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By Lénaick Menot, Anne-Sophie Alix, Charline Guérin, Sébastien Ybert, Ewan Pelleter, Florian Besson

Ifremer, on behalf of the French government, holds an Exploration Contract with the ISA for polymetallic nodules in the CCFZ. As part of its exploration activities, the NODULE (2015) cruise was conducted to acquire a 50 m resolution bathymetric coverage of the eastern sectors of the Contract. In 2017, Ifremer initiated an update of the Contract’s mineral resource estimate. Metal grades and nodule abundance were modelled using ordinary kriging. The inferred mineral resource is 436 Mt (wet) of polymetallic nodules at an average abundance of 10.7 kg/m² with a cut-off grade of 7 kg/m². Based on the geological data, seamounts, sedimentary basins and steep slopes contain no nodules. Technical studies of most of the contractors have determined that nodule collectors could not maneuver on slopes above 5 to 10°. Thus, Ifremer has selected a quite conservative slope threshold of 7 % (about 4°) and a backscatter threshold of -29.5 dB to delineate nodule-free areas. This has a significant impact on the resource estimate, as about 54 % of the eastern Contract areas are excluded. Near-seafloor high-resolution mapping and photographic transects, associated with finer-spaced box-core sampling could constitute a next step to better constrain the mineable areas and to get a higher level of confidence in the resource estimation.

Jan 1, 2018

By D. Cronan

Both the S.W. Pacific and Caribbean island arcs are host to submarine hydrothermal mineral deposits, the former more so than the latter. In the S.W. Pacific, the whole gamut of such deposits occurs on the sea floor, sulphides, silicates, Fe and Mn oxides, whereas during the limited studies to date in the Caribbean only hydrothermal Mn oxides have been found to occur on the sea floor there in any abundance. Comparisons between the respective Mn oxides are thus the most fruitful at the present limited stage of our knowledge of Caribbean submarine hydrothermalism. Southwest Pacific hydrothermal ferromanganese oxides and their possible relationships to underlying sulphide mineralisation or bedrock anomalies (the geochemical window concept) has been a fruitful field of research in recent years. Certain element enrichments in crusts may be indicative of underlying mineralisation (Rogers et al. 2001). However, more recent studies on buried hydrothermal crusts in the S.W. Pacific (Cronan et al. 2002) have shown there to have been postdepositional diagenetic uptake of elements in them, and thus these elements cannot be used with any confidence in geochemical exploration for buried sulphide deposits unless sediment involvement can be eliminated.

Jan 1, 2002

By Kokichi Iizasa

Modern Kuroko-type deposits have been much reported in submarine calderas and cauldrons in the EEZ of Japan since 1988. Some of them have been found based on heavy mineral analysis of sediments in which sulfide particles may be derived from hydrothermal sources in the ambient areas. From the end of August to early September 2007, in the middle Izu-Ogasawara arc south of Tokyo, ROV expeditions were carried out in submarine calderas in order to examine mineralogical features between intact heavy particles spouting out from sulfide chimneys and heavy minerals such as sulfides in sediments around sulfide mounds in Kuroko-type deposits, and to find more newly formed hydrothermal sulfide fields in those areas. Some preliminary results from the ROV expeditions are reported here.

Oct 15, 2007

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 Takashi Ito

Numerous studies have examined the distribution of deep-sea manganese deposits throughout geologic history. Here I summarize the recent results, focusing on the frequency of occurrence, burial age and mechanism, and the paleoceanographic implications.

