Hydrothermal circulation

Hydrothermal circulation in its most general sense is the circulation of hot water (Ancient Greek ὕδωρ, water,[1] and θέρμη, heat [1]). Hydrothermal circulation occurs most often in the vicinity of sources of heat within the Earth's crust. In general, this occurs near volcanic activity, but can occur in the deep crust related to the intrusion of granite, or as the result of orogeny or metamorphism.

Seafloor hydrothermal circulation

Hydrothermal circulation in the oceans is the passage of the water through mid-oceanic ridge systems.

The term includes both the circulation of the well-known, high-temperature vent waters near the ridge crests, and the much-lower-temperature, diffuse flow of water through sediments and buried basalts further from the ridge crests. The former circulation type is sometimes termed "active", and the latter "passive". In both cases, the principle is the same: Cold, dense seawater sinks into the basalt of the seafloor and is heated at depth whereupon it rises back to the rock-ocean water interface due to its lesser density. The heat source for the active vents is the newly formed basalt, and, for the highest temperature vents, the underlying magma chamber. The heat source for the passive vents is the still-cooling older basalts. Heat flow studies of the seafloor suggest that basalts within the oceanic crust take millions of years to completely cool as they continue to support passive hydrothermal circulation systems.

Hydrothermal vents are locations on the seafloor where hydrothermal fluids mix into the overlying ocean. Perhaps the best-known vent forms are the naturally occurring chimneys referred to as black smokers.

Volcanic and magma related hydrothermal circulation

Hydrothermal circulation is not limited to ocean ridge environments. The source water for hydrothermal explosions, geysers, and hot springs is heated groundwater convecting below and lateral to the hot water vent. Hydrothermal circulating convection cells exist any place an anomalous source of heat, such as an intruding magma or volcanic vent, comes into contact with the groundwater system.

Deep crust

Hydrothermal also refers to the transport and circulation of water within the deep crust, in general from areas of hot rocks to areas of cooler rocks. The causes for this convection can be:

  • Intrusion of magma into the crust
  • Radioactive heat generated by cooled masses of granite
  • Heat from the mantle
  • Hydraulic head from mountain ranges, for example, the Great Artesian Basin
  • Dewatering of metamorphic rocks, which liberates water
  • Dewatering of deeply buried sediments

Hydrothermal circulation, in particular in the deep crust, is a primary cause of mineral deposit formation and a cornerstone of most theories on ore genesis.

Hydrothermal ore deposits

During the early 1900s, various geologists worked to classify hydrothermal ore deposits that they assumed formed from upward-flowing aqueous solutions. Waldemar Lindgren (1860–1939) developed a classification based on interpreted decreasing temperature and pressure conditions of the depositing fluid. His terms: "hypothermal", "mesothermal", "epithermal" and "teleothermal", expressed decreasing temperature and increasing distance from a deep source.[2] Recent studies retain only the epithermal label. John Guilbert's 1985 revision of Lindgren's system for hydrothermal deposits includes the following:[3]

See also

References

  1. ^ a b Liddell, H.G. & Scott, R. (1940). A Greek-English Lexicon. revised and augmented throughout by Sir Henry Stuart Jones. with the assistance of. Roderick McKenzie. Oxford: Clarendon Press.
  2. ^ W. Lindgren, 1933, Mineral Deposits, McGraw Hill, 4th ed.
  3. ^ Guilbert, John M. and Charles F. Park, Jr., 1986, The Geology of Ore Deposits, Freeman, p. 302 ISBN 0-7167-1456-6
Auki (crater)

Auki is an impact crater in the Mare Tyrrhenum quadrangle of Mars, at 15.76 °S latitude and 263.13 °W longitude. It is 40.0 km in diameter and was named after Auki, a town in the Solomon Islands, in 2015 by the International Astronomical Union (IAU) Working Group for Planetary System Nomenclature (WGPSN).Auki Crater has a central peak. Impact craters generally have a rim with ejecta around them, in contrast volcanic craters usually do not have a rim or ejecta deposits. As craters get larger (greater than 10 km in diameter) they usually have a central peak. The peak is caused by a rebound of the crater floor following the impact.Strong evidence for hydrothermalism was reported by a team of researchers studying Auki. This crater contains ridges that may have been produced after fractures formed with an impact. Using instruments on the Mars Reconnaissance Orbiter they found the minerals smectite, silica, zeolite, serpentine, carbonate, and chorite that are common in impact-induced hydrothermal systems on Earth. Other evidence of post-impact hydrothermal systems on Mars from other scientists who studied other Martian craters.Impacts fracture rocks and create a great deal of heat that may last for many thousands of years.

