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By James C. Barker

Concern over the availability of domestic critical and strategic mineral supplies has led the Bureau of Mines to evaluate the reserve development potential of alternative sources in Alaska. Near the village of Platinum, on the southwest Alaska coast, the Red Mountain concentrically zoned ultramafic complex is a source of onshore alluvial placers containing platinum-group-metals (PGM). It has long been suggested that valuable placers may also underlie the shallow coastal waters of the Bering Sea. A direct correlation of placer PGM and chromium to ultramafic rocks in the area was studied by the Bureau and the extent of the complex was mapped. Magnetometer and gravity data and geological studies suggest the complex is a large lensoidal body trending several kilometers offshore to the southwest with a probable steep southeasterly dip. Multiple Pleistocene glaciations and marine transgressions have eroded the western and southwestern portion of the complex. Sediments containing PGM, chromium, and associated gold (largely derived from glacial till) have been transported northward along the advancing coastline by littoral currents. Beyond the breaker zone, these sediments are generally buried by recently winnowed sand and gravel transported by strong longshore tidal currents. There is also evidence that paleoplacer channels underlie the marine sediments.

Jan 1, 1986

By V. K. Banakar, R. P. Rajani, A. R. Chodankar

The Afanasiy-Nikitin Seamounts (ANS) in Eastern Equatorial Indian Ocean (Figure 1) are shown to be the exposed part of the presently buried 85°E Ridge system under the Bengal Fan sediment and were emplacement around 75-80 m.y. ago (Krishna, 2003). The first recovery of ferromanganese crusts from the ANS was made during 1994, and the samples (Figure 2) provided important clues on the evolution of this seamount (Banakar et al., 1997).

By Randolph A. Koski

Since 1985, numerous constructional sulfide-sulfate deposits in the form of mounds, pinnacles, chimneys, and sheets have been located between 40°45' and 41°05'N latitude in Escanaba Trough, the sediment-covered axial valley of the Southern Gorda Ridge. Single-channel seismic data indicate that three volcanic edifices up to 6 km in width penetrate as much as 500 m of turbidites that fill the valley; pillow and sheet flow lavas are exposed on the sea floor where these volcanoes breach the sediment surface. Observations from deeply towed camera systems and submersibles show that the largest hydrothermal deposits occur along the step-faulted northern flank of the central volcanic edifice and on the peripheries of steep-sided, sediment-capped hills, approximately 1 km wide and 100 m high, that rise above the valley floor. The sulfide deposits are highly oxidized, eroded, and partly buried by unconsolidated sediment; aprons of sulfide talus extend downslope from the mounds. Two types of sulfide have been sampled by dredging and submersible. The predominant mound and chimney material is pyrrhotite-rich massive sulfide with low amounts of Zn, Pb, Cd, and Ag. Coarse-grained zones with high porosity mark the location of myriad fluid channelways. Thin crusts of barite associated with pyrrhotite-rich sulfide have Au contents up to 2 ppm. Zoned fragments of polymetallic (Fe-Zn-Pb-Cu-As-Ag-Sb) sulfide dredged from a single site near 41°01'N latitude are part of a chimneylike vent structure with a

Jan 1, 1988

By Brian D. Bornhold

A comprehensive multi-disciplinary marine geological survey of northwestern Graham Island, Queen Charlotte Islands, British Columbia, Canada was conducted by Offshore Survey and Positioning Services Ltd. of Vancouver, B.C. on behalf of the Geological Survey of Canada; Energy, Mines & Resources Canada, Pacific Geoscience Centre, Sidney, B.C. Canada during October 1984 and July 1985. The aim of the survey was to map both the surficial geology and geomorphology in order to identify and evaluate the nature of the nearshore sedimentation and recent tectonics including stability (slumps and scarps) seafloor faults (frequency and displacements) and both the classification and consistency of soil type boundaries and properties. Data was acquired by utilizing conventional indirect applied marine geophysical techniques including side scan sonar, precision echo sounding and complimentary soil sampling. During October 1984 a total of 320 line kilometres of data including 180 soil samples were acquired. During July 1985 a total of 300 line kilometres of data were acquired including 150 soil samples.