By Katsuya Tsurusaki

Commercial mining of manganese nodules is expected to begin within the next 20 to 50 years in large areas of abyssal sea floor in the Pacific Ocean. While deep sea mining is expected to realize significant quantities of rare metals that are needed for modern technology, the mining operation will cause extensive resedimentation over large areas of deep sea floor, the effects of which are thought to be harmful to the benthic community. Our present knowledge of deep sea benthic ecology is so limited that we cannot predict the magnitude of the impact. In November 1994, the United Nations Convention on the Law of the Sea was enforced and giving added impetus to improving our understanding of the effects of future mining operations. In order to fully understand the impact of deep sea mining and to mitigate the harmful environmental effects, it is necessary to accumulate more information on the deep sea environment and benthic communities. To achieve these objectives and to understand the relationship between resedimentation and biological reaction, artificial impact experiments are being conducted by the USA and Germany. The former named BIE (Benthic Impact Experiment) began in 1991 and is being performed by NOAA (National Oceanic and Atmospheric Administration of the United State of America) in the North Equatorial Pacific Ocean. The latter named DISCOL (Disturbance and Recolonization Experiment in the Deep South Pacific Ocean) was started in 1989 and is being conducted in the South Equatorial Pacific Ocean by a scientific group from Hamburg University. The Metal Mining Agency of Japan (MMAJ) is also carrying out environmental studies. These studies, commenced in 1989, are being conducted in association with NOAA and include an experiment named the Japan Deep Sea Impact Experiment (JET).

Jan 1, 1996

By P. C. Hollick

Two marine diamond deposits on concession 2b off Namaqualand along the South African Coast, have been systematically mined over the past year by the mv Moonstar. The two deposits, Smith?s Ulcer and Wedge Point Basin, are comparable in morphology, straddled the same water depths and have similar geology yet have given very different recoveries when compared to their respective grade models. These differences are best ascribed to the different style of mineralisation observed within the two deposits which has been directly controlled by the bedrock morphology. The smith?s Ulcer deposit has been formed in a metagreywacke bedrock displaying a strong north-south trending foliation which dips steeply to the west. Consequently the mineralisation is confined to narrow north-south linear trends with limited lateral extent (less than 5m) making extraction extremely difficult and somewhat variable. RE factors (recovered grade versus estimated grade) for this deposit range from 0.5 to 1.1. The Wedge Point Basin deposit is formed in a micaceous metaquartzite with a conjugate southwest northwest joint set, the southwest lineation being the more prominent, and structural foliation dipping gently to the west. The resultant style of mineralisation is confined to basinal features defined by topographical lows and is fairly lateral in extent (in order of 50m). Extraction of the mineralisation from this deposit is less arduous with recoveries more uniform, RE factors are frequently in the range 2 - 3. This style of mineralisation is more in line with what is to be expected from marine alluvial deposits, the nugget effect of diamond concentration being responsible for the high RE factor. The long narrow linear trends observed in Smith?s Ulcer demonstrably require a specialised approach in successfully sampling, modeling and ultimately mining.

Jan 1, 1998

By Tetsuo Yamazaki

Natural methane hydrate has been scientifically studied as a carbon reservoir globally. However, in Japan, the potential for energy resource has been industrially highlighted. There is less domestic oil and natural gas resources in Japan, but many potential deposition areas for methane hydrate in ocean around Japan are the reasons. Less CO2 discharge from methane compared with coal, oil and conventional natural gas when the same calorie value we get is considered as the advantage for energy resource. However, because methane hydrate distributes in shallower sediment layer in ocean floor, accidental leakage of methane may occur while we utilize methane hydrate. Methane itself has 21-times impact on the greenhouse effect, if it reaches the atmosphere. Therefore, it is necessary to estimate the behavior in the environment after the leakage, if we want to use methane hydrate as energy resource. The mass balance after leakage of methane on seafloor and in water column is numerically studied through the analyses of methane emissions from natural cold seepages and hydrothermal activities in this research. The outline structure of mass balance ecosystem model shown in Fig. 1 is introduced. A numerical early diagenetic model CANDI (Carbon And Nutrient Diagenesis) developed by Boudreau (1996) for simulating the biogeochemical processes such as organic matter, oxidant, nutrient, bi-product, and pH diagenesis in aquatic surface sediments and C. CANDI improved by Luff and Wallmann (2003) for describing the formation process of calcium carbonates in CANDI are used as bases of the ecosystem modeling in surface sediment layer around seafloor methane emission. Two functions such as methane bubble dissolution and bacterial methane oxidation in water column are added to an existing physical plume dispersion model by Doi et al. (1999).

