A Study on Serpentinization of Serpentinites from the Ulsan Iron Mine

울산철광산 지역의 사문암의 사문석화 작용에 관한 연구

Serpentinite rocks which are composed mainly of olivine, serpentine and clinopyroxene, cropped out in the anorogenic Kyongsang sedimentary basin of South Korea. The serpentinites contain high content of MgO (36.87~41.99%) and 47~67 ppm Co, 1185~2042 ppm Ni and 979~3582 ppm Cr, which are quite similar to those of ultrabasic rocks such as peridotite and dunite. Isotopic compositions of serpentinites range from -95.5 to -105.7‰ in ${\delta}D$ and +1.7 to 7.1‰ in ${\delta}^{18}O$ corresponding to the continental antigorite type. A wide variation of oxygen isotopic values and $H_2O^+$ content of serpentinites reflect the different water/rock ratios during serpentinization processes. Formation temperature of serpentine minerals are estimated to be unusually high temperature of $488{\sim}646^{\circ}C$ by serpentine-magnetite isotopic fractionation, which belong to continental antigorite type. Calculated ${\delta}^{18}O$ value of serpentinized fluid during serpentinization is suggested that the hydrothermal fluid responsible for serpentinization be originated from the magmatic fluid with a minor influx of paleo-meteoric water in this area.