西太平洋富钴结壳矿物学和地球化学特征——以麦哲伦海山和马尔库斯-威克海山富钴结壳为例

The Mineralogical and Geochemical Characteristics of Co-rich Crusts from the Western Pacific:Taking the Co-rich Crusts from Magellan and Marcus-wake Seamounts as an Example

本文对分别取自西太平洋麦哲伦海山和马尔库斯-威克海山的两块富钴结壳进行了系统的矿物学和地球化学特征的研究,运用XRD、ICP-AES(MS)等测试技术分析了结壳的矿物物相组成、主微量元素和稀土元素的组成和赋存相态,并在此基础上探讨了结壳的成因类型及成矿物质来源。研究表明,结壳主要由锰、铁相矿物组成,其中锰相矿物主要为水羟锰矿,含少量钡镁锰矿及钠水锰矿,铁相矿物为针铁矿及隐晶质-非晶质相;两结壳样品的Mn、Fe、Co、Cu、Ni平均值与中太平洋及西北太平洋富钴结壳相比基本相当,分别是20.08%和19.01%、16.28%和16.52、0.68%和0.64%、0.15%和0.09%、0.34%和0.39%,但Mn/Fe比值均偏低;∑REE平均值分别为2 182.89×10-6和1 367.29×10-6,其中,麦哲伦海山结壳的稀土元素平均值明显比中太平洋及西北太平洋结壳高,而马尔库斯-威克海山结壳则略低;LREE/HREE平均值分别为10.14和7.67,均富集轻稀土,同时具有不同程度的Ce,Gd,Ho正异常和Y的负异常。相态分析结果显示,样品中Mn、Ni、Ba、Co、Cu、Zn、Sr、Ti、REE等元素主要赋存在锰相中,Fe、Al、Pb等元素则主要赋存在非晶质和结晶质铁相中;两结壳样品均属于水成成因,未受明显成岩作用和磷酸盐化作用的影响。

Two Co-rich crust samples collected from Magellan and Marcus-wake seamounts in western pa- cific have been studied for systematic understanding of their mineralogical and geochemical characteristics. By using XRD, ICP-AES（MS） methods, the mineral and geochemical composition, the leaching distribu- tion of major and rare earth elements of the samples have been determined, based on which, the genetic classification, material sources of the samples have been further explored. The results show that Maganese minerals and Iron minerals are the main components of the crusts, Vernadite are the main component of manganese oxide with a small amount of todorokite and Birnessite, and amorphous FeOOH is the most a- bundant component of the ferric mineral and only weakly Goethite peak can be identified under X-ray; The average concentration of Mn, Fe, Co, Cu, Ni of the samples equal that of crusts both in central and north- west Pacific, with an average value of 20. 08% and 19.01%, 16.28% and 16.52, 0. 68% and 0. 64%, 0. 15% and 0.09%, 0. 34% and 0.39%respectively, but the Mn/Fe ratio of the samples are lower; The average P,,REE value of the samples are 2 182.89×10-6 and 1 367.29×10-6 each, among them, the average ZREE value of the sample from Magellan seamounts is significantly higher than that of crusts in central and northwest Pacific, while the average ∑REE value of the sample from Marcus-wake seamounts crust is lower; The average LREE/HREE values of the samples are 10.14 and 7.67 respectively, sugges- ting that the samples are relatively enriched in LREE, and the REE diagram shows the positive anomaly of Ce, Gd, Ho and negative anomaly of Y in the samples; The element leaching results suggest that Co, Cu, Mn, Ni, Ba, Zn, Sr, Ti and REE are mainly occurred in Mn-oxide fraction, while Fe, A1 and Pb mainly exists in amorphous and crystalline Fe-oxyhydroxide fraction. The samples are both hydrogenetic and are slightly affected by diagenesis and phosphatization.