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Abstract <p>Using electron microprobe analysis and X-ray diffraction (XRD), we studied crystal fragments of four minerals of the fahlore group from the Mangazeyskoye Ag–Pb–Zn deposit (Yakutia, Russia) with 3.7–5.8 atoms per formula units (apfu) Ag and 13–12 apfu S. Both methods revealed a negative correlation between Ag and S contents in the fahlore chemical composition. The crystal structures of four Ag-bearing fahlores are refined using XRD. The parameters of their unit cells (<i>a</i><sub>0</sub>, Å) in group <InlineEquation ID="IEq1"> <EquationSource Format="TEX">\(I\bar {4}3m\)</EquationSource> <!--EarthSci2660046Lyubimtseva-m1--> </InlineEquation> (cubic) are as follows: 10.58829 for argentotetrahedrite-(Fe) (Ag<sub>3.68</sub>Cu<sub>2.32</sub>)<sub>Σ6</sub>(Cu<sub>4.04</sub>[Fe<sub>1.73</sub>Zn<sub>0.27</sub>]<sub>Σ2.00</sub>)<sub>Σ6.04</sub>(Sb<sub>3.94</sub>As<sub>0.03</sub>)<sub>Σ3.97</sub>S<sub>12</sub>S<sub>1.01</sub>; 10.53378 for argentotetrahedrite-(Zn) (Ag<sub>3.82</sub>Cu<sub>2.18</sub>)<sub>Σ6</sub>(Cu<sub>4.09</sub>[Zn<sub>1.71</sub>Fe<sub>0.28</sub>]<sub>Σ1.99</sub>)<sub>Σ6.08</sub>(Sb<sub>3.82</sub>As<sub>0.10</sub>)<sub>Σ3.92</sub>S<sub>12.74</sub>; 10.51544 for kenoargentotetrahedrite-(Fe) (Ag<sub>4.34</sub>Cu<sub>1.66</sub>)<sub>Σ6</sub>(Cu<sub>4.10</sub>[Zn<sub>0.96</sub>Fe<sub>1.03</sub>]<sub>Σ1.98</sub>)<sub>Σ6.08</sub> (Sb<sub>3.88</sub>As<sub>0.03</sub>)<sub>Σ3.92</sub>S<sub>12.47</sub>; and 10.48411 for kenoargentotetrahedrite-(Zn) (Ag<sub>5.83</sub>Cu<sub>0.17</sub>)<sub>Σ6</sub>(Cu<sub>3.96</sub>[Zn<sub>1.98</sub>Fe<sub>0.04</sub>]<sub>Σ2.02</sub>)<sub>Σ5.98</sub>(Sb<sub>3.99</sub>As<sub>0.02</sub>)<sub>Σ4.01</sub>S<sub>12</sub>S<sub>0.04</sub>. The XRD studies of the fahlore crystal structure with a high resolution (2θ<sub>max</sub> = 82°) allowed us to refine the positions of Ag and Cu atoms in site <i>M</i>(2) and to find for the first time a new sulfur site <i>S</i>(3). А high Ag content (3.7–5.8 apfu) shifts S from site <i>S</i>(2) in the center of the octahedron by 0.42–0.44 Å to site <i>S</i>(3), which is located on a 3<i>m</i> symmetry element. Quantum chemical modeling showed that the sequential substitution of Cu atoms by Ag atoms in octahedral cluster [SCu<sub>6</sub>]<sup>4+</sup> gradually shifts the S atom from the center of the octahedron that illustrates the transition from site <i>S</i>(2) in the pure Cu cluster to the refined site <i>S</i>(3) in cases of mixed clusters [S(Ag,&#xa0;Cu)<sub>6</sub>]. The unit cell parameter depends on the size of the [Ag,&#xa0;Cu]<sub>6</sub> octahedral cluster in the fahlore crystal structure, which is compressed with an increasing Ag content due to a decrease in the Ag1–Ag1, Cu1–<i>S</i>(3), and Ag1–<i>S</i>(3) distances.</p>

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Refinement of the Crystal Structure of Argentotetrahedrite: A New S(3) Site in Octahedral Cluster [Ag, Cu]6

  • 期刊论文

  • 发表日期：

    2026年5月31日

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  • N. G. Lyubimtseva,
  • G. V. Shilov,
  • D. V. Korchagin,
  • S. E. Borisovskiy,
  • A. N. Utenyshev,
  • S. M. Aldoshin,
  • N. S. Bortnikov

摘要

Abstract

Using electron microprobe analysis and X-ray diffraction (XRD), we studied crystal fragments of four minerals of the fahlore group from the Mangazeyskoye Ag–Pb–Zn deposit (Yakutia, Russia) with 3.7–5.8 atoms per formula units (apfu) Ag and 13–12 apfu S. Both methods revealed a negative correlation between Ag and S contents in the fahlore chemical composition. The crystal structures of four Ag-bearing fahlores are refined using XRD. The parameters of their unit cells (a0, Å) in group \(I\bar {4}3m\) (cubic) are as follows: 10.58829 for argentotetrahedrite-(Fe) (Ag3.68Cu2.32)Σ6(Cu4.04[Fe1.73Zn0.27]Σ2.00)Σ6.04(Sb3.94As0.03)Σ3.97S12S1.01; 10.53378 for argentotetrahedrite-(Zn) (Ag3.82Cu2.18)Σ6(Cu4.09[Zn1.71Fe0.28]Σ1.99)Σ6.08(Sb3.82As0.10)Σ3.92S12.74; 10.51544 for kenoargentotetrahedrite-(Fe) (Ag4.34Cu1.66)Σ6(Cu4.10[Zn0.96Fe1.03]Σ1.98)Σ6.08 (Sb3.88As0.03)Σ3.92S12.47; and 10.48411 for kenoargentotetrahedrite-(Zn) (Ag5.83Cu0.17)Σ6(Cu3.96[Zn1.98Fe0.04]Σ2.02)Σ5.98(Sb3.99As0.02)Σ4.01S12S0.04. The XRD studies of the fahlore crystal structure with a high resolution (2θmax = 82°) allowed us to refine the positions of Ag and Cu atoms in site M(2) and to find for the first time a new sulfur site S(3). А high Ag content (3.7–5.8 apfu) shifts S from site S(2) in the center of the octahedron by 0.42–0.44 Å to site S(3), which is located on a 3m symmetry element. Quantum chemical modeling showed that the sequential substitution of Cu atoms by Ag atoms in octahedral cluster [SCu6]4+ gradually shifts the S atom from the center of the octahedron that illustrates the transition from site S(2) in the pure Cu cluster to the refined site S(3) in cases of mixed clusters [S(Ag, Cu)6]. The unit cell parameter depends on the size of the [Ag, Cu]6 octahedral cluster in the fahlore crystal structure, which is compressed with an increasing Ag content due to a decrease in the Ag1–Ag1, Cu1–S(3), and Ag1–S(3) distances.