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首页> 外文期刊>Economic geology and the bulletin of the Society of Economic Geologists >Bimodal Distribution of Gold in Pyrite and Arsenopyrite: Examples from the Archean Boorara and Bardoc Shear Systems, Yilgarn Craton, Western Australia
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Bimodal Distribution of Gold in Pyrite and Arsenopyrite: Examples from the Archean Boorara and Bardoc Shear Systems, Yilgarn Craton, Western Australia

机译：硫铁矿和毒铁矿中金的双峰分布：来自澳大利亚西部伊尔加恩·克拉顿的太古代波拉拉和巴多克剪切系统的例子

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This study investigates the microstructures, geochemistry, and hydrothermal evolution of gold-bearing pyrite and arsenopyrite from six orogenic gold deposits in the Archean Eastern Goldfields Province, Western Australia. Scanning electron microscope (SEM), electron microprobe (EMP) and laser ablation-inductively coupled plasma-mass spectroscopy (LA-ICP-MS) analyses show that the gold-bearing minerals possess a number of similar textural features, including the occurrence of invisible gold within initial phases of growth, and later-stage visible gold associated with alteration rims. The alteration rims are characterized by a higher-than-average atomic mass (mainly owing to arsenic enrichment) and are preferentially located along fractures and grain boundaries in the pyrite and arsenopyrite. These observations suggest that visible gold formation is associated with hydrothermal alteration of preexisting pyrite and arsenopyrite. Textural observations and LA-ICP-MS data suggest that some invisible gold was remobilized from early-formed pyrite and arsenopyrite to form visible gold during development of these alteration rims. Gold may also have been added by hydrothermal fluids during a later stage of mineralization. In situ geochemistry and phase relationships of alteration rims are used to further constrain the hydrothermal process responsible for formation of alteration rims and visible gold in fractures. Based on sulfide stability relations, our data indicate that development of arsenopyrite alteration rims associated with late-stage visible gold formation was related to an increase in temperature (maximum increase from 310 deg to 415 deg C) and up to of sic orders of magnitude increase in sulfur fugacity, whereas changes in oxygen fugacity were less important. LA-ICP-MS analyses show that the relative and absolute variations in selected trace element (Au, Ag, Sb, Bi, Ba, Te, Pb, Co, and Mo) concentrations can also be used to distinguish between unaltered and altered pyrite and arsenopyrite. In general, trace elements within pyrite and arsenopyrite have a relatively uniform distribution, whereas later-stage alteration rims have more variable trace element distributions. Although the observed textures are typical of prograde metamorphic coronae, we suggest that they are the consequence of variations in fluid conditions and chemistry, and that mineralization occurred in response to syn- and/or postpeak metamorphic fluid infiltration.
机译：这项研究调查了西澳大利亚太古宙东部金矿省的六个造山金矿床中含金黄铁矿和毒砂的微观结构，地球化学和水热演化。扫描电子显微镜（SEM），电子探针（EMP）和激光烧蚀-电感耦合等离子体质谱（LA-ICP-MS）分析表明，含金矿物具有许多相似的组织特征，包括不可见元素的出现。生长初期的黄金，以及后期与轮辋相关的可见金。蚀变边缘的特征在于原子质量高于平均水平（主要是由于砷的富集），并且优先位于黄铁矿和毒砂中的裂缝和晶界处。这些观察结果表明可见的金形成与先前存在的黄铁矿和毒砂的水热变化有关。纹理观察和LA-ICP-MS数据表明，在这些蚀变边缘形成过程中，一些不可见的金从早期形成的黄铁矿和毒砂中迁移出形成可见的金。在矿化的后期，还可能通过热液添加了金。蚀变圈的原位地球化学和相位关系被用来进一步约束导致蚀变圈和裂缝中可见金形成的水热过程。根据硫化物的稳定性关系，我们的数据表明与后期可见金形成有关的毒砂黄铁矿蚀变边缘的发展与温度的升高有关（最大温度从310摄氏度升高到415摄氏度），并且上升幅度高达sic。在硫逸度中，氧逸度的变化不太重要。 LA-ICP-MS分析表明，选定的痕量元素（Au，Ag，Sb，Bi，Ba，Te，Pb，Co和Mo）浓度的相对和绝对变化也可用于区分未改变和改变的黄铁矿和毒砂。通常，黄铁矿和毒砂中的痕量元素具有相对均匀的分布，而后期蚀变边缘的痕量元素分布则变化较大。尽管观察到的纹理是渐进变质日冕的典型特征，但我们认为它们是流体条件和化学变化的结果，并且矿化作用是对同峰和/或峰后变质流体渗透的响应。

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