This heat can result in new minerals from hydrothermal circulation. On Earth impact craters have resulted in useful minerals. Some of the ores produced from impact related effects on Earth include ores of iron, uranium, gold, copper, and nickel. It is estimated that the value of materials mined from impact structures is 5 billion dollars/year just for North America. While nothing may be found on Mars that would justify the high cost of transport to Earth, the more necessary ores future colonists can obtain from Mars, the easier it would be to build colonies on the Red Planet.

Breccia pipe

A breccia pipe, also referred to as a chimney, is a mass of breccia (rock composed of broken fragments of minerals or rock cemented together by a fine-grained matrix), often in an irregular and cylindrical shape.

Carlin–type gold deposit

Carlin–type gold deposits are sediment-hosted disseminated gold deposits. These deposits are characterized by invisible (typically microscopic and/or dissolved) gold in pyrite and arsenopyrite. This dissolved kind of gold is called "Invisible Gold", as it can only be found through chemical analysis. The deposit is named after the Carlin mine, the first large deposit of this type discovered in the Carlin Trend, Nevada.

Chalcopyrite

Chalcopyrite ( KAL-ko-PY-ryt) is a copper iron sulfide mineral that crystallizes in the tetragonal system. It has the chemical formula CuFeS2. It has a brassy to golden yellow color and a hardness of 3.5 to 4 on the Mohs scale. Its streak is diagnostic as green tinged black.

On exposure to air, chalcopyrite oxidises to a variety of oxides, hydroxides and sulfates. Associated copper minerals include the sulfides bornite (Cu5FeS4), chalcocite (Cu2S), covellite (CuS), digenite (Cu9S5); carbonates such as malachite and azurite, and rarely oxides such as cuprite (Cu2O). Chalcopyrite is rarely found in association with native copper.

FEHM

FEHM is a groundwater model that has been developed in the Earth and Environmental Sciences Division at Los Alamos National Laboratory over the past 30 years. The executable is available free at the FEHM Website. The capabilities of the code have expanded over the years to include multiphase flow of heat and mass with air, water, and CO2, methane hydrate, plus multi-component reactive chemistry and both thermal and mechanical stress. Applications of this code include simulations of: flow and transport in basin scale groundwater systems

, migration of environmental isotopes in the vadose zone, geologic carbon sequestration, oil shale extraction, geothermal energy, migration of both nuclear and chemical contaminants, methane hydrate formation, seafloor hydrothermal circulation, and formation of karst. The simulator has been used to generate results for more than 100 peer reviewed publications which can be found at FEHM Publications.

Fluid inclusion

A fluid inclusion is a microscopic bubble of liquid and gas that is trapped within a crystal. As minerals often form from a liquid or aqueous medium, tiny blebs of that liquid can become trapped within the crystal, or along healed crystal fractures. These small inclusions range in size from 0.1 to 1 mm and are usually only visible in detail by microscopic study.

These inclusions occur in a wide variety of environments. For example, they are found within cementing minerals of sedimentary rocks, in gangue minerals such as quartz or calcite in hydrothermal circulation deposits, in fossil amber, and in deep ice cores from the Greenland and Antarctic ice caps. The inclusions can provide information about the conditions existing during the formation of the enclosing mineral.

Hydrothermal ore minerals typically form from high temperature aqueous solutions. The trapped fluid in an inclusion preserves a record of the composition, temperature and pressure of the mineralizing environment. An inclusion often contains two or more phases. If a vapor bubble is present in the inclusion along with a liquid phase, simple heating of the inclusion to the point of resorption of the vapor bubble gives a likely temperature of the original fluid. If minute crystals are present in the inclusion, such as halite, sylvite, hematite, or sulfides are present, they provide direct clues as to the composition of the original fluid.

In the recent years, fluid inclusion research has been extensively applied to understand the role of fluids in the deep crust and crust-mantle interface. Fluid inclusions trapped within granulite facies rocks have provided important clues on the petrogenesis of dry granulite facies rocks through the influx of CO2-rich fluids from sub-lithospheric sources. CO2-rich fluid inclusions were also recorded from a number of ultrahigh-temperature granulite facies terranes suggesting the involvement of CO2 in extreme crustal metamorphism. Some recent studies speculate that CO2 derived by sub-solidus decarbonation reactions during extreme metamorphism has contributed to the deglaciation of the snowball Earth (Santosh and Omori, 2008).

Fourier transform infrared spectroscopy can be used to determine the composition of fluid inclusions.

Huygens (crater)

Huygens is an impact crater on Mars named in honour of the Dutch astronomer, mathematician and physicist Christiaan Huygens.

The crater is approximately 467.25 km (290.34 mi) in diameter and can be found at 304.42°W 13.88°S, in the Iapygia quadrangle.

