Quantitative XPS characterization of “invisible gold” in Carlin-type gold ores through controlled acid erosion,Journal of Analytical Atomic Spectrometry

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Quantitative XPS characterization of “invisible gold” in Carlin-type gold ores through controlled acid erosion
Journal of Analytical Atomic Spectrometry ( IF 3.1 ) Pub Date : 2021-06-30 , DOI: 10.1039/d1ja00102g
Meizhi Yang _{1,

2} , Quan Wan _{1,

3} , Xin Nie ₁ , Suxing Luo ₄ , Yuhong Fu ₅ , Ping Zeng _{1,

2} , Wenqi Luo _{1,

2}

Affiliation

The occurrences of gold as lattice-bound ionic Au⁺ and nanoparticulate Au⁰ inclusions, collectively termed “invisible gold”, in pyrite have long been recognized as a most important characteristic of Carlin-type gold deposits. Yet, till now, few studies have quantitatively resolved the two chemical states of Au, reflecting substantial challenges in the characterization of Carlin-type gold ores. In this work, quantitative XPS analysis of “invisible gold” was carried out for the first time, which revealed valuable results including the total Au concentration, percentages of Au⁺ and Au⁰, size of Au⁰ nanoparticles, and Au/As ratio at different depths of the pyrite surface. A simple acid etching approach, which effectively removed the signal-blocking outermost pyrite rim of low Au content and the signal-interfering Mg carbonates, was demonstrated to be the key to enhancing the Au signal in XPS. The ascending Au concentration (0.0017–0.24 at%) with increasing depth and the variation of Au⁰ fraction (31.2 to 59.8 at%) with relatively stable As concentration (∼2 at%) indicate heterogeneous distribution of Au chemical states in pyrite particles, while the small Au nanoparticle size (minimum 1–2 nm) confirms the challenge of microscopic observation of “invisible gold”. Unlike ion beam etching techniques potentially suffering from sample damages, the non-oxidative acid etching method used in our study is considered non-destructive and capable of obtaining chemical states with reasonable statistical significance. We believe that the new findings from this work will provide useful information to improve our understanding of the still puzzling ore-forming mechanisms and to boost the related metallurgical efficiencies. Furthermore, our methodology may also be applied to the characterization of poorer Au ores and even other geological samples.

中文翻译：

通过受控酸蚀对卡林型金矿中“隐形金”的定量 XPS 表征

长期以来，黄铁矿中以晶格束缚离子 Au ⁺和纳米颗粒 Au ⁰包裹体形式出现的金，统称为“隐形金”，一直被认为是卡林型金矿床最重要的特征。然而，到目前为止，很少有研究定量解析 Au 的两种化学状态，这反映了 Carlin 型金矿石表征方面的重大挑战。在这项工作中，“不可见金”定量XPS分析反应进行的第一次，其揭示有价值的结果包括总的Au浓度，Au中的百分比⁺和Au ⁰，Au中的大小⁰纳米颗粒，以及黄铁矿表面不同深度处的 Au/As 比。一种简单的酸蚀刻方法可有效去除低 Au 含量的信号阻塞最外黄铁矿边缘和干扰信号的碳酸镁，被证明是增强 XPS 中 Au 信号的关键。Au浓度（0.0017–0.24 at%）随着深度的增加和Au ⁰的变化部分（31.2 至 59.8 原子％）具有相对稳定的砷浓度（~2 原子％）表明金化学状态在黄铁矿颗粒中的不均匀分布，而小的金纳米颗粒尺寸（最小 1-2 纳米）证实了显微镜观察的挑战“隐形黄金”。与可能遭受样品损坏的离子束蚀刻技术不同，我们研究中使用的非氧化酸蚀刻方法被认为是非破坏性的，并且能够获得具有合理统计意义的化学状态。我们相信，这项工作的新发现将提供有用的信息，以提高我们对仍然令人费解的成矿机制的理解，并提高相关的冶金效率。此外，

更新日期：2021-07-21

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