Seafloor Massive Sulfide Deposits
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Seafloor massive sulfide deposits or SMS deposits, are modern equivalents of ancient volcanogenic massive sulfide ore deposits or VMS deposits. The term has been coined by mineral explorers to differentiate the modern deposit from the ancient. SMS deposits were first recognized during the exploration of the deep oceans and the mid ocean ridge spreading centers in the early 1960s. Deep ocean research
submersible A submersible is an underwater vehicle which needs to be transported and supported by a larger ship, watercraft or dock, platform. This distinguishes submersibles from submarines, which are self-supporting and capable of prolonged independent ope ...
s, bathyspheres and remote operated vehicles have visited and taken samples of black smoker chimneys, and it has been long recognised that such chimneys contain appreciable grades of Cu, Pb, Zn, Ag, Au and other trace metals. SMS deposits form in the deep ocean around submarine volcanic arcs, where hydrothermal vents exhale sulfide-rich mineralising fluids into the ocean. SMS deposits are laterally extensive and consist of a central vent mound around the area where the hydrothermal circulation exits, with a wide apron of unconsolidated sulfide silt or ooze which precipitates upon the seafloor. Beginning about 2008, technologies were being developed for deepsea mining of these deposits.


Minerals

Mineralization in submarine magmatic-hydrothermal systems is a product of the chemical and thermal exchange between the ocean, the
lithosphere A lithosphere () is the rigid, outermost rocky shell of a terrestrial planet or natural satellite. On Earth, it is composed of the crust and the lithospheric mantle, the topmost portion of the upper mantle that behaves elastically on time ...
, and the magmas emplaced within it. Different mineral associations precipitate during the typical stages of mineralization that characterize the life span of such systems. Minerals present in a hydrothermal system or a fossil volcanogenic massive sulfide deposit are deposited passively or reactively. Mineral associations may vary (1) in different mineralized structures, either syngenetic (namely, passive precipitation in chimneys, mounds and stratiform deposits) or epigenetic (structures that correspond to feeder channels, and replacements of host rocks or pre-existing massive sulfide bodies), or ''structural zonation'', (2) from proximal to distal associations with respect to venting areas within the same ''stratigraphic horizon'', or horizontal zonation, (3) from deep to shallow associations (''i.e.'', stockworks to mounds), or ''vertical zonation'', (4) from early and climactic to late stages of mineralization (dominated by sulfides, and sulfates or oxides, respectively), or ''temporal zonation'', and (5) in various volcano sedimentary contexts, depending essentially on the composition of volcanic rocks and, ultimately, on the tectonomagmatic context. The most common minerals in ore-bearing associations of volcanogenic massive sulfide deposits (non-metamorphosed or oxidized) and their modern analogues are pyrite,
pyrrhotite Pyrrhotite (''Pyrrhus of Epirus, pyrrhos'' in Greek language, Greek meaning "flame-coloured"'')'' is an iron sulfide mineral with the formula Fe(1−x)S (x = 0 to 0.125). It is a nonstoichiometric compound, nonstoichiometric variant of FeS, th ...
,
chalcopyrite Chalcopyrite ( ) is a copper iron sulfide mineral and the most abundant copper ore mineral. It has the chemical formula CuFeS2 and crystallizes in the tetragonal system. It has a brassy to golden yellow color and a Mohs scale, hardness of 3.5 to 4 ...
, covellite,
sphalerite Sphalerite is a sulfide mineral with the chemical formula . It is the most important ore of zinc. Sphalerite is found in a variety of deposit types, but it is primarily in Sedimentary exhalative deposits, sedimentary exhalative, Carbonate-hoste ...
, galena, tetrahedrite- tennantite, marcasite, realgar,
orpiment Orpiment, also known as ″yellow arsenic blende″ is a deep-colored, orange-yellow arsenic sulfide mineral with formula . It is found in volcanic fumaroles, low-temperature hydrothermal veins, and hot springs and may be formed through sublimatio ...
, proustite- pyrargyrite,
wurtzite Wurtzite is a zinc and iron sulfide mineral with the chemical formula , a less frequently encountered Polymorphism (materials science), structural polymorph form of sphalerite. The iron content is variable up to eight percent.Palache, Charles, H ...
, stannite ( sulfides), Mn oxides, cassiterite,
magnetite Magnetite is a mineral and one of the main iron ores, with the chemical formula . It is one of the iron oxide, oxides of iron, and is ferrimagnetism, ferrimagnetic; it is attracted to a magnet and can be magnetization, magnetized to become a ...
,
hematite Hematite (), also spelled as haematite, is a common iron oxide compound with the formula, Fe2O3 and is widely found in rocks and soils. Hematite crystals belong to the rhombohedral lattice system which is designated the alpha polymorph of . ...
( oxides), barite, anhydrite (
sulfates The sulfate or sulphate ion is a Polyatomic ion, polyatomic anion with the empirical formula . Salts, acid derivatives, and peroxides of sulfate are widely used in industry. Sulfates occur widely in everyday life. Sulfates are salt (chemistry), ...
),
calcite Calcite is a Carbonate minerals, carbonate mineral and the most stable Polymorphism (materials science), polymorph of calcium carbonate (CaCO3). It is a very common mineral, particularly as a component of limestone. Calcite defines hardness 3 on ...
, siderite ( carbonates)
quartz Quartz is a hard, crystalline mineral composed of silica (silicon dioxide). The Atom, atoms are linked in a continuous framework of SiO4 silicon–oxygen Tetrahedral molecular geometry, tetrahedra, with each oxygen being shared between two tet ...
and native gold, and are differently distributed in the various associations schematized above. The most common hydrothermal alteration assemblages are chloritic (including Mg-rich ones) and phyllic alteration (dominated by “
sericite Sericite is the name given to very fine, ragged grains and Aggregate (geology), aggregates of white (colourless) micas, typically made of muscovite, illite, or paragonite. Sericite is produced by the alteration of orthoclase or plagioclase feldsp ...
”, mostly illite), and also silicification, deep and shallow talcose alteration, and ferruginous (including Fe oxides, carbonates and sulfides) alteration.