Jan 1, 1985

By Daisuke Monoe, Kisaburo Nakata, Rika Takeuchi, Tetsuo Yamazaki, Tomoaki Oomi, Tomohiko Fukushima

There are generally two methane passes in conjunction with the seafloor natural cold seepages, as is schematically shown in Fig. 1. The first pass consists of the coupled anaerobic oxidation of methane and anaerobic sulfate reduction, as well as sulfur oxidation in the bacterial mats and immobilization thereafter in the sediment layer and on the seafloor. Through the first pass, calcium and organic carbonates are formed in biological and chemical processes from the methane (Luff and Wallmann, 2003; Luff et al., 2004). The detailed structure of the seafloor methane consumption process unit and its biological and chemical processes were introduced in Yamazaki et al. (2005). The other pass consists of direct bubbling into the water column. Through this pass, organic carbonate is formed with biological oxidation, and a small amount of the methane escapes into the atmosphere. Methane flux is supplied to these two passes through the sediment layer from the deeper structures. The structure of the methane supply process unit was introduced in Yamazaki et al. (2006).

Sep 24, 2006

By Valery M. Yubko

During the last ten years seven applications for nodule-bearing areas of the World Ocean Floor International Region (IR) have been made by national companies of Russia (Yuzhmorgeologiya), France (IFREMER/AFERNOD), Japan (DORD), India (The State Department of Sea Resources Development), China (COMRA), Korea (KORDI) and the Interokeanmetal Joint Organization (IOM) of some East European countries and have been registered by the Preparatory Commission of the United Nations International Seabed Authority (ISA). Besides these groups registered within Resolution 11 of the Final Act of the III United Nations Conference on the Law of the Sea there are four international consortia registered in the USA [Kennecott (KCON), Ocean Mining Associates (DMA), Ocean Management Incorporated (OMI), and Ocean Minerals Company (OMCO)], which have interest in areas in the IR and can be considered as potential applicants. All registered areas (with the exception of the Indian Ocean) including the areas of potential applicants and also 6 areas, reserved for the ISA are located in the Clarion-Clipperton Zone of the Pacific Ocean. If within each area not less than one deposit of polymetallic nodule-bearing ores can be discovered, then, the total number of such deposits, for the present moment, is 20.

Jan 1, 1994

By Peter Halbach

Hydrothermal activity is well known from many locations on most mid-ocean ridges, however 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 27º51S / 63º56 E 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 water depth of about 2940 m close to the summit of an axial volcanic ridge called Mount Jourdanne. There 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 and pathways for fluid circulation, respectively.

Jan 1, 2001

By S. Rajendran

The western continental margin comprises of the southwest coast (Cape Comorin-Mangalore), centralwest coast or Konkan coast (Mangalore-Bombay), northwest coast (Bombay-Gulf of Kutch) and the Laccadives area. Placer deposits of heavy minerals occur in discontinuous patches on the beaches along many parts of the west coast. The richest offshore placer deposits occur along the 25 km stretch of the southwest coast from Neendakara to Kayamkulam. The National Institute of Oceanography (NIO) surveys show that the sediments off the Konkan coast consist largely of silty sand, sandy silt and clay and the concentration of ilmenite is higher than the onshore. The heavy mineral concentration ranges up to 90% and has mainly ilmenite and magnetite with minor quantities of apatite, rutile, zircon, kyanite etc. The heavy mineral sands extend below the clays to water depth down to 20 m. The heavy minerals sands vary in thickness from 2-10 m. Offshore placers can be mined by using wire-line, bucket ladder and hydraulic dredges. Wire-line, bucket ladder and hydraulic dredges. Wire-line dredges may employ drag buckets or clamshell and hydraulic dredges suction or airlift principles. The dredges can be located on flat bottom or catamaran barges. Dredging of very near shore placers may be achieved by operating from land. The bucket ladder type of dredger has greater digging ability and hence can be deployed for mining placers which are partly consolidated or cemented or where the most valuable part of the deposit lies at the contact between the alluvium and the bedrock. This type operates very economically up to 45 m depth and needs minimum power requirement per unit dredged. Suction type hydraulic dredges can be operated very effectively up to 60 m water depths. This system is quite ideal for the inner shelf. The maximum practical economic working water depths for wire-line dredges are about 150 m. With the drag bucket modified into large net buckets, the method can be utilized to greater depths. They can be used in areas of high water currents and swells. The type of bucket can be changed readily with change in the nature of alluvium or substratum. The hydraulic suction dredge is the most suitable system for mining unconsolidated sediments. When the sediments are semi-unconsolidated, a cutter head can be mounted on the lower end of the suction pipe to agitate the seabed.

