高晶晶，刘季花，张辉，等. 西太平洋采薇海山和徐福海山富钴结壳稀土元素地球化学特征及来源[J]. 海洋地质与第四纪地质，2022，42(3)： 87-99. doi: 10.16562/j.cnki.0256-1492.2021071302
引用本文: 高晶晶，刘季花，张辉，等. 西太平洋采薇海山和徐福海山富钴结壳稀土元素地球化学特征及来源[J]. 海洋地质与第四纪地质，2022，42(3)： 87-99. doi: 10.16562/j.cnki.0256-1492.2021071302
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GAO Jingjing，LIU Jihua，ZHANG Hui，et al. Geochemistry and sources of rare earth elements in cobalt-rich crusts from the Caiwei and Xufu seamounts, West Pacific Ocean[J]. Marine Geology & Quaternary Geology，2022，42(3)：87-99. doi: 10.16562/j.cnki.0256-1492.2021071302
Citation: GAO Jingjing，LIU Jihua，ZHANG Hui，et al. Geochemistry and sources of rare earth elements in cobalt-rich crusts from the Caiwei and Xufu seamounts, West Pacific Ocean[J]. Marine Geology & Quaternary Geology，2022，42(3)：87-99. doi: 10.16562/j.cnki.0256-1492.2021071302
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西太平洋采薇海山和徐福海山富钴结壳稀土元素地球化学特征及来源

Geochemistry and sources of rare earth elements in cobalt-rich crusts from the Caiwei and Xufu seamounts, West Pacific Ocean

    摘要
  • 摘要: 利用X射线衍射法、等离子体发射光谱法和等离子体质谱法分析了西太平洋采薇海山和徐福海山富钴结壳矿物相组成以及常微量元素含量，探讨稀土元素地球化学特征和物质来源。研究表明，富钴结壳样品主要结晶矿物为水羟锰矿，次要矿物包括石英、斜长石、钾长石和碳氟磷灰石，同时含有大量非晶态铁氧/氢氧化物。富钴结壳的Mn和Fe含量最高，Mn含量为16.20%～26.62%，Fe含量为8.56%～18.19%，老壳层（IV和V）发生了磷酸盐化作用。富钴结壳的稀土元素明显富集，轻稀土元素明显高于重稀土元素，稀土总量为1 842～2 854 µg/g，其中，Ce约占50%。老壳层中稀土元素含量明显高于新壳层，这可能与老壳层发生磷酸盐化作用有关。稀土元素配分模式呈现Ce正异常、Eu无异常，具有明显Ce富集特征。富钴结壳的稀土元素与Ce、Y、CaO、P2O5、Ba和Sr具有正相关性关系，与Fe、Al2O3、Na2O、K2O、MgO、TiO2、Pb和V具有负相关性关系，与Mn、Co、Cu、Ni和Zn相关性不明显。利用聚类分析方法，可以把富钴结壳的元素分成4组：①磷酸盐组：REE、Ce、Y、CaO、P2O5、Ba和Sr； ②亲锰元素组：Mn、Co、Cu、Ni和Zn；③亲铁元素组：Fe、TiO2、Pb和V；④碎屑元素组：Al2O3、Na2O、K2O和MgO。西太平洋采薇海山和徐福海山富钴结壳是水成沉积成因，稀土元素的来源推测为海水中稀土元素随磷酸盐组分共同沉淀而进入富钴结壳，从而导致稀土元素的富集。

     

    Abstract: Using the testing methods of XRD, ICP-OES and ICP-MS, the mineral composition, major and minor elements contents of cobalt-rich crusts collecting from the Caiwei Guyot and Xufu Guyot in the West Pacific Ocean have been determined. Based on the data, we discussed in this paper the geochemical characteristics and material sources of the REE. It is observed that the cobalt-rich crust is dominated by the crystalline mineral of vernadites, accompanied by the auxiliary minerals of quartz, plagioclase, potassium feldspar and carbon fluoride apatite. Amorphous ferric minerals also occur in certain amounts in the crusts. In terms of chemical composition, Mn contents change within 16.20%～26.62%, and Fe contents 8.56%～18.19%, which are the highest among the others. Phosphatization is observed in the old crust layers. REE are enriched in the cobalt-rich crusts. LREE are higher than HREE. REE contents are as high as 1 842～2 854 µg/g, in which Ce accounted for nearly 50%. Moreover, it is found that REE contents in the old layers are higher than that in the new layers, and it is believed that phosphatization in the old layers might play an active role in the REE distribution pattern. And REE diagrams show that there are positive Ce anomalies but no Eu anomalies, so Ce is relatively enriched. Meanwhile, REE show positive correlation with Ce, Y, CaO, P2O5, Ba and Sr, negative correlation with Fe, Al2O3, Na2O, K2O, MgO, TiO2, Pb and V, but no correlation with Mn, Co, Cu, Ni and Zn. By the way, the elements of the cobalt-rich crusts may be classified into four groups by clustering analysis. ①Phosphate group including REE, Ce, Y, CaO, P2O5, Ba and Sr. ② Mn group including Mn, Co, Cu, Ni and Zn. ③ Fe group including Fe, TiO2, Pb and V. ④ Detritus group including Al2O3, Na2O, K2O and MgO. In conclusion, cobalt-rich crusts from the Caiwei Guyot and Xufu Guyot of the West Pacific Ocean are hydrogenetic in origin, and REE are precipitated together with phosphate group in the seawater, that caused the enrichment of REE in the cobalt-rich crusts.

     

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