SEDIMENT HOSTED DISSEMINATED AND SKARN GOLD MINERALIZATION IN THE TAEBAEGSAN REGION, SOUTH KOREA

Taebaegsan, east-central South Korea has a long history of metal production from veins and skarns in sediments near granitoid intrusions. Here, a little-metamorphosed Cambrian and Ordovician marine sequence (Joseon Supergroup) crops out at the northeast end of the Ogcheon orogenic belt. Different facies of lower Paleozoic rocks, superposed in stacked thrust plates, host varied metal deposits (including zinc-lead skarns, tungsten, and gold-quartz veins). Unconformably atop these rocks, middle Carboniferous to Early Triassic mainly terrigenous, coal-rich rocks of the Pyeongan Supergroup were deposited. Jurassic (Daebo series) deep-seated and Cretaceous (Bulgugsa series) hypabyssal granitoids, each with different types of associated epithermal gold-silver vein ores, intrude the Paleozoic rocks. Iron-copper skarns with local coarse native gold formed adjacent to some hypabyssal plutons. The youngest igneous rocks (volcanics and felsic intrusions, some dated at less than 50 mA) typically are not mineralized. Geochemical sampling of streams and rocks identified gold and/or arsenic anomalies associated with altered, impure limestone and shaly dolomite. There are only limited, weathered exposures amid dense vegetation and agricultural fields. Although the region has many old mines and placers there is little indication of old prospect workings in some anomalous areas. A possible localization of anomalous gold is in hydrothermal rims on fine-grained pyrite. Polished and microprobe sections of samples from structures cutting oolitic Cambrian limestone show zones of gold and arsenic enrichment along the perimeters of pyrite grains. The anomalous areas commonly do not show a close relationship to intrusive rocks. The age of this type of mineralization also remains unknown.