摘要
To explore the geochemical characteristics and genesis of the elements in ferromanganese nodules from the Northwest Pacific,this study analyses the mineral composition,elemental content,occurrence phase and genetic mechanisms of samples by X-ray diffraction(XRD),inductively coupled plasma-optical emission spectrometry(ICP-OES),inductively coupled plasma-mass spectrometry(ICP-MS)and phase analysis methods.The results show that ferromanganese nodules are mainly hydrogenetic,and Mn/Fe content ratio ranges from 0.95 to 2.05.The major minerals are vernadite(δ-MnO_(2))and amorphous ferric oxyhydroxide(FeOOH),and the secondary minerals include todorokite,birnessite,quartz and plagioclase.Ferromanganese nodules contain high contents of Co(0.24%-0.42%),Cu(0.23%-0.73%),Ni(0.33%-0.86%)and rare earth elements(REEs,1192-1990μg/g),which have positive Ce and negative Y anomalies but no Eu anomaly.A cluster analysis suggests that the elements in ferromanganese nodules can be divided into three groups:hydrogenetic components,including Fe,Ti,Zr,P,Pb,Co,Ba,Sr,V and REEs;diagenetic components,including Mn,Ni,Mg,Zn and Cu;and detrital components,including Al,Na,K and Ca.According to chemical leaching,ferromanganese nodules can be divided into four phases:Na,Ca,Mg and Sr are mainly enriched in the carbonate phase;Mn,Co,Ni and Ba are mainly enriched in the Mn-oxide phase;Fe,P,Ti,Cu,Pb,V,Zn,Zr and REEs are mainly enriched in the Fe-oxide phase;and Al and K are mainly enriched in the residual phase.A combination of the two different methods reveal selective enrichment of metal elements from seawater by ferromanganese nodules,featuring multisource mineralization.Moreover,through ion exchange and adsorption,approximately 71.2%of REEs are enriched in the Fe-oxide phase,15.4%in the Mn-oxide phase and 12.4%in the residual phase,while REE contents in the carbonate phase are relatively low.In addition,under the oxic conditions of seawater,the oxidation of soluble Ce^(3+)to insoluble CeO_(2)together with Fe-Mn minerals results in Ce enrichment in ferromanganese nodules.This study provides a reference for the metallogenesis of ferromanganese nodules from the Northwest Pacific.
基金
The Fund of Laoshan Laboratory under contract No.LSKJ202203602
the National key R&D Program of China under contract No.2022YFC2803600
the Taishan Scholarship from Shandong Province.
作者简介
Corresponding author:Jingjing Gao,E-mail:gaojingjing8@163.com。
