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By Irina A. Pulyaeva

Hydrogenetic Fe-Mn crusts are ubiquitous in the ocean basins and play an important role in marine mineral-deposit research because of their widespread occurrence and high concentrations of valuable and rare metals. Directed research, which started in the last quarter of the 20th century, has provided significant results, with substantial amounts of data produced on Fe-Mn crusts structure, composition, and distribution in the global ocean. Detailed study of several seamounts has given confidence about the scale of Fe-Mn crust development and their characteristics. Now, commercial interests gain more and more attention. However, at the same time some theoretical questions related to Fe-Mn crust history including controls on metal sources and concentrations have not yet been answered. Here, we present the overview of age, composition, distribution, and geological setting of hydrogenetic Fe-Mn crusts from Pacific and Atlantic seamounts and discuss the geological evolution and conditions that led to the formation of potentially economic concentrations of metals. The age, composition, and distribution of Fe-Mn crusts in the Atlantic and Pacific oceans were determined by using a Fe-Mn deposits database compiled from our original data, published papers, published databases, and other international sources. Comparative analysis of Fe-Mn deposits from the Atlantic and Pacific oceans shows that there are similarities in basic characteristics of crust formation in both oceans. Simultaneously, there are significant differences in the scale of Fe-Mn crust distribution and composition that can be explained by differences in geological settings and characteristics of the deposition environment.

Jan 1, 2011

By Cornel E. J. de Ronde, Alexander Malahoff

Six active Kermadec arc submarine volcanoes, located between 34°S and 36°30'S were mapped and sampled between April and July 2005, using submersibles Pisces V and Pisces IV aboard the mothership R/V Ka'imikai-o-Kanaloa. The purpose was to study the relationship between hydrothermal activity, formation of hydrothermal mineral deposits, structure of the volcanoes, and the biodiversity of life associated with the hydrothermal vents. Of the volcanoes examined, all showed evidence of hydrothermal activity, including metal-rich plumes and helium anomalies. Only two of the volcanoes, namely Brothers and Clark, showed chimneys and surficial polymetallic sulfide deposition. Hydrothermal venting at a water depth of approximately 1,650 meters near the base of the northwest caldera wall of Brothers volcano has produced a field of chimneys, up to seven meters high and discharging black smoker venting. Temperatures up to 300°C were measured from the active vents. Clark volcano has a double cone summit at a water depth of 875 meters. The shallowest cone has a near-summit hydrothermal vent field with five-meter tall venting chimneys with smaller structures around the periphery. Water temperatures of 200°C were recorded for these chimneys.

By Sven Petersen

In April 2010 three REMUS6000 series autonomous underwater vehicles (AUVs) have been used to simultaneously map large areas near the Mid-Atlantic Ridge (3°N) axis in water depths ranging from 1,000m to 4,000m. One vehicle was provided by the Leibniz-Institute for Marine Science, IFM-GEOMAR (Kiel, Germany) the other two were provided by the Waitt Institute for Discovery (La Jolla, USA) and managed by the Woods Hole Oceanographic Institute (USA). The REMUS6000 vehicles, manufactured by Hydroid Inc. (USA), are "cigar-shaped" vehicles (4m long and weighing approx. 900kg) and consist of a tapered forward section, a cylindrical midsection and a tapered tail section. An internal titanium strongback, which extends through much of the vehicle length, provides the structural integrity and acts as a mounting platform for syntactic foam, equipment housings, various sensors and release mechanisms. The AUVs can be used in various payload configurations such as multibeam bathymetry, electronic still camera, or subbottom profiler. For these missions the electronic still camera configurations was installed. An EDGETECH 2200M dual frequency (120/410 kHz) side scan sonar was used to map the seafloor, but other frequencies are readily available for more options in resolution and range. The 120 kHz side scan transmitter was used for most missions in order to map large areas (increased range) and to be able to fly at higher altitudes (between 70m and 90m) above the rough seabed encountered in this area. The maximum slant range was between 600m and 700m on both sides resulting in a swath width of up to 1.2 km. Line spacing ranged from nearly 1,000m in flat areas down to 400m in steep terrain. Side-scan mosaics were generated with a 1m resolution. Selected areas were targeted by the higher resolution 410 kHz transmitter as well as by bottom photographs flying as low as a few meters above the seabed. The vehicles navigated autonomously using a combination of inertial navigation (Kearfott T-24 or T-16 INS) and long baseline acoustic navigation by computing their range to two moored acoustic transponders. Working efficiently in this rough topography at speeds above 3 knots was only possible due to the obstacle avoidance capabilities of these AUVs.

