EPITHERMAL AU-MINERALIZATION HOSTED IN CETACEOUS VOLCANIC ROCKS FROM SOUTHWESTERN PART OF THE KOREAN PENINSULA: A PRELIMINARY STUDY

Extensive epithermal systems hosted in Cetaceous volcanic rocks in the Sunshin gold mining area, southwestern part of the Korean peninsula host two contrasting styles of mineralization (e.g., low and high sulfidation environment) in close proximity to each other. They share many similarities with those from the circum-Pacific region related to subduction environment at plate boundaries. Au-mineralization is recognized within very thin chalcedonic or crystalline veins cementing or crosscutting the tuffaceous rocks in the Sunshin gold mining area. The veins consist of quartz, calcite, adularia, sphalerite, galena, pyrite, goldfieldite, chalcocite and covellite. Gold commonly occurs as fine-grained electrum and Au-tellurides such as calaverite, sylvanite and krennerite along grain boundary in sulfides. Three distinct types of fluid inclusion from quartz veins crosscutting tuffaceous rocks are associated with alteration and mineralization in the Sunshin gold deposit: Type I(liquid-rich), Type II(vapor-rich), and Type ‡W( CO2-bearing). Most fluid inclusions are extremely small (<10 microns) and complicated with multiple generations, which can be commonly found in near-surface epithermal systems. Homogenization temperatures and salinities of fluid inclusions range 136∼261°C and 0.5~6.2 wt% NaCl equiv. for Type I inclusions, 146∼310°C and 1.0∼4.7 wt% for Type II inclusions, and 160∼210°C and 1.0∼2.7 wt% for Type IV inclusions. It is assumed that these homegenization temperatures and salinities of the fluid inclusions decrease with time due to cooling and dilute near-surface waters. However, more investigations are needed to accurately determine and constrain the paragenesis of the inclusions for specific stages related to alteration and Au-mineralization.