陕南天台山、茶店一带磷块岩的时代和成因特征

陕西南部汉中天台山、勉县茶店和略阳何家岩、金家河一带磷块岩的时代,目前有三种看法,即:泥盆纪、震旦纪和寒武纪。这一带磷块岩的成因也比较复杂。在磷酸盐沉积、成岩以后,又受到变质、褶皱、断裂和水溶液活动影响。本文对天台山、茶店一带的磷块岩的成矿时代和生成特点提出一些初步意见。

THE AGE AND GENESIS OF PHOSPHORITES IN THE TIANTAISHAN AND CHADIAN ZONES, SOUTHERN SHANXI PROVINCE

On the basis of, geological data, such as phosphatized red alge (Solenoporaceae) in phosphorite and isotopic age(651 my.) of the phosphate-bearing sequences, it is suggested that the age of phosphorites in the Tiantaishan and Chadian zones can be ascribed to the Siuian Doushantuo age, but not to the Devonian or Cambrian Period.The phosphorites in the phosphate-bearing sequences can be divided into four types, viz, micritic, pelletal, psammitic and finecrystal phosphorites. The phosphate minerals in the phosphorites are mainly micritic, sparry and finecrystal apatite. The micritic apatite was directly precipitated from marine water and formed the micritic phosphorite and pellets. The sparry apatite was precipitated from pore water and formed cements in interstices between pellets. The finecrystal apatite formed finecrystal phosphorite, resulted from recrystallization and action of siliceous solution. In addition to the apatites, the phosphorites contain quartz, dolomite, calcite, sericite and organic carbon, etc.The phosphorites were formed in the transitional horizon from the siliceous clay rocks to carbonate deposites. They deposited in sedimentary environments of transitional and subtidal zones. The phosphorite was affected by metamorphism, solution and weathering.