Skarn

Skarns or tactites are hard, coarse-grained metamorphic rocks that form by a process called metasomatism. Skarns tend to be rich in calcium-magnesium-iron-manganese-aluminium silicate minerals, which are also referred to as calc-silicate minerals. These minerals form as a result of alteration which occurs when hydrothermal fluids interact with a protolith of either igneous or sedimentary origin. In many cases, skarns are associated with the intrusion of a granitic pluton found in and around faults or Shear zones that intrude into a carbonate layer composed of either dolomite or limestone. Skarns can form by regional, or contact metamorphism and therefore form in relatively high temperature environments. The hydrothermal fluids associated with the metasomatic processes can originate from either magmatic, metamorphic, meteoric, marine, or even a mix of these. The resulting skarn may consist of a variety of different minerals which are highly dependent on the original composition of both the hydrothermal fluid and the original composition of the protolith. Skarns or tactites are hard, coarse-grained metamorphic rocks that form by a process called metasomatism. Skarns tend to be rich in calcium-magnesium-iron-manganese-aluminium silicate minerals, which are also referred to as calc-silicate minerals. These minerals form as a result of alteration which occurs when hydrothermal fluids interact with a protolith of either igneous or sedimentary origin. In many cases, skarns are associated with the intrusion of a granitic pluton found in and around faults or Shear zones that intrude into a carbonate layer composed of either dolomite or limestone. Skarns can form by regional, or contact metamorphism and therefore form in relatively high temperature environments. The hydrothermal fluids associated with the metasomatic processes can originate from either magmatic, metamorphic, meteoric, marine, or even a mix of these. The resulting skarn may consist of a variety of different minerals which are highly dependent on the original composition of both the hydrothermal fluid and the original composition of the protolith. If a skarn has a respectable amount of ore mineralization that can be mined for a profit, it can therefore be classified as a skarn deposit. Skarn is an old Swedish mining term originally used to describe a type of silicate gangue, or waste rock, associated with iron-ore bearing sulfide deposits apparently replacing Palaeoproterozoic age limestones in Sweden's Persberg mining district. Skarns are composed of calcium-iron-magnesium-manganese-aluminum silicate minerals. Skarn deposits are economically valuable as sources of metals such as tin, tungsten, manganese, copper, gold, zinc, lead, nickel, molybdenum and iron. A skarn is formed by a variety of metasomatic processes during metamorphism between two adjacent lithologic units. Skarn can form in almost any lithology type such as shale, granite and basalt but the majority of skarns are found in lithology containing a limestone or a dolomite. It is common to find skarns near plutons, along faults and major shear zones, in shallow geothermal systems, and on the bottom of the sea floor. The mineralogy of skarn is highly related to the protolith. Skarn minerals are mainly garnets and pyroxene with a wide variety of calc-silicate and associated minerals. Typical skarn minerals include pyroxene, garnet, idocrase, wollastonite, actinolite, magnetite or hematite, epidote and scapolite. Because skarns are formed from incompatible-element rich, siliceous aqueous fluids a variety of uncommon mineral types are found in the skarn environment, such as: tourmaline, topaz, beryl, corundum, fluorite, apatite, barite, strontianite, tantalite, anglesite, and others.