Greisen is a highly altered

granitic A granitoid is a generic term for a diverse category of coarse-grained igneous rocks that consist predominantly of quartz, plagioclase, and alkali feldspar. Granitoids range from plagioclase-rich tonalites to alkali-rich syenites and from quartz- ...

rock or

pegmatite A pegmatite is an igneous rock showing a very coarse texture, with large interlocking crystals usually greater in size than and sometimes greater than . Most pegmatites are composed of quartz, feldspar, and mica, having a similar silici ...

, usually composed predominantly of

quartz Quartz is a hard, crystalline mineral composed of silica ( silicon dioxide). The atoms are linked in a continuous framework of SiO4 silicon-oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall chemical f ...

and

micas Micas ( ) are a group of silicate minerals whose outstanding physical characteristic is that individual mica crystals can easily be split into extremely thin elastic plates. This characteristic is described as perfect basal cleavage. Mica is ...

(mostly

muscovite Muscovite (also known as common mica, isinglass, or potash mica) is a hydrated phyllosilicate mineral of aluminium and potassium with formula K Al2(Al Si3 O10)( F,O H)2, or ( KF)2( Al2O3)3( SiO2)6( H2O). It has a highly perfect basal cleavag ...

). Greisen is formed by self-generated alteration of a granite and is a class of moderate- to high-temperature magmatic-hydrothermal alteration related to the late-stage release of volatiles dissolved in a magma during the solidification of that magma. Greisens are usually variably altered rocks, grading from coarse, crystalline granite, commonly vuggy with

miarolitic Miarolitic cavities (or ''miarolitic texture'') are typically crystal-lined irregular cavities or vugs most commonly found in granitic pegmatites, and also in a variety of igneous rocks. The central portions of pegmatites are often miarolitic as t ...

cavities, through to quartz and muscovite rich rocks, which may be locally rich in

topaz Topaz is a silicate mineral of aluminium and fluorine with the chemical formula Al Si O( F, OH). It is used as a gemstone in jewelry and other adornments. Common topaz in its natural state is colorless, though trace element impurities can mak ...

tourmaline Tourmaline ( ) is a crystalline Silicate mineral, silicate mineral group in which boron is compounded with elements such as aluminium, iron, magnesium, sodium, lithium, or potassium. Tourmaline is a gemstone and can be found in a wide variety o ...

cassiterite Cassiterite is a tin oxide mineral, SnO2. It is generally opaque, but it is translucent in thin crystals. Its luster and multiple crystal faces produce a desirable gem. Cassiterite was the chief tin ore throughout ancient history and remains ...

fluorite Fluorite (also called fluorspar) is the mineral form of calcium fluoride, CaF2. It belongs to the halide minerals. It crystallizes in isometric cubic habit, although octahedral and more complex isometric forms are not uncommon. The Mohs sca ...

beryl Beryl ( ) is a mineral composed of beryllium aluminium silicate with the chemical formula Be3Al2Si6O18. Well-known varieties of beryl include emerald and aquamarine. Naturally occurring, hexagonal crystals of beryl can be up to several ...

wolframite Wolframite is an iron, manganese, and tungstate mineral with a chemical formula of that is the intermediate between ferberite ( rich) and hübnerite ( rich). Along with scheelite, the wolframite series are the most important tungsten ore mineral ...

siderite Siderite is a mineral composed of iron(II) carbonate (FeCO3). It takes its name from the Greek word σίδηρος ''sideros,'' "iron". It is a valuable iron mineral, since it is 48% iron and contains no sulfur or phosphorus. Zinc, magnesium and ...

molybdenite Molybdenite is a mineral of molybdenum disulfide, Mo S2. Similar in appearance and feel to graphite, molybdenite has a lubricating effect that is a consequence of its layered structure. The atomic structure consists of a sheet of molybdenum ato ...

and other

sulfide Sulfide (British English also sulphide) is an inorganic anion of sulfur with the chemical formula S2− or a compound containing one or more S2− ions. Solutions of sulfide salts are corrosive. ''Sulfide'' also refers to chemical compounds la ...

minerals, and other accessory minerals. They may occur as small to large veins, or large zones in the roof of some granites. The rocks can sometimes be mined as ores of tin and other minerals.

Petrogenesis

Greisens are formed by endogenous alteration of granite during the cooling stages of emplacement. Greisen fluids are formed by granites as the last highly gas- and water-rich phases of complete crystallisation of granite melts. This fluid is forced through the interstitial spaces of the granite into veins and pools at the upper margins, where boiling and rock alteration occur.

