贵州织金磷块岩型稀土矿含矿岩系REE地球化学特征与稀土富集

The REE geochemical characteristics and REE enrichment of ore-bearing rocks of the Zhijin phosphorite-type REE deposit, Guizhou, China

贵州织金下寒武统戈仲武组(?1gz)磷矿富集大量稀土,但是磷块岩中REE富集机制问题尚不清楚。本文对贵州织金不同稀土含量区间(<262×10-6、262×10-6~527×10-6、527×10-6~761×10-6、>761×10-6)的磷块岩的研究表明,磷块岩的稀土配分均显示出Ce负异常、Eu无明显异常、MREE富集以及富集重稀土元素Y的特征。(La/Sm)N-δCe及δPr-δCe图解显示织金磷块岩Ce异常为真实的Ce异常,代表磷块岩形成在氧化环境。但当时海水的氧化环境并不是控制MREE富集的决定因素。(La/Sm)N-SmN、(Gd/Yb)N-YbN散点图显示MREE富集是稀土在富集过程中稀土发生分异的结果。(Dy/Sm)N-δEu散点图以及Eu无明显异常说明织金磷块岩形成过程中可能无热水作用的参与。地史时期'老磷块岩'普遍存在重稀土亏损的特征。

A large amount of REE resources is enriched in phosphorites within the Lower Cambrian Gezhongwu Formation in Zhijin County,Guizhou Province.However,the REE enrichment mechanism in phosphorites is not clear yet.In this paper,the research on the Zhijin phosphorites with different REE content ranges(<262×10-6,262×10-6-527×10-6,527×10-6-761×10-6,>761×10-6)indicates that REE patterns of all phosphorites show features of the Ce negative anomaly,no obvious Eu anomaly,MREE and Y enrichment.The(La/Sm)N-δCe andδPr-δCe diagrams show that Ceanomalies of the Zhijin phosphorites represent the real Ce anomaly which means the phosphorites were formed in an oxidized environment.However,the oxidized environment of seawater was not the decisive factor controlling the MREE enrichment at that time.The(La/Sm)N-SmN and(Gd/Yb)N-YbN scatter diagrams show that the MREE enrichment was resulted from the differentiation in the process of REE enrichment.The(Dy/Sm)N-δEu scatter diagram and no obvious Eu anomaly indicate that no hot water could be involved in the formation process of the Zhijin phosphorites.It’s believed that'old phosphorites'of geological history are commonly characterized with the HREE depletion.