Geochemistry and Significance of REE and PGE of the Cobalt-Rich Crusts from West Pacific Ocean Seamounts
Ren Jiangbo
He Gaowen
Yao Huiqiang
Zhang Huodai
Yang Shengxiong
Deng Xiguang
Zhu Kechao
Abstract：In order to discuss the differences of the formation mechanism between REE and PGE of the Co-rich Crust,in this study,rare earth elements (REE)and platinum-group elements (PGE)of the Co-rich Crusts from West Pacific Ocean Seamou-nts are compared and analyzed.The results show that ΣREY of Co-rich crusts ranges from 1 433.7×10 -6 to 2 888.0×10 -6 ,in which Ce accounts for nearly 50%.After being shale-normalized,REE patterns display relatively flat models but significant positive Ce anomalies.According to REE patterns and previous Nd isotope results,REE of Co-rich crusts have an affinity with continental crust attribution.Co-rich Crusts are also enriched in PGE and have rather high Pt content (1 1 5.5×10 -9 ~1 132.0× 10 -9 ),high (Pt/Pd)N and (Pt/Os)N ratios,with good correlation between Ir and Pt,Rh and Pt.After being chondrite-normalized,PGE patterns show relatively consistent models characterized by Os to Pt gradual enrichment and Pd element strong loss.Previous Os isotope of Co-rich crusts studies indicate provenance supply changes from mantle source to continental crust source,but the relative amounts of PGE internal elements remain stable in a certain extent.Our studies suggest that Co-rich crusts are selective when enriching rare earth.Ce positive anomaly in Co-rich crusts and Ce loss in seawater is probably due to the fact that Ce in seawater is favored by Co-rich crusts.Ce loss in seawater doesn??t change REE patterns of the newly formed Co-rich crusts,and the reason is probably that there is large number of authigenic phosphates characterized by negative anomaly of Ce,which are similar to seawater.In theory,the supply of rare earth in seawater should reach equilibrium with consumption of rare earth in seawater by oxides and phosphates.Importantly in this reaction,the choice of oxides of REE is more active,and phosphates show more inheritance.Despite the provenance supply changing,PGE patterns of Co-rich crusts are still stable.So the fractionation of PGE from seawater to Co-rich Crusts can also be considered for selective PGE absorption. For preference of Pt and Ir,exclusion of Pd and Os,Co-rich Crusts form a unique pattern of PGE.
Keywords：REEPGEcobalt-rich crustsWest Pacific Ocean Seamountsgeochemistry
Publication Date：2016-01-01
Online Publishing Date：2025-08-15(First online date of this platform, not the publication date of the document)
Pages：13( 1745-1757 )