Pegmatite

Classification：Igneous Rock

A rock containing large granular crystals. The simple pegmatite often contains minerals such as quartz, feldspar and mica. The complex pegmatite contains special chemical elements and minerals, making it a potential mineral resource.

Pegmatite is a kind of all kinds of plutonic rocks in Genesis is closely related to the coarse to coarse-grained rock or rock mass vein.

Pegmatite, a light colored crystalline rock composed of giant particles, is a silicate residue rich in volatile matter, which is slowly crystallized into the crevice of the igneous rock or surrounding rock.
Generally, it is flesh red and gray, and has large or coarse structure of acid to alkaline vein rock. It is often in a vein and is produced in groups. The mineral crystal is very thick, a few centimeters to several meters, with banded structure.
According to the mineral combination can be divided into: Pegmatite, nepheline syenite granite and gabbro Pegmatite Pegmatite.
Apart from crystal, feldspar and Muscovite as important minerals, the granite Pegmatite is often associated with minerals containing rare elements, such as beryl and niobium tantalite, which are important parent rocks of rare element deposits. Usually, a relatively complete Pegmatite vein of granodiorn can be divided into the marginal zone, the lateral zone, the middle zone and the core from outside.
According to the complexity of mineral species formation, it can be divided into simple Pegmatite and complex Pegmatite. Pegmatite, which is composed of feldspar, quartz and muscovite, is called simple Pegmatite, and the mineralized Pegmatite containing Li, Be, Nb, Ta and other rare elements is not only complex in mineral composition, but also very obvious and universal. Therefore, it is called complex Pegmatite, which is often developed on the basis of simple Pegmatite. .
There are many explanations for the causes, some theories think that the slow crystallization of the remnants of the volcano, and the influence of the strong diffusion conditions caused by high pressure, has not yet been universally acknowledged.

Mineral composition:
The main minerals are quartz, alkaline feldspar and plagioclase, secondary minerals and accessory minerals including hydrous minerals, trace elements and rare elements (Li, Be, La, Nb, Ta, W, Sn, U, Th, etc.) and normal igneous minerals, such as the rich F, Cl, B, and minerals, such as topaz, tourmaline, beryl, niobium. Tantalite, fluorite, etc.

Morphological character：
Pegmatite is complex in morphology and diverse in appearance. It can be consistent with the occurrence of surrounding rocks, and also can cut surrounding rocks. The relationship with surrounding rocks can be gradual and abrupt. Usually, there are many shapes, such as vein, lens, bladder, cylinder and irregular shape. The towel is dominant in all kinds of regular or irregular veins.
Pegmatite pulse can expand and shrink in direction and tendency, and can also appear in echelon arrangement and pinching out, forming a side row and bead like vein group. The size of Pegmatite veins varies greatly. The length varies from a few meters to a few hundred meters, and the thickness varies from several centimeters to several meters. The depth is usually from tens to hundreds of meters. There is no certain correspondence between the prolongation of Pegmatite pulse in the three degree space, and the longer and thicker veins on the earth surface do not necessarily extend, but vice versa.

Structural characteristics:
The coarse mineral crystal is one of the important features of Pegmatite which is different from other veins. It is often larger than the same minerals in the granites, many times, or even a thousand times more than that of the same minerals in the granite. For example, the largest known micro plagioclase in Pegmatite has a weight of lOOt, the beryl is 32t, the spodumene crystal is 14m, the area of the black mica reaches 7m2, and the Muscovite is 32m.
The granularity division of Pegmatite is different from that of ordinary intrusive rocks. It has its own unique standard: fine grain is O.5 - 2cm, medium grain is 2 - 5cm, coarse grain is 5 ~ 15cm, lump, 15cm. Pegmatite has two unique structures, one is the great structure characterized by the particularly coarse mineral particles, and two is the texture of the rock ten potassium feldspar and quartz. The various metasomatic structures are also common in Pegmatite. The most important internal structure of the Pegmatite body is the band structure, which shows a regular banded arrangement of the structure and mineralization of the Pegmatite vein from the side to the center. Well developed zonal structures can generally be divided into four zones.
The 1. edge zone is mainly composed of fine-grained K quartz, also known as fine-grained structural belt. The thickness of the belt is generally very small, from a few centimeters to a dozen centimeters, with irregular shape and discontinuity, which is generally not ore bearing.
The 2. lateral zone is made up of the feldspar and quartz of the image structure and coarse-grained structure, also known as the image coarse grain structure belt. The thickness of the belt is large, but it is unstable. There is no ore in general.
3. intermediate zone: the belt is located between the lateral zone and the core band, mainly composed of giant, massive plagioclase and quartz with a large thickness and better continuity, also known as a massive K stone belt. The belt is mineralized and is enriched in rare rare earth mineral deposits and muscovite and feldspar.
4. core band: often irregular in shape, often located in the middle of the Pegmatite vein, especially the center of its expansion part, usually composed of quartz block or quartz and lithiite. Sometimes appear in the central part of the kernel geode, and gem minerals output.

