东菲律宾海多金属结核微区元素赋存特征及成因意义  

Fine Scale Occurrence Characteristics of Elements in Polymetallic Nodules from the East Philippine Sea and Their Genetic Significance

作　　者：程宇龙 李东义 王爱军 徐勇航 CHENG Yulong;LI Dongyi;WANG Aijun;XU Yonghang(Laboratory of Ocean and Coast Geology,Third Institute of Oceanography,Ministry of Natural Resources,Xiamen 361005,Fujian,China)

机构地区：[1]自然资源部第三海洋研究所、海洋与海岸地质实验室,福建厦门361005

出　　处：《大地构造与成矿学》2023年第1期133-148,共16页Geotectonica et Metallogenia

基　　金：矿床地球化学国家重点实验室开放基金项目(202004);自然资源部第三海洋研究所基本科研业务费专项资金(海三科2019007);全球变化与海气相互作用专项(GASI-02-PAC-CJ05)联合资助。

摘　　要：多金属结核富含Mn、Fe、Co、Ni、Cu和REY(稀土元素和钇)等元素,具有巨大的潜在经济价值。东菲律宾海结核由包壳和核部岩屑(或泥团)构成,其Mn、Fe、Co、Ni和Cu含量介于南海结核和大洋结核之间,但该区域结核的微区特征尚不清楚。本文基于微区元素分析,探究了东菲律宾海结核的元素赋存特征及其成因意义。结果表明,东菲律宾海结核总体为水成成因,主要形成于氧化环境。结核包壳主要由含δ-MnO_(2)的水成型富铁层(FeO平均为28.7%,MnO平均为21.9%,Mn/Fe值平均为0.93)构成,但边部存在薄层(<100μm)的成岩型富锰层(FeO平均3.41%,MnO平均52.6%,Mn/Fe值平均为17.5),富锰层具有高NiO(2.71%)和CuO(1.45%)含量。根据Co经验公式估算,富锰层可能形成于末次盛冰期(LGM)以来。本研究还发现,结核核部气孔状岩屑中存在成岩成因的富锰矿物,其MnO含量为22.5%~64.7%,FeO含量为0.46%~7.05%,Mn/Fe值为3.96~126。相比包壳中富锰层,核部富锰矿物NiO(1.25%)和CuO(0.5%)含量明显减少。此外,核部富锰矿物具有从纹层状到纤维状的变化,且随MnO含量(43.8%→56.1%)增加,CoO(0.55%→0.02%)、NiO(2.04%→0.88%)、CuO(0.62%→0.43%)含量反而降低,指示了矿物演化过程中,Co、Ni和Cu倾向于保留在纹层状富锰矿物中。Polymetallic nodules are rich in Mn,Fe,Co,Ni,Cu and REY(rare earth elements and yttrium),which have great potential economic value.The nodules from the East Philippine Sea(EPS)are composed of the outer ferromanganese layers and the core rock fragments(or mud).The contents of Mn,Fe,Co,Ni and Cu in the EPS nodules are in ranges between those of the nodules from the South China Sea and the ocean.However,the fine scale characteristics of the EPS nodules are still not clear.Based on fine scale elements analysis,this paper explores the occurrence characteristics of elements in the EPS nodules and their genetic significance.The results show that the nodules are mainly hydrogenetic,forming mainly in oxidizing environment.The outer ferromanganese coats are mainly composed of hydrogenetic Fe-richδ-MnO_(2) layers(average FeO,MnO and Mn/Fe ratios are 28.7%,21.9%and 0.93,respectively),and thin(<100μm)diagenetic Mn-rich layers(average FeO,MnO and Mn/Fe ratios are 3.41%,52.6%and 17.5,respectively)of todorokite(or buserite)at the edge.The Mn-rich layers have high contents of NiO(average 2.71%)and CuO(average 1.45%).According to the empirical formula of Co,the Mn-rich layers may have been formed since the last glacial maximum(LGM).This paper also found that there are diagenetic Mn-rich minerals in the core vesicular rock fragment,which have contents of MnO,FeO and Mn/Fe ratios in ranges of 22.5%-64.7%,0.46%-7.05%and 3.96-126,respectively.Compared with the outer Mn-rich layers,the NiO(average 1.25%)and CuO(average 0.5%)contents of the Mn-rich minerals in the core are significantly lower.Besides,the core Mn-rich minerals show laminar to fibrous changes,for instances,MnO increases from 43.8%to 56.1%,CoO decreases from 0.55%to 0.02%,NiO decreases from 2.04%to 0.88%,and CuO decreases from 0.62%to 0.43%,implicating the remain of Co,Ni and Cu in laminar Mn-rich minerals during the process of mineral evolution.

关 键 词：东菲律宾海 多金属结核 微区元素赋存特征 核部富锰矿物 

分 类 号：P67[天文地球—海洋地质]