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By L. B. Khershberg

According to geochemical specialization, cobalt-manganese crusts (CMC) of the Magellan Seamounts are rich in cobalt and manganese and are complex in composition. Besides cobalt, manganese, and nickel, they contain such components, as platinum, copper, molybdenum, and rare earth elements, which enhance the value of this material. Factors and conditions responsible for Co-Mn ore-genesis and processes of cobalt-manganese crust formation are described in a number of Russian and foreign geological papers. The study of ore-concentrating processes in the Magellan Seamounts helped to solve an important applied problem, namely to reduce the time needed to reveal the factors of CMC formation mechanism. The authors of this research found seawater over the described area of Magellan Seamounts to be stratified and to contain high concentrations of manganese, iron, cobalt, nickel, copper, lead, and zinc. Diagrams of suspended Co, Mn, Ni, and other components in seawater (0-5500 m), as well as medium concentrations of basic elements (Co, Mn, and Ni) in ore deposits of metallogenic levels of Magellan Seamounts, were found to coincide both on guyots and abyssal plains. Detailed geological study of guyots in the Magellan Seamounts (Dalmorgeo, IOAN, Roskomnedra, and others) revealed that medium Co-Mn crusts cover bedrock rocks in narrow ribbon-like bodies along the edges of bathymetric intervals 1300-1600 m, 1400-2000 m, 2000-2500 m, and 2500-3000 m.

Jan 1, 2004

The seafloor occurrences of KODOS ferromanganese nodules can be classified into four facies based on the morphological types of nodules recovered and seafloor photographs. Facies A, B, and C are relatively unimodal whereas Facies D is bimodal in the size distribution of nodules. Both Facies A and B are highly covered by sediments, but Facies B is higher than facies A in nodule density. Facies C has a high density of small nodules and many traces of bioactivity. Facies D is irregular in nodule density, but occurs close to basement near scarps (Fig. 1). The transparent layer (TL) on subbottom profile records (von Stackelberg et al., 1987) is composed of three sedimentary units, which in cores are distinguished by color. The uppermost Unit I is postulated to be deposited during the past 0.21 Ma and the middle Unit II between 0.42 Ma and 0.21 Ma (MOMAF, 1997). There exists a hiatus between Unit II and Unit III. Unit III was deposited from 3.5 Ma to 1.5 Ma as determined by 10Be/9Be and/or 87Sr/86Sr dating (MOMAF, 2004). Internal textures observed on cut sections of nodules suggest four stages of nodule formation (Choi et al., 2000). The nuclei are either unbroken old nodules probably of hydrogenetic growth (1h and 2h) in Facies A and C, or nodule fragments probably of early diagenetic growth (2d) in Facies D, whereas there are both types in Facies B. The layers surrounding the hydrogenetic nodule nuclei are of hydrogenetic growth (3h and/or 4h) in Facies C, and are of early diagenetic growth (3d and/or 4d) in Facies A, B, and D. The layers surrounding the early diagenetic nodule fragments are mostly of early diagenetic growth (3d and 4d) in Facies A, B, and D. But hydrogenetic encrustations are also found as surface layers on the top in Facies B (Fig. 2).

Jan 1, 2005

By Olav Rune Godø

We present a science-based infrastructure for continuous online monitoring of the ocean interior including benthic, pelagic and the demersal habitats. It will reduce expensive ship based monitoring costs associated to offshore and coastal industries. We combine established Norwegian cabled observatory technology and German mobile seafloor robotic technology and thus supports the transition from local to spatial ecological monitoring. Both technologies are developed through science - industry partnerships. In Norway, the Institute of Marine Research has worked with Statoil ASA and Metas AS to install and operate the LoVe cabled observatory. The German technology is developed by iSeaMC and Kraken Robotik, two spinoff enterprises of the Helmholtz Alliance “ROBEX”. GEOMAR has recently developed a lander-based deep-sea crawler that operates autonomously based on the original iSeaMC crawler system using the Kraken Autonomy. Combined with the Spanish image processing and modelling expertise in the SME Deusto Sistemas SA the consortium hosts the capacity to establishing a complete semi-autonomous real-time monitoring system. Merging of existing technologies into one operational autonomous product through the unique competence of partners’ support international ambitions (e.g. Blue Growth, GES, Horizon 2020), and renew monitoring that assess impact of human use of the marine environment. The consortium has been invited to contribute to technology/science programs for the Yellow Sea and for European mining and offshore decommissioning industries, which demonstrates the leading role of our consortium. The project is funded through the EU Martera program and started in June this year.