Jan 1, 2011

By S. Rajendran

Gas Hydrates (Methane Hydrates) are solid, ice ? like substances composed of water and natural gas. They occur naturally in areas of the world where methane and water can combine at appropriate conditions of temperature and pressure and are found in the ocean bottom sediments and in some permafrost areas. Besides temperature and pressure, factors like bathymetry, sediment thickness, sedimentation rates, and total organic carbon content (TOC) also control gas hydrate formation in the sea. The stability of gas hydrates depends on the critical high pressure ? low temperature combination (0-17 bars, 0-25ºC), which in turn dependent on the mix of gases from which the mineral is formed. As the critical parameters can be altered by deposition, erosion or slumping of sediments, formation or melting of ice cover, rise and fall of sea level and sudden temperature changes induced by tectonic activities, current flows or volcanisms, the gas hydrates tend to be very unstable. It is becoming increasingly evident that naturally occurring gas hydrates are significant component of the shallow geosphere and are of societal concern in at least three major ways: as an energy resource, a geologic hazard and a major contributor for climatic changes.

Jan 1, 2010

By Ye Jun

Until now, more than 200 sites of sea-floor hydrothermal activities are known on the midocean ridge but few of them are documented on South Mid-Atlantic Ridge (SMAR). This on some extent restricts our directly understanding of the hydrothermal mechanism on SMAR. In 2011, During the Cruise 22 of R/V Dayangyihao, a masive sulfide field was discovered in the center part of the first-order ridge segment that bounded between Cardno Fracture Zone and Saint Helena Fracture Zone, near 15.16°S/13.35°W, which give us an opportunity to recognize the mechanism of hydrothermal systems on SMAR directly. This newly discovered hydrothermal field, which informally called SMAR 15°S, is situated in a SE-NW offset depression of an axial neovolcanic ridge, with water depth of about 2793m. In the water column around this field, strong turbidity and temperature anomalies were detected. Ten meters high venting chimneys, hydrothermal mounds as well as a large amount of hydrothermal vent shrimps were also observed and recorded by ROV and Deep tow camera on the ocean floor. The samples we collected from this field include sulfide chimney fragments, massive sulfides and basaltic rocks. In this study, we are focusing on the mineralogy and sulfur isotope geochemistry of sulfide samples for preliminarily uncovering the geological characteristics and hydrothermal processes of this hydrothermal field.

Sep 14, 2011

By Yannick C. Beaudoin

Southern Explorer Ridge (SER) is an anomalously shallow, intermediate-rate spreading ridge located 200 kilometers off the west coast of Vancouver Island, Canada. It ranges in depth between 2600 m (deepest basins) and 1760 m (bathymetric minimum). At least 60 sulfide deposits are known to be associated with hydrothermal vent fields along the ridge. For the first time geological data, including deposit locations, collected from 15 marine expeditions to SER since 1983 have been assembled in a GIS format. GIS processing techniques were employed to plot the distribution of base metal concentrations for recovered sulfide samples. The highest base metal concentrations are found in the vicinity of the Magic Mountain site (main active vent field), and also proximal to a side scan sonar anomaly referred to as AGOR 171. Individual samples near these locations have yielded values as high as 29.3 wt\% Cu, 34.3 wt\% zinc, 0.97 wt\% Pb, 2.0 ppm gold, and 664 ppm silver. Sample paucity is the key limiting factor that prevents adequate assessment of the areas economic potential.

