黔中寒武系底部磷块岩沉积特征

A Study on Sedimentary Characteristics of Phosphate Rock at the Bottom of the Cambrian in Central Guizhou Province, China

贵州织金—清镇一带寒武系底部发育以生物碎屑磷块岩为主的含磷建造,由于其富含稀土而闻名中外。通过对黔中地区10多条含磷岩系剖面的沉积学研究,发现其具有复杂的沉积结构构造,包括角砾状磷块岩、生物磷块岩、生物碎屑磷块岩、透镜状磷块岩、交错层理磷块岩、条带状磷块岩、纹层状磷块岩等。沉积相分析结果表明,清镇一带处于潮下低能环境,沉积条带状磷块岩为主。织金毛碑冲至戈仲伍一带为潮间-潮下高能潮道环境,沉积角砾状磷块岩为主。织金熊家场至习水大岩一线,处于潮上带沉积环境,织金水淹塘至纳雍一带为潮后潟湖低能环境,沉积白云岩和磷质白云岩为主。认为富磷洋流沿毛碑冲一带潮汐水道,涌入织金戈仲伍—兴联一带,大量的磷质在障壁后海湾沉积形成磷块岩。磷块岩的沉积中心位于织金戈仲伍—兴联一带,主要成磷环境为潮间-潮下高能环境。基于含磷岩系的区域沉积特征分析,恢复了成磷期古地理,编制了P2O5含量等值线图,圈定了富磷区域,并分析成磷控制因素。

Phosphorus bearing formation constituted by bioclastic phosphate rock at the bottom the Cambrian had developed in Zhijin--Qingzhen area, Guizhou Province. It is famous in world because of rich rare earth element in phosphate rock. On the basis of the study on sediment characteristics of 12 bearing- phosphorus sections, it shows that the phosphate rocks are of complicated sedimentary structure, such as breccia phosphate rock, biological phosphate rock, bioclastic phosphate rock, lenticular phosphate rock, cross-bedding phosphate rock, banding phosphate rock, and layer phosphate rock. The analysis on the facies of phosphorus bearing formation show that the banding phosphate rock is main deposited at sub-tidal zone with low-energy in Qingzhen area; the breccia phosphate rock is main deposited at intertidal and sub-tidal zone with high-energy in Maobeichong area; thedolomite and phosphorus dolomite is main deposited at supratidal zone and tidal lagoon with low-energy in Shuiyantang--Nayong and Xiongjiachang--Xishui area. Results show that rising ocean currents with abundant phosphorus pass Maobeichong tideway, and abundant phosphorus was deposited in barrier bay at Gezhongwu--Xinglian area. Therefore, the phosphorus deposit main developed at Gezhongwu --Xinglian area; the forming environment of phosphorus deposit is mainly at intertidal and sub-tidal zone with high-energy. The palaeogeographic map and contour map of P2O5 content in Meishucun stage are drawn. Additionally, the mineralizing factors ofphosphorite deposit and abundant phosphorus area were also analyzed in this paper.