 

Classification:
1. images and equal grain type Pegmatite
It is equivalent to the Pegmatite which only develops to the lateral zone. The rock mineral assemblage and structural structure are similar to the lateral zone of granitic Pegmatite.
2. block type Pegmatite
It is equivalent to Pegmatite, which develops to the middle zone but has no core and has no significant metasomatism. The central part of the rock mass is coarse-grained, pegmatite and massive pegmatite. The main minerals are feldspar, quartz and muscovite. They can contain a certain number of rare metal minerals.
3. completely heterotypic Pegmatite
It is equivalent to the crystallization of Pegmatite, which has formed a blocky quartz core. Obvious metasomatism and dolomitization are evident in such Pegmatite. The main minerals are plagioclase, quartz, Bai Yunmu, albite, and beryl and spodumene, among which muscovite, beryl and spodumene may all constitute industrial orebodies.
4. rare metal metasomatism Pegmatite
It is equivalent to the Pegmatite that has a strong metasomatism of rare metals after the formation of the kernel, and formed an metasomatism zone composed of albite, lithium-ion mica, beryl, niobium tantalite, cesium eclogite, apatite, uranium mineral and so on, and constitutes an important deposit of rare metals.
5. feldspodopyroxene type Pegmatite
No Pegmatite is composed of albite, Li Huishi, quartz and a large number of rare metal elements. Such Pegmatite constitutes an important rare metal deposit.

 

The theory of Genesis:
Magma theory
According to this view, Pegmatite and Pegmatite deposits are formed by slow and complete crystallization differentiation of high volatile magmas under favorable conditions.
Volatile components play an important role in the process of diagenesis and mineralization: high volatile components reduce the viscosity and crystallization temperature of magma, which is beneficial to the migration and crystallization of magma; the volatile components of the volatile components are large, and it is beneficial to the slow condensation crystallization of high volatile magma to form pegmatite structure.

Volatile components are easily combined with useful metals to form soluble complexes, so that these useful components are enriched and finally mineralizing in high volatile magmas.
There are two known causes of high volatile magma: one is the high volatile residual magma formed by the gradual converging of volatile components from the late condensation crystallization of the magma intrusion, and the other is the partial melting of the rocks during the metamorphic process, that is, the high volatile magma formed by the mixed rock formation.

Metasomatism of recrystallization
This view denies the existence of high volatile magma. It is believed that the Pegmatite and Pegmatite deposits were metasomatic and recrystallized from the crystalline rocks under the action of late hydrothermal fluids.
Forming conditions:
Physical conditions
The development of intact Pegmatite is very long, and its physical and chemical conditions are also changing greatly. According to the temperature data, the formation of the Pegmatite temperature from about 700 DEG C: following a continuous to 100 DEG C. Among them, the early formation of the long angled rocks formed between 700 and 600~E, and the main body of Pegmatite formed at 600 - 150 degrees C, and the rare metal mineralization usually occurred between 500 - 300 degrees C. Both theory and practice confirm that Pegmatite occurs at 3 to 8km or even deeper.
It is generally believed that there are two main reasons for the formation of Pegmatite in the larger depth, one is that the larger depth can make the heat lose slowly, which is beneficial to the long time crystallization of the system; the two is the high pressure condition made in the larger depth so that the rare metals such as potassium, sodium and other metals, such as lithium and beryllium, can be dissolved in a large amount. In the melt fluid or fluid system, the volatilization of the system is preserved for a long time, which is conducive to the formation of Pegmatite body.

