荆襄地区陡山沱组磷块岩的类型、成因和沉积环境

本文根据野外调查和室内初步研究成果并结合有关地质资料,分析、讨论了荆襄陡山沱组含磷岩系的磷块岩类型、成因和沉积环境。通过分析可知,组成磷块岩的磷灰石有不同的形成方式;磷块岩沉积在海退旋回中粘土和硅质沉积向碳酸盐沉积的转变阶段;磷块岩矿床形成在陆缘海内与深水有联系的浅水地带。 矿区含磷岩系特征综合于图1。

TYPES, ORIGIN AND SEDIMENTARY ENVIRONMENT OF PHOSPHORITE OF DOUSHANTO FORMATION IN JINGMEN-XIANYANG REGION, HUBEI PROVINCE

Of the phosphorites in Doushouto phosphate-bearing sequence there are five types, viz., micritic, pelletal, interclastic, algal and finecrystal phosphorites. The phosphate minerals in the phosphorites are the micritic, sparry, filamentary and finecrystal apatite. The micritic apatite is directly precipitated from marine water and forms the micritic phosphorite and the pellets. The sparry apatite is precipitated from pore water and acts as cement in pore space among pellets or filaments. The filamentary apatite in the algal phosphorite might be the algal filaments at first, which was perhaps replaced by phosphate later. The finecrystal apatite formed finecrystal phosphorite, resulting from recrystallization and action of siliceous solution.The phosphate-bearing sequence consists of three cyclothems. Every cyclothem consists basically of clay, silica, phosphate and carbonate rocks in ascending order. The phospha-tic rocks were deposited in a transitional horizon from deep water to shallow water during the regressive cyclothem. Their sedimentary environment is mainly shallow-water zone of epicontinetal sea maybe the subtidal and intertidal zone.