青海省祁漫塔格那西郭勒地区条带状铁矿的稀土和微量元素特征

Characteristics of rare earth elements and trace elements in Qimantage Naxiguole area banded iron formation,Qinghai province

那西郭勒铁矿是近年来东昆仑祁漫塔格古元古代金水口岩群中新发现的沉积变质型铁矿。为探讨那西郭勒铁矿的物质来源、形成环境,以那西郭勒条带状铁矿为研究对象,对矿石微量元素和稀土元素进行了系统测试。结果表明:矿石样品中∑REE和Y具有高度一致的特征,稀土总量较低,为68.51~103.29μg/g,Y/Ho比值较高;经太古界后平均澳大利亚页岩(PAAS)标准化后的稀土元素配分模式呈现重稀土富集、轻稀土亏损的分馏模式,且具有Eu,Y,La的正异常;铁矿石Ti/V比值为19~54.45,明显高于铁质页岩中Ti/V比值,可能与海底火山活动有关;Ni/Co比值平均为1.52,高度一致的Zr和Hf以及V和Sc的正相关。由此可见那西郭勒地区条带状磁铁矿的稀土元素来源为火山热液和海水的混合溶液,尽管磁铁矿的Ce/Ce*比值为0.86~0.92,但样品缺乏真正意义的Ce负异常,指示在铁矿沉积时海水的氧化还原状态为可能缺氧环境。

Naxiguole iron ore is sedimentary metallogenic type in Qimantage metallogenic belt which is originated in the Paleoproterozoic Jinshuikou Group. In order to explore Naxiguole iron ore material source and formation environment,taking its banded iron ore as the research object to systematic test ore trace elements and rare earth elements. The results show that： amount of rare earth elements（ ∑ REE） and Y of the iron ore sample has very consistent characteristics. The amount of rare earth elements is low,from 68.51 ~ 103.29μg/g,with high Y/Ho ratio. The normalized rare earth element distribution pattern of post-Archean Australian shale（ PAAS） shows heavy fractionation of heavy rare earth and light rare earth loss,and has positive anomalies of Eu,Y and La. Ti/V value distribution varies from 19 to 54.45 for iron ore,and is significantly higher than that in the iron shale,indicating it is closely related to submarine volcanic activity. Mean Ni/Co ratio is 1. 52,presenting positive correlation with Zr and Hf,V and Sc. The rare earth elements in banded iron ore at Naxig-uole area are from volcanic hydrothermal and mixture of sea water. The ratio of Ce/Ce＊ for magnetite is from 0.86 to 0.92,but the real sample Ce lacks negative anomaly,indicating that the redox state of seawater during the deposition of iron ore was a possible hypoxic environment.