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By Toru Yamasaki

A concept of plate-tectonic controls for the formation of seafloor massive sulfide (SMS) deposits in back-arc settings was established by Franklin et al. (2005). According to Franklin et al. (2005), a consequence of extension and rifting is subsidence, thinning of the crust, and the rise of hot, athenospheric mantle into the base of the crust. Underplating of the crust by mafic magmas results in low-pressure partial melting of the hydrated crust at a <15-km depth, and the generation of felsic anhydrous melts. The rapid ascent of hot felsic melts, along with mantle-derived mafic melts, results in bimodal volcanism that characterizes rift and volcanogenic massive sulfide deposits (VMS) environments. The rapid and focused advection of the magmatic heat within the rift to the near-surface environment which are required to sustain vigorous long-lived VMS hydrothermal systems. Faults within rift environments may also allow seawater to penetrate into subvolcanic intrusions and mix with magmatically generated metalliferous fluid or allow a direct magmatic contribution from shallow crustal level (3–12 km) magma chambers (Franklin et al., 2005, and references therein). In addition, the caldera-forming processes are favorable for the formation of VMS deposits and the focused high heat flow and cross- stratal structural permeability that is restricted in time and space to caldera development provides an explanation for the clustering of VMS deposits and their restriction to specific time-stratigraphic intervals and structures in the evolution of submarine central volcanic complexes (Franklin et al., 2005, and references therein). The concept is persuasive, although it is based on a series of logically constructed reviews mainly focused on ancient on-land deposits.

Jan 1, 2018

By Dennis Sánchez Mora, John Jamieson

INTRODUCTION Work by Humphris et al., (2002); Ondréas et al., (2009); Barreyre et al., (2012); and Escartín et al., (2015) has identified active and inactive hydrothermal sites along the Lucky Strike segment. The sites that contain the largest accumulation of known sulfides are located between the north and the southern zones (Figure 1), a vent site area that is referred to as the Main Lucky Strike hydrothermal field (Escartín et al., 2015). Hydrothermal fluid outflow has been linked to a shallow fault network (Barreyre et al., 2012). However, specific constraints on fault geometries have not been determined. Other off-axis sites at Lucky Strike, such as Capelinhos (high temperature vent), and Grunnus (inactive?), as well as a low temperature vent field (on-axis), Ewan, have been described by (Escartín et al., 2015). Given the spatial relationship between the Main Lucky Strike hydrothermal field (MLSHF), and the intersection of northern rift faults with the southern rift faults, a structural analysis of this area can provide insight into the fault controls on fluid flow that leads to hydrothermal venting and sulfide precipitation. METHODOLOGY Structural data (dip direction and dip) was determined using Leapfrog Geo 4.0 software. Bathymetric data was obtained from Escartín et al., (2015) and references therein. The bathymetry was imported into Leapfrog Geo (in UTM format) and, using the structural modelling tool, individual measurements with dip direction and dip data were collected with a focus on the northern volcanic rift and the southern central volcano (Figure 2a). All measurements were taken from what the authors consider as normal faults, and to aid the determination of individual measurements a “face dip” map was constructed, where the bathymetry is colored by slope angle (Figure 2b). All measurements are simultaneously plotted on a stereonet generated by the Leapfrog Geo Software. Data were divided into northern and southern, and western and eastern zones to determine the relationship between hydrothermal venting and the structural geometries at Lucky Strike (Figure 2c). Slip measurements for individual faults were determined along the dip of the fault with a measuring tool. Net slip, heave (horizontal displacement), and throw (vertical displacement) was calculated for each of the zones.

Jan 1, 2018

By LeRon E. Bielak

The marine minerals program of the Minerals Management Service (MMSI has undergone significant changes during 1991. Formerly the Office of Strategic and International Minerals, the program has been renamed and invested with additional responsibilities. The new name, Office of International Activities and Marine Minerals, (INTERMAR) reflects its dual mission. INTERMAR&apos;S role in the international area was broadened in January 1991 to provide the MMS with a focal point for identifying and coordinating international opportunities of mutual interest and benefit. Opportunities include energy and nonenergy minerals and a broad range of areas such as resource and environmental assessment and management, structural and operational safety, royalty management, regulatory matters and public affairs. Cooperative efforts involving information exchanges, training programs, research, and similar arrangements are receiving particular emphasis. Australia, Canada, France, Japan, Sweden, the United Kingdom and the USSR represent a growing list of countries with whom arrangements have been established. Support has also been lent to other Federal Agencies and the United Nations in areas where MMS expertise and resources can impart a significant contribution. Opportunities will also be explored which involve Pacific insular areas.