Jan 1, 2001

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 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 J. Bruce Gemmell

ODP Leg 158 drilled seventeen holes into the active TAG hydrothermal mound and underlying stockwork, 26°N, Mid-Atlantic Ridge. Drilling in five different areas, including a high-temperature black smoker complex and a lower-temperature white smoker vent field, revealed the multi-stage depositional history and character of sub-seafloor mineralization and alteration. The upper portion of the mound consist of massive pyrite and pyrite breccias which are underlain by pyrite-anhydrite breccias and then by quartz-pyrite breccias. Quartz-pyrite breccias grade down into silicified wallrock breccias. Chloritised basalt breccias occur at depths greater than 100 m. Several stages of quartz-pyrite±chalcopyrite veins occur in the stockwork zone and lower portions of the mound, whereas anhydrite±pyrite±chalcopyrite veins occur within the upper parts of the mound. Recovery of unaltered basalt near the edges of the mound has constrained the extent of the stockwork zone to a pipe-like feature 80 meters in diameter. A detailed sulfur isotope investigation of sulfides and sulfates within mound and the underlying stockwork zone has revealed the overall range of sulfide d34S analyses to be 0.35% to 10.27%. Anhydrite has a tight range of d34S values 20.55% to 21.56%. There are distinct differences in d34S values between the different textural types of pyrite (massive sulfide, breccia clasts, disseminations associated with alteration, and veins). The massive sulfide and breccia clasts have a similar distribution of d34S values (6%-8%), however the d34S values of the disseminated pyrite associated with the alteration are distinctly heavier (8%-10%). Vein sulfides have the lightest d34S values (5%-7%). Sulphur-isotope values at TAG are, in general, the heaviest reported for unsedimented mid-ocean ridge deposits.

Jan 1, 1998

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

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

Jan 1, 2018

By L. B. Khershberg

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

Jan 1, 2004

By Sven Petersen, Berit Lehrmann, Bramley J. Murton, Paul A. J. Lusty

"INTRODUCTIONToday’s metal mining focusses on land based ore deposits which only consider one third of the Earth’s surface. Through an increasing global demand of strategic metals used in the electronic and green industry (Zepf et al. 2014), ‘uneconomic’ sites of lower grade in more technical challenging grounds such as greater depth and/or more remote areas are developed by the mining industry often resulting in higher environmental impact. However, considering the steady growth of the Earth population a shortage of certain metals may occur (Krausmann et al. 2009). In 2010, the United Nations allowed commercial exploration for seafloor massive sulphides (SMS) in international waters with currently six contractor licenses being granted.Although the number of discovered vent sites has steadily increased since the first discovery of hydrothermal venting at the Galapagos Rift in 1977 (Corliss et al. 1979) with more than 600 sites being known today, their economic potential is poorly constrained. So far Nautilus Minerals Inc., a Canadian mining company, is the only company having conducted a NI 43-101 resource estimate for the Solwara site, located in the territorial waters of Papua New Guinea. Other studies using bulk geochemical data from 95 sites published in literature do exist (Hannington et al. 2011, Monecke et al. 2016) suggesting a global resource potential for today’s known SMS deposits of 600 million tons with a median grade of 3 wt.-% copper, 9 wt.-% zinc, 2 g/t gold and 100 g/t silver. However, the geochemical data being used originated mainly from easily recoverable, mainly non insitu surface grab-samples and are under current mineral resource classification schemes such as JORC code or NI 43-101 not even accepted for resource estimations. Furthermore surface samples such as high-temperature sulphide chimney and talus material are not representative for the entire deposits with information regards thickness and continuity of individual sulphide layers obtained through drilling being scarce. In addition, it remains unknown what geological processes occur once hydrothermal activity ceases and whether metal tenor becomes enriched, depleted or disappears."

Jan 1, 2017

By Irina Melekestseva

The Cu-Zn massive sulfides from the basalt-hosted Semenov-2 hydrothermal field (13°31.13´ N, 44°59.03´ W, MAR) are enriched in Au (22?188 ppm) and Ag (127?1787 ppm) [Ivanov et al., 2008] and elevated contents (ppm) of Se (269?289), Sn (123?125), and Sb (72?75). These may indicate heterogeneous substrate rocks and possible ultramafic rocks. Based on phase analysis, 70% of the gold in the massive sulfides is free. LA-ICPMS analysis has shown that the main carrier of the invisible gold is covellite (22.51? 226.64 ppm). Covellite is also characterized by elevated contents of Se, Mo, Sn, Te, Au, Bi, As, Ag, Sb, Tl, and Pb relative to the primary sulfides.