Jan 1, 2005

By L. B. Khershberg

Marginal seas of the Russian Far East constitute the northwestern segment of the Pacific underwater belt distinguished by distinct metallogenic specialization of shelf-extended ore-bearing magmatic complexes and associated polycyclic mineralization. The coastal part of this vast region is known to contain both multiple placer manifestations and deposits, and non-metalliferous minerals. The latter are sedimentary deposits, the products of weathering, which contain re-deposited placer minerals in industrial concentrations developed on the shelf by certain geological processes. The shelf part of the Far Eastern seas is a seawater-filled continental margin. Complex geophysical mapping and drilling from ships of shelf sedimentary thickness and foundation has revealed the units of contemporary and ancient relief accompanied by formation of industrial concentrations of placer gold, cassiterite, titanium-magnetite, zircon, monzonite, and other components at different stages of placer formation. According to the information collected by prospecting by ?Dalmorgeologia? Co. Ltd. and other companies, placer-host structures within trans-placer-concentrating structures (land-shelf) are: shelf-extended river plains, contemporary and ancient shorelines, beaches, drained areas, spits, bars, detritus deficit zones, and terraces and bodies accumulated underwater in the areas where along-shoreline flows unload their detritus. They all could be used as criteria/signs for mapping and targets for placer prospecting.

Jan 1, 2004

By G. Cherkashov

A new hydrothermal field with massive sulfide deposits was discovered in 2004 at 16º 38.4?N, 46º 28.5?W on the Mid-Atlantic Ridge. Hydrothermal signals had already been recorded from bottom waters and sediments in this area during cruise 19 of R/V Professor Logatchev in 2000. This site was revisited during the 24th cruise of R/V Professor Logatchev in February 2004 when samples of massive sulfides were recovered and video records of the deposits made. The basalt hosted hydrothermal field is situated at a depth of 3700-3750 m, 600 m above the inner floor on the eastern slope of the rift valley. Structurally, the new field is located at the intersection of a deep along-axis marginal fault and a transverse sub-latitudinal dislocation. Six sulfide mounds as well as associated metalliferous sediments were mapped (sampled and/or recorded by video profiling) within the hydrothermal site. The largest ore body, 500 x 225 m, in the southern part of the field consists of small blocky talus and relics of sulfide chimneys partly covered by iron oxyhydroxides. The chimneys are 1-5 m high. The southern and western boundaries of the massive sulfide deposit have not yet been delineated. More than 1,100 kg of massive sulfides and stockwork mineralization were sampled at 7 sites by dredge and TV-grab. Everywhere, iron sulfides were the principal minerals present. Pyrite in association with lesser amounts of chalcopyrite occurs in both massive sulfides and stockwork mineralization. Of particular interest is the chalcopyrite-siliceous stockwork where silicified and chalcopyritized basalts are intruded by a network of chalcopyrite veinlets. These zones could be fairly thick and enriched in base metals. Sphalerite was very rare.

Jan 1, 2004

By T. Semkova, G. Cherkashov, V. Rashidov, L. Anikeeva, G. Gavrilenko, G. Glasby

The Kurile Arc consists of at least 100 submarine volcanoes and 5 submarine calderas located mainly in the rear arc (Figure 1). The arc is seismically very active, particularly in the south, and is characterized by extensive volcanism and hydrothermal activity. At least one subaerial volcano on the arc (Medvezhy located on Iturup island) has an extremely shallow magma chamber and is intensely active.