Jan 1, 1991

By Andrea Koschinsky

Recent technological breakthroughs in the fields of ceramics, medicine, aerospace engineering and electronics (semi- and superconductors) are constantly creating new uses and an ongoing increasing demand for a variety of rare valuable trace metals. These so-called high-tech elements such as hafnium (Hf), titanium (Ti,) niobium (Nb), tantalum (Ta), zirconium (Zr), molybdenum (Mo), vanadium (V) and the rare earth elements (REE), many of them of strategic importance, occur inter alia at elevated and potentially economic concentrations in marine ferromanganese nodules and ferromanganese crusts, making those deep sea deposits potential future resources of these metals. As these metals are mostly present in the lattice of the manganese and iron phases, which are strongly intergrown, rather than in separate mineral phases within the nodules and crusts (Koschinsky and Hein, 2003), reductive dissolution of the host phases is a prerequisite to release and dissolve the valuable metals. To evaluate the association of these rare valuable metals with their mineral carrier phases, sequential leaching experiments were carried out on selected samples in a first step in our project.

Jan 1, 2011

By Doug Lockhart

The Marine Minerals Technology Center has taken advantage of recent price and performance .improvements in PC hardware and software to upgrade its seismic acquisition system. In the past, single channel, high resolution, seismic data was displayed on an analog plotter and stored on tape. Associated navigation data was logged by hand or on a chart plotter. The navigation and seismic data were synchronized with time so that they could be cross referenced. The Center&apos;s new system uses PC&apos;s for the acquisition of both seismic and navigation data. Off the shelf software products were purchased for each task. Elics Delphl performs the seismic acquisition and processing, and GeoResearch, Inc. Geolink provides the navigation interface. A navigation string is sent from the navigation PC to the seismic PC via an RS232 line. This string consists of a time and location fix, as well as speed and heading data. The navigation string is then imbedded in the header of the seismic record. The Geolink software is capable of monitoring other devices in addition to the GPS used for positioning. Device inputs are attributed to the location data to provide easy construction of a navigation GIs. Currently the Center is logging fathometer data along with the navigation. As a result, a map of bathymetry along the tracklines can be available shortly after completion of the cruise.

Jan 1, 1992

By Yves Fouquet

Recent exploration demonstrates that hydrothermal systems related to upper mantle ultramafic outcrops are common in the modern ocean. Most sites are located on slow spreading ridges with a low magmatic budget. Volcanogenic Massive Sulfide (VMS) deposits, associated with basalt, along the Mid Atlantic Ridge (MAR) are volcanically controlled near the topographic highs at the center of the segments. Three preferential settings are identified for ultramafic sulfide mineralization: 1) Off axis, on rift valley walls, near the amagmatic ends of the segments; 2) Non-transform offsets and 3) Ultramafic dome structures at the ridge transform fault intersection. The upper surface of these domes is often interpreted as a detachment fault. Three processes are considered for driving hydrothermal cells in ultramafic rocks: 1) regional heat flow at the ridge axis 2) Cooling of a deep gabbroic intrusion and 3) exothermic heat produced during serpentinisation. Along the Mid Atlantic Ridge, four types of ultramafic hydrothermal mineralization are observed: 1) High temperature (>350°C) sulfide mineralization related to low pH fluids, (ex. The Logachev field at 14°45? N and the Rainbow field at 36°14 N); 2) Medium temperature carbonate chimneys (<100°C) related to high pH fluids (ex. The Lost City site at 30°N); 3) Low temperature diffuse venting associated with extremely high methane discharge and pervasive alteration and silicification of both volcanic and ultramafic rocks (ex : The Saldanha field at 36°34 N); 4) Stockwork mineralization and quartz veins with sulfides related to gabbroic intrusions within ultramafic rocks (15°N). When compared to mineralization in a basaltic environment, sulfide deposits are enriched in copper, zinc and specific elements related to an ultramafic rock source such as Ni and Co. They are also significantly enriched in gold which, unlike in basaltic environments, has a bimodal occurrence both in low temperature Zn-rich assemblages and in high temperature Cu-rich mineral assemblages. The Cu-Zn-Co-Au deposits along the Mid Atlantic Ridge seem to be more common than on land where few similar VMS deposits are known. We consider that ultramafic VMS deposits on slow spreading ridges constitute a specific marine type of mineralization that is less easily than back arc deposits, incorporated into the continent during obduction processes.

