奉化-蔚珍地域의 錫, 重石鐵化作用

Tin, tungsten mineralization in Bonghwa-Uljin area

The tin and tungsten deposits are embedded around the age unknown Buncheon granite gneiss which intruded the Precambrian schists, gneiss and amphibolites in Bonghwa-Uljin area. Pegmatite dike swarm developed intermittently about 4km along the southern border of Buncheon granite gneiss at Wangpiri area. Thickness of pegmatite dikes range from 0.5 to 15m. Pegmetite is consisted of quartz, microcline, albite, muscovite and frequently topaz, tourmaline, garnet, fluorite, fluorapatite and lepidolite. Pegmatite dikes are greisenized, albitized and microclinized along dike walls. Cassiterites are irregularly disseminated through the intensely greienized and albitized parts of the pegmatite. Cassiterite crystals are mainly black to dark brown and contain considerable Ta and Nb. Average Ta and Nb contents of the four cassiterite samples are 5300 and 3400 ppm. The Ssangjeon tungsten deposits is embedded within the pegmatite dike developed along the northern contact of Buncheon granite gneiss with amphibolite. This pegmatite developed 2km along the strike and thickness varies from 10 to 40m. Mineral constituents of the pegmatite are quartz, microcline, plagioclase, muscovite, biotite, tourmaline and garnet. Ore minerals are ferberite and scheelite with minor amount of molybdenite, arsenopyrite, pyrrhotite, pyrite, chalcopyrite, sphalerite, galena, pentlandite, bismuthinite, marcasite, and fluorite. Color and occurrence of quartz reveals that quartz formed at three different stages; quartz Ⅰ, the earliest milky white quartz formed as a rock forming mineral of simple pegmatite; quartz Ⅱ, gray to dark gray quartz which replace the minerals associated with quartz Ⅰ; quartz Ⅲ, the latest white translucent quartz which replace the quartz Ⅰ and Ⅱ. All of the ore minerals are precipitated during the quartz Ⅱ stage. Fluid inclusion in quartz Ⅰ and Ⅱ are mainly gaseous inclusions and liquid inclusions are contained in quartz Ⅲ and fIuorite. Salinities of the inclusion in quartz Ⅰ and Ⅱ ranges from 4.5 to 9.5 wt.% and 5.1 to 6.0 wt.% equivalent NaCl respectively. Salinities of the inclusion in fluorite range from 3.5 to 8.3 wt.% equivalent NaCl. Homogenization temperatures of the inclusion in quartz Ⅰ, Ⅱ and Ⅲ range from 415 to 465℃, from 397 to 441℃ and 278 to 357℃. Data gathered in this study reveals that tin and tungsten mineralization in this area are one of prolonged event after the pegmatite formation around Buncheon granite gneiss.