Skarn deposits are abundant, variable, and economically important. They are a principal global source of tungsten, a major source of copper, and an important source of iron, molybdenum, zinc, and gold.

Skarn is an assemblage of dominantly calcium and magnesium silicates typically formed in carbonate-bearing rocks as a result of regional and thermal metamorphism, and by metasomatic replacement. Regional and stratiform metamorphic skarn deposits include, for example, skarn iron deposits that were derived from iron-rich sedimentary and volcanic rocks by recrystallization, isochemical meta-morphism, and bimetasomatism. Recrystallization, in particular, results in upgrading the quality of ore for concentration, beneficiation, and metallurgical recovery by increasing grain size of the ore minerals. The term “skarn” some Swedish iron ores of this type (Geijer and Magnusson, 1952). It is not normally used for skarn-type mineral assemblages produced by regional metamorphism of pre-existing deposits, for example highly metamorphosed lithofades of iron-formation (Gross, 1968; “Skarn iron”, subtype 20.4).

Thermal metamorphism of calcareous rocks by adjacent plutons causes a bimetasomatic exchange of ions between dissimilar lithologies, e.g., limestone and pelite, in addition to recrystallization of limestone. The resultant calc-silicate hornfels and marble is subsequently converted to anhydrous prograde skarn under the metasomatic influence of hot hydrothermal fluids emanating from the adjacent crystallizing pluton. Most economic concentrations of ore minerals occur during the cooling of the hydrothermal coincident with the onset of retrograde alteration. In rare instances, existing mineral deposits are converted to skarn deposits by metamorphism, as proposed by Sangster et al.for Meat Cove and Lime Hill, Nova Scotia; Johnson et al. (1990) for Franklin Furnace, New Jersey; Gemmell et al. (1992) for Aguilar, Argentina; and Hodgson (1975) for Broken Hill, Australia