Skarn


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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.

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

References in periodicals archive ?
Soloviev, "Geology, mineralization, and fluid inclusion characteristics of the Kumbel oxidized W-Cu-Mo skarn and Au-W stockwork deposit in Kyrgyzstan, Tien Shan," Mineralium Deposita, vol.
Three historical resource estimates in 1982, 1987, and 1993 were completed for the Zackly Main Skarn zone, one of the three known mineralized skarn zones located along the Zackly skarn trend.
The MVCP Project includes four near surface skarn mining centers with numerous newly recognized targets held within the 4.25 square miles of mining claims in the Yerington mining district, Nevada.
Geochemical characteristics and zircon LA- ICP -MS U-Pb dating of Galae skarn gold (copper) deposit, Tibet and its significance.
All over the skarn area in the form of a narrow strip with thicknesses of several meters to several of 10 meters are seen in an approximate trend of North West -southeast.
The work has generated an attractive new project located 40km west of Kempsey, where previous exploration had identified tin skarn (Basin One prospect) and Intrusion-Related Gold mineralisation in the Mt Jacob - Willi Willi area (Figure 1 in link below).
COMMENT: The Chontash Project was acquired in 2010 and the independent maiden resource estimate showed two types of potentially economic mineralization; a molybdenum skarn with some copper and gold enrichment (2.85Mt of ore at 0.196% Mo, 0.13% Cu, and 0.08 g/t Au in the inferred category) as well as a copper gold porphyry body which was "enveloped" by the skarn (0.38MT with 0.89% Cu and 0.43 g/t Au).
Associated with the Au mineralization are small skarn beds carrying massive sulphide lenses with up to 596 g/t Ag, 6.25% Pb, 4.5% Zn and 0.17% Bi.
The southern region of license 13602X has potential for skarn related mineralization, as suggested by the identification of skarns along the contact of a late Permian sub-volcanic intrusion with Devonian limestone.
At locality 5, thomsonite is found as transparent to translucent, colorless to gray, elongated rectangular blades flattened on {001}, as cruciform twins, and as divergent crystal aggregates on altered meionite, diopside and fluorapatite crystals exposed in voids in FPS skarn. Observed forms include {100}, {010}, {001}, and {110}.
The work index in the pit varies from in excess of 18 in indurated limestone to 12-14 in the iron-rich skarn. The hardness of the rock has not caused any mining problems to date, but has restricted the plant throughput.
At the POW Zone, drilling targeted a magnetic geophysical feature inferred to be associated with skarn alteration and sulphide mineralization.