Greisen

Classification：Metamorphic Rock

The granitoids are formed by metasomatism under the action of high temperature gasifying hydrothermal solution. The main minerals are quartz, mica, cassiterite, topaz, tourmaline and fluorite etc..

Greisen is mainly composed of muscovite, quartz, Topaz, tourmaline, fluorite and minerals such as cassiterite and wolframite.

Features：
Greisen is a metamorphic rock formed by high temperature gas and hydrothermal metasomatism, granitic rocks and other similar felsic rocks. The rock of shallow color, gray, grayish green or pale pink. Mineral composition is mainly quartz, mica, fluorite, Topaz and tourmaline, followed by rutile, micro plagioclase, albite, beryl, garnet and so on. The main mineral quartz is usually more than 50%, even up to 90%. The coarse-grained structure is a coarse-grained structure, or a granitic texture. Greisen is often distributed in the surrounding rocks near the top, edge or contact zone of granite intrusions at medium depth. The deposits closely related to Greisen include W, Sn, Mo, Bi, Nb, Ta and so on.

Classification and distribution:
According to the relative content of minerals, Greisen can be divided into quartz Muscovite Greisen, quartz TopazGreisen, tourmaline Muscovite Greisen, quartz fluorite Greisen and so on. Greisen is mostly distributed in the surrounding area of intrusive body, contact zone and surrounding rock. Tungsten, tin, bismuth, molybdenum, niobium, tantalum and other metal deposits are closely related to Greisen in Genesis. The Nanling area of China is an important origin of Greisen.

Important species:
The chemical composition of natural TopazGreisen is characterized by rich F and Al2O3, poor Na and K. The chemical composition has deviated from granite composition. The formation of Topaz cloud quartz melt probably underwent extreme crystallization differentiation and water melts in F containing albite granite. A large number of crystals of the felsic minerals lead to the extreme enrichment of the residual melt F and the initial dilution of Na and K. At the same time, the distribution of Na and K into the fluid phase leads to the further dilution of Na and K in the melt and the relative enrichment of Al2O3. Further studies are needed on the formation mechanism of TopazGreisen and Topaz cloud matrix melt.