Rare earth elements in Hamersley BIF minerals
Rare earth elements in Hamersley BIF minerals
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DOI：
10.1016/j.gca.2016.03.026
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发表时间：
2016-07-01
影响因子：
5
通讯作者：
Alibert, Chantal
中科院分区：
文献类型：
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作者：
Alibert, Chantal
通过激光烧蚀 ICP-MS 对来自西澳大利亚哈默斯利带状铁地层的矿物进行 Y 和稀土元素 (YREE) 分析，以研究从前体相到 BIF 矿物的成岩路径。一组磷灰石带有海水 REE 特征，证明水铁矿颗粒从水体中彻底清除 P 和 REE，并在孔隙水中微生物 Fe3+ 还原溶解水硅铁矿时释放出来，并最终主要隔离在自生磷灰石中。磷灰石和海水之间不存在分馏表明稀土元素首先作为完全水合的阳离子（即作为外球复合物）并入无定形磷酸钙中。铁氧化物和碳酸盐仅占全岩稀土元素预算的一小部分。它们的 REE 模式明显富集 Yb，并显示出一些 M 型四分体效应，与低碳酸根离子浓度的固体和盐溶液之间的实验 K-d(REE) 一致。据推测，赤铁矿是在 Fe2+ 催化水铁矿溶解的初始阶段通过溶解-再沉淀途径形成的。绿钠石的 REE 模式是在燧石菱铁矿样品中的石英中以亚微米颗粒形式发现的，与少量水铁矿溶解后在孔隙水中沉淀的自生起源一致。磁铁矿含有非常低的 YREE（ppb 水平），与赤铁矿相比，具有明显富集中稀土元素的均匀模式，并且包括轻稀土元素、Ba 和 As 耗尽的晚期种群。磁铁矿形成的聚集体和块状纹层被初步解释为反映了一些流体辅助的赤铁矿-磁铁矿在低级变质温度下的重新平衡或转变。 (C) 2016 Elsevier Ltd. 保留所有权利。
Minerals from the Hamersley banded iron formation, Western Australia, were analyzed for Y and rare earth elements (YREEs) by laser ablation ICP-MS to investigate diagenetic pathways, from precursor phases to BIF minerals. One group of apatites carries the seawater REE signature, giving evidence that P and REEs, thoroughly scavenged from the water column by Si-ferrihydrite particles, were released upon microbial Fe3+ reductive dissolution of Si-ferrihydrite in pore-water and finally sequestered mainly in authigenic apatite. The absence of fractionation between apatite and seawater suggests that REE were first incorporated into an amorphous calcium phosphate as fully hydrated cations, i.e. as outer-sphere complexes. The iron oxides and carbonates carry only a small fraction of the whole-rock REE budget. Their REE patterns are distinctly enriched in Yb and show some M-type tetrad effect consistent with experimental K-d(REE) between solid and saline solution with low carbonate ion concentrations. It is deduced that hematite formed at an incipient stage of Fe2+-catalyzed dissolution of Si-ferrihydrite, via a dissolution-reprecipitation pathway. The REE pattern of greenalite, found as sub-micron particles in quartz in a chert-siderite sample, is consistent with its authigenic origin by precipitation in pore-water after dissolution of a small amount of Si-ferrihydrite. Magnetite carries very low YREEs (ppb-level), has an homogeneous pattern distinctly enriched in the mid-REEs compared to hematite, and includes a late population depleted in light-REEs, Ba and As. Magnetite forming aggregates and massive laminae is tentatively interpreted as reflecting some fluid-aided hematite-magnetite re-equilibration or transformation at low-grade metamorphic temperatures. (C) 2016 Elsevier Ltd. All rights reserved.