Several mines in Jeonnam produce the ores of having high SK number of refractoriness. Among those for 5 mines, this paper deals with the relationahip between SK number and mineral composition of the ore, and with the genesis of the deposits. 1. Byok-Song and Chon-Un Mine: Mineral compositions of the ores are chiastolite, chloritoid(monoclinic), kaolinite, sericite, diaspore, corundum, and quartz. The ores having SK number of 36 or 37, consist chiefly of chiastolite and diaspore and a little amount of kaolinite, sericite, corundum, chloritoid, and quartz. The ores having SK number of 33 or 34 consist of chloritoid, sericite, kaolinite, chiastolite, and diaspore. With increasing the amount of chloritoid and sericite, and decreasing the amount of diaspore and chiastolite, the SK number of the ores decreases. The deposit, originally high alumina-bearing shale of Chon-Un San formation, seems to be formed by contact metamorphism(forming of chiastolite), regional metamorphism(forming of monoclinic chloritoid), and hydrothermal replacement(forming of large crystal of diaspore veinlets). 2. Song-Sauk Mine: Mineral compositions of the ores are chiefly pyrophyllite and quartz and a little amount of kaolinite, dickite, diaspore, and pyrite. Many spherical inclusions containing in pyrophyllite deposits, consist chiefly of diaspore and kaolinite, The inclusions have the high SK number of 38. Amount of spherical inclusions is about 5 % to the whole pyrophyllite ores. The SK number of other pyrophyllite ore is less than 32. Quartz and pyrite are chief minerals lowering the SK number of the ore. The deposits have been formed by hydrothermal processes by replacing the siliceous tuff of Mesozoic age. Spherical inclusions consisting of diaspore and kaolinite, show the selective replacement of hydrothermal solutions to the materials of feldspar in tuff. 3. Seung-San Mine: Mineral compositions of the ores are chiefly kaolinite, dickite, diaspore, and quartz. But some part of the mine consists of alunite deposits. The ores having SK number of 35 or higher consist chiefly of kaolinite and diaspore and a little amount of quartz. With increasing the amount of quartz and decresing the amount of diaspore, the SK number of the ore decreases. The deposits have been formed by hydrothermal processes by replacing the siliceous tuff and quartz porphyry. 4. Wan-Do Mine: Mineral compositions of the ores are chiefly pyrophyllite and quartz. But some ore contains a little amount of diaspore, kaolinite, pyrite, and chloritoid. The ores having high SK number of 36 consist chiefly of diaspore and pyrophyllite. Pyrophyllite ore has a SK number of 32 or lower. Amount of quartz and pyrite decreases the SK number of ores in this mine. Rhyolite was replaced by the action of hydrothermal solutions forming the pyrophyllite deposits.