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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 Tetsuo Yamazaki

Natural methane hydrate has been scientifically studied as a global carbon reservoir. However, in Japan, it?s potential as an energy resource has been industrially highlighted, because there are few domestic oil and natural gas resources in Japan, but many potential deposition areas for methane hydrate in the sea around Japan. Less CO2 discharge from methane compared with coal, oil and conventional natural gas for the same calorie value is considered an advantage for its use as an energy resource. Because methane hydrate is distributed at shallow depth in sediments on the ocean floor, accidental leakage of methane may occur while we utilize methane hydrate. Methane itself has a considerable impact on the greenhouse effect, if it reaches the atmosphere. Therefore, it is necessary to estimate its behavior in the environment after leakage if we want to use methane hydrate as energy resource. The mass balance after leakage of methane on the seafloor and in the water column can be studied through the analyses of natural cold seepages and hydrothermal activity.

Jan 1, 2004

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 Pierre-Yves Morvan

One of the numerous challenge for underwater mining is the positioning. This paper describes an architecture for the integration of an Ultra Short BaseLine (USBL), an Acoustic Synthetic BaseLine (ASBL) operating in Sparse Array mode and a Doppler Velocity Log (DVL) closely coupled with an Inertial Navigation System (INS) for precise subsea positioning in severe environments. By using such architectures, the INS can help to reduce the noise on the measurements coming from acoustic sensors. Another advantage is the capability to reduce the number of required transponders on the seabed, and as a consequence, reduce the time for the deployment and calibration of each transponder. The paper further describes sea-trials performed to assess the ability of a complete positioning system to provide decimetric positioning precision even with a single beacon deployed in the navigation area.

Jan 1, 2017

By Sup Hong

Herein, concept designs of two different types of mining robots are concerned, which are aimed for developments of deep seabed mineral resources: polymetallic nodules (PMN) and seabed massive sulfides (SMS), respectively. Continuous mining concepts are presented based on technical and environmental feasibility, where the environmental and functional differences for commercial productions are investigated. Needs and roles of versatile mining robots are explained as a key of continuous mining system. The functional requirements and design characteristics of mining robots to satisfy the top requirements from customers are described comparatively. Schemes of axiomatic design and quality function deployment (QFD) are utilized: functional requirements (FR) are defined, technical requirements (TR) are figured out, design parameters (DP) are derived, and degrees of importance of design parameters are evaluated. Analogy and discrepancy in remote operation methods are put side by side. A pilot scale mining robot for PMN and a commercial scale one for SMS are suggested in form of concept designs. PMN mining robot is shaped as a multiple configuration of unit robot modules in side dimension, in which the unit robot module consists of two tracks and two pick-up modules. SMS mining robot is based on a four-tracked vehicle. Main platform is mounted on the vehicle through turn-table. Excavation device consists of two-articulated boom and cutter tool. Crushing-and-pumping units are placed same in both robot platforms.

Jan 1, 2011

By Tetsuo Yamazaki

The importance of cobalt-rich manganese crusts on the Pacific seamounts for possible future rare metal sources has currently been recognized. The thin layer-type deposit characteristics affect not only the excavation efficiency but also the economy of mining venture. Considering the thin layer-type distribution and the utilization of some rare metals in cobalt-rich manganese crusts, a preliminary economic feasibility of the mining venture is evaluated. Under some preliminary technical assumptions, the possibility of cobalt-rich manganese crusts for future rare metal sources for Japan is examined. The important role of utilization of rare metals in the crusts is highlighted.

Jan 1, 2010

By Peter E. Halbach

The Central Indian Ridge (CIR), the boundary between the African and Indian plates, forms a SSE trending mid-oceanic accretionary system in the equatorial Indian Ocean (Fig. 1), extending to the northerly Carlsberg Ridge spreading center, and terminating at the Rodrigues Triple Junction (RTJ; 25°30'S, 70°06'E) by intersection with the Southwest Indian Ridge (SWIR) and the Southeast Indian Ridge (SEIR). Crustal divergence of the CIR proceeds at intermediate rates; a progressive increase of ocean floor accretion towards the south is documented: the present half spreading rate and ridge trend change from 1.80 cm/a and N142° at the equator to 2.73 cm/a and N152° north of the triple point. The topography of the central rift zone is rather smooth compared to slow spreading analogues such as the SWIR, but slightly more rugged than the SEIR. The rift valley is 500-800 m deep, 10-15 km wide and usually well defined. The inner floor, 2-4 km in width, is relatively flat along the axis and more variable in cross section, and lies at 2700-3200 m depth. Off set fracture zones striking generally N60° . in southern portions of the CIR and laterally displacing median valleys by as much as 8 km are often bent, uplifting crustal sequences up to several hundred meters. The length of individual spreading segments varies between a few and several tens of kilometers. The vertical displacement on normal faults are larger while lineaments are shorter than those of the faster spreading SEIR. The direction of lineaments measured on the southwestern and northeastern flanks of the southern CIR are N154° and