Jan 1, 2004

By S. Kim Juniper

The discovery of chemosynthetic-based ecosystems at hydrothermal vents in the deep ocean was arguably one of the most important findings in biological science in the latter half of the 20th century. More than 100 vent fields have been documented along the 60,000 km global mid-ocean ridge system. Over 500 new animal species, over 80% of which are endemic to the vents, have been described from this environment. Unusual, highly evolved symbioses between invertebrates and chemolithautotrophic bacteria are common at vents, producing concentrations of biomass that rival the most productive ecosystems on Earth. Hydrothermal vents ecosystems, because of their very limited area and the presence of endemic species, are highly vulnerable to human disturbance. Mining for polymetallic sulphide deposits poses the greatest future physical threat to hydrothermal vents and their biological communities. However, there is more immediate concern about the impact of concentrated scientific research activities. Some sites have been revisited by several research expeditions per year for more than a decade. As vent sites become the focus of intensive, long-term research, oversight organizations are discussing mitigative measures to avoid significant loss of habitat or oversampling of populations. Canada recently became the first national jurisdiction to set aside a hydrothermal vent site as a Marine Protected Area.

Jan 1, 2001

By Mayumy Amparo Cabrera-Ramírez

Polymetallic nodules are a widespread resource in the Pacific Ocean, particularly in the areas of Clarion-Clipperton (Cronan, 2000). The most abundant mineral phases are formed by iron and manganese oxides, with minor elements such as nickel, copper, cobalt, molybdenum and rare earths elements (Cronan, 1977; Cronan and Moorby, 1981; Iyer and Sharma, 1990; Mangini et al. 1990; Banerjee et al. 1991). In the Clarion-Clipperton Zone (CCZ), several authors mention that there are three main mineral species of manganese oxides, which have been recognized and which are associated with different processes of formation: todorokita (Mn2+, Ca, Mg) Mn34+ O7. H2), vernadite dMnO and birnessite enriched in Fe and (Na, Ca) 0.5 (Mn4+, Mn3+) 2O4. 1.5 H2O. In nodules of hydrothermal origin have been found todorokite, birnessite, vernadite, goethite and pyrolusite. Although there are many oxides and hydroxides of manganese and iron in amorphous and microcrystalline phases that make up the bulk of the nodule (Frondel et al. 1960; Cronan 1977; Dymond 1981; Calvert and Piper, 1984; Aplin and Cronan, 1985; Martin and Lallier, 1993; Achurra et al. 2009), identifying specific mineral phases is difficult due to the intergrowth of different phases and associated detrital material.

Jan 1, 2011

By Charles L. Morgan

The Minerals Management Service of the U.S. Department of the Interior and the State of Hawaii Department of Planning and Economic Development are investigating the cobalt-rich ferromanganese oxide crust deposits found within the Exclusive Economic Zones (EEZ) of the Hawaiian Islands and Johnston Atoll. The objective of this investigation is to complete a preliminary resource assessment and an Environmental Impact Statement for potential leasing of mineral rights to these crusts. The results of this effort will be summarized and published in a Draft Environmental Impact Statement in March 1986. Three oceanographic cruises to deposit sites in the Hawaiian Islands EEZ were conducted by the University of Hawaii in 1984. As a result, data and sample analysis yielded the following resource estimates (in thousand tonnes): (1) total crusts - 378,500; (2) cobalt - 2,500; (3) manganese - 76,200; (4) iron - 59,700; and (5) nickel - 1,400. These estimates do not include key factors such as deposit continuity, recoverability, and environmental sensitivity. A preliminary attempt to quantify some of these factors for one particular deposit is in progress and will consist of detailed field studies followed by laboratory analysis. Similar evaluations of the Johnston Island EEZ have also begun and are based upon field work conducted by West German researchers and the U.S. Geological Survey. The Johnston Island EEZ appears to have crust resources about as large as those contained in the entire Hawaiian EEZ.

