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By Henrik Schiellerup, Irene Zananiri, Johan Nyberg, Thomas Kuhn, Luis Somoza, Teresa Medialdea, Maria Judge, Pedro Ferreira, Gerry Stanley, Javier González

The GeoERA Co-Fund action is a joint contribution of 48 national and regional Geological Survey Organisations from 33 European countries “Establishing the European Geological Surveys Research Area to deliver a Geological Service for Europe (GeoERA)”. This is an ERA-NET action under Horizon 2020. The aim of GeoERA is to fund transnational projects contributing to the best use and management of the subsurface, addressing the following four themes: Geo Energy, Ground Water, Raw Materials and Information Platform. The European Commission recognises the significance of raw materials through its Raw Materials Initiative (RMI), the European Innovation Platform on Raw Materials (EIP-RM) and Horizon 2020 funding, specifically through Societal Challenge 5 – Climate Action, Environment, Resource Efficiency and Raw Materials. The GeoERA Raw Materials Theme will contribute to research and innovative developments for minerals inventory, minerals yearbook, exploration, mapping, modelling, metallogeny and critical raw materials in the pan-European framework including the sea. A major element in Europe’s long term economic strategy is to ensure security of supply for strategic and critical metals as part of the Blue Growth Strategy developing sectors that have a high potential for sustainable jobs and growth as seabed mining. The project MINDeSEA results of the collaboration between eight GeoERA Partners and four Non-funded Organizations at various points of common interest for exploration and investigation on seafloor mineral deposits. The Geological Surveys of Spain, Germany, Greece, Ireland, Norway, Portugal, Sweden and Ukraine are organisations with responsibility for coastal, marine geological investigation and mineral resources studies and mapping in their respective countries. The Non-funded participants: the Instituto Português do Mar e da Atmosfera; the United States Geological Survey; the All-Russia Scientific Research Institute for Geology and Mineral Resources of the Ocean; and the Geosciences Institute, host important databases, they have an international reputation for excellence in both science and technology, and are internationally-known experts on seafloor mineralisation and hydrothermal systems. This project addresses an integrative metallogenetic study of principal types of seabed mineral resources (hydrothermal sulfides, ferromanganese crusts, phosphorites, marine placers and polymetallic nodules) in the European Seas. The work program includes all the regional seas around Europe comprising the Atlantic Ocean, the Mediterranean Sea, the Baltic Sea and the Black Sea (Fig. 1). The MINDeSEA working group has both knowledge of and expertise in such types of mineralisation, providing exploration results, sample repositories and databases to produce innovative contributions. The importance of submarine mineralisation systems is related to the abundance and exploitation-potential of

Jan 1, 2018

By Alexander Malahoff

A shipboard research system capable of operating in waters of up to 2,000 m has been designed and implemented by the Hawaii Undersea Research Laboratory (HURL), University of Hawaii. It uses a remotely-operated ocean bottom survey camera system, ROV, bottom TV grab, the PISCES V submersible, and a submersible emergency recovery system aboard the 225-foot RN KA'IMIKAI-O- KANALOA. All systems are operated from the stern of the KA'IMIKAI with a mounted Caley telearm and articulated A-frame system. The system was designed for multi-purpose use of the telearm for launch and recovery of the PISCES V submersible on a lift recovery line (with or without diver assistance), or night-time operations with an electro-optical cable using either the HURL ocean floor sidescan, or photo and video system operated at 10 m above the ocean floor. The 1.14-inch diameter cable is also used to operate the RCV-150 garage/ROV system. The garage/ROV system has also been designed to act as a submersible rescue system with a submersible lift capability.

Jan 1, 1992

By M. C. I. Modenesi, J. E. Smith, M. Salvá-Ramírez, G. M. Castro, J. C. Santamarina

Annual metal consumption per capita has increased several orders of magnitude worldwide since the turn of the 19th century, yet grades of terrestrial ores are decreasing as reserves dwindle. Consequently, deep sea metal deposits are gradually transitioning from identified resources to economically viable reserves. Deposits in the Red Sea deeps along the axial trough result from tectonic and local hydrothermal processes. Continental rifting and ocean floor spreading produce fresh oceanic crust; concurrently, seafloor evaporites flow into the spreading zone and form isolated deeps. The deeps are often filled with hot stratified brines maintained by locally discharged fluids during hydrothermal circulation. Metalliferous sediments precipitate from the brines within the deeps. The ongoing multipronged study at KAUST involves: (1) acoustic characterization of the metalliferous accumulations using advanced signal processing techniques that capture the physics of granular materials; (2) comprehensive mineralogical and textural characterization of sampled sediments using SEM, EDS, XRD, XRF, and ICP-OES; (3) multiphysics instruments deployed to measure undisturbed sediment properties in-situ; (4) development of a distributed seafloor observatory for monitoring field operations; (5) innovative concentration and separation technologies; and (6) new strategies for proper tailings disposal purposely conceived for the unique field conditions in the Red Sea deeps.