Jan 1, 1994

By T. Kuhn

The Logatchev hydrothermal field is situated on the east inner flank of the rift valley of the MAR at 14°45?N and is hosted by serpentinized peridotites and minor gabbronorites while basalts are subordinate. Hydrothermal precipitates recovered from the Logatchev field during a recent R/V Meteor cruise include massive chalcopyrite chimneys, massive pyrite crusts, silicified breccias, abundant secondary Cu-sulfides, red jaspers, abundant Fe-Mn-oxyhydroxides as well as atacamite and Mn-oxides (Kuhn et al., 2004). Previous results of hydrothermal fluid studies in the Logatchev field are somewhat at odds with theoretical models of ultramafic-seawater reaction. Butterfield et al. (2003) suggested that the Fe component of orthopyroxene plays the more important role compared to olivine in ultramafic-hosted hydrothermal systems. This consideration is supported by the recovery of large amounts of Opx-rich gabbronorites and orthopyroxenites in the Logatchev field (Kuhn et al., 2004). A possible tool to constrain the contribution of the different rock types (ultramafics, mafics, MORB) to a seafloor hydrothermal system is the systematic analysis of 187/188Os ratios of the host rocks as educts and the sulfides as products. For instance, abyssal peridotites mainly display low 187/188Os ratios (<0.127); in contrast MORB and gabbronorites have radiogenic ratios of >0.13 (Snow and Reisberg, 1995), orthopyroxenite has ratios of about 0.174 (Büchl et al., 2002) and seawater has an ever higher 187/188Os of about 1 (Sharma et al., 1997). Therefore, massive sulfides predominantly leached from ultramafic rocks should have Os isotopic ratios plotting on a mixing line between the ultramafic rocks and seawater (in a 187/188Os vs. 1/Os diagram), whereas those derived from MORB, gabbronorites and/or orthopyroxenites will be plotting on different mixing lines.

Jan 1, 2004

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 Robert Ditchburn

Within New Zealand?s extended EEZ there exists a vast submarine hydrothermal mineral resource associated with the Kermadec intra-oceanic arc. Along this arc more than thirty submarine volcanoes have been explored by GNS-lead researchers and, of these, c. 60% are known to be hydrothermally active and a site of active seafloor mineralisation. Assessment of whether this mineralisation is economically viable in terms of grade and tonnage is now underway. A key aspect of these investigations is determining the age of the mineralization which will have a direct bearing on its mode of formation, the time elapsed to amass an economic deposit and, ultimately, its capacity for sustainable extraction. Intact barite-rich ?black-smoker? chimneys similar to that depicted here (86 cm long) have been recovered from Brothers volcano in the southern part of the arc. These and other hydrothermal deposits provide evidence of active volcanic massive sulphide (VMS) mineralisation along the arc, the age of which can be determined from the disequilibrium between isotopes within the thorium or uranium decay chains. A chimney from Mariana arc has also been dated using these radiometric methods. The principle dating technique for chimneys up to 15,000 years old uses the decrease in 226Ra/Ba due to radioactive decay after the VMS was deposited. An initial ratio is obtained from chimneys that are proven to be less than 100 years old and this involves dating with 210Pb, 228Ra and 228Th that have short half-lives compared with 226Ra.

Jan 1, 2005

Massive sulfides discovered in 1991 and further explored in 1993 in the eastern Manus back-arc basin, north of Papua New Guinea, represent one of the few modem seafloor occurrences known to he associated solely with highly siliceous volcanic rocks. As such they are very close analogs of ancient volcanogenic massive sulfide (VMS) ore deposits, and hence an excellent natural laboratory for developing new approaches for land-based VMS exploration. The Manus Basin lies between the active New Britain subduction zone and volcanic arc to its south and the opposed inactive Manus subduction trench to its north. It is being extended in a complex pattern of short neovolcanic zones and oblique transform faults. In its western sector, relatively mature back-arc spreading has created predominantly basaltic segments with characteristics and mineralization generally similar to those of mid- ocean ridges. At its far east, however, the basin is distinctly immature. The East Manus Volcanic Zone lies between two members of the Manus transform set, and is an en-echelon series of neovolcanic edifices constructed on extensionally thinned island arc crust formed during the earlier manus subduction episode. Individual edifices range from predominantly basaltic to predominantly dacitic in composition. Two of the edifices are known to be hydrothermally active, and a particulate plume with unknown source occurs in the seawater column above a third.

