PARAGENESIS AND MINERAL CHEMISTRY OF THE GEODO GOLD SKARN DEPOSIT, KOREA

The Taebacksan Basin located in middle-east Korean Peninsular, consists of calcareous sedimentary rocks and sandstone-shale of Paleozoic age, which were intruded by the Cretaceous granitic rocks. Sedimentary units of the Taebacksan Basin are highly folded and well developed numerous high angle thrust faults. The Geodo Au-skarn deposit which developed within Taebacksan Basin is also occurs adjacent into intruded granitic rocks. Skarn minerals consist mainly of a dominant andraditic garnet and diopsidic pyroxene and ore minerals comprise dominant magnetite, chalcopyrite, pyrite with minor bornite and hematite. Skarn minerals such as garnet and pyroxene are relatively early stage and form from moderate to high temperature, whereas ore minerals relatively belong to later stage. With respect to ore minerals, magnetite is earlier than sulfides and gold, and Cu-sulfides might be slightly earlier than Au. Ore mineralization stages of Geodo Au skarn deposit are divided into three stages, as iron-oxide stage, Cu-sulfide stage, and Au stage. Garnet composition defines Ad_54.7-81.65Gr_16.89-43.88Sp+Pyr_1.33-1.74 in the iron-oxide stage, Ad_42.55-48.3Gr_48.88-54.16Sp+Pyr_2.44-3.29 in the Cu-sulfide stage, and Ad_92.41-99.18Gr_0-6.56Sp+Pyr_0.35-1.27 in the Au stage. Pyroxene composition shows Hd_10.57-24.26Di_75.23-89.22Jo_0.21-0.51 in the Cu-sulfide stage and Hd_20.10-100Di_0-79.29Jo_0-0.86 in Au stage. Typically garnet from the study area shows complexly oscillatory zonation in the each stage, and garnet composition varies from Al-rich garnet in core to Fe-rich garnet in rim. It seems to be associated with different oxidation state. In Au-stage, golds mostly occur as electrum, and are associated with Bi-bearing minerals such as tetradymite and bismuthinite.