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By Andrew Bellamy

A thorough appreciation of the origin, formation, preservation and geometry of marine sand and gravel deposits is central in demonstrating that their extraction by dredging does not affect coastal processes or marine life. Geological evaluation underpins wave, tidal and sediment transport modeling and assists in predicting the nature and extent of seabed change during and after dredging. Marine sand and gravel deposits in the English Channel, southern North Sea and parts of the Irish Sea are of predominantly periglacial fluvial origin and record long histories of valley and floodplain cut and fill associated with Quaternary climatic and sea level oscillations. In the Bristol Channel, the influence of marine transgression and tidal dominance in sorting proglacial outwash deposits is evident in the distribution of sandbanks, scoured channels and gravel lags of this region. These deposits are relict and are unrelated to coastal sediment dynamics. Their extraction leaves seabed depressions which monitoring shows remain unfilled. The resultant offshore bathymetric changes and sediment removal in over 10 m water depth are not transmitted to the coastal zone as beach drawdown, wave height increases or sediment starvation. Applications for new aggregate dredging permissions in UK waters must be accompanied by an EIA and need to make a convincing case that the dredging will not affect rare or declining species and communities of marine life. Seabed recovery rates post dredging are now investigated and understood with reference to geological setting and the uniqueness of the sediment/biological character (biotope). Investigation of the continental shelf by the Industry and others reveals the large extent of gravel-dominated biotopes relative to commercially viable deposits.

Jan 1, 2004

By Michael W. Milner

Cold Ocean Placers: Polar storms, interstadial littorals and crustal adjustments. Polar storms with consistent strong winds in the Southern, Antarctic Ocean are responsible for placer deposits on both the east and west coasts of Australia, on the west coast of New Zealand, as well as on the coasts of South America and Africa. Arctic winds, confined by both land and ice, generate similar placers in Labrador and Greenland as well as on the coasts of Scotland, Norway, Hudson's Bay, Nome, Goodnews Bay, Kamchatka and the north coast of Siberia. Tasman and Labrador seas have several parallels to Newfoundland, including north-south polar waterways, young spreading ocean floors, and youthful coastal escarpments with glaciated coasts. Black sand beds in beach deposits on the modern and Pleistocene transgression strandlines, skewed to the distal ends of beaches, and set into either bedrock or sediment fill, are the locus of the light-heavy mineral placers with titanium, zirconium and rare earth elements; chromium; iron; and tin. Gold and platinum group elements are the ultra heavy minerals at one end of the spectrum and tend occur in proximal placers generated, either directly from bedrock sources, or as minor by-products in distal light-heavy mineral placers. Diamonds are unusual in that the value is only in the larger stones, despite the formation of beach sand and aeolian placers in the littoral zone, and the sites of concentration are in very high energy bedrock traps, on terraces that are mined to depths of 100 metres below sealevel.

Jan 1, 1995

By Valery M. Yubko

"The conceptual basis of the developed model is based on the ideas that evolution of geological-geomorphological structure of the CCZ is controlled by four types of geologic factors: geodynamic, sedimentary, volcano-tectonic and erosion-lithodynamic. In terms of time span two factors (geodynamic and sedimentary) can be considered as permanent and the other two as sporadic.The geodynamic factor is responsible for two interrelated geological processes. One is going under conditions of the axial zones of spreading centers and results in formation of the CCZ basement. Historically this process is considered as a starting point for each of the heterochronous fragments of the CCZ. The second one controls gradual shifting towards the Pacific Plate (Hawaiian direction) and subsidence to greater depths of the neogenic fragments (basement). Thus, those processes control basic topography, geomorphology and the seabed depth within the CCZ.Volcanogenic-hydrothermal activity of the EPR is one of the main sources of the ore components, which finally compose manganese nodules as a result of complicated processes of their dissemination and transportation to the bottom in dissolved and organically bound forms.The role of the other constant factor (sedimentary) is displayed in two ways. Firstly, initial relief is smoothed under the influence of this factor, which, subsequently, makes favorable conditions for manganese nodules formation. Secondly, it favors transportation of the majority of the ore components, participating in manganese nodules formation into zones of active nodules formation."