Jan 1, 2018

By Mark D. Hannington

Results of the R/V Sonne Cruise (Edison) to the Tabar-Feni Arc from March 11 to April 5, 1994, a joint German-Canadian research cruise aboard the vessel R/V Sonne, undertook detailed mapping of the Tabar-Feni island chain, Papua New Guinea. The Tabar-Feni chain is host to several large porphyry stocks and epithermal gold deposits, including the giant Ladolam gold deposit on the island of Lihir (minimum 19 million oz. Au). The principal objective of the cruise was to map the seafloor in the vicinity of recently active alkaline volcanic islands in the Tabar-Feni chain and to characterize the tectonic setting of large high-level porphyry and epithermal gold deposits in the region. Additional work was carried out on shallow-water hot springs associated with mineralized geothermal systems on the volcanic islands. Complete sets of 1:50,000 scale (20-m contour) maps of the seafloor were produced for each of the four island groups (Feni, Tanga, Lihir, Tabar). The Lihir group was the most active and the most interesting. At least 4 (and probably 6 or 7), previously unknown volcanic cones were discovered within about 10 miles south of Lihir. The volcanoes are clearly very young and appear to have erupted along extensional faults produced by regional plate rotation. This recent volcanic activity appears to reflect recent forearc extension and represents the southward propagation of volcanic activity towards New Ireland. One volcanic cone at 1,490 m water depth is hydrothermally active, with very large areas of diffuse venting (100-200 m across), densely populated by beds of giant clams (probably calyptogena). Other vent-specific fauna are also present, including crabs, snails, sulfide worms, scale worms, limpettes, etc. The clam beds sit on a crust of hydrothermally baked and indurated, sulfidic, hyaloclastite-rich muds. The mineralization consists mainly of fine-grained disseminated pyrite and amorphous Fe-sulfides. A second, much larger cone at a depth of 1,070 m is capped by massive vesicular lavas which are intensely fractured and mineralized. Abundant sulfides and amorphous silica occur in stockwork-like veins which

Jan 1, 1994

By Randolph A. Koski

Recent investigations located at least six major massive sulfide deposits (dimensions measured in tens to hundreds of meters) within a 50-km-long segment of Escanaba Trough, the sediment-covered axial valley of southern Gorda Ridge. The sediment fill is intercalated silt and sand turbidites and hemipelagic mud with a maximum thickness of 500 m. Several volcanic edifices, spaced at approximately 15-km intervals along the ridge axis, penetrate and locally breach the sediment. The largest sulfide deposits form mounds and ridges on the steep flanks of structurally unstable sediment-capped blocks that have been uplifted above the volcanic edifices; both sediment and sulfide deposits are undergoing rapid erosion and redeposition. Although hydrothermal activity appears to be absent at most sulfide fields, 220°C fluids are discharging from the tops of sulfide mounds near 41°00'N lat, 127°31'W long. Recent pillow lavas and sheetflows erupted onto the sediment-covered sea floor less than 500 m away from the active vent field. The massive sulfide deposits have compositional characteristics that differ from deposits formed on sediment-free spreading axes. The Escanaba Trough deposits include Fe- and Cu-rich, Zn- and Pb-poor massive sulfide mounds, polymetal (Zn-Fe-Pb-Cu-As-Ag-Sb-Sn) sulfide vent structures, abundant barite-rich chimneys, crusts, and sinter cones, and thermogenic petroleum in the sulfide and sediment. Sulfate-rich crusts have high Au values ranging between 2 and 10 ppm. The unusual mineral assemblage at Escanaba Trough

Jan 1, 1989

By T. Barryere, R. B. Pedersen, E. Reeves, A. Stensland, I. Thorseth, T. Baumberger

