帕里西维拉海盆西缘中段铁锰结核的地球化学特征和成因类型

Geochemical characteristics and genesis of the ferromanganese nodules in the middle western margin of the Parece Vela Basin

深海铁锰结核能有效记录海域内重大地质事件和气候环境信息,且富含多种金属物质极具资源潜力,因而广受关注。通过对帕里西维拉海盆西侧边缘中段海域内新发现的12个站位铁锰结核的地球化学特征研究,发现与全球主要成矿区内的铁锰结核相比,Mn及主要赋存在锰氧化物中的Ni、Cu、Mo的含量较低(分别为8.20%~25.24%、0.11%~0.54%、0.08%~0.31%和0.01%~0.03%),主要由铁的羟基氧化物吸附的Ti,以及还会与钙磷酸盐发生耦合置换反应的REY的含量较高(分别为0.45%~1.88%、0.04%~0.19%),含量中等的Co(0.06%~0.27%)在铁锰相物质和硅酸盐相内核中分散分布。样品REY的标准化配分模式显示出明显一致的Ce正异常和Y负异常。铁锰结核从海水中捕获的Ce^3+容易被氧化成难溶且不具有活性的Ce^4+,Y则在结核内存在形式不稳定,容易发生解吸,致使Ce和Y分别呈现出相对于其他REY逐步富集和亏损的特征。研究区形成时间较晚,铁锰结核生长发育的时间不足,且四周地形较高,缺乏与外界连通的水道,阻碍了诸如来自南极的富氧底层流的大规模进入。区域内结核样品主要为水成型,成岩成因组分的供给太低,降低了主要有用组分的含量。以上诸多因素可能会导致区域内的铁锰结核难以富集成矿。

Deep-sea ferromanganese nodules have been widely recognized as important records of the geological events and the climatic and environmental changes of deep oceans.They are also commonly regarded as potential resources in near future for their richness in a variety of valuable metals.In this paper,12 stations of ferromanganese nodule are newly discovered from the middle of western margin of the Parece Vela Basin and samples collected and analyzed for their geochemical characteristics.These ferromanganese nodules are low in Mn,Ni,Cu and Mo(8.20%~25.24%,0.11%~0.54%,0.08%~0.31%and 0.01%~0.03%,respectively),high in Ti,REY(0.45%~1.88%and 0.04%~0.19%,respectively)and moderate in Co(0.06%~0.27%)when compared to the high potential areas of the global oceans such as CCZ,CIOB,PB and CI.The Ni,Cu and Mo are strongly enriched in manganese oxides,but the Ti and REY are mainly absorbed from ocean water by the iron oxyhydroxides,and the REY3+with a monovalent element of similar size are easily replaced through coupled substitution by Ca2+from the Ca phosphates in the iron oxyhydroxides.The Ce and Y show pronounced positive and negative anomalies in the REYSN patterns,respectively.The Ce^3+oxidation and Ce^4+fixation occur easily on the surface of the ferromanganese nodules.Once the Ce^3+in the ferromanganese nodules is oxidized to Ce^4+,it is usually less mobile and will participate less in exchange reactions with the surrounding seawater.With time,this oxidative scavenging of Ce results in the preferential accumulation of redox-sensitive Ce relative to the non-redox-sensitive REY,but part of the Y is desorbed easily from the ferromanganese nodule surface,which produces positive Ce anomalies and negative Y anomalies.The research area is relatively young,and the growth of the ferromanganese nodules is not sufficient.Moreover,the surrounding terrain of the Parece Vela Basin is relatively high and there are less gateways connecting with the outside,which prevents the large-scale entry of the cold,dense and dissolved oxygen-rich bottom water such as Antarctic bottom water.The ferromanganese nodules of the region is dominated by hydrogenetic precipitation.However,the supply of the diagenetic precipitation components is too low,which will reduce the contents of valuable metals in the research aera.Therefore,it is low in resource potential.