Alteration facies

* Incipient greisen (granite): addition of

chlorite The chlorite ion, or chlorine dioxide anion, is the halite with the chemical formula of . A chlorite (compound) is a compound that contains this group, with chlorine in the oxidation state of +3. Chlorites are also known as salts of chlorou ...

, and

(original texture of granites retained). * Greisenized granite: quartz-muscovite-topaz-fluorite, ± tourmaline (some original texture of granites retained). * Massive greisen: quartz-muscovite ± topaz ± fluorite ± tourmaline (typically no original texture preserved). Tourmaline can be ubiquitous as disseminations, concentrated or diffuse clots, or late fracture fillings. Greisen may form in any wallrock environment, but typically in granites and

metamorphic Metamorphic rocks arise from the transformation of existing rock to new types of rock in a process called metamorphism. The original rock (protolith) is subjected to temperatures greater than and, often, elevated pressure of or more, causi ...

rocks.

Greisen environments

Greisens appear to be restricted to intrusions which are emplaced high in the crust, generally at a depth between 0.5 and 5 km, as the hydrous fluid separation from granite to produce greisenation cannot occur deeper than about 5 kilometres. The roof or upper aureole is mostly sealed shut to prevent most

fluids In physics, a fluid is a liquid, gas, or other material that continuously deforms (''flows'') under an applied shear stress, or external force. They have zero shear modulus, or, in simpler terms, are substances which cannot resist any she ...

escaping. This sealing is largely due to hornfelsing and silicification of the overlying rocks, and fracturing of these rock typically forms greisen veins. They are generally associated mostly with potassic plutonic rocks;

Alkali feldspar granite Alkali feldspar granite, some varieties of which are called 'red granite', is a felsic igneous rock and a type of granite rich in the mineral potassium feldspar (K-spar). It is a dense rock with a phaneritic texture. The abundance of K-spar gives ...

, and are rare in less potassium rocks like

granodiorite Granodiorite () is a coarse-grained ( phaneritic) intrusive igneous rock similar to granite, but containing more plagioclase feldspar than orthoclase feldspar. The term banatite is sometimes used informally for various rocks ranging from gr ...

diorite Diorite ( ) is an intrusive igneous rock formed by the slow cooling underground of magma (molten rock) that has a moderate content of silica and a relatively low content of alkali metals. It is intermediate in composition between low-sil ...

. Greisens are prospective for mineralisation because the last fluids of granite crystallization tend to concentrate incompatible metals such as tin,

tungsten Tungsten, or wolfram, is a chemical element with the symbol W and atomic number 74. Tungsten is a rare metal found naturally on Earth almost exclusively as compounds with other elements. It was identified as a new element in 1781 and first isol ...

molybdenum Molybdenum is a chemical element with the symbol Mo and atomic number 42 which is located in period 5 and group 6. The name is from Neo-Latin ''molybdaenum'', which is based on Ancient Greek ', meaning lead, since its ores were confused with lead ...

and

beryllium Beryllium is a chemical element with the symbol Be and atomic number 4. It is a steel-gray, strong, lightweight and brittle alkaline earth metal. It is a divalent element that occurs naturally only in combination with other elements to for ...

, and in places other metals such as

tantalum Tantalum is a chemical element with the symbol Ta and atomic number 73. Previously known as ''tantalium'', it is named after Tantalus, a villain in Greek mythology. Tantalum is a very hard, ductile, lustrous, blue-gray transition metal that ...

gold Gold is a chemical element with the symbol Au (from la, aurum) and atomic number 79. This makes it one of the higher atomic number elements that occur naturally. It is a bright, slightly orange-yellow, dense, soft, malleable, and ductile ...

silver Silver is a chemical element with the symbol Ag (from the Latin ', derived from the Proto-Indo-European ''h₂erǵ'': "shiny" or "white") and atomic number 47. A soft, white, lustrous transition metal, it exhibits the highest electrical ...

, and

copper Copper is a chemical element with the symbol Cu (from la, cuprum) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pink ...

. Tectonically, greisen granites are generally associated with generation of S-type suites of granites in thick arc and

back-arc A back-arc basin is a type of geologic basin, found at some convergent plate boundaries. Presently all back-arc basins are submarine features associated with island arcs and subduction zones, with many found in the western Pacific Ocean. Most of ...

fold belts where subducted

sedimentary Sedimentary rocks are types of rock that are formed by the accumulation or deposition of mineral or organic particles at Earth's surface, followed by cementation. Sedimentation is the collective name for processes that cause these particles ...

and

felsic In geology, felsic is a modifier describing igneous rocks that are relatively rich in elements that form feldspar and quartz.Marshak, Stephen, 2009, ''Essentials of Geology,'' W. W. Norton & Company, 3rd ed. It is contrasted with mafic rocks, wh ...

rock is melted.