Scientists were delighted to see branched channels in pictures taken with spacecraft that were sent in orbit around Mars. The existence of these channels is strong evidence that much water once flowed on the surface of the planet. Simple organisms may have once lived where water once was. An excellent group of these channels is shown in the picture below from the rim of Huygens taken with THEMIS.

Carbonates (calcium or iron carbonates) were discovered in a crater on the rim of Huygens. The impact on the rim exposed material that had been dug up from the impact that created Huygens. These minerals represent evidence that Mars once had a thicker carbon dioxide atmosphere with abundant moisture. Carbonates of these kinds only form when there is a lot of water. They were found with the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) instrument on the Mars Reconnaissance Orbiter. Earlier, the instrument had detected clay minerals. The carbonates were found near the clay minerals. Both of these minerals form in wet environments. It is supposed that billions of years ago Mars was much warmer and wetter. At that time, carbonates would have formed from water and the carbon dioxide-rich atmosphere. Later the deposits of carbonate would have been buried. The double impact has now exposed the minerals. Earth has vast carbonate deposits in the form of limestone.

Mineral hydration

Mineral hydration is an inorganic chemical reaction where water is added to the crystal structure of a mineral, usually creating a new mineral, usually called a hydrate.

In geological terms, the process of mineral hydration is known as retrograde alteration and is a process occurring in retrograde metamorphism. It commonly accompanies metasomatism and is often a feature of wall rock alteration around ore bodies. Hydration of minerals occurs generally in concert with hydrothermal circulation which may be driven by tectonic or igneous activity.

Moreux (crater)

Moreux is a crater in the Ismenius Lacus quadrangle on Mars with a diameter of 138 kilometers. It is located at 42.1° north latitude and 315.6° west longitude and was named by IAU's Working Group for Planetary System Nomenclature after Theophile Moreux, a French astronomer and meteorologist (1867–1954).

Rainbow Vent Field

The Rainbow hydrothermal vent field is a system of ultramafic-hosted hydrothermal vents located at 36°14'N on the Mid-Atlantic Ridge (MAR). It was discovered in 1994 from temperature readings of ten high-temperature black smokers at a depth of approximately 2.3 kilometres (1.4 mi), where fluids can exceed 365 °C (689 °F). The site is shallower and larger in area than many other vent fields along the Azores section of the MAR with an area of 1.5 square kilometres (370 acres). Located 370 km (229.91 mi) southeast of Faial Island, it is a popular geochemical sampling and modeling site due to close proximity to the Azores and definitive representation of serpentinization from hydrothermal circulation and synthesis.Vent geology, biology, and fluid content make Rainbow comparable to other hot hydrothermal vents of the Azores such as Lucky Strike and Menez Gwen. However; chlorinity, metal concentration, and pH distinguish it from neighboring vent fields. As a hot, ultramafic-hosted vent field, pH levels of fluids are extremely low with lots of H2 and CH4 generated from water interactions with mafic igneous rocks.

Though not actively considered for development, Rainbow lies within the MoMAR (Monitoring of the Mid Atlantic Ridge) survey area for a marine observatory.

San Cristóbal mine (Bolivia)

The San Cristobal mine in Lipez, Potosí Department, Bolivia is an open-pit silver, lead and zinc mine near the town of San Cristóbal, Potosí. The mine, operated by Sumitomo Corporation, produces approximately 1,300 metric tons of zinc-silver concentrate and 300 tons of lead-silver concentrate per day, as of August 2010, by processing 40,000 to 50,000 tons of rock. It is one of Bolivia's largest mining facilities and, according to Sumitomo, the world’s sixth-largest producer of zinc and third-largest producer of silver. It is located in southwestern Bolivia and hosts approximately 450 million ounces of silver and 8 billion pounds of zinc and 3 billion pounds of lead contained in 231 million tonnes of open-pittable proven and probable reserves. As the ore body is open both at depth and laterally, reserve expansion potential is considered excellent. The mine has been in various stages of development since the early 1980s but only recently came into full operation.

Schaeberle (Martian crater)

Schaeberle is a crater in the Iapygia quadrangle of Mars, located at 24.7° S and 309.9° W. It measures approximately 159 kilometers in diameter and was named after John Martin Schaeberle, an American astronomer (1853–1924).Impact craters generally have a rim with ejecta around them, in contrast volcanic craters usually do not have a rim or ejecta deposits. As craters get larger (greater than 10 km in diameter) they usually have a central peak. The peak is caused by a rebound of the crater floor following the impact.

Seafloor massive sulfide deposits

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 submersibles, 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.

Supercritical fluid

A supercritical fluid (SCF) is any substance at a temperature and pressure above its critical point, where distinct liquid and gas phases do not exist. It can effuse through solids like a gas, and dissolve materials like a liquid. In addition, close to the critical point, small changes in pressure or temperature result in large changes in density, allowing many properties of a supercritical fluid to be "fine-tuned".