Venting on ultraslow spreading ridges is far more abundant then previously predicted, and the discrepancy between observed and predicted vent field density may imply that non-magmatic heat sources are common along these ridges (Baker and German, 2004; Escartin et al., 2008; Rona et al., 2010; German et al., 2016). In this study we have estimated the flux from two hydrothermal vent sites situated on the slow to ultraslow spreading Mohns Ridge at the Arctic Mid-Ocean Ridge system (AMOR). The flux estimates have been made using the primordial isotope 3He in the non-buoyant plume above the Loki’s Castle vent field at the northern termination of the Mohns Ridge, and from the Jan Mayen vent fields area situated close to the southern termination of the ridge. Primordial 3He enters the oceans through degassing and mixing with hydrothermal fluids eventually to be discharged at the ocean floor primarily at hydrothermal vent sites and submarine volcanic eruptions (e.g. Clarke et al., 1969; Lupton and Craig, 1981; Lupton, 1998). Once introduced into the water column the concentration will only decrease by dilution due to its conservative behavior in the water column. Water column samples were collected using a CTD (conductivity, temperature, depth) probe (911plus Seabird) with a Niskin water bottle rosette. The water column above the Jan Mayen vent fields (JMVF) was sampled in the years 2006, 2011, 2012 and 2013 (82 samples) and the water column above the Loki’s Castle vent field was sampled in the years 2007, 2008 and 2009 (116 samples).

Jan 1, 2018

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 Kioshi Mishiro, Pratima Jauhari, Walter Williams

INTRODUCTION The UN-General Assembly adopted an Agreement on 28 July 1994 entitled ‘Agreement relating to the implementation of Part XI of the United Nations Convention on the Law of the Sea ((UNCLOS) of 10 December 1982’. The Agreement came into force on 16 November 1994, and consequently, the inauguration of the International Seabed Authority (ISA, or the Authority), located in Kingston, Jamaica. The Authority is the organization through which States Parties to the Convention (168, as of 25 July 2017) shall, in accordance with the regime for the seabed and ocean floor and subsoil thereof beyond the limits of national jurisdiction (the Area) established in Part XI and the Agreement, organize and control activities in the Area, particularly with a view to administering the mineral resources of the Area. The legal regime for the administration and development of the mineral resources of the Area as it now exists are available in Part XI of the Convention1 which contains the legal framework governing “activities in the Area” and in Annex III to the Convention which contains the “Basic Conditions of Prospecting, Exploration and Exploitation” with respect to the resources of the Area2. The 1994 Agreement relating to the Implementation of Part XI of the UNCLOS is the so- called ‘parallel system’; as elaborated in article 153 of the Convention. The essential elements of the ‘parallel system’ include assured access for States parties and their nationals to seabed mineral resources along with a system of site-banking, whereby ‘reserved areas’ are set aside for the conduct of activities by the Authority through the ‘Enterprise’ itself or in association with developing States or in joint venture with the contractor who provided the particular reserved site2.

Jan 1, 2018

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 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 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 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 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 Jae-Hyung Park

Since the Industrial Revolution, the land resources have been decreased rapidly as the industrialization. And this phenomenon brings to our mind an interest in deep-sea resource(manganese nodule). Hence, Korea has been participated in the development project of exploiting manganese nodule since 1983. Hwang and cho(1998) studied the economic efficiency evaluation of manganese nodule carrier. But they used the TAMU(Texas A&M University) model, and assumed deadweight and velocity of bulk-carrier. If we use some optimization technique, more economic manganese nodule carrier can be selected and evaluated without limited assumption. In this study, we evaluated the economic efficiency of manganese nodule carrier using genetic algorithms(GAs).

Jan 1, 2003

By Jonguk Kim

Hydrothermal sulfides were recovered from the16°50?S triple junction area in the North Fiji Basin, at a water depth of ca. 1900 m. The chimney samples can be divided into three groups according to their major metal contents: 1) type 1 (Fe-Cu-rich), 2) type 2 (Fe-Cu-rich with minor Zn), and 3) type 3 (Zn-rich) chimneys. Type 1 chimneys are mainly composed of chalcopyrite and pyrite, and are enriched in elements commonly precipitated under high temperature conditions (> 300°C), such as Cu, Co, Mo, and Se. Type 3 chimneys consist dominantly of sphalerite and marcasite with traces of pyrite and chalcopyrite, and are enriched in elements commonly associated with low temperature (150 to 250°C), such as Zn, Cd, Pb, As, and Ga. Type 2 chimneys show mineralogy similar to that of type 1 chimneys but their metal contents range between type 1 and type 3 samples. Trace element compositions of basaltic rocks indicate that magma generation in the triple junction area was influenced by two different sources: N-MORB and E-MORB. Sulfur and lead isotope patterns of the hydrothermal chimneys show distinct differences between the type 1 and type 3 chimneys. For example, type 1 sulfides are depleted in 34S and have lower Pb isotope ratios compared to type 2 and 3 chimneys. The d34S values (0.4 to 5.6?) of chimney sulfides are typical range of sulfur isotope composition of sediment free mid-ocean ridge hydrothermal system. Type 2 and 3 sulfides show slightly higher d34S values than type 1 sulfides, which can be explained by subsurface boiling of hydrothermal fluids followed by mixing of saline solutions with ambient seawater. Lead isotope compositions of the chimneys indicate that the Pb in type 1 and type 3 chimneys originates from hydrothermal leaching of N-MORB and E-MORB volcanic rocks, respectively. Considering that both these chimneys are located in the same area, our model suggests that type 1 chimneys formed by hydrothermal circulation controlled by an intrusion of N-MORB magma; the fluids were not influenced by boiling during the formation of type 1 chimneys. In contrast, type 3 chimneys are younger and were formed by hydrothermal circulation closely related to E-MORB magma intrusion at shallower depth. The necessary conditions for phase separation of the hydrothermal fluids that formed the type 3 chimneys might result from changed P-T conditions in a shallower high-temperature reaction zone beneath the hydrothermal venting site. Under these conditions the fluid may cross the two-phase boundary for seawater, ensuring subcritical phase separation. The mineralogical and geochemical properties of these chimneys suggest that type 1 and type 3 chimneys were probably black smoker and white smoker, respectively. Type 2 chimneys might be product of low-temperature replacement of type 1 chimneys, which is related to formation of type 3 chimneys.

