-enriched mineralization styles of these vent fields are similar to other shallow water hydrothermal systems at island arc volcanoes and contribute to the diversity of seafloor hydrothermal activity in the western Pacific region.

Jan 1, 2010

By Benoît Waquet

In a context of scarce mineral resources, coupled with an increasing global demand in metals due to the exponential growth of newly industrialized countries, the mining industry will inevitably have to deal with tomorrow?s resources: underwater deposits. Three types of offshore deposits are known to date: polymetallic nodules, cobalt-rich crusts and hydrothermal sulphides. The latter, regarding the political-economic context, is now considered most likely to be exploited in a near future. Operating a mine critically requires accurate knowledge on geotechnical properties of the ore. A question is thus to be asked: Is there a particular spatial organization of geotechnical properties in a hydrothermal sulfide mound? In the present study, geotechnical properties have been measured for 29 sulfide samples of known origin, completed by 14 measurements on Western Pacific specimens from Yamazaki et al. (1990) and Yamazaki and Park (2003). From these geotechnical data on 43 sulfide samples, we can provide some answers to this question above, crucial for future exploitation of underwater mines.

Jan 1, 2010

By Jeremy Spearman, Mark Lee, Jon Taylor, Neil Crossouard, Bramley Murton

"SUMMARYThis paper describes challenges faced when executing a programme of monitoring to measure the dynamics of currents and sediment plumes at a seamount and the solutions identified to deliver the measurements. The study site was the Tropic Seamount, which extends some 3300m above the surrounding seabed and is found at the southern limit of the Canary Island Seamount Province. The purpose of the study, which forms part of the Marine E-tech project, was to provide information on the interaction of flows with the seamount and to assess the behaviour of sediment plumes that could be generated from potential seabed mining operations targeting the recovery of ferromanganese crusts. Since the crest of the seamount is submerged to a depth of 1000m, much of the work was undertaken using remotely operated and autonomous vehicles supported by measurements from the surface vessel. Despite only limited information on currents being available for planning purposes, the combination of short term forecasting using a 3-dimesional hydrodynamic model of the study area coupled with the collection and analysis of reconnaissance data collected during the first phase of measurement activities made it possible to plan and execute a number of detailed hydrodynamic experiments on the seamount crest. The results of these experiments have advanced the understanding of the behaviour of sediment plumes in the deep ocean and will ultimately improve our ability to manage the impacts which may arise from deep sea mining operations."

Jan 1, 2017

By Jorge MRS Relvas

Recent research both on active and fossil systems has demonstrated that shallow subseafloor replacement processes are not only viable depositional mechanisms for massive sulfide mineralization, but likely contributed as a major component of the mineralization occurring in large VHMS deposits and in many present-day seafloor hydrothermal systems. In the giant Neves Corvo deposit, as in many others VHMS deposits of the Iberian Pyrite Belt, there is overwhelming evidence for silicate-sulfide replacement processes being largely responsible for the efficiency of the ore-forming systems and huge size of the deposits. Textural evidences at all scales, coupled with a well-constrained mass-balance geochemical analysis, indicate that extensive replacement in the lavadominated volcanic rocks of the footwall sequence, and disseminated replacement mineralization in the volcaniclastic and/or sedimentary units were major mechanisms of ore formation in the Neves Corvo deposit. Shallow metal deposition prior to fluid discharge on the seafloor is likely to play a major role in seafloor massive sulfide mineralization. This premise should be envisaged as critical in evaluating the economic potential of seafloor resources, and should certainly be part of the equation when plans for seafloor mineral exploration missions are drawn.

Sep 14, 2011

By G. A. Tret’yakov, V. A. Simonov, I. Yu. Melekestseva, V. V. Zaykov, N. N. Ankusheva

The Kyzyl-Tashtyg massive sulfide polymetallic deposit is situated 120 km north-east of Kyzyl (the capital of Tuva Republic, Russia). It is located in the Ulug-O volcanic zone which is interpreted as the northern segment of the Kaa-Khem rift in Sayano-Tuva marginal sea, one of the Paleoasian Ocean margin (Fig. 1) [Zaykov, 2006]. Since its discovery in 1946 the deposit has been studied by many researchers. Significant information was published by Kuzebny et al. [2001] and Zaykov [2006] who proposed volcanogenic-sedimentary genesis. A single reference in English about Kyzyl-Tashtyg is available [Herrington et al., 1999].

