2018 年 52 巻 4 号 p. 149-169
Skarns are rocks consisting mainly of calc-silicate minerals (skarn minerals) such as clinopyroxene and garnet, formed by hydrothermal metasomatism along the contact zone typically between limestone and granitic rock. They are sometimes associated with economical Pb–Zn, Mo, Cu, Fe, Sn, and W mineralization (skarn deposits). Skarns consist mainly of one or two skarn minerals, and often show a zonation. In case of skarns (endoskarns) derived from Al-rich rocks such as granitic rocks and sedimentary rocks, in addition to temperature and pressure, the supply of Ca from limestone controls the zonation. On the other hand, in case of skarns (exoskarns) derived from limestone, the supply of Si, Al, Fe and Mg from related granitic rock and other rocks, degassing of CO2, and redox state govern the zonation. The mineralized metal species in skarn deposits are determined by the granitic rock related to the skarn formation. Isotope analyses revealed that magmatic water supplied from the related granitic rock is greatly involved in the early stage of skarn formation, and influence of meteoric water tends to increase in the later stage.
