湖北宜昌白果园陡山沱组磷块岩地球化学特征研究  

Geochemical Characteristics of Phosphorites in the Doushantuo Formation at Baiguoyuan,Yichang,Hubei Province

作　　者：密文天[1] 李德亮 范昱 

机构地区：[1]成都理工大学博士后科研流动站,四川成都610059 [2]重庆地质矿产研究院,重庆400042 [3]中国石油化工股份有限公司西北油田分公司,新疆乌鲁木齐830011

出　　处：《地质与勘探》2011年第6期982-993,共12页Geology and Exploration

基　　金：教育部高等学校博士点基金"寒武系牛蹄塘组热水沉积中的微生物群的研究"(编号:20095122110013)资助

摘　　要：湖北宜昌地区白果园含磷岩系位于黄陵背斜西北部,属于宜昌磷矿的一部分;磷块岩形成于震旦纪陡山沱期大海侵时期,其富磷层位于陡山沱组樟村坪段。对白果园剖面进行地球化学方面研究,得出以下认识:(1)白果园磷块岩富集层主要为以P2O5与CaO构成的磷酸盐矿物、以CaO、CO2为特征的碳酸盐矿物和Al2O3与SiO2构成的粘土矿物及硅质矿物,Al2O3与SiO2含量比其它地区磷块岩高,但P2O5含量低于平均值;(2)磷块岩中Cu、Pb、Ba、Zn、As、U、Mo等的富集与生物作用有关,Co、Ni含量较低,Sr在磷块岩中含量为655×10-6;(3)白果园磷块岩的轻稀土含量最高,中稀土次之,重稀土最低,ΣREE值不高,该磷块岩稀土元素配分模式与典型的生物成因的磷块岩稀土元素配分模式较为接近;(4)樟村坪段砂屑磷块岩Ceanom值为-0.091,其它含磷层位的Ceanom值均>-0.1,显示为还原环境。这可能是较为封闭的沉积环境及海水滞留造成的,或是生物活动导致局部水体Eh值下降;(5)白果园陡山沱组剖面与同期其它地区剖面可以进行碳同位素变化趋势的对比,陡山沱期的早-中期碳同位素有正偏移的趋势,这与生物复苏有关,同时出现磷块岩沉积;中期δ13C值达到最高,反映了较高的生物生产率和高的有机碳埋藏速率;陡山沱后期,δ13C值逐渐降低。Phosphatic series of Baiguoyuan in Yichang is located in the northwest of the Huangling anticline, which is a part of Yichang phosphate. The phosphorite was formed in the transgression of the Sinian Doushantuo period. The emrichment phosphorus lies in the Zhang cun-ping layer of Doushantuo Formation. From geochemical study on the profile of Baiguoyuan, we obtained the following conclusions ： （ 1 ）. The rich layer of phosphorite in Baiguoyuan is mainly composed of phosphate mineral, which is constituted by P2O5 and CaO, carbonate minerals characterized by CaO and CO2, clay minerals and silica minerals made up of A1203and SiO2. The content of A12O3and SiO2 is higher than other areas. But the content of P2O5 is lass than the average content. （2）. The enrichment of Cu, Pb, Ba, Zn, As, U and Mo in phosphorus are associated with biological activity. The content of Co and Ni is relatively low, and the content of Sr is 655×10^-6. （3）. The content of LREE is highest, and HREE is lowest, ∑REE is very low. The distribution pattern of phosphorite＇s REE in Baiguoyuan is close to the distribution pattern of biological phosphorite＇s REE. The Ce_anom of phosphorite in the Zhaug cun-ping layer is -0. 091 ,and other phosphatic layers Ce is all more than-0.1 ,which reflects a reduced sedimentary environment. This feature may be caused by closed sedimentary environment and stran- ded water, or biological activity leading to the value of Eh＇s declining in the local water. （5）. The trend of δ13C_carb in Doushantuo Formation of Baiguoyuatl could be compared to that of elsewhere around the world. It is found that the δ13C_carb bValues showed the trend of positive excursion at the early - middle stage of Doushantuo period. It related to biological recovery and sedimentary of phosphorite. The δ13C_carb value was highest at the middle stage of Doushantuo period, which shows a higher biological productivity and a higher burial rate of organic carbon. The δ13C_carb Value decreased at the late stage of Doushantu

关 键 词：震旦系 陡山沱组磷块岩成因 地球化学特征湖北宜昌 

分 类 号：P595[天文地球—地球化学]