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 Se-Won Chang

This is a part of the joint KIGAM-GNS-NIWA 3-year study of ferromanganese nodules on the Campbell Drift, east of Campbell Plateau to determine age distribution, growth rates and geochemical evolution in relation to geographic setting. During the research voyage SAA3 by R/V Tangaroa (TAN 9909) in July-August 1999, seafloor sampling and camera towing were conducted along the two transects across the known flow path of the Deep Western Boundary Current (DWBC) perpendicular to the lowermost margin of the Campbell Plateau and Bollons Seamount. The four major nodule facies, SHH (slope hydrogenetic nodules with high density), AHH (abyssal hydrogenetic nodules with high density), ADH (abyssal diagenetic nodules with high density), and ADL (abyssal diagenetic nodules with low density) were identified. Two additional minor nodule facies, SIB (slope irregular nodules with ice-rafted boulders) and SHB (slope hydrogenetic nodules with boulders and crust), of localized distributions are also identified.

Jan 1, 2003

By Julian Malnic

Transplanting the steps used in exploring and developing mineral deposits on land into the marine environment will help developers. While familiar to oil and gas explorers and many other sea-based industries, the marine environment is so alien to the 90s terrestrial miner that the phrase ?terrestrial mines in the sea? is useful for reinforcing the fundamental parallels in mining sulphides at sea and on land. As on land, the processes of ?pre-feasibility study? and ?feasibility study? will determine the economics of mining a deposit. For many, the step into the sea can detract from the need to follow these familiar and recognised steps used when any new deposit is found on land. The technology to mine sulphides in the 1500 to 2000 m depth range exists. Currently, it is not found in a single, integrated and commercially available system but every element available to build such as system is. Transplanting the thinking of the leaders of the terrestrial mining industry into the sea will perhaps be the greatest challenge and reinforcing the basic steps of discovery - pre-feasibility through to feasibility is the best way to achieve this. After all on land one doesn?t ask ?Can we profitably mine it?? before one can authoritatively answer ?What have we found??. Research by Nautilus Minerals Corporation suggests that the mining of seafloor massive sulphides (SMS) will not only be profitable but potentially lower in both capital and operating costs than prevail in most terrestrial deposits. Nautilus is also acutely aware that with the first SMS deposits under title, it will be setting the standards for seafloor mining into the new millenium. Indeed, we have trained on us not only the eyes of the mining industry waiting to see if SMS deposits really do offer radically better returns, but other stakeholders of the sea and the capital markets. Mistakes by any SMS developer could land all developers in ?hot water?. The rush to exploit our deposits for economic gain will be tempered by ensuring there is adequate public debate and consultation for our environmental code. Failure in any facet of a marine mining development could set back the move to the ocean floor.

Jan 1, 1998

By Alexander Malahoff

The summit of L_ihi submarine volcano changed dramatically after seismic activity beneath L_ihi during the month of August 1996. Bathymetric re-surveys of the L_ihi edifice using SeaBeam, Simrad and deep-towed Reson-Focus multibeam systems showed the presence of new north-south striking fissures, normal faults and a new pit crater located at the site of a former 300-meter high volcanic cone. Comparisons between the pre-1996 SeaBeam data and the new bathymetry show a net loss of about 100 million cubic meters of rock volume on the summit. This loss is localized at a new pit crater -- the 300-meter deep by 1,300-meter wide Pele's Pit. Submersible observations with Pisces V show the northern edge of Pele's Pit to be bounded by a normal fault located north of the site of the former Pele's Vents cone that has disappeared into the new pit crater. A new hydrothermal field, the Ikaika Vents, extending from a water depth of 1,311 meters to 1,287 meters has formed at the northeastern edge of the floor of Pele's Pit. Submersible observations of these new Ikaika Vents during September 1996 showed vigorous venting at the site with extensive white-colored bacterial mats hanging off the rock face above the vents. Follow-up mapping and sampling of the vent sites during August 1997 showed vent temperatures of up to 198°C, dense populations of vent shrimps around the vents and a centimeters-thick veneer of fine-grained polymetallic sulfide mineralization along the rock walls above individual vents. The mineralogy of the sulfides shows a barite, chalcopyrite, sphalerite, and pyrite composition.