Jan 1, 2017

By Akira Usui

Fine-scale geochemical, mineralogical, and structural variations in ferromanganese crusts are believed to be the long-range records of paleoceanographic conditions and geological events on the small to global scales in the world oceans, which is useful in reconstructing marine environment. The chemical profiles of thick hydrogenetic ferromanganese crusts and nodules were determined by ICP/ES at 2-3 mm intervals at several locations over the Japanese Islands, Magellan Seamounts, Marshall Islands, and South Pacific Basins, together with Be-10 dating. We found general trend of Co enrichment (or high ratio of Co/Mn) in the upper layers of crusts, or outer layers of nodules, which formed in younger period probably after the late Miocene. This general trend of higher Co concentration in the surface may be true over the western to the Pacific, but local variations in growth patterns and shorter-range fluctuations in chemistry and structure were found as well. The growth rate is sometimes three times faster at the shallower depth even in a single seamount. The in-depth fluctuation of Co is well correlated with the ratios Mn/Fe ratio and Ce/La, suggesting changes in redox conditions during the growth of hydrogenetic ferromanganese crusts.

Jan 1, 2002

By Makoto Yuasa, Akira Usui, Shipboard Scientists of SIP Cruises, Atsushi Suzuki, Shingo Kato, Kyoko Yamaoka, Akira Nishimura, Kiyo Kisimoto, Katsuhiko Suzuki

"We report here on current topics of our project, based on the results of recent cruises and laboratory analysis, about the diversity of compositions and configurations of the hydrogenetic ferromanganese deposits in several Northwestern Pacific Seamounts. This recent research has discovered important aspects of these deposits regarding the mode of variation with water depth, topography and substrate geology, possible bacterial mediation, temporal variation with age in mineralogy, and major and minor element chemistry. All cruises and analysis have been supported by the facilities and staff of the Japan Agency of Marine-Earth Science and Technology (JAMSTEC), Japan Oil, Gas, and Metal resources Corporation (JOGMEC), Geological Survey of Japan, and Kochi Core Center (KCC) using a remotely operated vehicle (ROV), a monitored rock drilling system, dredges, and manned-submersibles in the NW Pacific seamounts,The results indicate that most of the rock outcrops on the slopes, shoulders, and much of flat tops are covered with maximum 10-cm thick crusts, but the thickness, metal content, and microstructural properties are not always uniform over the seamounts, but variable in space and time. The micro-stratigraphic description of whole-rock samples indicates a history of deposition and sedimentation, which control the diversity in bulk composition and abundance caused by the variable incorporation of iron-manganese precipitates into the deposits during variable environmental conditions. We conclude that hydrogenetic precipitation of iron-manganese oxide has taken place for more than 20 million years at a growth rate about 4-6 mm/my, in water depths below 1000m. The results indicate a fairly continuous and constant metal deposition since the middle Miocene age or older to the present. Our case study of geological sciences at a model seamount within the Japanese EEZ suggests that scientific knowledge is useful and essential in exploring mineral deposits, economic estimation, and designing systems, if supported by well-combined geological and oceanographic and biological research. The distribution map of ferromanganese deposits and geological map will be published soon in 2017 to be issued by the Geological Survey of Japan."

Jan 1, 2017

By Sophia Katsouri

Hydrothermal circulation that produces sulfide deposits in the marine environment can also produce sulfide deposits in lakes. The major differences in terms of process are (1) in lakes the hydrothermal fluid is meteoric water of low salinity whereas in the marine setting it is saline and (2) the rocks that are leached of metals to produce the deposits are continental crust in one case and oceanic crust in the other. We have examined sulfides that are presently forming in two lakes ? Lake Tanganyika in east Africa and Lake Oyunuma in Hokkaido, Japan. Tanganyika is the second largest lake in the world and the second deepest rift lake, after Lake Baikal in southeastern Siberia. Two hydrothermal fields are known in its northern basin at Pemba and Cape Banza (Tiercelin et al., 1993). At Pemba, CO2 and CH4-rich, low temperature (53-88°C) hydrothermal fluids are forming decimeter-tall chimneys at 2-46 m water depth. Our microscopic and x-ray diffraction study of samples from the Pemba site reveal marcasite and pyrite to be the most common sulfides. Minor minerals include barite, hematite, bornite and chalcopyrite. Quartz and feldspar are also identified and were probably incorporated from the surrounding lake sediments. At Cape Banza, aragonite chimneys, up to 70 cm high, are venting fluids at 66-103°C.

