SILICEOUS COMPONENT AND SILICEOUS ROCK IN PHOSPHORITE STRATA
磷块岩中的硅质组分和硅质岩

A lot of siliccous components and even siliccous rocks existed in phosphorusbcaring series. They appeared as authigenous quartz, siliceous band, chert coneretion, siliccous cement and silicified products.The texture of siliccous cements can be divided into four types: microquartz cement, microchalcedony cement, fine crystalline quartz filling void or rounding grain in pectinate form, and mediumcoarse quartz filling void.Compared with carbonate, phosphate and mud cement, the siliceous cement usually occurred in lower part of columnar section of phosphorite deposit,in deep water area of platform in plane.This may indicate the direction of phosphorite prospecting. There are various macro-and microshape textures of silicification in phosphorite deposit, such as banded, patchy, lenticular,organismpseudomorphic, mineral-pseudocrystal, replaced residual, antisequence texture and so on.The antisequence texture is similar to the first generation cement inthe form of pectination, but it is not earliest cement.Instead, it is later cement formed by replacement.The result of replacement reduced seriously the P_2O_5 content. The siliceous components in basin type phosphorite mainly came from diagenetic differentiation of mudstone that is rich in silica and phosphate.Together with other evidences it indicates that the formation of phosphorite deposit may be associated with seafloor volcanism.The siliceous components in platform type phosphorite mainly came from mixing seawater with terrigenous water. It can be explained with the model of mixing water silicification proposed by L. P. Knauth in 1979.