By Kokichi Iizasa

Kuroko-type deposits exist in Japanese EEZ. Some of them are present in the Izu-Ogasawara oceanic island arc south of Tokyo. Major two Kuroko-type deposits occur in the area. One is the Sunrise hydrothermal field occurring on the caldera floor of Myojin knoll, which is likely to be the developed stage in sulfide mineralization. Another is present in the crater of Suiyo seamount that is the early stage of sulfide mineralization. The two deposits are here presented on the growth history based on samples recovered by Benthic Multicoring System (BMS).

Jan 1, 2002

By Sang-Mook Lee

The Manus back-arc basin behind the New Britain Trench is one of the major sites of active seafloor hydrothermal vent-fields which are considered to be modern-day analogue of felsic volcanic-hosted polymetallic massive sulfide deposits abundant in ancient geological record. Many of these deposits represent multi-million dollar resources, and yet very little are known about the fundamental processes leading to their formation. In November 2000 January 2001, the PACMANUS hydrothermal system in this region will be targeted by the Ocean Drilling Program Leg 193 to investigate the internal anatomy. A number of observations that suggest that the tectonic, magmatic and hydrothermal processes in the eastern Manus basin spreading center are unusual in that they can not be explained by a simple back-arc opening due to subduction of the New Britain Trench. Geochemistry of submarine volcanoes in the eastern Manus basin, for instance, shows affinity to arc rather than back-arc type volcanoes. Yet these submarine volcanoes lie too faraway from the Benioff-Wadati zone. One hypothesis is that the magmatic and subsequent hydrothermal activity of this region is a direct result of the irregularities in the deep crust and upper mantle structure and that the tectonic process is controlled by the sharp inflection of the New Britain Trench. According to this hypothesis, the two major southeast-trending strike-slip faults in the eastern Manus Basin, Djaul and Weitin Faults, should extend farther down and join to the New Britain Trench. They would form a transform arm of the triple junction with the New Britain Trench southeast of New Britain Island and southwest of Bougainville Island forming the other two arms. A trench-trench-transform triple junction can not be stable over time, and therefore a slight change in the plate velocity may lead to a dramatic change in the configuration of the plate boundaries. If so, the instability of the triple junction may cause large tectonic deformations, such as mantle uplift under the Manus basin due to mantle rupturing by transform faults, and therefore may explain the arc-style volcanism and unusual compositions of hydrothermal deposits in the eastern Manus basin.

Jan 1, 2000

By Hyun Sub Kim

Subsea mineral deposit exploration aboard the R/V Onnuri was performed along the northern Central Indian Ridge (CIR) between 8°S and 17°S in December 2009 ~ January 2010 (09IR Leg01 and 09IR Leg02) and December 2010~ January 2011 (10IR Leg01, 10IR Leg02, and 10IR Leg03). Final goal of the expedition for the first Korean research cruise on mid ocean ridge system is to define seafloor massive sulfide ore bodies through searching the active hydrothermal vents nearby spreading centers as well as to elucidate the nature of spreading segments of the northern CIR area where no systematic survey have been operated before by mapping and sampling of volcanic rocks. The preliminary result of topographical interpretations of bathymetry clearly display ocean core complex between 10°S and 11°S. The ocean core complex is featured by topographic-high area with corrugated surface. Lineaments of corrugations of the ocean core complex are clearly perpendicular to abyssal hill direction which is triggered by symmetric-normal faults. Ocean core complex are favor for hydrothermal fluid path because of the long-lived faults. In further exploration, more detailed examination, including systematic CTD casting and tows, need to narrow down actual venting site around ocean core complex. Magnetic field survey is able to estimate the location of hydrothermal vents with the properties that high temperature of hydrothermal fluids over Curie-point can cause thermal demagnetization. In magnetization intensity map, most of low magnetization zones are located at the nodal point over the ridge axis and the ocean core complex.