Jan 1, 2001

By Tae-kyeong Yeu

KIOST has developed the pilot mining robot, named MineRo ?? from early-2011 to mid- 2012. The robot consists of two unit-modules having an identical mechanical structure and hydraulic system. One unit-module has two track systems, two pick-up devices, two crushers, one lifting pump and one thruster. The pick-up device is fitted on the frame of the track device. All actuators are driven hydraulically, which are manipulated by valves and the controllers. Each unit-module is equipped with one dual HPU of 250kW / 4,000V. PWM-16 (INNOVA AS) as hydraulic valve controller is adopted, which outputs PWM signals of 16 channels and can be used under pressure in oil-filled box. To measure angular velocity or displacement of hydraulic actuator, turbine-type flow-meters are adopted. The flow-meter has RF (Radio Frequency) type pulse detector, which extends the flow range by eliminating drag on the rotor. Two track motors, two crusher motors, lifting pump, one thruster can be controlled their velocities through feedback of the measured flow-rates. As well as the flow-rates, the states of the hydraulic system such as hydraulic pressures, temperatures, leakages are measured through a self-developed flow-pressure canister. In that canister, multi-channel amplifier boards are installed, through which the vast amount of data is acquired and transmitted to the main controller using serial communication.

Sep 14, 2011

By James R. Herring

An unusual combination of ten new, deep (-100 m) coreholes and an extensive high-resolution seismic reflection network enables us to produce a detailed study of the phosphorite resources in the Tertiary strata of the Georgia continental shelf. These strata are mixtures of a terrigenous facies, notably quartz and clay along with minor amounts of other aluminosilicate minerals, and of a marine facies, notably phosphorite and carbonate. Phosphatic sediments occur throughout the cores, however the richest phosphorite beds are in the middle Miocene (Serravallian) sediment, where they constitute up to 70 percent of the sediment mass. Major zones of phosphate enrichment occur chiefly at major unconformity boundaries (tops of Oligocene, lower and middle Miocene, upper Miocene, and lower and upper Pliocene) and at prominent intrastratal reflectors representing minor unconformities within units. Phosphorite co-occurs with the clay minerals, especially palygorskite, but correlates inversely with carbonate and detrital quartz, indicating a low-energy depositional environment. The clay minerals present in these strata, which have an environmental consequence on recovery of the phosphorite, are varying concentrations of smectite, kaolinite, mica, palygorskite, and sepiolite. Phosphatic resources have been determined within only the Miocene strata. Sediment volume for this unit to the 100 m isobath on the continental shelf has been established using the high-resolution seismic reflection network that has been calibrated using the deep coreholes. Phosphorite grains larger than 0.1 mm average about 40% of the sediment. In turn, most of the remainder of the sediment in this size range is quartz, which is separable from phosphate grains using conventional flotation techniques. Our estimate is that 300 Gt of phosphorite lie within the Miocene strata of the Georgia continental shelf.

Jan 1, 1994

By Charles L. Morgan

For the past twenty years or so the oceans of the world have been transformed in the minds of most Americans from the ultimate and nearly infinite receptacles for sewage and other wastes to an almost sacrosanct and threatened last refuge of Mother Nature from man on Earth. While this general movement has helped somewhat to moderate the flows of pollutants into the oceans, it has had severe and sometimes devastating impacts upon various attempts to develop seabed mineral resources. Marine mining proposals have been easy targets for attack. In most cases, they have short or no histories and involve prototype or first-generation methods. They commonly lack major financial backing, and do not command significant public support. Their constituents are limited. Opposition movements to such proposals have been able to evoke strong support by appealing to this "last refuge" image and depicting mining operations as the final assault. In mounting these public appeals, the movements obtain visibility and support. Because of the small and sometimes tentative status of the constituencies which support particular proposal s, the potential liabilities for opposition movements are minimal.

Jan 1, 1989

By Jan Magne Markussen

The aim of the paper is to analyze the viability of commercial exploitation of polymetallic nodules, the time aspect for exploitation and the probable organization of commercial projects. METHOD My methodological point of departure is to view the various factors in context, and to differentiate between the various groups of actors. This involves taking as my starting point the interaction that exists between economics, technology, politics, law, the environment, and even psychology and ideology, and acknowledge that the various actors may well have differing motives for their engagement.

Jan 1, 1992

By William D. Siapno

The International Marine Minerals Society has now come of age! Previously known as the International Marine Mining Society, it was an informal group without officers, by-laws or official status. Despite the lack of formal structure, the Society has cosponsored symposia both in Europe and in North America including the 16th Annual Underwater Mining Institute in Halifax, Nova Scotia, last year. The roster of members is now sufficient to emerge as a fledgling professional society. To this end an ad hoc committee was appointed to prepare by-laws stating the objectives of the Society, provide the procedures for the election of officers and other guidelines essential for the operation of the organization. This paper briefly summarizes the history of the group, the by-laws, together with membership requirements.

