Gamma-enhancement of reflected light images: A rapid, effective tool for assessment of compositional heterogeneity in pyrite
Gamma-enhancement of reflected light images: A rapid, effective tool for assessment of compositional heterogeneity in pyrite
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反射光图像的伽马增强：评估黄铁矿成分异质性的快速有效工具
DOI：
10.2138/am-2020-7606
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发表时间：
2020-04
影响因子：
3.1
通讯作者：
Xu Jing
中科院分区：
文献类型：
--
作者：
Zhu Qiaoqiao;Cook Nigel J.;Xie Guiqing;Ciobanu Cristiana L.;Jian Wei;Wade Benjamin P.;Xu Jing
摘要黄铁矿中微量元素的变化是一个重要的地质作用特征。常规的反射率观测通常无法约束这种变化，由于典型的微妙和几乎察觉不到的变化，反射率所带来的偏离理想的化学计量。这种差异可能很难或不可能在使用标准光学显微镜的常规抛光切片中观察到，至少在没有油浸的情况下。化学蚀刻和染色，虽然广泛使用，是破坏性的，危险的，或两者兼而有之，蚀刻过程是不完全可重复的。本文采用γ校正方法增强反射光中获得的光学数字信号差异，以抑制中国东部典型热液矿床存款中黄铁矿的成分不均匀性。γ增强图像显示了由成分不均匀性引起的显著反射率变化，这一点通过定量电子探针分析和定性成像得到了证实。γ增强图像中较高的反射率域对应于自由电子有效数量的增加，而较暗的域归因于黄铁矿中痕量/微量元素取代导致这些自由电子的减少（例如，As）。伽玛校正通过增强反射率的变化，提供了一种快速、有效、非破坏性的方法来抑制黄铁矿的成分非均质性。单独使用，这种方法是无法确定的化学成分，由于同时取代，造成不同的增加或减少反射率，在大多数矿石矿物。然而，γ校正可能足以在扫描电子显微镜成像和矿物成分定量研究之前预测光学显微镜下微量/次要元素的替代，并且可能有助于约束演化矿石系统中黄铁矿的结构和成分之间的联系，这也可以应用于具有可忽略的双反射率的其他矿石矿物。
Abstract Trace/minor element variation in pyrite is a feature that has proved invaluable for reconstructing a wide range of geological processes. Routine reflectance observations commonly fail to constrain this variation due to the typically subtle and barely perceptible change in reflectance brought about by deviation from ideal stoichiometry. Such differences may be difficult or impossible to observe in conventional polished sections using standard optical microscopes, at least without oil immersion. Chemical etching and staining, although widely used, are destructive, hazardous, or both, and the etching process is not completely reproducible. Here we use the γ correction method to enhance optical digital signal differences obtained in reflected light to constrain compositional heterogeneity in pyrite from a representative hydrothermal ore deposit in eastern China. The γ-enhanced images show significant reflectance variation caused by compositional heterogeneity, confirmed by quantitative electron microprobe analysis and qualitative imaging. Higher reflectance domains in γ-enhanced images correspond to increases in the effective number of free electrons, whereas darker domains are attributed to the decrease of these free electrons by trace/minor element substitution in pyrite (e.g., As). Gamma correction provides a rapid, effective, non-destructive method to constrain compositional heterogeneity of pyrite through enhancement of reflectance variation. Used alone, this method is unable to determine the chemical composition due to simultaneous substitutions, causing a disparate increase or decrease of reflectance, in most ore minerals. Nevertheless, γ correction may be sufficient to predict the substitution of trace/minor elements under the optical microscope prior to scanning electron microscope imaging and quantitative investigation of mineral composition and may help constrain links between textures and compositions of pyrite in evolving ore systems, which could also be applied to other ore minerals with negligible bireflectance.