东太平洋CC区多金属结核铂族元素(PGEs)的特征及其意义

为了研究多金属结核的成矿机理，对中国大洋第45航次在东太平洋CC区（Clarion-Clipperton zone）所获得的20枚多金属结核进行了主量、微量及铂族元素分析测试，并与其他区域不同类型的多金属结核进行了对比。结果表明，研究区多金属结核基本为混合型结核，其PGEs总质量分数（w（ΣPGE））为77.2×10-9~197×10-9，平均值为136×10-9，明显低于库克（Cook）岛海域典型的水成型结核的值（w（ΣPGE）=306×10-9）；研究区结核球粒陨石标准化PGEs配分模式与水成型结核及富钴结壳非常相似，均呈现明显的Pt正异常及从Os到Pt逐渐富集、从Pt到Pd逐渐亏损的特征，结合海水的PGEs配分特征及前人研究结果，表明结核中PGEs应该直接来源于海水；研究区多金属结核w（ΣPGE）与w（Fe₂O₃）表现为正相关，与w（MnO）表现为负相关，而Cook岛海域水成型结核w（ΣPGEs）则与w（MnO）表现为正相关，与w（Fe₂O₃）表现为负相关，表明不同成因类型的多金属结核PGEs的赋存载体有所不同，水成型结核中PGEs主要赋存在锰矿物相中，而混合-成岩型结核则主要赋存在铁矿物相中，且成岩作用越强，结核富集PGEs的能力越低。研究成果对于东太平洋多金属结核成矿机理及其赋存载体研究有一定的指示意义。 

Characteristics and significance of platinum-group elements (PGEs) in polymetallic nodules from CCZ,East Pacific

The major, trace and platinum-group elements (PGEs) concentration of 20 polymetallic nodules obtained during the DY-45th Cruise from Clarion-Clipperton Zone (CCZ) of East Pacific were analyzed.The results show that the polymetallic nodules in the study area are basically mixed-type, and its total PGEs contents (ΣPGE) range from77.2×10-9 to 197×10-9, with an average of 136×10-9, which is significantly lower than that of hydrogenetic nodules in sea area of Cook Island (ΣPGE=306×10-9).The chondrite-normalized PGEs patterns of our study nodules are very similar to that of hydrogenetic nodules and cobalt-rich crusts, with all being characterized by positive Pt anomalies, gradual enrichment from Os to Pt and depletion from Pt to Pd.Combined with the characteristics of PGEs distribution in seawater and previous studies, it is suggested that PGEs in nodules should be derived directly from seawater.It is found that ΣPGE of polymetallic nodules in the study area are positively correlated with Fe and negatively correlated with Mn, but are positively correlated with Mn and negatively correlated with Fe in the sea area of Cook Island, indicating that the PGEs host-phases in different genetic nodules are different.PGEs in hydrogenetic nodules may mainly occur in manganese mineral phases, while mixed type-diagenetic nodules may mainly occur in iron mineral phases and the stronger the diagenesis is, the lower the ability of nodules is to enrich PGEs.