Jan 1, 1998

By Jan M. Peter

Many massive sulfide deposits and districts around the World contain rocks that are variously referred to as ?exhalites?, banded iron formation (IF), ?Algoma-type? IF, ferruginous chert, jasper, jasperoid, cherty tuff, tuffite, tuffaceous exhalite, chloritic IF or sulfide IF. With few exceptions, such rocks are thought to be (in part) fossil hydrothermal sediments deposited from hydrothermal fluids vented into a submarine rift environment. Such hydrothermal sediments are associated with a wide variety of ancient base-metal sulfide deposits (e.g., Cyprus-, Besshi-, Kuroko-, and Broken-Hill-type deposits), and hydrothermal sediments are commonly associated with some of the largest base metal sulfide deposits in the world. Analogs of ancient hydrothermal sediments can be found around many modern seafloor hydrothermal deposits which themselves precipitate from high-temperature (350°-400°C) hydrothermal fluids. Hydrothermal fluids are quenched on contact with ambient seawater, and most of the metals are immediately precipitated to form the mound and chimney deposits. However, for kinetic and solubility reasons, not all metals and other species are immediately precipitated at the vent site. Fine particles (up to several hundred microns in diameter) of sulfides, sulfates, carbonates, oxides, silica, Fe-oxyhydroxides, clays, and other phases are precipitated from the hydrothermal fluids in the water column above the deposits. These particles or "particulates" are carried upward for several hundred meters in a buoyant hydrothermal plume (which is typically several hundred meters thick) until it reaches a neutral density, and disperses laterally from the vent site. Modelling of plume dynamics has shown that the majority of particulates are deposited by gravitational settling a few hundred meters from the vent site, and Å99% of particulates are deposited within 3 kilometers. However, signals from modern plumes have been detected even hundreds of kilometers from their source. Factors which can affect the morphology of the plume (and the resultant fallout pattern) include: particulate size, shape and density, bottom topography, and the direction and velocity of bottom currents.

Jan 1, 1998

By Tetsuo Yamazaki

Metal market prices rose drastically in 2006, and most broke historical records as shown in Figs. 1-4. This increase has been basically driven by economic growth in Asian countries, especially China. The growth trend is expected to continue for several years. Then, India will follow the same growth trend. Their metal demands keep the price levels high for 20 years or more. One more additional important factor on the metal market prices is hedge funds come into the market. Japan imports all metals for domestic use from overseas. The amounts imported were 1.27 million tons in copper, 0.32 million tons in lead, 0.59 million tons in zinc, 0.20 million tons in nickel, and 1.18 million tons in manganese, respectively in 2006 (Source: http://www.jogmec.go.jp/j_resourse/index.html#03). Though mainly we import the concentrates and our domestic customer smelters take the part of metallurgical leaching, the payment necessary for purchasing the concentrates is estimated about US$ 10 billions in 2006. The payments in 2005 and in 2003 were about a half and a quarter of the 2006, respectively. Japan must have effective counter measures to reduce the future payments.

Sep 24, 2006

By Irina Dobretsova, Anna Sukhanova, Anatoly Kondratenko, Svetlana Babaeva, Sergey Andreev

"With the acceptance of an application and a signed contract for prospecting deep-sea sulfides (2012) between the Russian Federation and the ISA, at present it is particularly important to assess the quality of oceanic sulfide minerals and to reliably estimate their resources.Some procedures of geochemical classification (chemical analyses, mineral composition of SMS) and calculations (density of ore, density of the mineral part of the ore, porosity and moisture contents) were used for estimation of mineral resources potential.The key characteristics for estimating the predicted resources of hydrothermal ore fields are the metal contents and the density of wet and dry sulfide ores. However, in the future it is impossible to provide an estimate of the predicted resources without taking into account the following important factors:- the quantitative ratio of main sulfide minerals;- proportion of non-metallic components (opal, quartz, talc);- the replacement of primary minerals by copper sulfides;- texture-structural features of sulfide ores.The offered mineral classification of the SMS is based on the prevalence of minerals in the ores and partly on their composition. The main ore-forming minerals of SMS are pyrite, chalcopyrite and sphalerite. Sulfide mineralization is accompanied by the presence of nonmetallic minerals, where quartz and opal prevail, and where we also meet aragonite, talcochlorite and anhydrite."