Jan 1, 1986

By Eric J. Foell

Recognizing that the planned commercial exploitation of polymetallic nodules in the deep sea should be accompanied by environmental studies in order to protect this largest and least understood ecosystem of our planet, the German Ministry for Research and Technology has since 1989 funded a longterm and large-scale disturbance-recolonization (DISCOL) experiment in the abyssal Peru Basin of the equatorial South Pacific Ocean. The circular study site is located at 4150m depths and encompasses about 10km2 of relatively flat, heavily sedimented sea floor with low (< 15%) nodule coverage near an existing German nodule mining exploration license area. The RV SONNE, a large and well-equipped multi-purpose research vessel, served as platform for all environmental cruises conducted to date. The initial DISCOL expedition (SO-61, Feb.-March 1989) was carried out in two legs. During DISCOL 1/1, a study site was selected, a pre-disturbance baseline assessment was undertaken, and sea floor disruption was begun using the "plow-harrow", a uniquely designed disturber device towed repeatedly across the circular study area. During DISCOL 1/2, disturber deployments continued until the device had created 78 criss-crossing and partially overlapping tracks along which nodules were essentially plowed under while sediment from up to 15cm below the seabed had been turned over and exposed at the surface. In addition to the obvious within disturber track impacts, sediment mobilized by plowing drifted off with the prevailing near-bottom current and redeposited downstream, blanketing nearby areas not directly disturbed. Immediately after the disturbance phase, an initial post-impact sampling series was performed. The DISCOL Experimental Area (DEA) was revisited about six months (DISCOL 2, SO-64, Sept. 1989), three years (DISCOL 3, SO-77, Feb. 1992), and seven years (ATESEPP SO-106, Jan.-March 1996) after disturbance to collect further post-impact samples, monitor changes in the benthic community and follow the recolonization process. In addition to benthic community studies, plankton investigations were initiated during the third DISCOL cruise (SO-77) and continued during three further cruises (SO-78, SO-79 and SO-80/2) in 1992.

Jan 1, 1996

By Sukumar Bandopadhyay

The Marine Minerals Technology Center (MMTC) was authorized by an act of the United States Congress in 1996. The act established several marine minerals research centers in the U.S., including one at the University of Alaska Fairbanks. The Alaska MMTC is funded through the Minerals Management Service of the Department of the Interior and concentrates its research in the Arctic seas region. Recent research projects at the MMTC include, among others, application of a geographic information system (GIS) to the gold placer deposits offshore Nome, Alaska, development of a marine gold placer reserve definition model using a neural network, and development of an expert system model for submarine tailings disposal (STD) planning and decision-making. Although geostatistics remains the most prevalent method used today for ore grade estimation, researchers have made numerous improvements over the years for accurately predicting grades of ore using other estimation techniques. One such technique, the neural network, has recently emerged as an alternative to geostatistics for grade estimation purposes. A neural network is a non-linear, model-free estimator that is well-suited for noisy and/or sparse data environments. Neural networks perform best with non-linear spatial data, contrary to the stationary assumption of ordinary Kriging techniques. In the marine placer ore reserve definition model, the neural network technique was used to estimate placer gold reserves offshore Nome. This study demonstrated the utility of neural network modeling over other traditional ore reserve estimation methods, especially for high cut-off grades. Some of the relevant issues of neural network modeling were also addressed in the study. In testing, the neural network produced results that were close to those from geostatistical techniques including Kriging, polygonal, and inverse distance methods.

Jan 1, 2005

By Richard H. T. Garnett

The Chilean part of the archipelago of Tierra del Fuego, situated south of latitude 62o S, is within that country?s Región de Magallanes y Antártica, and separated from the remainder of Chile by the Magellan Strait. In recent geological history several phases of Quaternary age glaciers originating in the Andean and Dawinian Cordilleras eroded assumed primary gold deposits and entrained their related alluvial deposits. Piedmont glaciation extended to the east and south over m0st of the land and beyond the present-day coastline into extensive areas exposed during the resulting lowered relative sea level. During interglacials particulate gold incorporated unevenly in the widespread drift, till and moraines was fluvially released and concentrated into streams and flood gravels. Coastal erosion enriched various beaches with gold. From 1868 onwards Tierra del Fuego hosted a major gold rush whereby early, labour intensive, beach mining eventually developed into inland dredging. But continued mining activity was interrupted and then terminated by several external factors. Most miners, always seeking ?greener pastures?, joined the rush to the new discoveries in the Klondike (1896) and Nome, Alaska (1899). In 1904 the international boundary, established in 1881, became the subject of a major dispute not settled until 1984, The Panama canal?s opening in 1914 turned Tierra del Fuego, previously on the Pacific-Atlantic shipping route, into a remote backwater. World War II brought opposing foreign naval forces to the actual islands where most gold had been taken from the beaches. It also crippled the dredging industry which lost its coal supply and never recovered. Nevertheless, some small scale mining continues to this day.

