Covellite CuS as a matrix for “invisible” gold: X-ray spectroscopic study of the chemical state of Cu and Au in synthetic minerals

Тагиров, Б. Р.; Trigub, Alexander L.; Kvashnina, Kristina O.; Shiryaev, A. A.; Чареев, Д. А.; Nickolsky, Maximilian S.; Абрамова, В. Д.; Kovalchuk, E. V.

doi:10.1016/j.gca.2016.07.015

Cited by 26 publications

(32 citation statements)

References 33 publications

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“…In all cases, the large unit cell allowed gamma point approximation to be employed. Our previous investigations [1,12,13] demonstrated the high accuracy of this approach to DFT calculations in the case of sphalerite-type structures. The discrepancy between the calculated interatomic distances and EXAFS results was 0.02, 0.01, and 0.04 Å for the 1st, 2nd, and 3rd coordination shells, respectively.…”

Section: Density Functional Theory (Dft) Calculationsmentioning

confidence: 83%

“…The formation energies of sphalerite solid solutions (E FE , [12,14]) were obtained using the calculated total energies. We considered the following models: two In atoms substitute for two Zn atoms in ZnS crystal structure; two In atoms substitute for two Zn atoms in ZnS crystal structure with the formation of a vacancy at Zn position; one In and one Cu atom substitute for two Zn atoms in ZnS crystal structure.…”

Section: Density Functional Theory (Dft) Calculationsmentioning

confidence: 99%

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Probing the Local Atomic Structure of In and Cu in Sphalerite by XAS Spectroscopy Enhanced by Reverse Monte Carlo Algorithm

et al. 2020

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The distortion of atomic structure around In and Cu dopants in sphalerite ZnS was explored by extended X-ray absorption fine structure (EXAFS) spectroscopy enhanced by reverse Monte Carlo (RMC) simulation (RMC-EXAFS method). These data were complemented with quantum chemical Density Functional Theory (DFT) calculations and theoretical modeling of X-ray absorption near edge spectroscopy (XANES) spectra. The RMC-EXAFS method showed that in the absence of Cu, the In-bearing solid solution is formed via the charge compensation scheme 3Zn2+↔2In3+ + □, where □ is a Zn vacancy. The coordination spheres of In remain undistorted. Formation of the solid solution in the case of (In, Cu)-bearing sphalerites follows the charge compensation scheme 2Zn2+↔Cu+ + In3+. In the solid solution, splitting of the interatomic distances in the 2nd and 3rd coordination spheres of In and Cu is observed. The dopants’ local atomic structure is slightly distorted around In but highly distorted around Cu. The DFT calculations showed that the geometries with close arrangement (clustering) of the impurities—In and Cu atoms, or the In atom and a vacancy—are energetically more favorable than the random distribution of the defects. However, as no heavy In atoms were detected in the 2nd shell of Cu by means of EXAFS, and the 2nd shell of In was only slightly distorted, we conclude that the defects are distributed randomly (or at least, not close to each other). The disagreement of the RMC-EXAFS fittings with the results of the DFT calculations, according to which the closest arrangement of dopants is the most stable configuration, can be explained by the presence of other defects of the sphalerite crystal lattice, which were not considered in the DFT calculations.

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Section: Density Functional Theory (Dft) Calculationsmentioning

confidence: 83%

Section: Density Functional Theory (Dft) Calculationsmentioning

confidence: 99%

Probing the Local Atomic Structure of In and Cu in Sphalerite by XAS Spectroscopy Enhanced by Reverse Monte Carlo Algorithm

et al. 2020

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“…Two structural positions exist for copper in covellite: The tetrahedral and triangular coordination geometries with S atoms [34,35]. The Ge K-edge spectrum collected for covellite suggests that Ge 4+ substitutes for Cu + only in four-fold coordination geometry (i.e., in the tetrahedral site).…”

Section: Discussionmentioning

confidence: 99%

Germanium Crystal Chemistry in Cu-Bearing Sulfides from Micro-XRF Mapping and Micro-XANES Spectroscopy

et al. 2019

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Germanium is considered a critical element, with a demand that has sharply increased due to booming high-technology industries. To understand Ge incorporation mechanisms in natural systems, we investigate Ge speciation in Cu-bearing sulfide minerals using synchrotron X-ray fluorescence (XRF) chemical mapping and Ge K-edge µ-X-ray absorption near-edge structures (µ-XANES) spectroscopy. The samples investigated include (i) a homogeneous chalcopyrite from the Kipushi polymetallic deposit (Central African copperbelt, D.R. Congo) and (ii) a zoned Ge-rich chalcopyrite from the Barrigão Cu deposit (Iberian pyrite belt, Portugal). First, our spectroscopic analysis supports the occurrence of tetrahedrally-coordinated Ge4+ in chalcopyrite, independently from origins or zoning patterns observed for these minerals. Then, based on statistical analyses of XRF chemical maps, we demonstrate that tetravalent germanium most likely incorporates chalcopyrite through the Fe crystallographic site via coupled substitutions with the following form: (2x + 3y)Fe3+ ⟷ (x + 2y)(Ge,Sn)4+ + x(Zn,Pb)2+ + y(Cu,Ag)+, although the presence of lattice vacancies cannot be completely excluded.

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“…This implies that the high-temperature ore fluids are strongly undersaturated with respect to native Au. Therefore, at high temperatures during the early stages of porphyry ore formation, Au can be deposited only in an "invisible" (or refractory) state, either in the form of nanoscale particles or as a component of solid solutions (e.g., Tagirov et al [36], Trigub et al [37]). A decrease in temperature results in a drastic decrease in Au solubility.…”

Section: Effect Of Temperature Ph and Chlorinity On Au Solubilitymentioning

confidence: 99%

Stability of AuCl2− from 25 to 1000 °C at Pressures to 5000 bar and Consequences for Hydrothermal Gold Mobilization

et al. 2018

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Abstract:Gold is transported in high-temperature chloride-bearing hydrothermal fluids in the form of AuCl 2 − . The stability of this complex has been extensively studied, but there is still considerable disagreement between available experimental data on the temperature region 300-500 • C. To solve this problem, we measured the solubility of gold in HCl/NaCl fluids (NaCl concentration varied from 0.1 to 3 mol·(kg·H 2 O) −1 ) at 450 • C and pressures from 500 to 1500 bar (1 bar = 10 5 Pa). The experiments were performed using a batch autoclave method at contrasting redox conditions: in reduced experiments hydrogen was added to the autoclave, and in oxidized experiments the redox state was controlled by the aqueous SO 2 /SO 3 buffer. Hydrogen pressure in the autoclaves was measured after the experiments in the reduced system. The gold solubility constant, Au (cr) + HCl • (aq)

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Covellite CuS as a matrix for “invisible” gold: X-ray spectroscopic study of the chemical state of Cu and Au in synthetic minerals

Cited by 26 publications

References 33 publications

Probing the Local Atomic Structure of In and Cu in Sphalerite by XAS Spectroscopy Enhanced by Reverse Monte Carlo Algorithm

Probing the Local Atomic Structure of In and Cu in Sphalerite by XAS Spectroscopy Enhanced by Reverse Monte Carlo Algorithm

Germanium Crystal Chemistry in Cu-Bearing Sulfides from Micro-XRF Mapping and Micro-XANES Spectroscopy

Stability of AuCl2− from 25 to 1000 °C at Pressures to 5000 bar and Consequences for Hydrothermal Gold Mobilization

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