Jan 1, 2017

By Natalia Konstantinova, Kira Mizell, James R. Hein, Georgy Cherkashov, Amy Gartman, Pavel Mikhailik

INTRODUCTION Ferromanganese (FeMn) crusts from Mendeleev Ridge, Chukchi Borderland, and Alpha Ridge, in the Amerasia Basin, Arctic Ocean, are similar based on morphology and chemical composition. The crusts are characterized by two- to four-layered stratigraphy. The chemical composition of the Arctic crusts differs significantly from hydrogenetic crusts from the North Pacific Prime Zone (PCZ; Hein et al., 2013), such as a high mean Fe/Mn ratio (2.6 versus 1.3) and low Si/Al ratio (1.8 versus 4.0), with lower Mn, Ca, Ti, P, Ba, Co, Cu, Ni, Pb, Sr, and Zn and higher Si, Al, Mg, As, Li, V, Sc, and Th. Based on Arctic FeMn crust mineralogy, chemical composition, and growth rates, crust formation was dominated by three processes: Precipitation of Fe-Mn (oxyhydr)oxides from ambient ocean water, sorption of metals by the Fe and Mn phases, and fluctuating but large inputs of terrigenous debris (Konstantinova et al., 2017; Hein et al., 2017). The Mn and Fe phases are hydrogenous and reflect bottom ocean-water chemistry and the aluminosilicate phase contains stable detrital minerals such as quartz, feldspars, zircon, monazite, and clay minerals. A precise method of studying the distribution of elements in FeMn crust phases is sequential leaching that dissolves four mineral phases of different stability step-by-step, in the following order: easily leachable phase, mostly bio-calcite; manganese oxides; iron oxyhydroxides; and residual aluminosilicate minerals (Koschinsky and Halbach, 1995). Twelve bulk crusts and crust layer samples obtained from six hydrogenous FeMn crusts were studied. Those crusts were collected during Russian (Arktika 2012) and USA (HLY0805, HLY0905, and HLY1202) research cruises from different parts of the Amerasia Basin (Mendeleev and Alpha Ridges, Chukchi Borderland). Samples were chosen for the sequential leaching experiments based on their morphology, location, and water depth. Hydrogenetic crust (D07-33) from the Tuvalu EEZ, central-west Pacific Ocean, was included in the experiment for comparison. Recovery during the four-step sequential leaching, with respect to the bulk analyses, was between 80% and 120%.

Jan 1, 2018

By Colin Devey

As marine research scientists we especially appreciate the uniqueness and complexity of the deep-sea hydrothermal vent fauna and environments, and are particularly interested in preserving vents for their scientific, aesthetic, ecological, and potential economic values. In fact, because of the specialized nature of the equipment required to work at deep-sea hydrothermal vents, such as occupied and unoccupied research submersibles, scientists are the primary group of people who have the opportunity to visit these extraordinary environments. The potential for significant impact of scientific activities on a single vent site or a population of vent animals pales in comparison to the potential for disturbance by volcanic/tectonic events or industrial mining/harvesting activities. Nonetheless, we recognize that some scientific activities could adversely affect individual sites or impact communities more than is necessary, if research activities are not carefully planned and executed. In addition, because only a limited number of sites are currently known and scientists from a wide variety of disciplines frequently work at single locations, we recognize the potential for use conflicts among scientists, at sites where scientific activity is intense.

Aug 24, 2006

By Yves Fouquet

Results of the two main drilling operations on hydrothermal fields demonstrate that the two dimensional submersible operations need to be followed by drilling expeditions to study the third dimension of hydrothermal systems and understand hydrothermal and ore forming processes. Two types of environments were drilled recently in basaltic environment on slow spreading ridge, and on a sedimented ridge. Similar work has still to be done and targets to be discussed in other environments such as back-arc basins for felsic rocks environments and slow spreading ridges for ultramafic rock environments.

Jan 1, 2011

By Peter Halbach

Within the frame of the German-Indonesian cooperative Bandamin research project two short cruises (7 station days each) were carried out which led to the Flores-Banda basin located north of the active volcanic arc. This basin is part of a large island-arc subduction-collision system resulting from a complex plate tectonic situation in which three major plates collide with each other. The eastern part of the Sunda-Banda convergent margin also includes the transition from subduction of oceanic lithosphere to collision of the Australian continental crust with the arc. This transitional part is cut and displaced by various large obliquely striking fault systems. Thus, the south eastern and eastern arc segments represent geological conditions which are suitable for the development of hydrothermal convection and potential mineral precipitation. Our study area lies north of the transitional section between Flores and Wetar. We started with a high-resolution bathymetric mapping of 240 km2 in a region some 36 km north of the island of Lomblen. A small submarine neovolcanic ridge was discovered striking approximately NW-SE and consisting of several submarine volcanic structures. In the northwest of the study area, the active subaerial Komba Volcano (Batu Tara) marks the youngest continuation of the ridge system examined. From the ridge we collected fresh and hydrothermally altered volcanics with disseminated sulfides (pyrite, pyrrhotite, markasite, and chalcopyrite), together with ferrugenous gossans.

