修水地区下寒武统富铀地层特征及其铀富集的成因

发布时间：2018-06-18 12:02

  本文选题：富铀地层 + 沉积成岩作用　； 参考：《南京大学》2017年硕士论文

【摘要】：修水碳硅泥岩型铀矿是我国南方碳硅泥岩型铀矿的重要组成部分。前人认为修水地区的碳硅泥岩型铀矿是在沉积成岩过程中铀预富集的基础上,又经历了热液作用或者淋积作用而富集成矿。在修水地区,碳硅泥岩型铀矿的赋矿地层也是富铀地层,说明沉积环境影响着碳硅泥岩型铀矿的分布。但是,前人对于赋矿地层的研究主要集中于大尺度的沉积相方面,对于具体的沉积环境及其与铀富集的关系研究很少。本研究对修水地区下寒武统王音铺组至观音堂组下部富铀地层钻孔样品(U含量为9.37～202PPm)进行了细致的显微观察和分析,揭示这些钻孔样品显示明显的沉积成岩特征,未发现明显热液叠加/淋积作用现象,表明本区下寒武统地层只经历了沉积成岩作用,而没有经历过明显的热液作用或者淋积作用。在此基础上,进一步分析了修水地区下寒武统地层中U含量与沉积环境因素(沉积盆地中的生物生产力、底层水体的氧化还原状态、及盆地与广海间的流通性)之间的关系。研究结果显示:修水地区下寒武统王音铺组和观音堂组下部地层大部分样品中的U含量与TOC含量呈正相关;王音铺组上部U含量最高(202ppm)的样品沉积时的初级生物生产力也最高,经扫描电镜观察和电子探针分析,发现其中有机质中包裹着沥青铀矿,两者关系密切,U与有机质很可能是一起沉积-成岩富集的;U含量最高的样品中的绿泥石中,八面体位置有空缺,六次配位ⅥAl的数量明显大于四次配位ⅣAl,显示为沉积成岩阶段的绿泥石;U含量最高的样品中也没有发现典型的热液成因或者淋积成因的矿物;修水下寒武统地层源区的化学风化程度很高,说明古气候是温暖湿润的;在缺氧硫化的强还原沉积环境下沉积的王音铺组地层的U含量明显高于在缺氧非硫化环境下沉积的观音堂组下部地层中的U含量,而且在强还原硫化环境下,沉积时盆地处于开放流通性程度较高时期的样品,其U含量明显高于盆地处于开放程度较低时期的样品。综合这些观察和分析得出,早寒武世王音铺组上部地层沉积时,高生物生产力所形成的有机质降解时大量耗氧,导致底层水沉积环境处于强还原硫化状态,同时,沉积盆地处于适当的开放程度,U在强还原硫化环境下形成的沉积物中达到较高的程度富集乃至矿化的水平。
[Abstract]:Xiushui Carbon-Si-mudstone uranium deposit is an important part of Carbon-Si-mudstone type uranium deposit in southern China. It is believed that the Carbon-Si-mudstone type uranium deposits in Xiushui area were enriched by hydrothermal or leaching processes on the basis of uranium preenrichment during sedimentary diagenesis. In Xiushui area, the ore-bearing strata of carbon-silicon-mudstone type uranium deposits are also uranium-rich strata, indicating that the sedimentary environment affects the distribution of carbon-silicon-mudstone type uranium deposits. However, previous researches on ore-bearing strata are mainly focused on large-scale sedimentary facies, but few on the specific sedimentary environment and its relationship with uranium enrichment. In this study, detailed microscopic observation and analysis of the uranium rich formation samples from the lower part of the Lower Cambrian Wangyinpu formation to the Guanyintang formation in Xiushui area were carried out. The results showed that these borehole samples showed obvious sedimentary diagenetic characteristics. There is no obvious hydrothermal superposition / leaching phenomenon which indicates that the Lower Cambrian strata in this area have only experienced sedimentary diagenesis but have not experienced obvious hydrothermal action or leaching. On this basis, the relationship between U content in Lower Cambrian strata and sedimentary environmental factors (biological productivity in sedimentary basin, redox state of bottom water body, and circulation between basin and Guang Hai) in Xiushui area is further analyzed. The results show that the U content in most samples of lower Cambrian Wangyinpu formation and Guanyintang formation in Xiushui area is positively correlated with TOC content, and the primary biological productivity of samples with the highest U content in the upper part of Wangyinpu formation is the highest. By scanning electron microscopy and electron microprobe analysis, it was found that the organic matter is covered with asphaltene uranium ore, and the relationship between the U and the organic matter is probably the chlorite in the sample with the highest content of U in the sedimentary diagenetic enrichment. There is a vacancy in octahedral position, and the quantity of VI Al in six times coordination is obviously larger than that in fourth coordination 鈪，

本文编号：2035413