Burke, Oxford Univ. Press, Oxford Monographs on Geology and Geophysics, v. M, and Dalziel, I. Schuur, C. Viele, G. Wiens, D. Frohlich, C. B4, p. Mueller, R. Divenere, V. Storey, E. King and R. Livermore eds. Klepeis, K. B9, pp.
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PDF Coffin, M. Such masses, which can be a few kilometres in diameter, may bring salt to or near the surface. They can also form structures in the intruded sedimentary strata that are favourable for the accumulation of hydrocarbons. Figure 1 shows the present day occurrence of marine anhydrite, potash and magnesium evaporite deposits. Although evaporite deposits formed in ancient marine basins are extensive on land, many of these also extend beneath the sea, not only under the continental shelves but also under some marginal ocean basins.
Although falling within the range of EEZ, very few of these known areas of anhydrite, potash and magnesium evaporite deposits extend into the ELCS. Possible exceptions to this may be the Grand Banks and Newfoundland deposits, west Africa and north-western Australian deposits. However, very little data exist on the abundance or concentration of these deposits. Because of the widespread occurrence of anhydrite, gypsum and common salt on land, and the ease of obtaining salt by evaporation from seawater in many coastal regions, these minerals are already widely available.
Consequently, there is little value in marine deposits except perhaps in areas far removed from other supplies. To our knowledge, no attempt has been reported to quantitatively estimate potential marine resources of evaporitic salt and anhydrite deposits, but they probably amount to at least tens of trillions of tonnes Warren, Potash deposits in evaporite basins are not as widespread as salt and gypsum, but individual deposits are generally in the range of hundreds of millions to billions of tonnes.
References: South American Database
Potash resources in marine deposits are probably in the range of tens of billions of tonnes, some of which maybe economically recoverable. Thick beds of a magnesium salt and tachydrite calcium-magnesium hydrate , previously known only in trace concentrations, occur in areas associated with potash deposits in the Sergipe salt basin along the eastern coast of Brazil and in the Congo basin along the mid-southwestern coast of Africa.
Some massive polymetallic sulphides located on spreading centres near deep-ocean trenches also contain galena lead sulphide and native gold. Polymetallic mineral deposits on the seafloor are intimately related to the formation of new oceanic crust by seafloor spreading and volcanic activity. Hydrothermal fluids leach and transport metals and other elements at depth from their volcanic host rock to the surface of the seafloor. Lower temperature systems are also present and generate mineralisation of considerable economic potential.
Submarine massive polymetallic sulphide bodies are principally found along the earth's major tectonic boundaries. High-temperature hydrothermal activity and large accumulations of polymetallic sulphides are located from at least 25 different sites world wide Fig. Plate tectonic setting has an important influence on the composition of PMS deposits. For example, back-arc basins related to subduction zones are important sites for base-metal and gold mineralisation. The shallow depths less than 1, m and high gold content make such sites potentially viable for mining.
Very little is known about the total metal content of marine PMS deposits and their sub-surface extent. Because of their depth greater than 2, m and remote locations from shore, it is unlikely that seafloor PMS deposits, such as those located in international waters on the mid-ocean ridges e. However, massive sulphide mining may have some economic viability in the near future where there are high gold and base-metal grades at sites that are located close to land and in water depths less than 2, m Broadus, Figure 2 shows the locations of known hydrothermal activity, PMS deposits and their geologic setting, and can be used to identify those areas where conditions for recovery may become viable.
Although none of these areas currently lie within any potential ELCS, even for those that are already known, the logistical difficulty for their recovery make them all currently uneconomic. Marine manganese nodules and crusts Traditionally, manganese nodules have provided a source for much speculation about economically viable mineral resources in the deep ocean. Their abundance, composition, including strategically valuable metals and their occurrence as loose material lying on the surface of the seabed make nodules potentially attractive to future mining. The currently known distribution of manganese nodules and crusts on the ocean floor is based on information acquired by sidescan sonar, drill cores, dredged samples, seafloor photos, video camera records and direct observation from submersibles.
