Polymetallic nodules and cobalt (Co)-rich crusts are enriched in platinum-group elements (PGEs), especially platinum (Pt) and may be important sinks of PGEs. At present, little information is available on PGEs in polymetallic nodules, and their geochemical characteristics and the causes of PGEs enrichment are unclear. Here, PGEs of polymetallic nodules from abyssal basin in the Marcus-Wake Seamount area of the Northwest Pacific Ocean are reported and compared with the published PGEs data of polymetallic nodules and Co-rich crusts in the Pacific. The total PGEs (LPGE) content of polymetallic nodules in study area is 258×10⁻⁹ in average, markedly higher than that of Clarion-Clipperton Zone (CCZ) nodules (ΣPGE=127×10⁻⁹) and lower than that of Co-rich crusts in the Marcus-Wake Seamount (ΣPGE=653×10⁻⁹), similar to that of Co-rich crusts in the South China Sea (ΣPGE=252×10⁻⁹). The CI chondrite-normalized PGEs patterns in different regions of polymetallic nodules and cobalt-rich crusts are highly consistent, with all being characterized by positive Pt and negative Pd anomalies. These results, together with those of previous studies, indicate that PGEs in polymetallic nodules and Co-rich crusts are mainly derived directly from seawater. Pt contents of polymetallic nodules from the study area are negatively correlated with water depth, and Pt/ΣPGE ratios in nodules there are also lower than those of the Co-rich crusts in the adjacent area, indicating that sedimentary water depth and oxygen fugacity of ambient seawater are the possible important controlling factors for Pt accumulation in crusts and nodules.

中文翻译：

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西北太平洋多金属结核中铂族元素的地球化学特征

多金属结核和富钴结壳富含铂族元素（PGE），尤其是铂（Pt），并且可能是PGE的重要汇。目前，关于多金属结核中PGE的信息很少，其地球化学特征和PGE富集的原因尚不清楚。在此，报告了西北太平洋马库斯-威克海山地区深渊盆地的多金属结核的PGEs，并将其与已公布的太平洋多金属结核和富钴结壳的PGEs数据进行了比较。研究区域中多金属结核的总PGE（LPGE）含量平均为258×10 ^-9，明显高于克拉里昂-克利珀顿区（CCZ）的结核（ΣPGE= 127×10 ^-9）并低于马库斯威克海山的富钴结壳（ΣPGE= 653×10 ^-9），与南海富钴结壳的相似（ΣPGE= 252×10 ^-9））。多金属结核和富钴结壳不同区域的CI球粒陨石归一化PGEs模式高度一致，均具有正Pt异常和负Pd异常特征。这些结果以及先前的研究结果表明，多金属结核和富钴结壳中的PGE主要来自海水。研究区多金属结核中的铂含量与水深呈负相关，且结核中的Pt /ΣPGE比值也比邻近地区的富Co结壳低，表明沉积水深度和周围环境的氧逸度海水可能是控制Pt在结壳和结核中积累的重要控制因素。