Jan 1, 1996

By Satya Nandan

• A review of the structure and mandate of the Authority – its main functions. • The different types of mineral resources found in the deep seabed – their global distribution. • The Development of Regulations for Prospecting and Exploration of Polymetallic Nodules, Cobalt-Rich Crusts and Polymetallic Sulphides including environmental regulations and guidelines. • Early constraints for deep seabed mining – Improving conditions for mining – Future prospects for mining.

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 James R. Hein

Methane and hydrogen sulfide vent from a cold seep above a shallowly buried methane hydrate in a mud volcano located 24 km offshore of Los Angeles, California in 800 m water. Bivalves, authigenic calcite, and methane hydrate were recovered in a 2.1 m piston core. Aragonite shells of two bivalve species are unusually depleted in 13C (to -19? d13C), the most 13C-depleted shells of marine macrofauna yet discovered. Carbon isotopes for both living and dead specimens indicate that they used in part carbon derived from anaerobically oxidized methane (AOM) to construct their shells. Although the?d13C values are highly variable among specimens, most fall within the range -12 to -19?. This variability may be diagnostic for identifying cold-seep/hydrate systems in the geologic record. Authigenic calcite is abundant in the cores down to about 1.5 m subbottom, the methane hydrate horizon. The calcite is strongly depleted in 13C d13C = -46 to -58?) indicating that AOM was the main carbon source. Three sources of methane are likely: a geologic hydrocarbon reservoir, and biogenic and thermogenic degradation of organic matter in basin sediments. Oxygen isotopes indicate that most calcite formed out of isotopic equilibrium with ambient bottom-water, under the influence of gas hydrate dissociation and strong methane flux. High concentrations of Ag, Hg, Cd, Tl, and other elements in mud volcano sediment reflect leaching of basement rocks by fluids circulating along an underlying fault. Fossil (geologic) methane was likely transported with these fluids.