These data form the basis of the analysis of this resource assessed here. Manganese nodules are concentrations of iron and manganese oxides, that can contain economically valuable concentrations of nickel, copper and cobalt together, making up to 3 wt. They range from millimetres to tens of centimetres in diameter and occur mainly on the deep-seafloor.
Apart from manganese and iron oxide, nickel, copper and cobalt, the nodules include trace amounts of molybdenum, platinum and other base metals Cronan, ; Manheim, Additionally, manganese rich crusts, similar in composition to the nodules, occur on rocky outcrops and in places on unconsolidated clastic sediments. They are most common on old seamounts and the submerged flanks of ocean islands where they can be enriched by up to two per cent in cobalt Halbach et al. The major mineral phases of iron and manganese oxides control the uptake and retention in the nodules of minor elements such as nickel, copper, cobalt, molybdenum and rare earth elements Cronan, Of the large number of complex hydrous manganese oxide mineral phases identified, todorokite and birnessite are the most common.
In addition, nodules and crusts contain a variety of non-metallic minerals, amorphous material and biological debris that may comprise up to 25 wt. These include clay minerals, quartz, feldspar and chlorite, mostly of detrital origin along with varied proportions of silica gels, chalcedony, calcareous and phosphatic components. Trace elements of greatest economic interest are nickel, copper, and cobalt table 1. The amounts and proportions of constituents vary considerably within single nodules, between nodules of different sizes, and between nodules from different regions and ocean basins Calvert, ; Hayes et al.
The composition of manganese crusts varies from 15 to 31 wt. Crusts can also contain significant amounts of nickel, lead, cerium, molybdenum, vanadium and other minor metals including those of the platinum group elements Manheim, The composition of manganese nodules and crusts also varies according to the different environment settings table 2.
Although nodules form at a rate of up to a few tens of millimetres per million years Ku,; Cronan, ; Calvert, , the most extensive nodule fields tend to occur on oceanic crust that is Mesozoic or younger in age. They are found mainly below the carbonate compensation depth in areas with low clastic sedimentation and with high biological productivity in overlying surface waters Cronan, , The metals contained in nodules and crusts are attributed to discharge of hydrothermal solutions along active plate boundaries, leaching of metals from the bottom sediments and volcanic rocks during diagenesis and the deposition of metal-rich clastic or colloidal sediment from continental erosion Greenslate, et al.
Figure 3 shows the distribution and density of all known manganese nodules and crusts for which quantitative chemical analyses are reported and where estimates of their abundance have been mapped. These data have been compiled from sites where dredges, cores, submersibles and bottom photographs have been taken. Therefore, the analyses presented here are only preliminary and should not be taken as anything other than a guide to this resource. Figures 4 to 7 show the abundance of the four elements that are of greatest economic importance in these deposits: manganese, copper, nickel and cobalt.
Cobalt is an especially important metal for which marine manganese nodules and crusts comprise a significant host.
SDMPlay/Environmental_data__A1B_description.R at master · cran/SDMPlay · GitHub
According to Clark et al. Cobalt-rich manganese-iron crusts cover thousands of square kilometres in the Atlantic Ocean and are found on the Blake Plateau, Sierra Leone Rise, and the east flank of the Mid-Atlantic Ridge. Here crusts have cobalt contents of up to 1 wt. Manheim reports a mean cobalt content of 0. The average metal content in crust samples from the Hawaiian Archipelago and Johnston-Palmyra Region in the Pacific is: 0.
Here, abundant nodules have a up to 30 wt. They have a combined content of nickel and copper of up to 3. These contain elemental concentration up to 20 wt. The elemental density on the seafloor range up to 1. These contain elemental concentrations and densities on the seafloor of up to 10 wt. The combined nickel and copper concentration is up to 2 wt. However, occurrences are infrequent throughout much of the area.
Manganese nodules, with up to 2 wt. However, their metal content appears to be generally low with combined copper and nickel of only 2 wt. Here combined copper and nickel contents comprise wt. Nodules are sparsely and irregularly distributed through broad areas of the Atlantic.