Chemical conditions:
The effect of mineralizer: mineralizer is usually very common in the Pegmatite alkali metasomatism in industrial value (such as potassium long fossilization, albite, mica, cloud angling, etc.), and the rare element mineralization of Li, Be, Nb and Ta often occurs during the process of alkali metasomatism.

Formation process:
Post magmatic stage
At this stage, the rocks are formed by condensation and crystallization of magma, and the diagenetic temperature is between 600 and 800oC.

At the early stage of this stage, the initial stage of condensation and crystallization after high volatile magma intrusion into favorable tectonic space formed the edge zone of Pegmatite. The main minerals in the marginal zone are feldspar and quartz. Because the temperature of the surrounding rock is low, the temperature of the magma is relatively fast, so the rock is usually composed of fine pegmatite. The marginal zone is generally discontinuous and contains no useful minerals.
Later stage, after the formation of the marginal zone, the content of volatile components in the magma increased relatively, and the temperature decreased relatively slowly. The main minerals in the lateral zone are plagioclase, potassium micro plagioclase, quartz, muscovite and so on. The rocks usually have fine grain pegmatite structure. When the composition of magma reaches the ratio of quartz to feldspar, the common texture of the lateral zone is formed. The outer zone is also generally discontinuous, and a small amount of minerals such as beryl can appear, but generally do not form ore bodies.

The stage of gas formation:
With the continuous crystallization of silicate minerals in the marginal zone and the lateral zone, the content of volatile components is increasing, and the diagenetic and metallogenic medium gradually changed from magma to supercritical fluid, and the temperature of diagenesis and mineralization is between 600 and 400oC, forming the intermediate zone and the core.
In the early stage, the main minerals were crystallizing, and the main minerals were potassium feldspar, potassium micro plagioclase, quartz and Bai Yunmu. In the condition of rich rare elements and rare earth elements, the mineral of beryl, spodumene and rare earth elements could be formed.
With the change of temperature, the change of fluid composition and the enhancement of water effect, many metasomatism, such as dolomite, sodium feldspar, and rare metals (rich in rare elements), form a lithofacies belt of metasomatic minerals and a large number of important industrial value dolomite, spodumene, lithium-mica, etc. Metasomatism can be extended to hot water solution stage.
The main minerals formed in this stage (including superimposed metasomatism) are potassium feldspar, potassium micro plagioclase, quartz, Bai Yunmu and albite. In the rare and rare earth elements, there are rare metal minerals such as beryl, Li Huishi, lithium-ion mica and rare earth minerals. The rocks have coarse grain pegmatite structure and resembling images. Structure and massive pegmatite structure and metasomatism. The middle belt is generally continuous, which is the favorable part of ore hosting.

The core is located in the central part of Pegmatite body (vein). The main mineral is quartz with massive and mega structure, and is also called quartz core. In Feldspar (and Li Huishi), the development of the kernel depends on the morphology and differentiation of Pegmatite. It can have a perfect kernel when the difference is complete. When the differentiation is incomplete, it can not have a kernel or only develop in the expanding part of the Pegmatite vein. The core is the output part of quartz (silica) orebody, and the core hole is often seen in the core. It is an important metallogenic site of gem minerals such as crystal and topaz.

Hot water solution phase:
This stage begins when the temperature falls below 400oC. Because the ambient temperature has dropped below the critical temperature of water, the ore-forming medium has been transformed from supercritical fluid to hot water solution. This stage is still in the kernel part of mineral crystallization that mineralization and geode, such as crystal etc.. In addition, an important metasomatism can also take place, and continue to form corresponding mineral belts and ore bodies. Metasomatism occurs mostly in the transition zone between the intermediate zone and its nucleus, and is an important metallogenic site of the rare metals of muscovite, spodumene and lithium mica.

Pegmatite and minerals:
In 1997, with the production of two large Saline Lake deposits in South America, the supply and demand patterns of the world's traditional rational resources have changed greatly. In the past few years, China first discovered emerald in the granite Pegmatite of Yuanyang, Yunnan, and its large number of emerald crystal specimens and raw stones appeared in the international market in 1996, and were very popular.