Jan 1, 2004

By Katsuya Tsurusaki

Commercial mining of manganese nodules is expected to begin within the next 20 to 50 years in large areas of abyssal sea floor in the Pacific Ocean. While deep sea mining is expected to realize significant quantities of rare metals that are needed for modern technology, the mining operation will cause extensive resedimentation over large areas of deep sea floor, the effects of which are thought to be harmful to the benthic community. Our present knowledge of deep sea benthic ecology is so limited that we cannot predict the magnitude of the impact. In November 1994, the United Nations Convention on the Law of the Sea was enforced and giving added impetus to improving our understanding of the effects of future mining operations. In order to fully understand the impact of deep sea mining and to mitigate the harmful environmental effects, it is necessary to accumulate more information on the deep sea environment and benthic communities. To achieve these objectives and to understand the relationship between resedimentation and biological reaction, artificial impact experiments are being conducted by the USA and Germany. The former named BIE (Benthic Impact Experiment) began in 1991 and is being performed by NOAA (National Oceanic and Atmospheric Administration of the United State of America) in the North Equatorial Pacific Ocean. The latter named DISCOL (Disturbance and Recolonization Experiment in the Deep South Pacific Ocean) was started in 1989 and is being conducted in the South Equatorial Pacific Ocean by a scientific group from Hamburg University. The Metal Mining Agency of Japan (MMAJ) is also carrying out environmental studies. These studies, commenced in 1989, are being conducted in association with NOAA and include an experiment named the Japan Deep Sea Impact Experiment (JET).

Jan 1, 1996

By Rahul Sharma

Although, mining of minerals such as polymetallic nodules and sulphides from the deep sea floor has been delayed due to the combination of factors such as current availability of Cu, Ni, Co, Mn (and other metals) on land and their fluctuating prices; these deposits are still considered as the alternative source for metals in the 21st century. Exclusive rights for exploration in the ?Area? (beyond the national jurisdictions of any country) given to eight countries and consortia by the International Seabed Authority and the estimated resource of 300 million tonnes in a typical area of 75,000 km2 is expected to yield about $17.5 billion (at December 2008 metal prices) in 20 years life span of a single nodule mine-site. In order to recover 3 million tonnes of nodules, an area of 300 sq km only will be mined annually (i.e. <1 km2/day) for an optimum abundance of 10 kg/m2. However, during mining, large quantity (22 tonnes/day) of sediments associated with nodules would be resuspended that could lead to certain environmental impacts on the benthic ecosystem. Several small-scale benthic impact experiments in the Pacific and Indian Oceans, have given some insight into the possible environmental impacts and the restoration processes, but the possibility of extrapolating these findings to a commercial mining scale remains an issue to be considered. An estimated capital expenditure of $1.05 billion and operating expenditure of $4.2 billion for a single deep-sea mining venture will have to be weighed against the availability of mineral ores on land as well as the metal prices in the world market. None-the-less, development of technologies for mining and metallurgical processing, as well as formulation of regulations and guidelines for potential ?contractors? to mine these minerals have been progressing consistently. These coupled with recent efforts by certain ?entrepreneurs? to initiate mining of seafloor massive sulphides in the EEZ of certain countries, indicate the continuing interest and support the perception that such deposits could well be the future sources of metals. This paper analyzes the current status and discusses the economic, environmental, and technical issues that need to be addressed for sustainable development of deep-sea minerals.

Jan 1, 2010

Although Mn, Fe, Cu, Ni, and Co have been the main interests since the ferromanganese nodules had been found, the other major components such as Si and Ca might be very important controlling factors in the processing due to the locally variable content. It is because of the fact that SiO2 and CaO are added to decrease the smelting temperature in the reduction-smelting method for manganese nodule processing. We have compiled the 707 chemical data for KODOS (Korea Deep Ocean Survey) ferromanganese nodules, which have been acquired from 1994 to 2001 and have been also standardized from 2001 to 2003 to avoid the discrepancy between the data sets. All 707 chemical data were used for the hierarchical cluster analysis to get the elemental correlations and also classified by the morphological types. The averages from each station were classified by the facies groups (Fig. 1) and the localities. Then all data are plotted on the SiO2-CaO-MnO phase diagram at 1773°K to compare with the best compositional area in the nodule smelting. Variations and distributions of SiO2 and CaO as well as those of Mn, Fe, Cu, Ni and Co in KODOS ferromanganese nodules were also reviewed. The mineral phases assigned by the cluster analysis are CFA (Carbonate Fluorapatite), Fe-oxide, Al-silicate, and Mn-oxide. MnO contents are generally higher than SiO2 contents in most of the morphological types except for the Is- and It-type. The Dt- and Tt-type show wider range and the E-types show high anomaly in their CaO contents. The stations which belong to facies group A and B show generally higher MnO contents than SiO2 contents, however, the stations of facies group C and D show wide range in their MnO and SiO2 contents.

