山东韩旺新太古代条带状铁矿的稀土和微量元素特征

Characteristics of Rare Earth Elements and Trace Elements in Hanwang Neo-Archaean Banded Iron Formations,Shandong Province

山东韩旺条带状铁矿是一个新太古代大型鞍山式铁矿床,本文主要对韩旺条带状铁矿进行了岩石学和岩石化学方面的研究,并与国内外该类型矿床进行对比。岩石学研究结果认为其经受了绿片岩相至低角闪岩相变质作用,磁铁矿部分受到变质重结晶,但局部仍保存有化学沉积的特征。在TFe-(CaO+MgO)-SiO2图解中,其分布与五台山条带状铁矿和世界条带状铁矿分布区一致。韩旺铁矿稀土元素含量较低,具有太古宙海洋沉积的特征,在PAAS(太古宙后平均澳大利亚沉积岩)标准化的稀土配分曲线中显示轻稀土的相对亏损和重稀土的相对富集,具有较强的Eu的正异常和明显的Y的正异常,无明显的Ce异常,这一特征与我国鞍山弓长岭和五台山及世界许多地区的太古宙BIF特征一致。微量元素中Ti、V、Co、Ni、Mn、Sr、Ba等元素的含量都较低,在原始地幔标准化的微量元素配分曲线中具U、Ta、La、Ce、P正异常,K、Nb、Sr、Hf、Zr负异常。文章中也对韩旺条带状铁矿中Sr/Ba、Ti/V等元素的比值与其他地区进行了对比。综合研究结果认为韩旺条带状铁矿具有与火山热液伴生的铁质,形成于海洋化学沉积环境。

Hanwang banded iron formations（BIF） in Shandong Province constitute a large iron deposit of Anshan type formed in Neo-Archaean.In this paper,petrology and petrochemistry of Hanwang BIF were studied and a comparison was made with other BIF in the world.Petrological studies show that the BIF suffered greenschist facies to low amphibolite facies metamorphism and part of the magnetite was recrystallized whereas the other part of the magnetite preserved the characteristics of chemical sediments.In the diagram of TFe-（CaO＋MgO）-SiO2,Hanwang BIF has a consistent distribution area with Wutaishan BIF and other BIF in the world.The REE contents of Hanwang BIF are low,showing characteristics of marine sediments in Archean.In the PAAS-normalized REE pattern,LREE are depleted and HREE are enriched relatively,with strong Eu positive anomaly,obvious Y positive anomaly and no visible Ce anomaly.These Hanwang BIF characteristics are itentical with characteristics of Gongchangling,Wutaishan and many other Archean BIF in the world.As for trace elements,contents of Ti,V,Co,Ni,Mn,Sr and Ba are low.In trace elements distribution diagram normalized by primary mantle,U,Ta,La,Ce and P have positive anomalies,whereas things are just the opposite for K,Nb,Sr,Hf and Zr.The ratios of Sr/Ba,Ti/V and some other elements are also considered in this paper.A comprehensive study of Hanwang BIF shows that its ferruginous material was associated with volcanic hydrothermal solution and was formed in a marine chemical sedimentary environment.