In 1990, the emerald deposit was first discovered in Yunnan Province, China. It occurs in the granitic Pegmatite vein of the deep continental metamorphic rock series.
In 1987, Professor Luo Gufeng, a Chinese scholar, used electronic diffraction to confirm the pyroxene produced in Suchang Pegmatite of Heishan, Chengde, Hebei.
In August 1987, more than 4000 construction troops of the Fourth Engineering Bureau of China's water conservancy and hydropower project, which had not taken off their robes from the Longyangxia hydropower station, had the first sound of the first cannon in the rare mountain and canyon. The strata located in the Li Jiaxia hydropower station are the crustal strata of 1 billion years ago. The sedimentary bodies that erupted from the depths of the earth are characterized by the rapid development of the "4 to 5" "rock" in geology, and the rock fracture trough at the bottom of the isthmus is vertical and horizontal. It is a black cloud of the longer banded mixed rock, the black cloud angle flicker and the granitic Pegm. ATITE veins, the broken rock mass can be seen everywhere.
In June of 1983-1985, the Fujian geological and Mineral Resources Bureau of Fujian Province, in collaboration with the geological brigade and testing center of North Fujian, carried out a systematic study of the Pegmatite in the Nanping area. It was found that the mineral composition in the area of Pegmatite was very complex, with more than 80 species, especially rare and phosphate minerals, in China's similar Pegmatite It is extremely rare.
In 1985, the Xi'an test center of Shaanxi geological and Mining Bureau of China also reported that there was a high iron content in Pegmatite of Shang County, Shaanxi.
The two minerals were discovered in Muscovite albite spodumene type Pegmatite in granitic Pegmatite field, Nanping, Fujian, China in 1985. 1984 found the typical triphylite in Chinese Fujian Nanping rare metal granite Pegmatite.
In 1984, when the rare metal granite Pegmatite ore field in Nanping, Fujian, China was studied, the light colored stone was found in Pegmatite, which is the first time in China. In 1984, China was first discovered in the Muscovite - albite - spodumene - type Pegmatite of Pegmatite Tanaka, Nanping, Fujian. The distribution of microcracks along the coarse grained primary beryl is the product of the late hydrothermal alteration of Pegmatite.
In 1983, when working in Nanping District of Fujian, China, the first discovery of phosphorus, aluminum, iron and barium was found in the granite Pegmatite of the source area.
In 1980, a series of mid member phosphorous ferromanganese ore was found in Pegmatite, Qinggil, Xinjiang. In addition, as far back as 1980, in Xinjiang Qinggil rich beryllium Pegmatite, a group of phosphor manganese iron ore with intermediate composition was found.
In 1974, it was found in the crevice of the white termitite in a region of Canada. China's phosphorus, aluminum and iron barium found in the Pegmatite of Nanping in 1983 "mainly in the IV type quartz hydroxyl phosphor aluminum stone belt.
In 1972, the Soviet Union found Ishikawa Ishi in Ural Pegmatite.
In 1972, the Soviet Union found Ishikawa Ishi in Ural Pegmatite.
In 1967, the Pegmatite vein of sapphire was also found in Pu Li Town, Taiwan, China. In July 1954, the two office of the general committee of the general committee sent two technical teams, including Yang Shi Wenhe Ceng Zhuorong, and so on, led by Lazutkin and the two leaders of the general committee of the general committee of the general committee of the general committee. To Haicheng, Liaoning, a radioactivity survey was carried out on the Pegmatite opencast feldspar in Dagan.
After 1948 have reported the augelite produced in rare metal minerals in Pegmatite.
In 1944, the Japanese Guandong army secretly exploited the uranium containing rare earth niobate minerals produced in Haicheng, Haicheng, China, the black dilute gold, yttrium niobate and yttrium niobium ore, which were transported to Japan by aircraft and carried out in secret in the study of uranium extraction and atomic bombs.
In 1927, Schwartz and others described the contact zone between the rasp Pegmatite and the rock of the schist, and found that the Pegmatite was poor in phosphorus, but it was rich in the schist, and Pegmatite was rich, but no obvious signs of being brought into the schist were found.
In 1912, Schaller was first reported in Pegmatite, California, USA, and has been found in the lithium Pegmatite in Sweden, the Soviet Union, France, Morocco and other countries, but no reports have been reported at home.
It was first discovered in Pegmatite in Greenland in 1901, but has no industrial value. After half a century, it was found for the first time in altered granite in China, with high content and industrial value.
In 1887, it was first found in the alkaline Pegmatite of Ard island in southern Norway, and then found in the tin veins in marble near the Arantes granite contact zone in southwestern Africa.