Platinum group elements and gold in ferromanganese crusts from Afanasiy-Nikitin seamount, equatorial Indian Ocean: Sources and fractionation
Platinum group elements and gold in ferromanganese crusts from Afanasiy-Nikitin seamount, equatorial Indian Ocean: Sources and fractionation
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DOI：
10.1007/s12040-007-0002-x
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发表时间：
2007-04
影响因子：
1.9
通讯作者：
V. Banakar;J. Hein;R. Rajani;A. R. Chodankar
中科院分区：
文献类型：
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作者：
V. Banakar;J. Hein;R. Rajani;A. R. Chodankar
东赤道印度洋阿法纳西-尼基京海山铁锰结壳中主要元素的关系似乎是非典型的。Mn/Co和Fe/Co比值之间的高度正相关（r= 0.99），而与Co、Ce和Ce/Co比值之间的相关性较弱，表明ANS铁锰结壳不同于太平洋海山铁锰结壳，反映了区域特有的化学特征。ANS铁锰结壳中的铂族元素（PGE：Ir、Ru、Rh、Pt和Pd）和Au主要来自海水，主要为陆源，少量为宇宙成因。Ru/Rh（0.5-2）和Pt/Ru（7-28）与大陆玄武岩中的比值非常接近，而Pd/Ir比值（<2）与CI球粒陨石（0.01）相似。黄铁矿标准化的PGE模式是类似的火成岩，除了Pd是相对亏损。铁锰结壳形成的水深对主量元素和铂族元素的富集具有一级控制作用。水深与Mn/Co、Fe/Co、Ce/Co、Co和铂族元素之间的相关性均达到显著水平（r> 0.75）。在主要氧化物相的胶态沉淀过程中，海水中PGE-Au的分馏通过Co和Ce与Ir、Ru、Rh和Pt的良好线性正相关（r> 0.8）; Au/Co与Mn/Co的良好线性正相关（r> 0.8）;以及Pd与水深、Co标准化主要元素比率和其他PGE的弱相关或无相关（r< 0.5）来表示。相对于其他PGE的Pt的强富集（高达1 ppm）及其与Ce和Co的正相关性表明了所有三种元素的高浓度的共同联系，这可能涉及Mn氧化物和Fe-羟基氧化物表面上的氧化反应。PGE-Au的分馏及其与氧化还原敏感的Co和Ce的正相关性可能在重建过去的海洋氧化还原条件和水团中具有应用价值。
The major element relationships in ferromanganese (Fe-Mn) crusts from Afanasiy-Nikitin seamount (ANS), eastern equatorial Indian Ocean, appear to be atypical. High positive correlations (r= 0.99) between Mn/Co and Fe/Co ratios, and lack of correlation of those ratios with Co, Ce, and Ce/Co, indicate that the ANS Fe-Mn crusts are distinct from Pacific seamount Fe-Mn crusts, and reflect region-specific chemical characteristics. The platinum group elements (PGE: Ir, Ru, Rh, Pt, and Pd) and Au in ANS Fe-Mn crusts are derived from seawater and are mainly of terrestrial origin, with a minor cosmogenic component. The Ru/Rh (0.5–2) and Pt/Ru ratios (7–28) are closely comparable to ratios in continental basalts, whereas Pd/Ir ratios exhibit values (<2) similar to CI-chondrite (∼1). The chondrite-normalized PGE patterns are similar to those of igneous rocks, except that Pd is relatively depleted. The water depth of Fe-Mn crust formation appears to have a first-order control on both major element and PGE enrichments. These relationships are defined statistically by significant (r> 0.75) correlations between water depth and Mn/Co, Fe/Co, Ce/Co, Co, and the PGEs. Fractionation of the PGE-Au from seawater during colloidal precipitation of the major-oxide phases is indicated by well-defined linear positive correlations (r> 0.8) of Co and Ce with Ir, Ru, Rh, and Pt; Au/Co with Mn/Co; and by weak or no correlations of Pd with water depth, Co-normalized major-element ratios, and with the other PGE (r< 0.5). The strong enrichment of Pt (up to 1 ppm) relative to the other PGE and its positive correlations with Ce and Co demonstrate a common link for the high concentrations of all three elements, which likely involves an oxidation reaction on the Mn-oxide and Fe-oxyhydroxide surfaces. The documented fractionation of PGE-Au and their positive association with redox sensitive Co and Ce may have applications in reconstructing past-ocean redox conditions and water masses.