Jan 1, 2011

By Tetsuo Yamazaki

Deep-sea rare-earth element-rich mud (REE Mud) distributes in pelagic clayey sediment column on ocean seafloor at 4,000-6,000 m deep. The thickness ranges 5-80 m and the burial depth 0-100 m. The REE content ranges 600-2,250 ppm in Pacific and one of the richest, maximum 6,500ppm, has been found in Marcus Is. exclusive economic zone. By applying a conventional hydraulic excavation and lifting methods, the economy of REE Mud mining around Marcus Is. is preliminary examined. Because the waste content in REE Mud is high and the disposal cost in Japan is very expensive, the mining is recognized far away from economy.

Sep 14, 2011

By Malcolm Clark, Robin K. H. Falconer

There are a number of likely impacts from mining operations, but a key issue is uncertainty about the environmental effects of sediment plumes created by disturbance to the seafloor and discharge of processed waters. The New Zealand National Institute of Water and Atmospheric Research (NIWA) is undertaking a research project to improve understanding of such impacts (relevant to both mining and trawl fisheries), by examining the extent and persistence of sediment plumes, the immediate impact and subsequent recovery of seafloor exposed to these plumes, and the effect on functioning of ecologically significant species. The project will use a combination of field survey experimentation with in situ observations and controlled laboratory-based experiments. The field work begins in May 2018 when an area of up to 1km2 at depths of 400-500 m on the Chatham Rise, 450 km east the New Zealand South Island will be subjected to disturbance by an upgraded former NOAA Benthic Disturber. The suspended sediment load created by the disturbance will be tracked and monitored, with the effects on seafloor animals examined by pre-and post-disturbance sampling. A wide range of seafloor sampling, benthic landers, towed cameras, oceanographic moorings and water column monitoring will be carried out over a three week period. Monitoring surveys will be repeated in 2019 and 2020 to determine the longer-term resilience and recovery of disturbed communities. The laboratory-based side of the programme, also starting in 2018, involves holding live deep-sea corals and sponges in tanks at NIWA, and exposing them to various levels and duration of particle loads in the water in order to reveal lethal thresholds as well as sub- lethal effects of settled and suspended sediment.

Jan 1, 2018

By P. Mikhailik

Recently, characterized by fast development high- and nano-technology, demand for rare and trace metals has increased. One of such metals is gallium. Gallium compounds, mainly GaAs, are used in medicine, to manufacture optoelectronic devices, microwave techniques, devices of solar power and infrared optics, etc. The basic gallium industrial deposits are known only on land. There are bauxites (50 ppm), nepheline rocks and ores (36-38 ppm, minerals concentrators are nepheline and sodalite), Zn-Pb-Cu ores (5000-12000 ppm, minerals concentrators are gallite, germanite, sphalerite, bornite), sulphide-polymetallic and Pb-Zn ores (10-32 ppm, minerals concentrators sphalerite, chalcopyrite) (Vershkovskya et al., 1998). High concentration of gallium are observed in hydrothermal massive sulphides of a Mid-Okinawa Trough (The South Chinese Sea) and Sujo seamount (The Philippine Sea) (Noguchi et al., 2007). As it is known, deep-sea massive sulphides and associated Fe-Mn crusts are products of hydrothermal fluid discharge. High-temperature massive sulphides precipitation are the first, and low-temperature Fe-Mn crusts deposition is the last process of hydrothermal mineralization (Cronan, 1982). Hydrogenic crusts and nodules of the World ocean are characterized by low concentration of Ga, close to clarke (19 ppm) (Kobaltbogatye.., 2002). Hydrogenic crusts from the Sea of Okhotsk are exception, because Ga concentrations are exceeded clarke in 3,5 times (Mikhailik, et al., 2009). Complex studying of Fe-Mn crusts from deep-sea basins volcanic seamounts of the Sea of Japan has shown their hydrothermal-sedimentary genesis (Mikhailik, 2009). High gallium concentration (up to 850 ppm) was established in these crusts by ICP-MS (Agilent 7500C). Microprobe research (JXA-8100) of samples Fe-Mn crusts has not revealed the gallium minerals concentrators. It suggests that, gallium in Fe-Mn crusts of the Sea of Japan is sorb substance.

