Selenium isotopes trace the source and redox processes in the black shale-hosted Se-rich deposits in China
Selenium isotopes trace the source and redox processes in the black shale-hosted Se-rich deposits in China
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DOI：
10.1016/j.gca.2010.12.021
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发表时间：
2011-03
影响因子：
5
通讯作者：
H. Wen;J. Carignan
中科院分区：
文献类型：
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作者：
H. Wen;J. Carignan
本文分析了中国南方遵义镍钼硒存款、拉尔玛硒金存款和鱼塘坝硒存款的黑色页岩和有关干酪根和硫化物组分的硒同位素组成，以确定金属来源和成藏过程，这两个主题在科学界存在分歧。遵义Ni-Mo-Se多金属存款中Se的δ 82 Se值范围有限（−1.6‰ ~ 2.4‰，平均值为0.6‰），表明Se主要是以H2Se的形式随H2S沿着迁移，并以硒化物或硫化物的形式直接沉淀。La'erma Se-Au存款中Se的δ 82 Se值范围较大（−3.8‰ ~ 5.4‰，平均值为0.3‰），表明Se在氧化还原作用后发生再分配，导致动力学同位素分馏。迄今为止，在渔塘坝硒存款矿床中发现了天然陆地样品中最大的Se同位素变化，δ 82 Se值从−12.77‰变化到4.93‰。根据存款中Se同位素的变化，沿着其它地质和地球化学证据，“氧化还原模式”（表生蚀变）解释了自然Se在存款中的存在。总的来说，热液系统可能是一个潜在的重要硒源，形成经济矿床相比，海水来源。值得注意的是，我们的研究表明，无论是次生热液或表生蚀变是一个关键因素在黑色页岩中富集硒。硒的再分布，以及可能的其他氧化还原敏感的金属，如钼，铬和V，导致同位素分馏，可用于指纹这样的蚀变/沉淀过程。
We analyzed the Se isotopic composition of black shales and related kerogen and sulfide fractions from the Zunyi Ni–Mo–Se deposit, the La’erma Se–Au deposit and the Yutangba Se deposit in southern China to constrain metal sources and accumulation processes, both subjects of disagreement in the scientific community. Se at the Zunyi Ni–Mo–Se polymetallic deposit displayed a restricted range of δ82Se values (−1.6‰ to 2.4‰ with a mean of 0.6‰) suggesting a major hydrothermal origin where aqueous Se was probably transported as H2Se, along with H2S, and precipitated directly as selenides or in sulfides. Se at the La’erma Se–Au deposit covers a larger range in δ82Se values (−3.8‰ to 5.4‰ with a mean of 0.3‰), suggesting Se redistribution following redox transformations, leading to kinetic isotopic fractionation. The largest Se isotopic variation so far in natural terrestrial samples was found in the Yutangba Se deposit, with δ82Se values varying from −12.77‰ to 4.93‰. On the basis of variations in Se isotopes in the deposit, along with other geological and geochemical evidence, the “redox model” (supergene alteration) explains the occurrence of native Se in the deposit. Overall, hydrothermal systems may be a potentially important Se source to form economic deposits in comparison to seawater sources. Significantly, our study indicates that either secondary hydrothermal or supergene alteration is a key factor in Se enrichment in black shales. Redistribution of Se, and probably other redox-sensitive metals like Mo, Cr and V, leads to isotopic fractionation which may be used to fingerprint such alteration/precipitation processes.