Jan 1, 1985

By Bjørn Eske Sørensen, Kristian Drivenes, Przemyslaw Kowalczuk, Kurt Aasly, Gavyn Rollinson, Ben Snook

Efficient and successful mineral processing is dependent on detailed knowledge of the materials and minerals that are to be separated and concentrated. Common bulk methodologies such as XRD and XRF are fast and easy, and can provide an overview of the mineralogy and bulk chemistry of the material. However, they will not provide any textural information. Knowledge of the often intricate interaction between minerals in seafloor massive sulfide deposits is crucial in plant design for mineral processing. Samples from the Loki’s Castle hydrothermal vent have been characterized by X-ray diffraction (XRD), X-ray fluorescence (XRF), optical microscopy, Scanning Electron Microscopy (SEM), QEMSCAN, Electron probe microanalyzer (EPMA), and Electron Backscatter Diffraction (EBSD). Processing experiments used froth flotation and leaching techniques. The typical line of operation in ore characterization is shown in Figure 1. Mineral processing may be commenced after any stage of ore characterization. However, it is ideal to have completed as many steps in the ore characterization as possible in order to have the most information of the initial feed material. The main economic minerals in the samples are isocubanite (CuFe2S3), chalcopyrite (CuFeS2), and sphalerite (ZnS), with minor galena (PbS) and trace amounts of Au and Ag. The minerals show complex intergrowth textures down to the nanometer scale. These samples exemplify the need for advanced microtextural analyses to adequately characterize ore material prior to processing. The complex textures hamper the use of flotation as an efficient technique, due to the inability to sufficiently liberate the different minerals and problems with selectively floating isocubanite. Thus, leaching was the preferred method for extracting metals.

Jan 1, 2018

By Akira Usui

Occurrence of hydrogenetic ferromanganese crusts has been well documented over inactive seamounts in the central and southern Pacific Ocean. It has been thus believed that the hydrogenetic crusts develop preferentially at water depths between about 800 to 2500 meters. In fact, according to the Manganese Crust Database (F. Manheim, 1988), only two occurrences are known at water depths below 5000 m out of 819 occurrences cited in the database. Unexpectedly, we found typical hydrogenetic ferromanganese crusts from deep-sea floors; 1) outcropping old volcanic basement over the Philippine Sea Plate (abandoned spreading centers and subducting old oceanic crusts) and 2) one from the slope of an abyssal hill in the Central Pacific Basin (Cretaceous deep-sea basin) at water depths ranging between 5200 to 6100 meters. We report their occurrences with submersible observations from Shinkai 6K, physical parameters (such as thickness of crusts about 2-4 cm in maximum), chemical composition, petrology of substrate, and results of Be-10 dating for some samples in comparison with typical Co-rich manganese crusts from the Central Pacific seamounts. The preliminary chemical and mineralogical analyses reveal that they are of typical hydrogenetic origin, and typical of iron-manganese oxide mineral, vernadite, slow and probably continuous growth, and lower content of Co than the Central Pacific seamount crusts. The occurrences and nature of the crusts indicate that deep-sea floors are also optimal for the growth of hydrogenetic crust even at 5000 m water depth or deeper, only if oxygenated deep waters are supplied and the sea-floor morphology keeps stable enough for significant geological time period. Additional details of chemical analyses will be prepared by November and to be shown in the conference.

Jan 1, 2001

By Ian B. Clark

In October-November 1993, the Centre for Cold Ocean Resources Engineering, Memorial University of Newfoundland and University of Victoria jointly carried out reconnaissance surveys at Pine Cove, Baie Verte, Newfoundland. Pine Cove is the site of a multi-year study examining the environmental impact of a shallow water small-scale marine placer gold mining operation. The reconnaissance survey data collected will be used to develop a multi-year environmental effects monitoring (EEM) program for Pine Cove, Baie Verte, but more generally an EEM protocol for shallow water small-scale marine placer mining, which meets the requirements of Canadian government regula¬tors such as Environment Canada and the Department of Fisheries and Oceans. The Pine Cove mining operation is currently scheduled for the summer of 1995, and will use two mining methods: a hydraulic suction dredge in shallow water (<10 meters) operated by a scuba diver, and a hydraulically actuated clamshell dredge in deeper water (-30 m). A centrifugal concentrator will be used to extract the heavy minerals from the mined marine sediments, and the tailings will be returned to the sea floor via a suspended discharge pipe. The reconnaissance work at Pine Cove included geophysical, geochemical, oceanographic and biologi¬cal surveys, providing data which will enable prediction of the potential environmental impacts of the proposed mining operation. The geophysical surveys showed the sea floor to be covered by varying