By Shinichi Takagawa

The deep sea hydrothermal deposits are one of the most prospecting resources, and various works to develop these mines are now underway. There are also various methods for the pre-site survey of the mines: acoustic survey, electro-magnetic survey, and others. However, as a precise method at the final survey, drilling/coring is indispensable to confirm the three-dimensional distribution and to grasp the dignity of the ores for the final decision of industrialization. This drilling/coring at the final survey is done at many points with distance of 15~25m between each point for on-land deposits. This means that 1km by 1km square area requires (1,000m/25m)2 ~ (1,000m/15m)2 = 1,600 ~ 4,500 holes. The drilling/coring depths will be around 30m or more for the hydrothermal deposits. This depth seems very shallow, but because the stratum is very brittle and is very difficult to core, the average core recovery ratio is around 50%, and 0% core recovery happens very often. Thus, the indispensable work of coring for grasping the dignity of ores is a very difficult work although the coring depth is shallow, and also the required number of holes is enormous. Conventional drilling/coring method on the ocean is to use drillship. However, the cost is very huge. Recently a new technique has come out which is to use remotely controlled drilling machine on seafloor. This machine seems to have a very good performance. However, it is reported that the available inclination of the seafloor where the machine sits on must be less than 15 degrees. The sea floor inclinations of active hydrothermal vents area are usually very steep and slopes of 45 degrees or more are prevailing and it seems very hard to carry out drilling/coring for the machine at these steep slopes, although it is impossible to mine the ore at these areas because the temperature is too high to work there. The inclination of the sea floor at the dead or paused hydrothermal vents area where ore recovery is possible may be not so steep, and the machine may work well. However, the required number of holes is still a very heavy burden. In order to solve these problems, the author proposes a new concept of drilling/coring system operated from a conventional research ship. This concept is still a desk plan, but the author wants to realize this system at any means.

Jan 1, 2011

By G. Cherkashov

The geodiversity of seafloor massive sulfides (SMS) deposits at the slow- and ultra-slow spreading ridges is of great variety (Fouquet et al., 2010). Tectonics and magmatism are the two principal factors which control SMS formation and localization. The geological setting of SMS deposits is determined by their position relative to the rift valley and by the types of rocks hosted (Table 1). Depending on the first parameter, SMS deposits could be localized at [ ] the axial volcanic ridge or at the flank of the rift valley. Basalts, deep-seated gabbro, and serpentinized peridotites are distinguished among the hosted rocks. The outcrops of deep-seated rocks are exposed at the flanks of the rift valley. The tectonic mechanism of the lower crust and mantle rocks exhumation process is connected with very large offsets along the detachment faults, resulting in a forming oceanic core complex (OCC) (Smith et al., 2006; MacLeod et al., 2009). The SMS related to OCCs are represented by such ore clusters as Ashadze, Logatchev, Semyenov, and some others (Table 1) and are increasing steadily in number. This fact in combination with widespread OCC formation at the slow-spreading ridges (Escartin et al., 2008) and high grades of metals in SMS related to OCCs has provoked considerable scientific and economic interest in these types of deposits. It could be mentioned in this regard that the first two applications to the International Seabed Authority for prospecting and exploration of sulfides have been submitted for the areas in the spreading centres with wide distribution of the core complexes.

Jan 1, 2011

By Andrea Koschinsky, Luise Heinrich

(for an oral presentation) Activities for preparing future deep-sea mining offer the unique opportunity to study environmental conditions and anticipate adverse environmental impacts prior to the commercialization of the activity. Until know, environmental research has first and foremost focused on understanding direct impacts occurring at the seafloor or in the water column such as the removal of substrate, the suspension of sediment or the creation of particle plumes. Impacts occurring above the sea surface have thus far rarely been considered. The operation of deep-sea mining equipment, as well as of mining and transport vessels will be associated with a considerable energy demand. In the open ocean, this energy will be provided by heavy fuel oil (HFO), which is the cheapest and most common marine fuel. The combustion of HFO will be associated with the release of greenhouse gases and other pollutants. Deep-sea mining will thus directly add to already critical air pollution levels caused by international shipping. To contribute to a holistic assessment of deep-sea mining impacts and to address the previously outlined knowledge gap, we present the methodology to quantify the fuel consumption and associated emissions of a potential typical commercial manganese nodule mining operation in the Clarion-Clipperton Zone (Fig.1). Using the mine set up and energy demand estimates from a study commissioned by the German Federal Ministry of Economic Affairs and Energy supplemented by information from literature, we anticipate emissions of carbon dioxide (CO2), carbon monoxide (CO), methane (CH4), nitrous oxide (NO2), nitrogen oxides (NOx), sulfur oxides (SOx), particulate matter and non-methane volatile organic compounds.

Jan 1, 2018

By V. V. Ivanov, A. I. Khanchuk, E. V. Mikhailik, M. G. Blokhin, P. E. Mikhailik

At present, marine ferromanganese crusts of seamounts are of great interest as a source of high-tech metals. The metals most enriched in these deposits are essential for a wide variety of green-tech, emerging-tech, and energy applications (Hein et al., 2013). There is a grate number data on the content of major and minor metals (thousands analyses). However, information on the content of such elements as platinum, gold and silver in the world literature is limited. The concentrations (N – number of analyses) of platinum, gold and silver in the Pacific are 418 ppb (N = 105), 35 ppb (N = 72), 1.02 ppm (N = 26), respectively, and in the North Pacific Prime Zone - 477 ppb (N = 66), 55 ppb (N = 13), 0.1 ppm (N = 4); in the Atlantic Ocean is 567 ppb (N = 2), 6 ppb (N = 2), 0.20 ppm (N = 18), in the Indian Ocean, 211 ppb (N = 6), 21 ppb (N = 2), 0.37 ppm (N = 9) respectively; (Hein et al., 2013). The northern part of the Pacific is poorly studied in this question. The samples of ferromanganese deposits (FMD) was recovered from the Govorov Guyot (Magellan seamounts), MZh-33 Guyot (Marshall Islands), as well as the Detroit Guyot (Imperor Ridge) and Yomei Guyot (Fe-Mn placer Holes 431 and 431A DSDP, Imperor Ridge).

Jan 1, 2018