Jan 1, 1993

By Terence Day

The traditional approach to mineral resource development is to identify the resource and then to undertake an environmental impact assessment of the effects of developing the resource. However, the traditional approach tends to ignore or underestimate cumulative, indirect and synergistic effects (Therivel et al., 1992). Moreover, traditional environmental impact assessment puts the project proponent in a position where the environmental impact assessment is used to defend on environmental grounds, a decision which has already been taken on technical and economic grounds. An alternative approach is to undertake an area-wide or strategic environmental assessment, (United States Department of Housing and Urban Development, 1981; Kelly et al., 1987). Strategic environmental assessment consists of the compilation and analysis of environmental data and information on an area. The data and information includes physical and chemical oceanographic data, biological surveys, social and economic parameters such as recreation and resource use, and ecosystem stressors such as dumping areas and sewage outfalls. Strategic environmental assessment is being increasingly used in the U.S. to provide scientific information to evaluate national or regional objectives for development and conservation of coastal and oceanic resources (National Oceanic and Atmospheric Administration, 1991). The strategic environmental assessment process lends itself very well to an evaluation of offshore sand and gravel re- sources in Atlantic Canada, because although the potential resource is widespread, the environmental constraints on development are potentially serious, but highly variable. The approach has the merits of identifying areas which are least susceptible to environmental damage, and of concentrating the exploration efforts on that part of the resource which is most viable from the perspective of integrated resource management and marine conservation.

Jan 1, 1995

By Cheong-Kee Park

Since 1983, Korea Ocean Research and Development Institute (KORDI) have performed surveys on deep-sea mineral deposits in various areas with respects to their occurrences in Pacific ocean including manganese nodules in the C-C area of Northeast Pacific, Co-rich manganese crusts in various seamounts of West Pacific and hydrothermal sulfide deposits in back arc basins of Southwest Pacific. Among the results of these activities of KORDI, remarkable things were the registration as a pioneer investor in 1994 through the Government of Korea and the accomplishment of relinquishment on the allocated area in 2002 according to the relevant regulations. KORDI is faced to handle detailed surveys to select the optimum mining sites in the allocated area of 75,000 km2 and environmental studies to meet the requirements of the regulations or recommendations of the ISA. In respects of future exploration strategies, it is considered that methods and tools of previous exploration activities should be changed to the highly advanced technology. Establishment of an advanced exploration system and actual practice in appropriate areas become one of important tasks of KORDI in exploring deep-sea minerals, particularly manganese nodules. A technical strategy for future detailed surveys in the allocated area is realization of simultaneous and precise data acquisition on bottom information, such as variations of microtopography, nodule distribution, and transparent layer thickness of sediments in relatively small area (10 km x 10 km) representing certain specific regions, by high resolution survey technology. It would be not only a challenge for new exploration system in deep-sea environment, but also a mission for deep seabed mining venture.

Jan 1, 2003

By N. Wang

The City of Honolulu mines sand from nearshore deposits for beach maintenance. The suction dredging operation creates a discharge plume which is carried by currents and other motions until it settles out of the water column. The dispersion of such a plume is influenced by distribution of particle size, as well as site dynamics. Interest in dispersion characteristics stem$ from concern about possible deleterious influences of such a plume on the nearshore environment. The behavior of such plumes has been modeled by Brandsma and Divoky (1976), as well as others. This study is an attempt to calibrate a plume model (modified from Brandsma and Divoky&apos;s model by Wang), using concentration, turbidity, and fluid velocity measurements of a small plume taken under field conditions. This calibrated model could then be used to predict dispersion characteristics of a much larger plume. Sand suction-dredged at a depth of 12m with a four-inch pipe and discharged at midwater was used to create a test plume closely simulating the conditions found during regular mining operations. Water samples containing suspended material were taken at varying distances from the discharge, from which concentrations were measured in the lab. Transmitted natural light measurements were used to provide estimates of turbidity. Current velocities were measured using current meters, as well as drogue-following methods. These data were then used to help estimate the vertical diffusion coefficient in the model.