Jan 1, 1994

By Richard H. T. Garnett

The first, profitable, marine placer mining started with tin 100 years ago but no major industry developed until the mid-20th. Century. Dredging at sea yielded cassiterite in both South Thailand and Indonesia, and remains an important state-run industry in the latter country. Malaysia and Russia have also contributed production, and the coastal waters of Tasmania and England have been explored. Marine placer deposits of gold have been examined in New Zealand, Chile, Argentina, Russia and West Africa. Philippino deposits were dredged during the 1930s. Fifty years later, at Nome in Alaska, gold was recovered by dredging from the offshore, and the technical/economic benefits of a seabed-deployed crawler were first demonstrated. Off the coast of Namibia placer diamonds were recovered by airlift mining during the 1960’s, but De Beers effectively started the existing marine diamond industry in 1989. The Wirth drill and a crawler continue to be used by the company, and plans recently have been announced for operations in South African waters. Other commodities such as mineral sands, platinum group minerals, and chromite have been investigated offshore in several worldwide localities.

Aug 24, 2006

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 Alister C. Skinner

The Marine Operations and Engineering section of the British Geological Survey based in Edinburgh, Scotland have, over the last 30 years, developed and operate a series of remotely operated, and powered, seabed coring systems. These systems were initially developed to provide a cost-effective solution to ground truth seismic reflection data for regional geological mapping, where the only solution that existed was conventional and expensive drill-ships. Since the early 1990?s these tools have been used for many other applications in industry and science. Currently the systems can operate in up to 2000 m water depth for 5m seabed penetration and up to 4500m water depth for a specialised oriented core drill which collects a scribed core to 0.8m below seabed. Scientific applications focus on determining the geology of an area and follows pre-determined geophysical interpretations. It usually also follows other coring attempts with non-powered coring equipment which is invariably unsuccessful if the strata is over-consolidated sediments or hard rock. Commercial applications include cable and pipeline route surveys, diamond, gold and base metal exploration, beach reclamation and aggregate materials evaluation. In many cases there is a blend of science and commercial investigation typified by coring in hydrothermal vent areas or carrying out geological coring in a frontier oilfield province. The versatility of the drills allows cost effective and rapid operations in remote and hostile areas where a rapid investigation may be the only one possible in a short weather window. The deepwater operational capability also allows science and commercial assay to be obtained ahead of potential exploitation and allows formulation of scientific theories or commercial project plans based on sound core data. Being mobile and compact these corers may be used from suitable (Dynamically Positioned or Anchored) vessels of convenience and thus provide a cost effective platform for sampling different types of seabed geology on an international basis.

Jan 1, 2004

By U. Schwarz-Schampera, C. Rühlemann, H. -R. Kudrass

Within 2006 BGR will conclude a contract with the UN International Seabed Authority (ISA) for the exploration of polymetallic nodules. The contract covers an area in the Pacific nodule belt between the Clarion and Clipperton fracture zones, that which is about 75.000 km2 in size at water depths between 4200 and 5000 m (see Fig. 1). Up to now, 7 consortia or state parties have acquired similar exploration “licenses” for polymetallic nodules in the central Pacific Ocean and the Indian Ocean. These licenses of the UN authority are required according to the UN convention on the law of the sea (UNCLOS) as the areas of interest are located outside of national EEZs. The “licenses” then reserve exclusive rights to the applicant for a time span of about 15 years.

Aug 24, 2006

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 Hans Smit

Start here.

Jan 1, 2018

By Odyssey Marine Exploration

Odyssey is a world leader in marine exploration and has undertaken expeditions in varying environments throughout the world addressing many commercial and regulatory demands. Odyssey works in a variety of settings such as shallow coastal territorial waters, abyssal plains in exclusive economic zones, and high seas in international waters on projects involving mineral exploration, environmental analysis, oceanographic survey, and recovery operations. Odyssey Marine Exploration (Odyssey) excels in adaptively managing programs from initial concept through realization of commercial goals while successfully satisfying the regulatory and engineering demands of deep sea projects. This poster presentation reveals best practices throughout a project life cycle and presents case studies in areas including but not limited to: • Research practices to identify and define valuable subsea resources • Project planning and licensing to achieve project goals and meet regulatory requirements • Optimizing offshore operations to achieve desired results • Designing projects to support processing and commercial programs

Jan 1, 2018

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