Jan 1, 2005

By R. W. Nesbitt

The TAG and Broken Spur hydrothermal mounds are located on the Mid Atlantic Ridge (MAR) at 260N and 290N (respectively). Both were initially discovered by exploratory work from surface vessels and both have since been investigated by submersibles. The discovery of TAG resulted from a NOAA Trans-Atlantic Geotraverse (Rona et al. 1975) which fortuitously sampled low temperature materials on the east wall of the MAR rift valley and follow up operations (Rona et al. 1986) located the high temperature (365°C) mound some 5km to the west. In 1994, ODP deep sea drilling (Leg 158) at over 3,500 metres of water recovered core to a depth of 150 m below surface (Herzig et al. 1998) and for the first time allowed a geological interpretation of an active mound. The Broken Spur mound was accidentally discovered in 1993 when sulphide fragments were observed on a deep-sea towed camera system (Murton 1993). Later that year, exploratory submersible dives by Alvin located the hydrothermal field and the area was again explored by submersible in 1994 and 1997. Despite the amount of work carried out, our geological understanding of the MAR mounds is limited. Much effort has gone into measuring fluid chemistry whilst practical difficulties have inhibited good geological mapping of the sulphide areas. It is clear from both TAG and Broken Spur that the mounds are not necessarily located in the areas of highest heat potential. Indeed, TAG is some 2 km from the rift valley axis and has been operational for several tens of thousands of years. Hence, heat availability is not a major consideration and the most obvious control is a structural one. Mapping on Broken Spur indicates a series of isolated vent-sulphide areas, concentrated around a minor graben. Their distribution, size and nature all indicate that they are residual parts of a much larger sulphide body which was at least the size of the present TAG field. The evidence is for a cyclical pattern of mound growth -mass wasting? rejuvenation and the Broken Spur mound appears to be in the rejuvenation stage of the cycle. Mound cyclicity must be related to the supply of hot water which itself is a function of the connectivity of fracture systems. Hence, we return to the theme that the major controls in mound development are structural ones.

Jan 1, 1998

By Evgeny G. Gurvich

While direct study of high temperature hydrothermal activity and the associated mineral formation as well as study of their scales are possible in the modern ocean, researchers are deprived of such opportunity for past geologic time. Even in cases where hydrothermal deposits that formed in the geological past are preserved they have been covered by sediments or overlain by lava and have become inaccessible after a time for obser-vation and sampling. Rarely are these buried hydrothermal deposits found during deep-sea drilling or coring operations, and their direct study on an ocean scale is impossible at present. Even within hydrothermal fields, without special preliminary detailed surveys, the probability of intersecting hydrothermal edifices that are covered by sediments becomes a rare event.

Aug 24, 2006

By T. Semkova, G. Cherkashov, V. Rashidov, L. Anikeeva, G. Gavrilenko, G. Glasby

The Kurile Arc consists of at least 100 submarine volcanoes and 5 submarine calderas located mainly in the rear arc (Figure 1). The arc is seismically very active, particularly in the south, and is characterized by extensive volcanism and hydrothermal activity. At least one subaerial volcano on the arc (Medvezhy located on Iturup island) has an extremely shallow magma chamber and is intensely active.

By Lauro Calliari

Detailed geological studies using side scan sonar, bottom sampling and piston cores along the Rio Grande do Sul inner continental shelf and coastline indicate the occurrence of elongate deposits of calcareous shells fragments containing high calcium carbonate content. On the inner shelf these deposits lie at a depth between 15 and 50 meters and have been interpreted as ancient shorelines. They occupy an area of 965 km2 with a economic potential of 1 billion tons. Chemical analyses indicate a mean composition of 34.8% of calcium; 0.16 ppm of fluoride. According to the regional economy such composition make it highly recommended for a variety of uses including poultry feed and cement.

Jan 1, 1995

By H. Shimoda, K. Tamaki, K. Iizasa, M. Watanabe, K. Okamura

Modern Kuroko-type deposits occur in submarine calderas of island-arc fronts and back-arc rifts in Japan. They occur primarily on or adjacent to caldera boundary faults. Hydrothermal sulfides in the Myojinsho submarine caldera are one of Kuroko-type deposits, but their occurrence is different from other deposits found within the area 200 km2 around the Quaternary volcanic front of Izu-Ogasawara arc.

Aug 24, 2006

By Luana Karvel, Lars Kullerud, Morten Sørensen, Øystein Halvorsen, Øivind Lønne, Elaine Baker, Tina Schoolmeester, Joan Fabres, Yannick Beaudoin

The UNEP Shelf Programme (USP) is the access point for a collaboration of international organizations with expertise in marine geoscience and maritime law. It was established in response to a United Nations resolution, stating that the United Nations Environment Programme (UNEP), working through the Global Resource Information Database (GRID) system, should work in conjunction with Intergovernmental Oceanographic Commission of UNESCO (IOC) and the International Hydrographic Organization, to assist coastal States, and in particular developing States and small island developing States (SIDS) with submissions to establish the outer limits of their continental shelf under Article 76 of the United Nations Convention on the Law of the Sea (UNCLOS).