Probably the most economically interesting concentrations are found on the Blake Plateau, in shallow water to the east of Florida. In the Mediterranean Sea, nodules off the west coast of Italy are of special interest for similar reasons. Although the mineralogy, composition and origin of manganese nodules are relatively well known, assessments of their resource potential are not well documented.
Potential resource estimates for copper, nickel and cobalt in nodules were made during the s and s and are summarised in Volume I of the United Nations Seabed Mineral Series. The abundance of nodules however, remains a major source of uncertainty and any global estimates must be subject to non-definable degree of error.
While accepting the uncertainties and limitations of past and present resource estimates, using the methods described here it is possible to broadly estimate the resources held by manganese nodules and crusts within potential ELCS regions Table 3. Elemental resources for these ten countries range from: million tonnes of manganese for Antarctica to Even for those countries with the lowest abundance of nodules and crusts present in their ELCS, the elemental resources range from: 2.
At the scale of this global study, it is not possible to determine specifically where resources contained in nodules and crusts occur at grades above or below economically viable cut-off limits e. However, it is possible to rank countries according to the average grade of manganese nodules and crusts in their ELCS.
These areas, on average, are characterised by higher grades and may in future have locations favourable for manganese nodule and crust recovery. Marine hydrocarbon deposits Generally, large quantities of hydrocarbons can be formed only at depths within sedimentary sequences greater than 1, - 2, meters.
Formation of exploitable reservoirs of hydrocarbons requires migration from their source rocks to geological traps comprising a porous reservoir rocks and overlain by an impermeable horizon. Common geological traps for hydrocarbons include: shales, salt domes evaporites , and anticlinal folds of permeable and non-permable strata.
In addition to liquid hydrocarbons, natural gas is also common. Sedimentary sequences in excess of 1, m thick in areas of high-heat flow, comprising organic-rich layers overlain by porous rocks that are in turn overlain by domed impermeable strata provide ideal environments for hydrocarbon formation and retention. The estimated reserves of oil world wide at the beginning of the 21st Century are about one trillion barrels.
Similarly, the total world wide resources of natural gas are estimated at about 4, trillion cubic feet, of which about 26 percent are marine.
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However, offshore hydrocarbon resources may be ten times larger, in which case they are likely to provide the majority of future hydrocarbon production IEA, Figure 8 summarises the major offshore oil and gas provinces of the world Klett et al. These reserves of oil and gas are located almost exclusively on the continental shelves and are characterised by sedimentary sequences greater than 1, m in thickness.
Of the twenty-five largest offshore production fields, eight are in the Persian Gulf and eight others are in the North Sea. In the future, offshore oil supply growth is expected to occur increasingly from areas outside the North Sea and the Persian Gulf. By , five fields, two off Brazil and one each in West African waters, the Gulf of Mexico and the Norwegian Sea, are expected to move into the top 25 producers, with several other potential major producers off West Africa and in the deep-water Gulf of Mexico approaching similar production levels IEA, A qualitative indication of resource potential, and hence a relative ranking of ELCS regions and their coastal states, can be made by comparing the known reserve province against the location of those countries with significant sedimentary sequence thickness Klett et al.
This shows the continental shelf and rise contains the largest accumulations of sediment often in excess of 10 km , that also have a high probably to include organic-rich source rocks deposited when the proto-ocean basins were narrow and had restricted circulation Rona, ; Schneider, The abyssal plains probably contain insufficient thickness of sediments less than 1 km to yield hydrocarbon accumulations. Kornicker, Editor Merrill W.
American Geophysical Union Washington, D. Elliot, Chairman John B. Anderson, Steve Cairns, Samuel C. Colbeck, Rodney M. Feldmann, E. Imre Friedmann, Dennis E. Hayes, Charles R. Stilwell, William J. Zinsmeister, authors. ISBN 1. Paleontology, Stratigraphic. Paleontology- -Tertiary. La Meseta Formation Antarctic regions I. Stilwell, Jeffrey D. Zinsmeister, William J. M75 '. Washington, DC Figures, tables, and short excerpts may be reprinted in scientific books and journals if the source is properly cited.
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