Jan 1, 2010

By Jonguk Kim

Hydrothermal exploration aboard the R/V Onnuri was performed along the northern Central Indian Ridge (CIR) between 8°S and 12°S in January 2010. The main objectives of this first Korean research cruise on mid ocean ridge system was 1) to understand the nature of spreading segments of the northern CIR area, where no systematic survey have been operated before, by mapping and sampling of volcanic rocks and 2) to discover new hydrothermal venting along the spreading center of northern CIR. During the first leg (IR09 Leg1) bathymetric data, in ~50 km width, were collected by multibeam echo sounding system (EM120), which reveals the exact location and structure of axial rift valley of northern CIR between ~ 8°S and 17°S. Then, rock sampling and CTD casts and tows were performed in northern half of the multibeam survey area in the second leg (IR09 Leg2). The results of bathymetric survey clearly display ocean core complex between 10°S and 11°S. The ocean core complex is featured by topographic-high area with corrugated surface. Lineament of corrugations of the ocean core complex are clearly perpendicular to abyssal hill direction which are triggered by symmetric-normal faults. Symmetrical and asymmetrical segments are characterized by parallel abyssal hills and ocean core complex and/or subparallel abyssal hills, respectively. Geochemical analyses of basaltic glasses from spreading axis show geographic trend of increasing of incompatible elements north to south along the spreading axis, which might be influenced by Reunion hotspot plume. However, local but clear enrichment of incompatible elements is observed in volcanic lava from segment 2, which suggests possible local mantle heterogeneity of uncertain source. Lots of serpentinite and gabbroic rocks with coarse-grained feldspar was recovered in the ocean core complex. Ultramafic and/or mafic rocks indicate the gentle-domed block was traveled from upper mantle. Along the spreading axis of the northern CIR, significant hydrothermal plume signatures were detected by CTD castings and tows. Plume signatures were observed at all 5 surveyed segments, suggesting vigorous hydrothermal activities along the northern CIR. However, the optical signals (light transparency and backscattering) of the nearly every cast along the axial valley of the CIR showed increased background level, which might be due to higher level of suspended particles within the axial valley not only by widespread hydrothermal plumes but also by other processes like resuspension. Onboard dissolved methane analysis indicates that the greater part of the plume signals are originated from hydrothermal venting, not by resuspension. However, more detailed examination, including analyzing additional hydrothermal tracers, need to distinguish actual hydrothermal plume signature.

Jan 1, 2010

By Virginie Tilot de Grissac

This project funded by Government of Flanders (Belgium) and coordinated by the Intergovernmental Oceanographic Commission proposes to draw recommendations for conservation of the biodiversity and for minimizing the impact of future nodule mining from the description of the referential state of suprabenthic megafaunal assemblages within a nodule ecosystem in the Clarion-Clipperton Fracture Zone (CCFZ). The description of this specific ecosystem is based on the analysis of about 200 000 photographs and some 55 hours of film collected by French and American exploratory cruises. The video and hotographic sampling has been achieved by means of different towed and remote control devices designed for Ifremer and NOAA including the manned submersible “the Nautile.”

Aug 24, 2006

By Evgeny G. Gurvich

While direct study of high temperature hydrothermal activity and the associated mineral formation as well as study of their scales are possible in the modern ocean, researchers are deprived of such opportunity for past geologic time. Even in cases where hydrothermal deposits that formed in the geological past are preserved they have been covered by sediments or overlain by lava and have become inaccessible after a time for obser-vation and sampling. Rarely are these buried hydrothermal deposits found during deep-sea drilling or coring operations, and their direct study on an ocean scale is impossible at present. Even within hydrothermal fields, without special preliminary detailed surveys, the probability of intersecting hydrothermal edifices that are covered by sediments becomes a rare event.

Aug 24, 2006