Geological Features and the Distribution of Sepiolite Deposits in Sichuan Province

The sepilite deposits in South China commonly occur at the top of the Lower Permian Qixia Formation or at the bottom of the Maokou Formation. The sedimentary environments of the deposits are characterized by shallower sea water of the Yangzi Sea, the semi-closed conditions, enough silicon and magnesian supply, weak hydrodynamic conditions, slightly higher salinity of sea water, alkalic pH values and abundant bioligic fossils. It is suggested that the deposits occur in lagoons and tidal zones or on the platforms near seas. On the basis of the early Maokouian palaeogeographic maps, however, they are mostly confined to the area from below the storm wave base of the Yangzi Sea to the upper shelf side on the upper-lower continental shelf boundary, i. e., the area from Ningqiang, Shanxi Province to Shimen, Hunan Provinve. The presence of the element Sr in the area might have resulted in the formation of "chrysanthemum-stone" composed of celestite from the ore-bearing strata or the strata above or below them. The siliceous and calcareous concretions and nodules have also been recognized in the ore beds as lumps and eyeballs. Sepiolite clay occurs right in the claystone which are referred to as the "eyelid" around these concretions, nodules and eyeballs. Besides,sepiolite is usually preserved in the geological environments with low temperatures and pressures. The well-known sepiolite deposits abroad tend to be confined chiefly to the Mesozoic and Cenozoic strata, whereas those in South China to the Lower Permian strata. Therefore, it is necessary to find sepiolite deposits in the areas of the above-mentioned strata where geological structures are simple, volcanic activity is rare or absent, crustal movement is less strong and the strata slope gently.