Sep 14, 2011

By J. R. Hein

East Diamante is a submarine volcano in the southern Mariana arc that is a complex caldera about 10 km x 5 km (elongated ENE-WSW), and breached on its northern and southwestern sectors. A large field of barite-sulfide mounds was discovered in June 2009 and revisited in July 2010 aboard the R.V. Natsushima using the Hyper-dolphin ROV. The mound field occurs on the NE flank of a cluster of resurgent domes inside the caldera. The mound field extends for more than 100 m long and is about 30 m wide, and is aligned along a NE-SW rift valley. A sample of dacite yielded a 40Ar/39Ar age of 20,000±400 years. Individual mounds are typically 1-3 m tall and 0.5-2 m wide, with lengths from about 3 to more than 5 m. The mounds are composed of barite-dominant layers interbedded with Zn-sulfide-rich barite layers. Rare inactive spires and chimneys cap some mounds. Fe and Mn oxides are currently forming small (<1 m diameter, ~0.5 m tall) subsidiary mounds on the top of some of the sulfate/sulfide mounds and drape the flanks of others. Both diffuse- and focused-flow fluids emanate from the subsidiary oxide mounds. Ages of the basal sulfate/sulfide mounds cluster around 4,000 years old based on 226Ba/Ba, whereas the oxides are less than 5 years old based on 228Th/228Ra. Most mound and chimney samples are dominated by barite and amorphous silica; sulfides occur in variable amounts that in decreasing order of abundance include sphalerite, galena, pyrite, and chalcopyrite. Anglesite, cerrusite, and a Pb phosphate occur as late-stage interstitial phases. Some mound samples have fragmental textures; layered clasts composed of chalcopyrite and pyrite may have been derived from collapsed chimneys. Despite the abundance of barite, samples contain high concentrations of Zn (to 23 Wt.%), Pb (to 13 wt.%), Ag (to 500 ppm), and Au (to 15 ppm). Copper is enriched in a few mounds samples, up to 3 wt.%, but is typically <1 wt.%. Other significant metal enrichments include Sb (to 1320 ppm), Cd (to 1180 ppm), and Hg (to 55 ppm).

Jan 1, 2011

By Sukumar Bandopadhyay

The Marine Mining Technology Center (MMTC) was authorized by an act of the United States Congress in 1996. The act established several marine minerals research centers in the U.S., including one at the University of Alaska Fairbanks. The Alaska MMTC is funded through the Minerals Management Service of the Department of the Interior and concentrates its research in the Artic seas region. Recent research projects at the MMTC include, among others, a geographic information system (GIS) application to the gold placer deposits offshore Nome, Alaska, a marine gold placer reserve definition model using a neural network, and development of an expert system model for submarine tailings disposal (STD) planning and decision-making. Although geostatistics remains the most prevalent method used today for ore grade estimation, researchers have made numerous improvements over the years for accurately predicting grades of ore using various other estimation techniques. As a result, the neural network has recently emerged as an alternative to geostatistics for grade estimation purposes. A neural network is a non-linear, model-free estimator that is well-suited for noisy and/or sparse data environments. Neural networks perform best with non-linear spatial data, contrary to the stationary assumption of ordinary Kriging techniques. In the marine placer ore reserve definition model, the neural network technique was used to estimate placer gold reserves offshore Nome. This study demonstrated the utility of neural network modeling over other traditional ore reserve estimation methods, especially for high cut-off grades. Some of the relevant issues of neural network modeling were also addressed in the study. In testing, the neural network produced results that were close to those from geostatistical techniques including Kriging, polygon, and inverse distance methods.