Distribution

Examples of greisen are: * Tin and

deposits of

Cornwall Cornwall (; kw, Kernow ) is a Historic counties of England, historic county and Ceremonial counties of England, ceremonial county in South West England. It is recognised as one of the Celtic nations, and is the homeland of the Cornish people ...

Ardlethan Ardlethan () is a small service town in the Coolamon Shire in New South Wales, Australia. Ardlethan is at the intersection of the Burley Griffin Way and Newell Highway. Ardlethan lays claim to be the birthplace of the Australian kelpie. Histo ...

New South Wales ) , nickname = , image_map = New South Wales in Australia.svg , map_caption = Location of New South Wales in AustraliaCoordinates: , subdivision_type = Country , subdivision_name = Australia , established_title = Before federation , es ...

Australia Australia, officially the Commonwealth of Australia, is a sovereign country comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands. With an area of , Australia is the largest country by ...

(tin-antimony greisen) * Timbarra gold mine,

, Australia (gold greisen deposit) * Anchor Mine, Lottah,

Tasmania ) , nickname = , image_map = Tasmania in Australia.svg , map_caption = Location of Tasmania in AustraliaCoordinates: , subdivision_type = Country , subdi ...

, Australia (tin copper topaz greisen) * Pitinga topaz granite, Brazil (tin, topaz, beryl) * Lost River,

Alaska Alaska ( ; russian: Аляска, Alyaska; ale, Alax̂sxax̂; ; ems, Alas'kaaq; Yup'ik: ''Alaskaq''; tli, Anáaski) is a state located in the Western United States on the northwest extremity of North America. A semi-exclave of the U ...

, USA (tin greisen) * Sisson Brook, Burnt Hill and other deposits,

New Brunswick New Brunswick (french: Nouveau-Brunswick, , locally ) is one of the thirteen provinces and territories of Canada. It is one of the three Maritime provinces and one of the four Atlantic provinces. It is the only province with both English and ...

Canada Canada is a country in North America. Its ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, covering over , making it the world's second-largest country by to ...

(tin-tungsten-molybdenum greisen) * Erzgebirge, Czech Republic (tin greisen) * Panasqueira Mine,

Portugal Portugal, officially the Portuguese Republic ( pt, República Portuguesa, links=yes ), is a country whose mainland is located on the Iberian Peninsula of Southwestern Europe, and whose territory also includes the Atlantic archipelagos of th ...

Tin and

Tungsten Tungsten, or wolfram, is a chemical element with the symbol W and atomic number 74. Tungsten is a rare metal found naturally on Earth almost exclusively as compounds with other elements. It was identified as a new element in 1781 and first isol ...

deposit * The Tin Range Tungsten-Tin deposit,

Stewart Island/Rakiura Stewart Island ( mi, Rakiura, ' glowing skies', officially Stewart Island / Rakiura) is New Zealand's third-largest island, located south of the South Island, across the Foveaux Strait. It is a roughly triangular island with a total land ar ...

, New Zealand

References

*Evans, A.M., 1993. ''Ore Geology and Industrial Minerals, An Introduction.'', Blackwell Science, *Reed, B.L., 1986, ''Descriptive model of Sn greisen deposits'', in Dennis P. Cox and Donald A. Singer, eds, ''Characteristics of mineral deposit occurrences: U.S. Geological Survey Bulletin 1693'', http://pubs.usgs.gov/bul/b1693/html/bull217y.htm *Taylor, R.G., 1979, ''Geology of tin deposits'': Elsevier, Amsterdam, 543 p. {{ISBN, 0-444-41805-9 *Mustard, R. 2004. Textural, mineralogical and geochemical variation in the zoned Timbarra Tablelands pluton, New South Wales. Australian Journal of Earth Sciences, 51. *Richardson, G.C. (2016) Lottah and the Anchor: the history of a tin mine and a dependent town: North East Tasmania. Tasmania Forty South Publishing Pty Ltd, Hobart, 265 pages and maps.

External links

Lenharo, S.L.R., Pollard P.J., Born H., ''Matrix rock texture in the Pitinga Topaz Granite, Amazonas, Brazil'', Brazilian Geoscience Reviews, vol 30, 2000 (pdf)
Igneous rocks Economic geology