By G. Rehder, C. Hensen, P. Linke, J. Bialas, M. Haeckel, W. Weinrebe, K. Wallmann

Research on marine gas hydrate and the methane cycle has a tradition at IFM-GEOMAR. In summer 1996 during a cruise with RV SONNE offshore Oregon (USA) scientists of the former GEOMAR recovered the largest amount of gas hydrate from the seafloor. This discovery stimulated research on marine gas hydrates in Germany and induced funding of scientific programs such as LOTUS and OMEGA with numerous innovative technologies within the special program GEOTECHNOLOGIEN of BMBF and DFG. The primary objectives of ongoing and future research are to achieve a comprehensive knowledge of: • gas hydrate distribution and quantity; • variation and regulation of gas hydrate formation and dissociation as well as of the related fluid flow; • functioning of chemosynthetic communities in methane oxidation, carbonate precipitation and methanotrophy as biological barrier against methane emission and • delineating the escape routes of methane to the hydrosphere and atmosphere.

Aug 24, 2006

By Marco Figoni

The increased interest on deep water minerals resources is a challenge for both mining and oil industry. The exploration and production of oceans minerals require a synergy between of different technologies. While mining industry is leading the dredging and processing part of the system, oil industry is contributing through development of ore lifting technology based on existing subsea knowledge. The paper presents an overview, based on published projects around the world, of different approaches to marine mining. Several exploration techniques and offshore production systems were already designed and assessed, all of them with apparently positive results. Exploration phase is well advanced and in continuous expansion allowing the discovery of increasing resources around the world of different nature but production can be considered to be in an early stage. Different from onshore mining, subsea operations require a closer cooperation with international and local authorities to preserve as much as possible the environment. There are still many uncertainties at respect and all the exploration process must be carefully evaluated to allow subsea mining to develop in a sustainable manner. Technically, mining at seabed was already demonstrated and the process is based on three main components, namely seafloor mining tools, riser and lifting system and production vessel support. This layout is based on the concept that ore must be disaggregated at seafloor first, transported to surface in form of slurry that must be dewatered before loading to be transported to processing plants onshore. The challenges are rising because the environment and safety must be taken into consideration as a priority when evaluating the efficiency of the system. The most critical challenges regarding the production operations, especially in deep water are the deep-sea excavation process, the transport of large slurry volumes, the slurry abrasivity, the power supply management and the subsea

Sep 14, 2011

By Akira Usui

Iron and manganese are very mobile metallic elements in the surface aqueous environment, particularly in the oceans. The elements are easily precipitated as oxides or dissolved back into water, controlled mainly by redox conditions, and the oxide precipitates often selectively accumulate other metallic elements. We have found clear evidence of fine-scale variations in chemistry, mineralogy, isotope composition and microstructures within various iron-manganese nodules and crusts, such as in the deep-sea basins and seamounts of the Pacific Ocean, and in shallow waters in the Baltic Sea. The patterns of variation with depth (that is time-lapse profiles of the deposits) are often correlated among samples and sometimes between remote localities. These fine-scale variations most probably reflect past depositional conditions and possibly image the environmental change, although they remain to be correlated to any physicochemical, geological, or oceanographic parameters. The hydrogenetic ferromanganese crusts have grown widely in the northwestern Pacific, accelerated by intensive circulation of oxygenated bottom waters during the last several millions of years, or earlier. The fine-scale (in millimeter) in-depth compositional and textural patterns with Be-10 growth-rate curves suggest significant changes in growth rate and also occasionally show a common microstratigraphic pattern among samples. Some of the samples indicate a correlation in growth pattern between remote locations, while others suggest short-range difference of oceanographic conditions with water depths.

Jan 1, 2004