贵州织金磷矿岩稀土元素地球化学特征研究

STUDY ON REE GEOCHEMISTRY OF ZHIJIN PHOSPHORITES,GUIZHOU PROVINCE

贵州织金戈仲伍剖面戈仲伍组磷质岩主要为生物碎屑白云质、硅质磷块岩,普遍形成生物碎屑结构,以小壳类动物化石及藻类化石为主。采用电感耦合等离子体-质谱仪(ICP-MS)对戈仲伍组磷质岩样品的稀土元素含量进行测定分析,结果表明:磷质岩中普遍富集稀土元素,含稀土总量ΣREE较高,尤其富集Y重稀土元素;磷质岩具Ce负异常,指示环境处于氧化程度相对较高状态;稀土元素北美页岩标准化模式曲线为帽状形态,指示在磷质岩形成过程中有生物或有机质参与作用;磷质岩普遍具Eu正异常、稀土总量较高、ΣLREE/ΣHREE比值较高的特征,暗示戈仲伍组磷矿具有正常海相沉积伴有海相热水沉积混合成因的特征。

The phosphorites of Gezhongwu Formation in Zhijin county mainly consist of bioclast dolomitic and siliceous phosphorite. They generally show bioclast structure and are mainly made of small shelly fossils and alga fossils. The REE contents of phosphorites are analyzed by Finnigan Mat Element high resolution ICP-MS. The results of analysis suggest that the phosphorites are rich in REE, especially in Y element and the total REE concentrations are high. The Zhijin phosphorites show a record of the negative Ce anomalies,which indicate an oxidzing marine depositional conditions.PAAS normalized REE concentrations plotted against respective atomic numbers are chatacterized by slight enrichment of MREE,forming the hat-shaped REE patterns.The patterns suggest that fauna played an important role in the phosphorite formation.The phosphorite characters of positive Eu anomaly,the high ΣREE and the high ratio of ΣLREE and ΣHREE suggest that Zhijin phosphorites belong to the normal marine deposition associated with hydrothermal activity.