Journal of the Korean Society of Mineral and Energy Resources Engineers ISSN:2288-0291(Print) 2288-2790(Online) 한국자원공학회지

The main ore body of the Sangdong Tungsten Mine is a roughly lenticular body, located at the gentler southern limb of the large asymmetrical syncline, and 40 to 50 meters below the top of the Myobong Formation which is of Middle and Upper Cambrian in age.The ore body strikes between N75˚W and N80˚W and dips between 15˚NE and 30˚NE, which are essentially parallel to the bedding of the surrounding rocks. The thickness of the orebody varies from 3 meters to 5 meters, although in some localities it is as thick as 6 meters. The symmetrical zoning is charaaacteristic of the main ore body, and it is divided into three distinct zones, i.e. biotite-hornblende zone, hornblende-diopside zone and diopside-garnet zone. Biotite-hornblende zone is located at the central portion of the ore body forming an ore shoot. The main components of the ore are, in the order of abundance, quartz, biotite, muscovite, fluorite, scheelite and other sulphide minerals. Evidence of biotization and chloritization by the ascending hydrothermal quartz veins abound. The quartz veins have introduced considerable quantity of scheelite, molybdenite, bismuthinite, pyrite, chalcopyrite and fluorite; and the ore contains 1.5 to 2.5% WO3. Hornblende-diopside zone surrounding central ore shoot contains less quartz, biotite and muscovite, and hornblende increases considerably. Diopside increases at the outer margin of the zone. Average ore grade decreases to 0.8 to 1.2% WO3, and it decreases outwards. Garnet-diopside zone consists of diopside, garnet, epidote and magnetite; and scheelite is confined to the vicinity of the intruding quartz veins. The farther from the ore shoot the lesser is the number of quartz veins, and the ore grade decreases consequently. The ore grade in the garnet-diopside zone is 0.2 to 0.5% WO3.Zonal structure of the main ore body is attributed to the two or three different stages of mineralization, that are: 1) primary mineralization forming skarn minerals 2) hornblendization and 3) hydrothermal replacement by quartz veins. The primary mineralization introduced very little mineralization of tungsten. Hydrothermal solution which brought intense hornblendization enriched the ore to 1% WO3 or more. Finally, hydrothermal replacement by quartz veins altered the hornblende to biotite and muscovite, forming central ore shoot which is richest in scheelite, molybdenite and bismuthinite.