震旦纪陡山沱组的泥晶磷块岩

泥晶磷块岩(micritic phosphorite)是磷块岩的主要类型之一。我国的磷块岩矿床也多有这种矿石。过去往往把组成泥晶磷块岩的磷酸盐矿物叫做胶磷矿(collophane)。扫描电镜、X-射线衍射等观察结果表明,胶磷矿实际上也是结晶质磷灰石,只是由于颗粒极其微小而已。由这种泥晶磷灰石组成的泥晶磷块岩也同样不像过去描述的那样单调,而是具有比较复杂的结构、构造。

MICRITIC PHOSPHORITES IN THE SINIAN DOUSHANTUO FORMATION

Micritic phosphorites in Doushantuo formation are mainly spread in Guzhang, Yuanling, Luxi, Chenxi and Huaihua areas in West-Hunan province, and located in eastern of pericontinerital sea during the Duoshantuo age. Phosphate-bearing sequence consists basically of clay, silica, phosphate and carbonate rock in ascending order. The micritic phosphorite is main type of the phosphate rock.The phosphate minerals in micritic phosphorites are micritic, fibrous and finecrystal apatites. The micritic apatite was directly precipitated from marine water. The fibrous apatite was pricipitated from interstitial water among micritic apatite lumps. The finecrystal apatite was mainly produced by recrystallization of the micritic apatite and formed under the influence of siliceous solution. In addition to apatite, the micritic phosphorite also contain illite, quantz, dolomite and calcite, etc..The micritic phosphorites were in the transitional horizon from the clayay or siliceous to carbonate deposites in Doushantao Formation. In general, they deposited in sedimentary environments of transitional zone.