Jan 1, 1991

By William C. Hirt

Column flotation is a promising technique for processing as-mined, cobalt-rich, ferromanganese crust to separate the valuable crust component from barren substrate-rock, either aboard ship or within the water column. Column flotation testing was carried out in a seawater medium using samples obtained from the U.S. Exclusive Economic Zone (EEZ) in the mid-Pacific Ocean near Johnston Atoll. The collector reagent was a mixture of diesel fuel, fatty acid, and sulfonate previously developed at the U.S. Bureau of Mines for crust flotation using conventional flotation cells. Results are dependent upon particle size and reagent dosage, especially *as these factors affect froth volume and stability. Column flotation results are compared with previous studies in conventional cells. An overview of how column flotation might be applied in an offshore mining and processing system is given.

Jan 1, 1992

By Art Wright, Steinar L. Ellefmo, Kurt Aasly, Mike Williamson, Fredrik Søreide, Martin Ludvigsen, Michael Zylstra

Exploring for minerals on the seabed is challenging and expensive – and the ability to collect representative sub surface samples is essential. The research project MarMine led by NTNU has together with Seattle based Williamson and Associates developed and tested an ROV-based drill rig for mineral (seafloor massive sulfides and crusts) and rock sampling. The ROCS system is a single stroke drill and is simple, robust and possible to use from various larger ROVs. For the vehicle to provide a stable platform, the vertical bollard pull of the ROV and the vehicle mass are important variables. The developed drill uses a thin wall drill bit and barrel and operates at high RPM to reduce the required down weight and drilling moments. The system also contains an emergency release to be used if the core barrel is stuck. The drill is hydraulically powered with cylinders operating the tower and a rotation unit. It can rapidly be modified to provide samples from softer samples like unconsolidated material. At the Arctic Mid Ocean Ridge, a work class ROV was deployed with the drill mounted for testing at 2700 m depth in basalt rock. The recovery from the system was above 80%. Such core samples can be used for chemical analyses of metal and mineral grades, mineralogy and rock mechanical testing. The system provides a probing tool for marine mineral exploration, with low cost, low operational complexity and low risk. Proper resource estimation requires drilling deeper into the deposit, but the short core samples provided by the ROCS provide valuable a priori information planning for more extensive drilling campaigns.

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 Ning Yang, Yuxiang Chen, Ming Chen

An ultraviolet laser Raman spectrometer was developed to detect and analyze material components of seawater, seafloor sediment and rock at a depth of 7000m maximally. Wave length of the excitation resource of the spectrometer is set to 355nm, which can enhance eigen scattered intensity and detecting sensitivity, and avoid fluorescence interference. Miniaturization design was adopted for deep-sea application. Design of the optical system and pressure cartridge, material selection and seal design of the observation window, and design of the Lithium batteries are the key technologies in the procedure of research and development. The spectrometer was carried by a Lander sank to sea bottom of the Pacific's Mariana Trench for verification. During the sea trials, data acquisition for Raman spectra was conducted for analyzing seawater in the detection area, and the spectrometer was verified synthetically. According to the data, the spectrometer is stable and practicable with high resolution and precision, and it is appropriate to detect and analyze composition of substance under the tremendous ocean.

Jan 1, 2017

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 Nicholas Dyriw, Georgy Cherkashov, Tamara Stepanova, John Parianos, Anna Firstova

"Seafloor massive sulfide (SMS) deposits are a new frontier in global metal resources. Hydrothermal chimney’s (black smokers) precipitate Cu, Zn, Ag and Au rich from hot fluids (>250°C) during interaction with cold seawater ~2-4°C. Here we compare the sulfide mineralogy and geochemistry of Cu-sulfide chimney samples from two different tectonic locations: Solwara 1, a Cu-rich, transitional arc-back arc (Arc-BA) type SMS ore deposit and; Ashadze-1, a Cu-rich, ocean ridge type SMS deposit (Hannington et al., 2011).This work represents the first stage of a project aimed at investigating and understanding the significance of high Cu concentrations in SMS systems. Comparing these particular systems is significant because they share critical similarities despite being located at different seafloor depths, hosted in different rocks and are located in two different endmember tectonic environments. Critical similarities include: 1) age of mineralization, ~6000 years to current (Firstova et al., 2016; Johns et al., 2014); and 2) high copper contents, with chalcopyrite dominating sulfide mineralization (Firstova et al., 2016; Lipton, 2012). The reason for high Cu concentrations in both of these locations is still not entirely understood. The youthfulness (<6000y to current) of both locations is important because it reduces the possibility of increased zone refining, allowing us to understand the source characteristics better. This research will advance our understanding of the copper systematics of SMS systems by investigating and comparing the mineralogical and geochemical signatures from two, Cu-rich, end-member type SMS sites."

Jan 1, 2017