Sep 14, 2011

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 Raymond A. Binns

In this first sub-seafloor examination of an active hydrothermal system hosted by felsic volcanic rocks at a convergent plate margin, we drilled 13 holes altogether, achieving deep cored penetrations at two sites. Our aims were (1) to delineate the lateral and vertical variability in mineralisation and alteration patterns below the PACMANUS hydrothermal site near the 1650-1700 m-deep crest of Pual Ridge in the eastern Manus back-arc basin, so as to understand links between volcanological, structural and hydrothermal phenomena, and (2) to establish the nature and extent of microbial activity within the system. Technological innovations vital to success included our precise location of holes on small targets with drill-stem video, the use of a new hard-rock re-entry strategy, and deployment of casing with a new hammer drill. Other technical achievements were the first ODP application of an advanced diamond coring system, and the first direct comparison in a hardrock environment between structural images obtained by wireline methods and by logging-while-drilling (resistivity-at-bit).

Jan 1, 2002

By Delphine Pierre, Jean-Marie Augustin, Anne-Sophie Alix, Charline Guérin, Cecile Cathalot, Yves Fouquet, Arnaud Gaillot, Ewan Pelleter, Carla Scalabrin, Florian Besson

With the world’s growing demand for metals, seafloor massive sulfides (SMS) deposits are now seen as a possible mineral resource that could contributes to secure metal supply for human needs. SMS deposits are characterized by high concentrations of base metals and at some place high contents of precious and rare metals. Since 1977 and the discovery of the first high temperature (HT) hydrothermal vent and its sulfide mineralization and high biodiversity, more than 300 sites are known today. If the exploration strategy for detection of active hydrothermal sites is now robust, their associated mineralization will not (and must not) constitute a potential target for deep-sea mining due to environmental concerns and technical limitations. Recent studies on SMS deposits are rather focused on extinct and buried mineralized sites characterized by a lower biomass. Several geophysical techniques to explore and detect extinct SMS (eSMS) and buried SMS (bSMS) have been developed (e.g. Kawada and Kasaya, 2017; Szitkar et al., 2017, 2014) using different approaches (e.g. regional or local scale; ship-based or using underwater vehicles) with several degrees of success or limitation. Here we present results from acoustic surveys performed on the TAG hydrothermal district during the BICOSE (2014) and LEVE-SMF (2016) cruises and direct observation provided by HOV (Nautile) dives carried out during HERMINE cruise (2017). Acoustic data were acquired using two different multibeam echosounders (MBES): the hull-mounted Kongsberg EM122 (12 kHz, R/V L’Atalante) and the ROV-mounted RESON SeaBat 7125 (400 kHz, ROV Victor) (Figure 1). After processing, acoustic seafloor backscatter data from both MBES provides complementary qualitative results in relation to the seafloor composition. The analysis of the seafloor backscatter data obtained by near-seafloor surveys with the high-resolution 400 kHz MBES shows a clear relationship between low backscatter strength values and areas covered with pelagic and hydrothermal sediments whereas high backscatter strength values are associated to pillow lavas and basaltic scree. Intermediate backscatter strength values are rather related to old and younger eSMS as well as to mineralization on TAG active mound.

