Skarn

skarn

In geology, a metamorphic zone developed in the contact area around igneous rock intrusions when carbonate sedimentary rocks are invaded by and replaced with chemical elements that originate from the igneous rock mass nearby. Many skarns also include ore minerals; productive deposits of copper or other base metals have been found in and adjacent to skarns. The typical rock of a skarn is hornfels, a fine-grained, flinty rock produced by the heat and solutions given off by the intruding magma.

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skarn [skärn]

(geology)

A lime-bearing silicate derived from nearly pure limestone and dolomite with the introduction of large amounts of silicon, aluminum, iron, and magnesium.

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Skarn 

a metasomatic rock composed of calcareous, magnesium, and iron silicates and aluminosilicates and originating in a high-temperature aureole of magmatic rocks as a result of the chemical interaction of carbonaceous rocks with magma, intrusive rocks, or other aluminosilicate rocks in hot, magmatogenic solutions. A distinction is made between calcareous skarns and magnesian skarns. Calcareous skarns are composed of calcium, magnesium, and iron silicates and aluminosilicates; they include pyroxenes of the diopside-hedenbergite series and garnets of the grossular-andradite series and originate chiefly at shallow and moderate depths (up to 10-12 km) in the postmag-matic stage in contact limestones with aluminosilicate rocks. Magnesian skarns have magnesium-bearing minerals and include forsterite, diopside, spinel, and phlogopite; they are formed during the reactive interaction of dolomites with intrusive magma or at great depths (more than 10–12 km) in contact with aluminosilicate rocks in the postmagmatic stage.

Skarns are chiefly contact lenticular and sheet-like deposits; tubular or veined bodies in carbonate or aluminosilicate rocks are less common. Skarn bodies have a characteristically zonal structure. Large ore bodies, especially those of iron, copper, lead, zinc, tungsten, and molybdenum, and bodies of nonmetal-lic useful minerals, such as phlogopite and borates, often coincide with skarns. These special types of deposits—”skarn deposits”—are of considerable commercial significance. In the USSR, for example, such ore deposits include the Magnitogorsk iron-ore deposit in the Urals, the Sokolov-Sarbai iron-ore deposit in Kazakhstan, the Altyn-Topkan complex-ore deposit in Middle Asia, and the Tyrnyauz tungsten-molybdenum ore deposit in the Caucasus. Analogous nonmetal deposits of borates are located in Siberia, and those of phlogopite are located in the Baikal Region, on the Aldan Plateau, and in the Pamirs.

REFERENCES

Korzhinskii, D. S. “Ocherk metasomaticheskikh protsessov.” In Osnovnye problemy ν uchenii o magmatogennykh rudnykh mestorozhdeniiakh, 2nd ed. Moscow, 1955.
Zharikov, V. A. “Skarnovye mestorozhdeniia.” In Genezis endogennykh rudnykh mestorozhdenii. Moscow, 1968.

V. A. ZHARIKOV