Skarn

Skarn

Photographed by Michael P. Klimetz

Magnetite-Copper Sulfide Skarn

Ertsberg/Grasberg Complex

IRIAN JAYA

[ISLAND OF NEW GUINEA]

Skarn is a metamorphic rock that is usually variably colored green or red, occasionally grey, black, brown or white. It usually forms by chemical metasomatism of rocks during metamorphism and in the contact zone of magmatic intrusions like granites with carbonate-rich rocks such as limestone or dolostone. Skarns in the igneous environment are associated with hornfels. Skarns are, in their broadest sense, formed by mass and chemical transport and reactions between adjacent lithologies. They need not be igneous in origin, though. Two adjacent sedimentary layers such as a banded iron formation and a limestone may react to exchange metals and fluids during metamorphism, creating a skarn. However, the widest use of the word is in describing the metasomatised zones of wall rock adjacent to granites. Skarns are often hosts for copper, lead, zinc, iron, gold, molybdenum, tin, and tungsten ore deposits. The term tactite is reserved for carbonate rocks that have been contact metasomatized.