///The Yangcun talc deposit in Guangfeng County of Jiangxi Province is one of the superlarge talc deposits in the world. The talc ore consists mainly of oolite granular talc with a small amount of quartz, carbonates and disseminated organic matter, assuming typical sedimentary oolite granular structure. The authors hold that the required silicon in talc was probably provided by silica-rich hydrothermal fluid with slightly higher 87Sr/86Sr values than the seawater. It is considered that the Yangcun talc deposit may have a syngenetic hydrothermal sedimentary origin. Magnesium was mainly derived from magnesium-rich seawater and silicon was mainly derived from silicon-rich and high 87Sr/86Sr hydrothermal fluid which was formed by seawater infiltrating and leaching of the old crustal strata.