Jan 1, 2005

By D. S. Cronan

Mineral exploration problems in the S.W. Pacific are not unique to that region, but a combination of favourable circumstances render it an ideal area to attempt to solve such problems. The land area of the S.W. Pacific island nations is only a fraction of the total sea area they can claim under current International Law. Hence, they have a great need to explore and evaluate their offshore areas. For the past ten years the focus of this work has been CCOP/SOPAC which has individually and jointly with other groups initiated and maintained far reaching marine mineral exploration programmes. In association with CCOP/SOPAC the writer has obtained and analysed approximately 650 sediment samples from the S.W. Pacific region for seventeen elements. Multivariate statistical techniques have been applied to the data set. The aim has been to identify chemically anomalous sediments reflecting either sea floor mineralisation and/or mineralisation on adjacent land areas.

Jan 1, 1985

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 Tony van der Steen

Subsea mining system are designed for the following, principally different, tasks: Dreding - The destruction and removal of seabed sediments overlaying the bedrock. Cleaning - The competence of the system to systematically remove the deposits from an undulating hard bedrock with irregular pulleys, channels and fissures. Factors that influence the choice of dredging equipment for a specific project are project requirements such as environmental conditions, location and water depth. However, the most important selection criteria are soil conditions. As a consequence, possible dredging systems, must be evaluated for the following, principally different, characteristics: Dredging proficiency - The destruction of the strata by the equipment. System stability - The capability of the soil to support the subsea equipment The above parameters are determined by the strength characteristics and the bearing capacitv_ of the soil. The author describes the processes involved in excavating the subsea deposits and (transporting the gathered soil as a water-soil mixture to the surface using different excavation and transport methods.

Jan 1, 1998

By Richard H. T. Garnett

On the western continental shelf of southern Africa diamonds derived from onshore sources are concentrated in gravels within drowned terrestrial and marine geomorphological features. First discovered offshore in the late 1950&apos;s, they are known to exist for about 1400 km along the Namibian and South African coast in water depths of up to 200 m. Shallow water operations yielded 1.5 Mct during the decade ending 1970 when De Beers acquired a majority of the offshore leases and commenced a 15 year exploration program. Deeper water and the prevailing sea conditions required the development of new, unique, marine mining equipment. The first large scale mining production of 22 kct was achieved by De Beers in 1989 with an output of 22 kct. Annual marine output from all sources now exceeds 0.6 Mct worth some US.$ 170 M, and rising to 0.7-0.8 Mct for 1998. Exploration has also been taking place in the waters of West Africa, Australia, and Indonesia. Exploration is by means of high resolution geophysics followed by sampling using a variety of drills, airlifts and seabed-mounted machines which imitate the eventual mining process. Surveying is now probing depths of 500 m. Smaller scale mining by several junior companies has traditionally involved diving and airlift systems. Increasingly, however, they are adopting different and improved techniques which to date have been employed only by De Beers Marine as contractor to Namdeb. Marine exploration and unit mining costs are high compared to those applicable to alluvial deposits onshore. By 1996 the total development costs incurred by De Beers alone reportedly had exceeded US.$ 500 M. However, the financial rewards are commen-surate because of the higher recovered grades. The operations are not without risk for the total of nearly 10 large and medium scale production vessels deployed by various organisations. The greatest shortfalls are experienced in the estimated throughput, not the grade.

Jan 1, 1998