鲕粒,豆粒磷块岩的显微结构和生成特点

晚震旦世陡山沱组和早寒武世渔户村组、辛集组磷矿中有各种鮞粒、豆粒磷块岩。豆粒、鮞粒内核的成分和结构复杂,有来自陆地的各种岩石砂屑、细砾,也有盆内沉积物破碎成的各种内碎屑。鮞粒、豆粒的壳层是同心纹层状磷灰石,它是内核在富磷海水扰动中逐层淀积而成。大部分豆粒、鮞粒在滨海高能浅水中与陆源砂、砾和岔内碎屑沉积在一起,少量鮞粒则沉积在滨外深水低能环境巾。豆粒、鮞粒和碎屑等沉积后又被不同物质胶结。

MICROSTRUCTURES OF PISOLITIC AND OOLITIC PHOSPHORITES AND THEIR GENETIC CHARACTERISTICS

There are six types of pisolitic and oolitic phosphorites in the Doushantuo, Yuhucun and Xinji Formation, viz., ruduceous, sandy, dolomitic, siliceous, micritic pisolitic phosphorites and siliceous oolitic phosphorite. These phosphorites consist of phosphatic pisolites, oolites and various cements or matrices. The mineral composition forming lamella of pisolite and oolite is mainly micritic apatite that was directly precipitated from marine water. It has concentric laminated structure. The nucleus are mainly quartz sand, dolomite clast and various phosphatic intraclast. The intraclasts occurred in a sedimentary basin and were produced from broken phosphatic deposits. The mineral constituents of the cements are quartz, dolomite, limonite and a small amount of kaolinite, which were precipitated from pore water among the pisolites or oolites. The constituents of matrices are quartz sand, metamorphic rock gravel, dolomite and phosphatic intraclasts. They deposited together with pisolites and oolites at the same time. The pisolitic phosphorites were mainly deposited in high-energy environments of tidal flat and tidal shoal, and the oolitic phosphorite deposited in low-energy environments of deep water zone.