Jan 1, 2018

By Jan M. Peter

The Early Norian Windy Craggy massive sulfide deposit is within the allochthonous Alexander terrane of the Insular tectonic belt in extreme northwestern British Columbia (Figure 1). Host rocks are the Middle Tats Volcanics, part of an informally-named volcano-sedimentary succession of mixed graphitic argillites and mafic pillowed and massive volcanic flows and sills of Upper Triassic age (Figure 2) that have suffered only lower greeschist-facies metamorphism. The volcanic rocks are light rare earth element (LREE)-enriched and display a variably developed back-arc subduction signature. Major and trace element compositions of the host argillite show that it contains an appreciable hydrothermal component, as evidenced by low high Fe and Mn contents. These sediments therefore record steady, continuous hydrothermal activity punctuated by intermittent turbidity currents sweeping into the basin. The deposit consists of at least two discrete sulfide lenses (the North and South Sulfide Bodies), as shown in Figure 3, a level plan at the elevation of the exploration workings. Published reserves at 0.5% copper cut-off are 297.4 million tonnes grading 1.38% Cu, 0.08% Co, 0.21 g/t Au and 3.9 g/t Ag (as of December 1991). However, the deposit is larger than this and further drilling is required to delineate it completely. Mineralization comprises massive sulfide, stringer/stockwork, and finely bedded to laminated sulfides and exhalites. Stockwork mineralization consists of sulfide-quartz-chlorite veins with attendant chlorite and silica alteration. Mineralization consists predominantly of massive pyrrhotite andlor pyrite with lesser chalcopyrite and magnetite. Figure 4 is an oblique section through the North Sulfide Body, the most northerly sulfide mass shown in Figure 3, which shows the distribution of the pyrite and pynhotite-rich massive mineralization and the stringer zone. The North Sulfide Body contains appreciable sphalerite, whereas the South Sulfide Body contains only trace amounts. Gangue minerals include quartz, chlorite, calcite, siderite, ankerite, stilpnomelane and magnetite. The minor hydrothermal exhalite sediments are comprised of chert, carbonate, and minor

Jan 1, 1993

By T. Kuhn

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

Jan 1, 2004

By Jonguk Kim

Texture and geochemical composition of hydrogenous ferromanganese crust from relatively adjacent three seamounts (OSM2 at 157°35&apos;E, 13°55&apos;N, Lomilik at 161°37&apos;E, 11°42&apos;N and Lemkein at 165°05&apos;E, 9°18&apos;N) near the Marshall Islands in the western Pacific (Figure 1) were investigated in order to elucidate their growth history. These seamounts, located in different latitudes, are along a line that is parallel with the direction of Pacific plate movement. Thick crusts commonly have three or four distinct layers (Figure 2): (1) layer 1, uppermost layer, is black, dense, and has a botryoidal, columnar, or laminated texture; (2) layer 2, overlain by layer 1, is Fe-stained, porous to vuggy and filled with sediment; (3) layer 3, phosphatized layer, is black, massive, dense, and impregnated by CFA, (4) layer 4 shows parallel to undulatory laminated texture and cut by CFA-filled veins. Layer 1 and 2, unphosphatized young layer, are observed in crust samples collected from all seamounts. However, lower part of the crust shows different textures in different seamounts. Both layer 3 and 4 are found in thick crust from OSM2 but layer 4 is absent in crust samples from Lemkein and Lomilik. All the uppermost layers (layer 1) from three seamounts have similar textural and geochemical characteristics. Layer 2 is overlain by layer 1, is porous, partly Fe-stained, and sediment-infilled. In previous studies, layers 1 and 2 have grown in different oceanic environment. Textural and geochemical properties show that layer 1 has grown under relatively higher bottom water activity and lower productive environment than layer 2. Carbonate and detrital materials in layer 1 are not abundant compared to layer 2. Layer 2 can be assumed to have grown under equatorial high productivity zone (EHPZ) while layer 1 has started to grow when the seamount left from the EHPZ.

Jan 1, 2003

By Chul H. Jo

The functions of miner mainly include the pick-up manganese nodules laying on the surface of the seafloor, the separation them from sediments, the crushing the nodules and the covey to the inlet of the flexible hose. The miner is connected with umbilical cable that can supply power, instrument signal, communication data, etc. The major concerns of the system is to monitor and control the launching and retrieval operation, the landing, maneuvering and track keeping, to monitor the pick-up operation and to monitor the hydraulic system. Also as per the seafloor profile the track and pick-up processes need to be controlled. The recent research and development of deep sea miner is mainly focused on the efficient performance and workability in deep water. To communicate and control the miner, navigation and positioning system have been applied. As the miner is being deployed or retrieved, it is very critical to avoid any damage to the device that would be caused by the dynamic behavior of surface vessel or the minor itself with wave and current motion. The fast deployment and retrieve should be considered very important to minimize the possible damage. The paper introduces the various type of deployment devices and recommend the possible system to the miner developed by KRISO.

Jan 1, 2003