Jan 1, 2004

By Dorothy B. Niell, O&apos

In its first three years of operations, the in-house programs of the continental Shelf Division of the Marine Minerals Technology Center (MMTC/CSD) have focused on the development of drill systems - technology and the improvement of techniques and applications of reconnaissance methods to marine mineral deposit characterization. Many of the technological advances made to date have been in direct response to specific requests from industry for drill systems needs, and from federal and state agencies seeking technical support for various research efforts. These cooperative programs have proven to be an extremely efficient and effective way for the MMTC to achieve some of the main program goals that were established for the organization at the outset: primarily, to encourage and assist U.S. industry in marine minerals research activities and to encourage cooperative work among research institutions, government agencies, and industry. The primary achievements of the MMTC/CSD to date include the development of the Remote Placer Drill System for rapid reconnaissance drilling of precious metal placer deposits (including both pneumatic prototype and hydraulic production

Jan 1, 1991

By Samantha Whisman, James R. Hein

Hydrothermal marine manganese-oxide deposits (HMMD) are cemented and variously replaced volcaniclastic and biogenic sediments that were mineralized by distal, low- temperature, hydrothermal fluids. HMMD predominantly form below the seabed as sediment-hosted statabound deposits but can also form on the seabed. These deposits form at oceanic and back-arc basin spreading centers, volcanic arcs, and mid-place hotspot volcanoes. HMMD have traditionally not been considered to have an economic potential because they were considered to be devoid of economically valuable critical elements. This contrasts with their non-hydrothermal counterparts, ferromanganese crusts and nodules, which are enriched in many critical elements. However, manganese is now one of the critical metals and HMMD have the highest manganese contents (up to 55% Mn, so- called battery-grade Mn) of all the types of deep-ocean mineral deposits. There is a growing demand for this critical metal and an upward trend exists in the price of manganese on the global market. Also, other critical elements can occur in high concentrations in some HMMD and their economic potential has not been considered, especially for lithium (up to 0.17%) and molybdenum (up to 0.24%), but also vanadium (to 820 ppm), chromium (to 346 ppm), and nickel (to 0.45%), among others. Which of these critical elements are enriched and their concentrations depend on the types of rocks leached at depth by the hydrothermal fluids, the composition of hydrothermal minerals precipitated in the higher temperature parts of the circulation system, and the types of sediments mineralized by the manganese oxides. For example, mineralization of a carbonate sediment resulted in the highest lithium contents, whereas leaching of ultramafic rocks at depth as a rule results in the highest chromium and nickel contents in the HMMD. These deposits are known to be widespread, especially in volcanic arcs, but their lateral and vertical extents and consequently size, tonnage, and grade have not been determined. Most samples of hydrothermal deposits have been collected by dredging and therefore the in situ relationships often are not known. One sample from the Mariana volcanic arc, west Pacific, was collected by ROV at 1274 m water depth from a layered outcrop 6.6 m thick that may be a sequence of pervasively mineralized volcaniclastic layers and offers the first clue as to the potential vertical extent that these deposits may attain. However, only the top ~0.4 m-thick layer was sampled, so it is not known whether the mineralization extents throughout the outcrop. Although large manganese deposits of various origins occur on the continents, they consist of manganese carbonates, silicates, or complex mixtures of manganese minerals. In contrast, marine hydrothermal HMMD exhibit relatively simple mineralogy that would make processing of this potential ore much simpler.

Jan 1, 2018

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 P. Halbach

Hydrothermal activity is well known from many locations on most mid-ocean ridges, but no hydrothermally mineralized area had yet been found at the ultraslow spreading southwest Indian Ridge up to October 98 when the Japanese RV Yokosuka with the submersible Shinkai 6500 investigated this area. A massive sulfide field was discovered near 27°51S / 63°56E in the 11th segment west of the Rodriguez Triple Junction. The Free University of Berlin had joined this cruise and taken over the responsibility for the study of the respective sulfide mineralizations. Hydrothermal minerals were sampled during two dives at a water depth of 2940 m close to the summit of an axial volcanic ridge called Mount Jourdanne. Massive sulfides occur on the seafloor as small smooth mounds with an average area of about 5 m2. Their surfaces are weathered and have a reddish to brownish colour. In addition to these mound-like structures, small tube-like chimneys were observed; these chimneys rise approximately 30 to 40 cm above the floor and are less than 10 cm in diameter. No indications of hydrothermal fauna could be detected. All the hydrothermal features are spatially related to faults and smaller fissures controlled by an E-W trending graben system crossing the summit region of the submarine volcano. Such tectonized areas are generally considered to be ideal for hydrothermal activity because they may have both a magmatic heat source in the deeper underground as well as pathways for the fluid circulation.

Jan 1, 2002