A missing link between ancient and active mafic-hosted seafloor hydrothermal systems – Magmatic volatile influx in the exceptionally preserved Mala VMS deposit, Troodos, Cyprus
A missing link between ancient and active mafic-hosted seafloor hydrothermal systems – Magmatic volatile influx in the exceptionally preserved Mala VMS deposit, Troodos, Cyprus
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DOI：
10.1016/j.chemgeo.2021.120127
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发表时间：
2021-02
期刊：
影响因子：
3.9
通讯作者：
Andrew J. Martin;I. McDonald;Gawen R. T. Jenkin;K. McFall;A. Boyce;J. Jamieson;C. MacLeod
中科院分区：
文献类型：
--
作者：
Andrew J. Martin;I. McDonald;Gawen R. T. Jenkin;K. McFall;A. Boyce;J. Jamieson;C. MacLeod
对古火山成因块状硫化物（VMS）和活跃形成的海底块状硫化物（SMS）矿床进行对比观测，对于了解海洋热液系统中金属富集的来源和过程至关重要。对于镁铁质VMS存款，位于塞浦路斯Troodos蛇绿岩内的Mala VMS丘是不寻常的，因为黄铁矿富含岩浆挥发性元素（Au、Cu、Te和Se），硫化物δ 34 S值平均值为− 3.8‰ ± 1.9‰（1σ，n= 28），石膏平均为+14.5‰ ± 2.0‰（1σ，n= 26）-与Troodos VMS黄铁矿的平均为+4.6‰ ± 2.8‰形成鲜明对比。到目前为止，这种组合的功能已被观察到，只有在积极形成的SMS存款在不成熟的，俯冲影响的环境，很少在古老的VMS存款在长英质环境。传统上，火成岩的淋滤被认为是镁铁质VMS矿床中金属的主要来源。然而，在马拉，也许是其他活跃的SMS矿床在镁铁质环境中，我们认为，Au，Cu，Te和Se wereallysourced从岩浆挥发相的直接贡献，其中SO2经历了沉淀，签名，后来由反应海水覆盖在存款成熟，因此通常不会保存在古代类似物。因此，Mala的特殊保存提供了在镁铁质VMS存款形成的早期阶段岩浆挥发性贡献的证据。
Reconciling observations between ancient volcanogenic massive sulfide (VMS) and actively forming seafloor massive sulfide (SMS) deposits is critical for understanding the sources and processes that govern metal enrichment in marine hydrothermal systems. For a mafic VMS deposit, the Mala VMS mound located within the Troodos ophiolite, Cyprus, is unusual as pyrite is enriched in magmatic volatile elements (Au, Cu, Te and Se), sulfide δ34S values average − 3.8‰ ± 1.9‰ (1σ,n= 28), and gypsum averages +14.5‰ ± 2.0‰ (1σ,n= 26) - in stark contrast to the bulk of Troodos VMS pyrite, which averages +4.6‰ ± 2.8‰. To date, this combination of features has only been observed in actively forming SMS deposits in immature, subduction-influenced environments and rarely in ancient VMS deposits hosted in felsic environments. Traditionally, the leaching of igneous rocks is considered as the primary source of metals in mafic VMS deposits. However, at Mala, and perhaps other active SMS deposits in mafic environments, we suggest that Au, Cu, Te and Se wereinitiallysourced from the direct contribution of a magmatic volatile phase where SO2underwent disproportionation, a signature that is later overprinted by reacted seawater during deposit maturation and is therefore not usually preserved in ancient analogues. Thus, the exceptional preservation of Mala provides evidence of a magmatic volatile contribution in the early stages of mafic VMS deposit formation.