Greisen is a highly altered granitic rock or pegmatite. Granite (ˈɡrænɪt is a common and widely occurring type of intrusive, Felsic, igneous rock. Pegmatite is a very coarse-grained Igneous rock that has a grain size of 20 mm or more such rocks are referred to as pegmatitic. Greisen is formed by autogenic alteration of a granite and is a class of endoskarn. Skarn is a Metamorphic rock that is usually variably colored green or red occasionally grey black brown or white
Greisens appear as highly altered rocks, partly coarse, crystalline granite, partly vuggy with miarolitic cavities, disseminated halide minerals such as fluorite, and occasionally metallic oxide and sulfide ore minerals, borate minerals (tourmaline) and accessory phases such as sphene, beryl, topaz, etcetera. Metasomatism is the chemical alteration of a rock by Hydrothermal and other fluids Vugs are small to medium-sized cavities inside rock that may be formed through a variety of processes Miarolitic cavities (or miarolitic texture) are typically crystal lined irregular cavities or Vugs most commonly found in granitic Pegmatites A halide is a Binary compound, of which one part is a Halogen Atom and the other part is an element or radical that is less Fluorite (also called fluorspar) is a Mineral composed of Calcium fluoride, Ca[[Fluorine F2]] An oxide is a Chemical compound containing at least one Oxygen atom as well as at least one other element The term sulfide ( sulphide in British English) refers to several types of Chemical compounds containing Sulfur in its lowest Oxidation An ore is a volume of rock containing components or Minerals in a mode of occurrence that renders it valuable for mining Tourmaline is a Crystal Silicate mineral compounded with elements such as Aluminium, Iron, Magnesium, Sodium, Lithium Titanite or sphene is a Calcium Titanium nesosilicate Mineral, Ca[[titanium Ti]] Si[[oxygen O]]5 The Mineral beryl is a Beryllium Aluminium cyclosilicate with the Chemical formula Be3Al2(SiO36 Topaz is a Silicate mineral of Aluminium and Fluorine with the Chemical formula Al 2 Si[[oxygen O]]4(
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Petrogenesis
Greisens are formed by endoskarn 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 crystalisation of granite melts. This fluid is forced into the interstitial spaces of the granite and pools at the upper margins, where boiling and alteration occur.
Alteration facies
- Incipient greisen (granite): muscovite ± chlorite, tourmaline, and fluorite. Muscovite (also known as Common Mica, Isinglass, or Potash mica) is a phyllosilicate Mineral of Aluminium This discusses some chlorine compounds Chlorite is also a type of mineral see Chlorite group.
- Greisenized granite: quartz-muscovite-topaz-fluorite, ± tourmaline (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, typical assemblages developed in aluminosilicates.
Greisen environments
Greisens appear to be restricted to intrusions which are emplaced high in the crust, generally at a depth between 0. In Geology, a crust is the outermost solid shell of a planet or moon 5 and 5 km, with upper aureoles which are sealed shut to prevent fluids escaping. This is generally required, as the boiling to produce greisenation cannot occur deeper than about 5 kilometres.
They are also generally associated only with potassic igneous rocks; S-type granite, not I-type granodiorite or diorite. Granite (ˈɡrænɪt is a common and widely occurring type of intrusive, Felsic, igneous rock. Granodiorite (ˌgrænəˈdaɪəraɪt/ /ˌgreɪn- is an intrusive Igneous rock similar to Granite, but contains more Plagioclase than Potassium feldspar Diorite (ˈdaɪəraɪt is a grey to dark grey intermediate intrusive Igneous rock composed principally of Plagioclase Feldspar (typically Greisens are prospective for mineralisation because the last fluids of granite crystallization tend to concentrate incompatible elements such as potassium, tin, tungsten, molybdenum and fluorine, as well as metals such as gold, silver, and occasionally copper. Potassium (pəˈtæsiəm is a Chemical element. It has the symbol K (kalium from qalīy Atomic number 19 and Atomic mass 39 Tin is a Chemical element with the symbol Sn (stannum and Atomic number 50 Tungsten (ˈtʌŋstən also known as wolfram (/ˈwʊlfrəm/ is a Chemical element that has the symbol W and Atomic number 74 Molybdenum (məˈlɪbdənəm from the Greek word for the metal " Lead " is a Group 6 Chemical element with the symbol Mo Fluorine, fluorum meaning "to flow" is the Chemical element with the symbol F and Atomic number 9 Gold (ˈɡoʊld is a Chemical element with the symbol Au (from its Latin name aurum) and Atomic number 79 Silver (ˈsɪlvɚ is a Chemical element with the symbol " Ag " (argentum from the Ancient Greek: ἀργήντος - argēntos gen Copper (ˈkɒpɚ is a Chemical element with the symbol Cu (cuprum and Atomic number 29
Tectonically, greisen granites are generally associated with generation of S-type suites of granites in thick arc and back-arc fold belts where subducted sedimentary and felsic rock is melted. This article discusses the geologic usage for the philosophical or architectural usage see Architectonics ' Or see Plate tectonics. In Geology, a subduction zone is an area on Earth where two tectonic plates meet and move towards one another with one sliding underneath the other Sedimentary rock is one of the three main rock types (the others being igneous and Metamorphic rock) Felsic is a term used in Geology to refer to Silicate minerals, Magma, and rocks which are enriched in the lighter elements such as Silicon
Distribution
Typical greisen deposits include
- Tin deposits of Cornwall
- Ardlethan, Lachlan Fold Belt, Australia (tin-antimony greisen)
- Timbarra, Lachlan Fold Belt, Australia (gold greisen deposit)
- Anchor Mine, Tasman Fold Belt, Australia (tin greisen)
- Pitinga topaz granite, Brazil (tin, topaz, beryl)
- Lost River, Alaska, USA (tin greisen)
- Erzgebirge, Czech Republic (tin greisen)
See also
- List of rock textures
- Metasomatism
- Granite; specifically for S-type and I-type distinction
- Ore genesis
External links
- USGS descriptive Sn greisen model
- 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)
References
Evans, A. Tin is a Chemical element with the symbol Sn (stannum and Atomic number 50 Cornwall ( Kernow ˈkɛɹnɔʊ is the most southwesterly county of England, on the Peninsula that lies to the west of the River Tamar Ardlethan is a small service town located in the Coolamon Shire in New South Wales Australia. The Lachlan Fold Belt ( LFB) or Lachlan Orogen is a geological subdivision of the east part of Australia. For a topic outline on this subject see List of basic Australia topics. Alaska ( Аляска Alyaska) is a state in the United States of America, in the northwest of the North American continent This page is intended to be a list of rock textural and morphological terms Metasomatism is the chemical alteration of a rock by Hydrothermal and other fluids Granite (ˈɡrænɪt is a common and widely occurring type of intrusive, Felsic, igneous rock. The various theories of ore genesis explain how the various types of mineral deposits form within the Earth's crust. M. , 1993. Ore Geology and Industrial Minerals, An Introduction. , Blackwell Science, ISBN 0-632-02953-6
Reed, B. L. , 1982, Tin greisen model, in Erickson, R. L. , ed. , Characteristics of mineral deposit occurrences: U. S. Geological Survey Open-File Report 82-795, p. 55-61.
Taylor, R. G. , 1979, Geology of tin deposits: Elsevier, Amsterdam, 543 p.
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