麦哲伦海山群MK海山富钴结壳稀土元素的赋存相态

Existing Phase of Rare Earth Elements in Co-Rich Fe-Mn Crusts from Seamount MK of Magellan Seamount Cluster

利用ICP-OES和ICP-MS,分析了麦哲伦海山群西北端MK海山2 170 m水深的MKD23B-3号富钴结壳样品,获得了其剖面上主元素、稀土元素（REE）和Y含量数据,并基于元素含量间的线性相关关系,研究了REE和Y的赋存相态。结果显示：该样品剖面从基岩到表面可划分为5层,第Ⅰ、Ⅱ层为磷酸盐化壳层,第Ⅲ、Ⅳ、Ⅴ层为未磷酸盐化壳层。在未磷酸盐化壳层中,REE和Y主要赋存在δ-MnO2相中;而在磷酸盐化壳层中,REE和Y除了赋存在Fe、Mn氧化物相中外,主要赋存在独立于碳氟磷灰石（CFA）的矿物相态中,可能为稀土的磷酸盐。并提出利用磷酸盐中REE/Y估算富钴结壳磷酸盐化壳层次生稀土的方法,据此估算了MK海山富钴结壳磷酸盐化壳层次生稀土的量。在该样品中,次生稀土占稀土总量的42%~88%,近一半以上的稀土是次生的,磷酸盐化作用对于REE和Y的次生富集具有显著的贡献;因此解读磷酸盐化富钴结壳的稀土元素（特别是Nd同位素）古海洋记录必须排除次生稀土元素的干扰。

The Co-rich Fe-Mn crust sample,MKD23B-3,was dredged from Seamount MK of Magellan Seamount cluster at a water depth of about 2 170 m.Major elements,rare earth elements（REE） as well as Y compositions along the section of this sample are analyzed by ICP-OES and ICP-MS.The existing phases of REE and Y are investigated based on linear correlation analysis.The section of this sample can be divided into 5 layers from substrate to surface,the layers Ⅰ-Ⅱ of this Co-rich Fe-Mn crust are phosphatized and the layers Ⅲ,Ⅳ and Ⅴ are non-phosphatized.In non-phosphatized layers,REE and Y are mainly distributed in the phase of δ-MnO2.In phosphatized layers,besides in the phase of δ-MnO2 and Fe oxyhydroxides,REE and Y are mainly consisted in the phase（probably REE phosphate） independent from carbonate fluorapatite.A new method for calculation of secondary REE in phosphatized Fe-Mn crusts is proposed,and the secondary rare earth elements in the phosphatized layers Ⅰ and Ⅱ of Co-rich Fe-Mn crust MKD23B-3 are calculated.In the phosphatized layers,the secondary rare earth elements are 42%-88% of total rare earth elements,which indicates nearly more than half of total REE in phosphatized Fe-Mn crustal layers are secondary,and the effect of phosphatization is significant during the enrichment of secondary REE.It＇s concluded that the contamination of secondary rare earth elements should be excluded from the paleoceanographic record of REE（especially Nd） in phosphatized Fe-Mn crusts.