Jan 1, 2004

By S. Rajendran

The area of the Exclusive Economic Zone (EEZ) of India is about 2.014 million km2 and the resource evaluation of placer deposits is one of the objectives of Government of India. Placers are detrital metallic minerals found on beaches and in the near shore areas. Quantitatively more important are placer deposits of light heavy minerals such as zircon, ilmenite and rutile. Rivers and other drainage channels are the main carriers of the placers which contain heavy minerals like magnetite, ilmenite, garnet, zircon, monazite, rutile etc. The present beach as well as part of the shelf was land during Pleistocene as a result of the world wide lowering of the sea levels. The coast line shifted a number of times. Hence, the heavy mineral placers on the beaches are expected to extend to offshore areas chiefly with Pleistocene lowered sea level strands. India has extensive deposits of heavy mineral placers along the beaches. Placer deposits of heavy minerals occur in discontinuous patches on the beaches along many parts of the east and west coasts. Along the central west coast of India (12??N - 19? N lat.) the placer containing 14 - 17% ilmenite form an estimated reserve of 4 million tons. On the Ratnagiri coast of Maharashtra, the proportion of heavy mineral varies between 54 and 70% in the bulk samples, consisting mainly of 14 - 39% magnetite and 16 - 30% ilmenite. The National Institute of Oceanography (NIO) surveys show that the sediments off the central west coast consist largely of silty sand, sand silt and clay. The core samples show that a reddish brown clay overlay olive gray clay which in turn overlay heavy mineral rich sands. The heavy mineral concentration ranges upto 90% and has mainly ilmenite and magnetite with minor quantities of apatite, rutile, zircon, kyanite etc. Siddiquie et al. reported 42 - 75% TiO2 in the ilmenite.

Jan 1, 1998

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 Roger Amato

The 1982 United Nations Convention on the Low of the Sea includes provisions under Article 76 for extending a coastal State&apos;s jurisdiction beyond the 200-nautical-mile (nm) Exclusive Economic Zone (EEZ) and for establishing the seaward limits of sovereign rights over natural resources. Article 76 prescribes a set of methodologies for determining these outer limits based on physiography and sediment thickness. The methodologies were applied to each of the five continental* margin areas of the United States - Atlantic, Pacific, Gulf of Mexico, Alaska, and Pacific Islands-using existing digital hydrographic and geologic data. Figures 1 and 2 show the results of applying the methodologies to the Atlantic, Pacific, Alaskan, and Gulf of Mexico continental shelves. Figure 1 depicts the preliminary limits of each of the Article 76 determinations for the Atlantic and Gulf of Mexico continental shelves. The Atlantic limits were described by Carpenter, Thormahlen, and Amato (1995) at the 26th Underwater Mining Institute.1 The limits for the Alaskan continental shelves are shown in Figure 2. Additional areas beyond the 200 nm EEZ are highlighted. These include a small area north of the U.S. - Canada boundary, containing 7,000 km2, a large area north of Point barrow (395,000 km2), and a third area north of the Aleutian Islands (178,000 km2). The shelf between the first two areas appears to have sediments thick enough to qualify for the 1 percent method (Irish Formula); however, year-round ice cover has prevented acquisition of seismic or drill data. The entire northern Alaska shelf is prospective for petroleum The Gulf of Mexico (Figure 1) has two small areas beyond the EEZ known as "doughnut holes." One is south of Louisiana and includes part of the Sigsbee Escarpment, an area believed to have potential for oil and gas. Oil was found on Sigsbee Knoll in cores from Deep Sea Drilling Project&apos;s Leg 1 cruise in 1968. The Sigsbee areas contains about 6,000 km2. The second area is south of the Florida panhandle and contains about 12,000 km2.

Jan 1, 1996