富钴结壳中矿物组成对稀土元素分布的制约

摘要

Rare earth elements (REEs)are important tracers for geochemical cycles,and are also world strategic re-sources.In this study,we investigated the mineral and REEs characteristics of Co-rich crusts from Johnston island to show that REEs distributions are constrained by their mineral compositions.On the basis of their mineral char-acteristics,the Co-rich crusts can be classified into type A,type B,and type C.The vernadite contents decrease from type A via type B to type C;and type B shows the highest apatite contents.Birnessite and todorokite are enriched in type C crust.Type A crusts are enriched in REE3+ and Ce,whereas type B crusts are characterized by high con-tents of Ce and Y.In type A crust,REE3+ and Y that originated from seawater are specified adsorbed on the Fe-phase.Cerium is enriched in Mn-mineral via the oxidation from Ce3+to Ce4+ and separation from other REEs.In type B crust,REEs mainly form independent minerals,part of Ce and LREE3+ are absorbed in the Fe-phase,and part of Y enter in apatite.In type C crust,REEs show the enrichment phenomena in Mn-minerals,and also part of Y are absorbed in apatite.%为探讨富钴结壳中矿物组成对稀土元素分布的制约，对约翰斯顿岛富钴结壳中矿物组成及稀土元素特征进行了研究。依据主要矿物组成，富钴结壳可以分为3种类型，分别命名为 A、B、C。由 A到 C，水羟锰矿含量逐渐降低，B 类中磷灰石含量最高，C 类中水钠锰矿和钙锰矿含量最高。A 类结壳中富集 REE3＋、Ce，B 类结壳中富集 Ce 和 Y。A 类富钴结壳中，REE3＋、Y 以专属吸附的方式富集在铁氧化物上，Ce3＋氧化成 Ce4＋与其他 REE 分离，吸附在锰矿物上。B 类结壳中，稀土元素主要以独立矿物的形式存在，另有部分 Ce、LREE3＋吸附于铁相中，部分 Y 存在于磷灰石中。C 类结壳中，稀土元素主要赋存在锰矿物中，部分 Y 存在于磷灰石中。