Types of metasomatic rocks: temperature conditions, buildups, features of composition, minerageny
Authors:   The Zavaritsky Institute of Geology and Geochemistry of the Ural Branch of RAS, DVORNIK Gennadiy Petrovich 
Published: December 2020

The relevance of the work is due to the importance of metasomatic rocks associated many ore and non-metallic mineral resources. Purpose of the work: study of temperature conditions of formation, the characteristics of the chemical and mineral composition, the mineralogy of metasomatites. Results. The extended classification of the main types of metasomatic rocks (alkaline, basic, acidic) formed in the early alkaline and acid stages of the hydrothermal process is given. Temperature conditions of formation, features of chemical and mineral composition and metasomatite mineralogeny are considered. Alkaline metasomatites are subdivided into potassium (pyroxene phenites, microclinites, biotite-orthoclase metasomatites, gumbaites) and sodium (nepheline-pyroxene phenites, albites, sodic alterations). Deposits of tungsten, molybdenum, gold and uranium are associated with potassium metasomatites (gumbaites), and deposits of beryllium, lithium, tantalum, and niobium are associated with sodium metasomatites (albite). The main metasomatic rocks (basificates) include calcium and iron-magnesian metasomatites (calcareous and magnesian skarns, diopside-lapis lazuli metasomatites, rhodingites, kamaforites, carbonatites, apocarbonate calcites, dolomite-ankerite, magnesite and sideroplesite metasomatites). The formation of deposits of iron, boron, and phlogopite is associated with skarn; deposits of rare-earth elements, tantalum, niobium, and apatite are associated with carbonatites. Acid metasomatites are subdivided into aluminous and siliceous. Aluminous metasomatites include propylites, chloritolites, microcline-sericite and tourmaline-sericite metasomatites, secondary quartzites, argillizated rocks. Alumina deposits (kaolins, bentonites) are associated with secondary quartzites. Siliceous metasomatites include the largest number of species: uralite metasomatites, greisens, listvenites and berezites, chlorite-sericite-quartz and sericite-quartz metasomatites, charoitites, serpentinites, nephrites, anthophyllite metasomatites, carbonate-talc metasomatites and talcites, magnetite quartzites, jaspers, jasperoids. There is a group of metasomatites among them consisting of quartz in association with hydrous alumosilicates (muscovite, topaz, and chlorite). The other group includes low-alumina metasomatites, the mineral composition of which is dominated by hydrous calcium and magnesian silicates (charoite, serpentine, antophyllite, tremolite, talc). The third group is represented by metasomatites of quartz composition (magnetite quartzites, jaspers, jasperoids). The formation of deposits of iron, tin, tungsten, molybdenum, gold, polymetals, nonmetallic raw materials (asbestos, talc, charoite, nephrite, jasper) is associated with siliceous metasomatites. Conclusions. According to the formation temperature, high-temperature (above 500o С), medium-temperature (500–300о С) and low-temperature (below 300o С) metasomatic rocks are distinguished. The average compositions of alkaline metasomatites are characterized by high concentrations of potassium or sodium oxides, the predominance of feldspars (orthoclase, microcline, albite) in association with pyroxenes, carbonates. The main metasomatites are distinguished by high contents of calcium, magnesium and iron oxides at low silica concentrations prevailing in the mineral composition of silicates (pyroxenes and garnets) or carbonates (calcite, dolomite, magnesite, breunnerite). The composition of acid metasomatites is characterized by high concentrations of alumina or silica, the predominance of hydrous aluminosilicates, silicates and quartz.