首页> 外文期刊>The American mineralogist >Replacement of pyrrhotite by pyrite and marcasite under hydrothermal conditions up to 220 °C: An experimental study of reaction textures and mechanisms
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Replacement of pyrrhotite by pyrite and marcasite under hydrothermal conditions up to 220 °C: An experimental study of reaction textures and mechanisms

机译:在高达220°C的水热条件下用黄铁矿和镁铁矿代替黄铁矿:反应结构和机理的实验研究

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The transformation of pyrrhotite to Fe disulfide (pyrite and/or marcasite) under hydrothermal conditions was studied experimentally by probing the effects of temperature (up to 220 °C, vapor-saturated pressures), ∑S(-II) concentrations, pH, and availability of oxygen on reaction progress and on the resulting textures. The pyrrhotite to Fe disulfide reaction proceeded by a dissolution-reprecipitation mechanism under all conditions. Marcasite and pyrite formed under both oxic and anaerobic conditions, which is inconsistent with the traditionally assumed polysulfide route for FeS2 formation (oxidants required for polysulfide formation). The nature of the products was controlled by the level of supersaturation of the solution with respect to Fe disulfide minerals. Marcasite formed preferentially at low pH or S(-II)-deficient solutions (saturation index 1000), while pyrite was the main product at saturation indices >1000. Different textures were obtained for the replacement of pyrrhotite by either pyrite or marcasite. Pyrite formation proceeded by direct replacement of pyrrhotite and, simultaneously, by overgrowth from solution. The pyrite crystals were >10 μm in size and randomly oriented. In comparison, marcasite crystals were <1 μm in size, and no significant overgrowth was observed. At pH_(21°C) <3, the marcasite nanocrystals showed the well-known crystallographic relationship with pyrrhotite, but at pH _(21°C) 3.96, the marcasite crystallites were randomly oriented. These experimental results confirm that the preservation of the crystallographic orientation is not a distinguishing feature between dissolution-reprecipitation and solid-state reactions. The different textures among pyrite and marcasite reflect the dominance of crystal growth (pyrite) vs. nucleation (marcasite) as a precipitation mechanism.
机译:通过探索温度(最高220°C,蒸气饱和压力),∑S(-II)浓度,pH和温度的影响,对水热条件下黄铁矿向二硫化铁(黄铁矿和/或镁铁矿)的转化进行了实验研究。氧气在反应进程和生成的质地上的可用性。在所有条件下,黄铁矿与二硫化铁反应都是通过溶解-再沉淀机理进行的。镁铁矿和黄铁矿在有氧和厌氧条件下均形成,这与传统上假设的用于形成FeS2的多硫化物途径(多硫化物形成所需的氧化剂)不一致。产物的性质由溶液相对于二硫化铁矿物的过饱和程度控制。在低pH或缺乏S(-II)的溶液(饱和指数为1000)下,优先生成马氏体,而在饱和指数> 1000时,黄铁矿是主要产物。获得了不同的质地,以黄铁矿或镁铁矿替代黄铁矿。通过直接替换黄铁矿以及同时从溶液中过度生长来进行黄铁矿的形成。黄铁矿晶体的尺寸> 10μm,且取向随机。相比之下,镁铁矿晶体的尺寸小于1μm,未观察到明显的过度生长。在pH_(21°C)<3时,镁铁矿纳米晶体与黄铁矿具有众所周知的晶体学关系,但在pH _(21°C)3.96时,镁铁矿微晶是随机取向的。这些实验结果证实,晶体取向的保持不是溶解-再沉淀与固态反应之间的区别特征。黄铁矿和镁铁矿中不同的织构反映了晶体生长(黄铁矿)与成核(镁铁矿)作为沉淀机制的优势。

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