In Situ Raman Spectra Characterization of Zonal Arsenic-Bearing Pyrite and Arsenopyrite in the Baiyunpu Gold Deposit, Hunan
GAO Shang1, 2, HUANG Fei2*, LIU Jia3, SU Li-min4, WANG Wei1
1. State Key Laboratory of Mechanical Behvior and System Safety of Traffic Engineering Structures, Shijiazhuang Tiedao University, Hebei Province Technical Innovation Center of Safe and Effective Mining of Metal Mines, Shijiazhuang 050043, China
2. College of Resource and Civil Engineering, Northeastern University, Shenyang 110819, China
3. Gemmological Institute, China University of Geosciences, Wuhan 430074, China
4. The Sixth Geological Team of the Hebei Bureau of Geology and Mineral Resources Exploration, Shijiazhuang 050081, China
Abstract：Arsenic-bearing pyrite and arsenopyrite are important gold-bearing minerals in various types of gold deposits. They often develop multi-stage concentric rings, which provide a lot of information for understanding the genesis and formation process of the deposit. The variation characteristics of morphology and composition of zonal arsenic-bearing pyrite and arsenopyrite grains had been fully studied, but no systematic in-situ Raman spectra data have been reported. Meanwhile, the study of Raman peak migration in layered zones can also provide some reference value for understanding the occurrence forms of invisible gold. Electron microprobe analysis results show that arsenic-bearing pyrite decreases first and then increases in S and Fe content from the core to the outer layer (Py1→Py2→Py3), and opposite in As content (up to 10.86% in Py2). The content of Au is positively correlated with that of As, and it is also relatively enriched in Py2 (up to 0.14%). From the core to the outer layer of arsenopyrite (Apy1→Apy2), the S and Fe content decreases, while the As content increases. In situ Raman spectra analysis shows that there are three main Raman peaks in different layered zones of arsenic-bearing pyrite, corresponding to Fe-[S2]2- deformation vibration peak (Eg), Fe-[S2]2- stretching vibration peak (Ag) and S-S stretching vibration peak (Tg) of pyrite, respectively. The Raman shifts of inner core Py1 are concentrated in 345.8~346.9, 382.0~382.9 and 434.6~434.8 cm-1. That of intermediate zone Py2 are concentrated in 331.9~338.7, 359.2~365.4, 404.3~414.2 cm-1; and that of outer zone Py3 are 343.0~344.9, 375.5~378.3 and 417.3~431.5 cm-1. The Raman peaks of Py2 shift significantly to low frequency with the offset ranging from 3.1 to 27.2 cm-1. It is concluded that the Raman shift change of pyrite is mainly related to the substitution of As and Au ions. The invisible gold in arsenic-bearing pyrite may enter the lattice in the form of chemical bonding state, resulting in the change of chemical bonding force constant and reduced mass, and it leads to the decrease of Raman peak vibration frequency and the shift to low frequency. There are six Raman peaks in arsenopyrite of 136.2~139.8, 174.8~179.4, 198.9~200.7, 307.0~314.2, 338.5~343.9 and 407.8~410.5 cm-1, which is similar to the data of R050071 sample in RUEFF database and some reference value in relevant pieces of literature. In addition, the Raman peaks of Apy2 shift slightly to low frequency related to Apy1, and the offset ranges from 0.7 to 5.4 cm-1. We thought that the change of Raman shifts in arsenopyrite is mainly related to the vibration migration caused by the isomorphic substitution of S ions by As ions. The study on in-situ Raman spectra characteristics of zonal arsenic-bearing pyrite and arsenopyrite from Baiyunpu samples provide abundant Raman spectra data for the identification of pyrite and arsenopyrite minerals with different compositions, and provide an important reference for revealing the frequency shift of Raman peaks measured in different layered zones and exploring the existence state of invisible gold.
Key words：Arsenic-bearing pyrite; Arsenopyrite; Growth zoning; In situ Raman spectra; Frequency shift
高 尚，黄 菲，刘 佳，苏丽敏，王 伟. 湖南白云铺金矿含砷黄铁矿和毒砂环带的原位拉曼光谱研究[J]. 光谱学与光谱分析, 2020, 40(08): 2525-2530.
GAO Shang, HUANG Fei, LIU Jia, SU Li-min, WANG Wei. In Situ Raman Spectra Characterization of Zonal Arsenic-Bearing Pyrite and Arsenopyrite in the Baiyunpu Gold Deposit, Hunan. SPECTROSCOPY AND SPECTRAL ANALYSIS, 2020, 40(08): 2525-2530.
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