Economic importance

Economic extraction of SMS deposits is in the theoretical stage, the greatest complication being the extreme water depths at which these deposits are forming. However, apparent vast areas of the peripheral areas of these black smoker zones contain a sulfide ooze which could, theoretically, be vacuumed up off the seafloor. Nautilus Minerals Inc. (Nautilus) was engaged in commercially exploring the ocean floor for copper, gold, silver and zinc seafloor massive sulfide (SMS) deposits, and mineral extraction from an SMS system. Nautilus' Solwara 1 Project located at 1,600 metres water depth in the Bismarck Sea,
Papua New Guinea Papua New Guinea, officially the Independent State of Papua New Guinea, is an island country in Oceania that comprises the eastern half of the island of New Guinea and offshore islands in Melanesia, a region of the southwestern Pacific Ocean n ...
, was an attempt at the world's first deep-sea mining project, with first production originally expected in 2017. However, the company went bankrupt in 2019 after failing to secure funding for the project.


Known SMS deposits

Deep ocean drilling, seismic bathymetry surveys and mineral exploration deep sea drilling has delineated several areas worldwide with potentially economically viable SMS deposits, including: *
Lau Basin The Lau Basin is a back-arc basin (also addressed as "interarc basin") at the Australian-Pacific plate boundary. It is formed by the Pacific plate subducting under the Australian plate. The Tonga-Kermadec Ridge, a frontal arc, and the Lau-Colvill ...
** Kermadec Volcanic Arc ** Colville Ridge * Bismarck Sea * Okinawa Trough * North Fiji Basin (see d'Entrecasteaux Ridge) *
Red Sea The Red Sea is a sea inlet of the Indian Ocean, lying between Africa and Asia. Its connection to the ocean is in the south, through the Bab-el-Mandeb Strait and the Gulf of Aden. To its north lie the Sinai Peninsula, the Gulf of Aqaba, and th ...


See also

* Hydrothermal circulation * Mid ocean ridge * Ore genesis * RISE project


References

{{reflist


External links


''The dawn of deep ocean mining'', Steven Scott, Feb. 2006
* Bertram C., A. Krätschell, K. O'Brien, W. Brückmann, A. Proelss, K. Rehdanz (2011). Metalliferous sediments in the Atlantis II deep -Assessing the geological and economic resource potential and legal constraints. Resources Policy 36(2011), 315–329. Economic geology Oceanography Sedimentary rocks