王琳璋,曾志刚. 西北太平洋采薇海山富钴结壳矿物学和地球化学特征[J]. 海洋地质与第四纪地质,2023,43(5): 36-49. DOI: 10.16562/j.cnki.0256-1492.2022091901
引用本文: 王琳璋,曾志刚. 西北太平洋采薇海山富钴结壳矿物学和地球化学特征[J]. 海洋地质与第四纪地质,2023,43(5): 36-49. DOI: 10.16562/j.cnki.0256-1492.2022091901
WANG Linzhang,ZENG Zhigang. Mineralogical and geochemical features of Co-rich crust on Caiwei Guyot, Northwest Pacific Ocean[J]. Marine Geology & Quaternary Geology,2023,43(5):36-49. DOI: 10.16562/j.cnki.0256-1492.2022091901
Citation: WANG Linzhang,ZENG Zhigang. Mineralogical and geochemical features of Co-rich crust on Caiwei Guyot, Northwest Pacific Ocean[J]. Marine Geology & Quaternary Geology,2023,43(5):36-49. DOI: 10.16562/j.cnki.0256-1492.2022091901

西北太平洋采薇海山富钴结壳矿物学和地球化学特征

Mineralogical and geochemical features of Co-rich crust on Caiwei Guyot, Northwest Pacific Ocean

  • 摘要: 富钴结壳是一种富含Mn、Co、Ni和稀土元素(镧系元素加钇,简称REY)等元素的海底矿产资源。本文研究的富钴结壳样品是“科学”号在2018年HOBAB5航次于西北太平洋采薇海山的山顶边缘上通过电视抓斗获得的。利用扫描电镜、X射线衍射仪(XRD)、电感耦合等离子体发射光谱仪(ICP-OES)和电感耦合等离子体质谱仪(ICP-MS)分析了富钴结壳的显微构造、矿物学特征和地球化学特征,并探讨了其成因类型和形成机制。富钴结壳的结构从内到外可分为土黄色的疏松层(C8-5)、黑色铁锰致密层(C8-2、C8-3和C8-4)和发育葡萄状球体的粗糙表面(C8-1)。土黄色疏松层孔隙度较高,主要组成矿物为水羟锰矿、石英、钙长石、钠长石、钙十字沸石和钡镁锰矿,Mn的含量较低,Al的含量较高。黑色的铁锰致密层孔隙度较低,呈柱状构造,主要组成矿物为水羟锰矿、石英、钙长石和钠长石,Al含量有所下降,Mn含量升高, 说明陆源物质的供应逐渐变少。在富钴结壳的生长后期,其主要显微构造由柱状构造向斑杂构造转变,二者的过渡区域为铁锰氧化物与富Si碎屑物质组成的层状构造。富钴结壳各层位的Mn/Fe比值为1.16~1.85,且各层位Ce呈正异常,Y呈负异常,以上特征表明富钴结壳为水成成因型,其金属元素来源于氧化性海水,未受到热液活动的影响。依据富钴结壳的年代学数据,可知从渐新世末期到上新世中期,富钴结壳的生长过程一直受控于太平洋深层水。Co/(Fe+Mn)和Co/(Ni+Cu)的不断升高表明富钴结壳一直在氧化性较高的海水环境中生长。相较于其他大洋和海区,采薇海山富钴结壳具有高含量的Co、Ni和REY,具有极高的经济价值和开采价值。

     

    Abstract: Co-rich crusts are a kind of marine mineral resources rich in Mn, Co, Ni and rare earth elements (lanthanide and yttrium, abbreviated as REY). The Co-rich crust sample studied in this paper was collected on the mountaintop edge of Caiwei Guyot in the Northwest Pacific Ocean onboard research vessel “Kexue” (Science) with a TV grab during the HOBAB5 cruise expedition in 2018. The microstructure, mineralogy, and geochemistry of the Co-rich crust were analyzed by scanning electron microscope, X-ray diffraction (XRD), inductively coupled plasma atomic emission spectrometer (ICP-OES), and inductively coupled plasma mass spectrometry (ICP-MS), and its genetic type and formation mechanism were discussed. The textures of the Co-rich crust could be divided into yellowish loose layer (C8-5), black dense ferromanganese layers (C8-2, C8-3 and C8-4), and rough surface in black botryoidal shape (C8-1) from inside to outside. The yellowish loose layer is composed of Fe-vernadite, quartz, albite, anorthite, todorokite, and phillipsite. It has high porosity with a high content of Al and low content of Mn. The black dense ferromanganese layers have low porosity and are mainly columnar in structure, and the main component minerals are Fe-vernadite, quartz, albite, and anorthite. Compared with C8-5, the content of Al decreases but the content of Mn increases, indicating that the supply of terrigenous materials gradually decreased. In the later growth process of the Co-rich crust, its microstructure changed mostly from columnar structure to mottled structure, and the transition area is in layered structure and composed of ferromanganese oxides and Si-rich clastic materials. The Mn/Fe ratios of layers of the Co-rich crust range from 1.16 to 1.85, and each layer shows positive Ce anomaly and negative Y anomaly. The above characteristics indicate that the Co-rich crust in the study area shows its hydrogenetic origin and is not affected by hydrothermal activities, whose metal elements are derived from oxidizing seawater. According to the chronological data, we conclude that the growth process of the Co-rich crust was controlled by Pacific Deep Water from the late Oligocene to the middle Pliocene. The continuous increases of Co/(Fe+Mn) and Co/(Ni+Cu) indicate that the Co-rich crust has been growing in a highly oxidizing marine environment. Compared with other oceans and seas, the Co-rich crust on Caiwei Guyot is enriched in Co, Ni and REY, and shall has very high economic value and mining prosperity.

     

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