Supercritical fluids occur in the atmospheres of the gas giants Jupiter and Saturn, and probably in those of the ice giants Uranus and Neptune. In a range of industrial and laboratory processes, they are used as a substitute for organic solvents. Carbon dioxide and water are the most commonly used supercritical fluids, being used for decaffeination and power generation, respectively.

Terby (crater)

Terby is a crater on the northern edge of Hellas Planitia, Mars. It is in the Iapygia quadrangle. The 174 km diameter crater is centered at 28°S, 73°E with an elevation of −5 km. It is named after François J. Terby. It is the site of an ancient lakebed and has clay deposits. Using data from Mars Global Surveyor, Mars Odyssey, Mars Express and Mars Reconnaissance Orbiter missions researchers believe Terby's layers were formed from sediments settling under water. Crater counts show this happened during the Noachian period. It used to be thought that Terby Crater contained a large delta. However, newer observations have led researchers to think of the layered sequence as part of a group of layers that may have extended all the across Hellas. There is no valley large enough at the northern rim of Terby to have carried the large amount of sediments necessary to produce the layers. Other details in the layers argue against Terby containing a delta. Fan deposits are some of the thickest on Mars. Hydrated minerals, including Fe/Mg phyllosilicates, have been detected in several layers.

Vein (geology)

In geology, a vein is a distinct sheetlike body of crystallized minerals within a rock. Veins form when mineral constituents carried by an aqueous solution within the rock mass are deposited through precipitation. The hydraulic flow involved is usually due to hydrothermal circulation.Veins are classically thought of as being the result of growth of crystals on the walls of planar fractures in rocks, with the crystal growth occurring normal to the walls of the cavity, and the crystal protruding into open space. This certainly is the method for the formation of some veins. However, it is rare in geology for significant open space to remain open in large volumes of rock, especially several kilometers below the surface. Thus, there are two main mechanisms considered likely for the formation of veins: open-space filling and crack-seal growth.

Volcanogenic massive sulfide ore deposit

Volcanogenic massive sulfide ore deposits, also known as VMS ore deposits, are a type of metal sulfide ore deposit, mainly copper-zinc which are associated with and created by volcanic-associated hydrothermal events in submarine environments.These deposits are also sometimes called volcanic-hosted massive sulfide (VHMS) deposits. The density generally is 4500 kg/m3. They are predominantly stratiform accumulations of sulfide minerals that precipitate from hydrothermal fluids on or below the seafloor in a wide range of ancient and modern geological settings. In modern oceans they are synonymous with sulfurous plumes called black smokers.

They occur within environments dominated by volcanic or volcanic derived (e.g., volcano-sedimentary) rocks, and the deposits are coeval and coincident with the formation of said volcanic rocks. As a class, they represent a significant source of the world's copper, zinc, lead, gold and silver ores, with cobalt, tin, barium, sulfur, selenium, manganese, cadmium, indium, bismuth, tellurium, gallium and germanium as co- or by-products.

Volcanogenic massive sulfide deposits are forming today on the seafloor around undersea volcanoes along many mid ocean ridges, and within back-arc basins and forearc rifts. Mineral exploration companies are exploring for seafloor massive sulfide deposits; however, most exploration is concentrated in the search for land-based equivalents of these deposits.

The close association with volcanic rocks and eruptive centers sets VMS deposits apart from similar ore deposit types which share similar source, transport and trap processes. Volcanogenic massive sulfide deposits are distinctive in that ore deposits are formed in close temporal association with submarine volcanism and are formed by hydrothermal circulation and exhalation of sulfides which are independent of sedimentary processes, which sets VMS deposits apart from sedimentary exhalative (SEDEX) deposits.

There is a subclass of VMS deposits, the volcanic- and sediment-hosted massive sulfide (VSHMS) deposits, that do share characteristics that are hybrid between the VMS and SEDEX deposits. Notable examples of this class include the deposits of the Bathurst Camp, New Brunswick, Canada (e.g., Brunswick #12); the deposits of the Iberian Pyrite Belt, Portugal and Spain, and the Wolverine deposit, Yukon, Canada.

Wave base

The wave base, in physical oceanography, is the maximum depth at which a water wave's passage causes significant water motion. For water depths deeper than the wave base, bottom sediments and the seafloor are no longer stirred by the wave motion above.

Wislicenus (crater)

Wislicenus is an impact crater on Mars, located in the Sinus Sabaeus quadrangle at 18.4° south latitude and 348.6° west longitude. It measures approximately 140 kilometers in diameter and was named after German astronomer Walter Wislicenus (1859–1905). The name was adopted by IAU's Working Group for Planetary System Nomenclature in 1973.

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