Distribution and substitution mechanism of Ge in a Ge-(Fe)-bearing sphalerite

Nigel J Cook, Barbara Etschmann, Cristiana L Ciobanu, Kalotina Geraki, Daryl L Howard, Timothy Williams, Nick Rae, Allan Pring, Guorong Chen, Bernt Johannessen, Joel Brugger

Research output: Contribution to journalArticleResearchpeer-review

Abstract

The distribution and substitution mechanism of Ge in the Ge-rich sphalerite from the Tres Marias Zn deposit, Mexico, was studied using a combination of techniques at μm- to atomic scales. Trace element mapping by Laser Ablation Inductively Coupled Mass Spectrometry shows that Ge is enriched in the same bands as Fe, and that Ge-rich sphalerite also contains measurable levels of several other minor elements, including As, Pb and Tl. Micron- to nanoscale heterogeneity in the sample, both textural and compositional, is revealed by investigation using Focused Ion Beam-Scanning Electron Microscopy (FIB-SEM) combined with Synchrotron X-ray Fluorescence mapping and High-Resolution Transmission Electron Microscopy imaging of FIB-prepared samples. Results show that Ge is preferentially incorporated within Fe-rich sphalerite with textural complexity finer than that of the microbeam used for the X-ray Absorption Near Edge Structure (XANES) measurements. Such heterogeneity, expressed as intergrowths between 3C sphalerite and 2H wurtzite on [110] zones, could be the result of either a primary growth process, or alternatively, polystage crystallization, in which early Fe-Ge-rich sphalerite is partially replaced by Fe-Ge-poor wurtzite. FIB-SEM imaging shows evidence for replacement supporting the latter. Transformation of sphalerite into wurtzite is promoted by (111)* twinning or lattice-scale defects, leading to a heterogeneous ZnS sample, in which the dominant component, sphalerite, can host up to ∼20% wurtzite. Ge K-edge XANES spectra for this sphalerite are identical to those of the germanite and argyrodite standards and the synthetic chalcogenide glasses GeS2 and GeSe2, indicating the Ge formally exists in the tetravalent form in this sphalerite. Fe K-edge XANES spectra for the same sample indicate that Fe is present mainly as Fe2+, and Cu K-edge XANES spectra are characteristic for Cu+. Since there is no evidence for coupled substitution involving a monovalent element, we propose that Ge4+ substitutes for (Zn2+, Fe2+) with vacancies in the structure to compensate for charge balance. This study shows the utility of synchrotron radiation combined with electron beam micro-analysis in investigating low-level concentrations of minor metals in common sulfides.
Original languageEnglish
Pages (from-to)117-132
Number of pages16
JournalMinerals
Volume5
Issue number2
DOIs
Publication statusPublished - 2015

Keywords

  • Germanium
  • Oxidation state
  • Sphalerite
  • Synchrotron radiation
  • XANES spectroscopy (Ge; Fe; Cu K-edges)

Cite this

Cook, Nigel J ; Etschmann, Barbara ; Ciobanu, Cristiana L ; Geraki, Kalotina ; Howard, Daryl L ; Williams, Timothy ; Rae, Nick ; Pring, Allan ; Chen, Guorong ; Johannessen, Bernt ; Brugger, Joel. / Distribution and substitution mechanism of Ge in a Ge-(Fe)-bearing sphalerite. In: Minerals. 2015 ; Vol. 5, No. 2. pp. 117-132.
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title = "Distribution and substitution mechanism of Ge in a Ge-(Fe)-bearing sphalerite",
abstract = "The distribution and substitution mechanism of Ge in the Ge-rich sphalerite from the Tres Marias Zn deposit, Mexico, was studied using a combination of techniques at μm- to atomic scales. Trace element mapping by Laser Ablation Inductively Coupled Mass Spectrometry shows that Ge is enriched in the same bands as Fe, and that Ge-rich sphalerite also contains measurable levels of several other minor elements, including As, Pb and Tl. Micron- to nanoscale heterogeneity in the sample, both textural and compositional, is revealed by investigation using Focused Ion Beam-Scanning Electron Microscopy (FIB-SEM) combined with Synchrotron X-ray Fluorescence mapping and High-Resolution Transmission Electron Microscopy imaging of FIB-prepared samples. Results show that Ge is preferentially incorporated within Fe-rich sphalerite with textural complexity finer than that of the microbeam used for the X-ray Absorption Near Edge Structure (XANES) measurements. Such heterogeneity, expressed as intergrowths between 3C sphalerite and 2H wurtzite on [110] zones, could be the result of either a primary growth process, or alternatively, polystage crystallization, in which early Fe-Ge-rich sphalerite is partially replaced by Fe-Ge-poor wurtzite. FIB-SEM imaging shows evidence for replacement supporting the latter. Transformation of sphalerite into wurtzite is promoted by (111)* twinning or lattice-scale defects, leading to a heterogeneous ZnS sample, in which the dominant component, sphalerite, can host up to ∼20{\%} wurtzite. Ge K-edge XANES spectra for this sphalerite are identical to those of the germanite and argyrodite standards and the synthetic chalcogenide glasses GeS2 and GeSe2, indicating the Ge formally exists in the tetravalent form in this sphalerite. Fe K-edge XANES spectra for the same sample indicate that Fe is present mainly as Fe2+, and Cu K-edge XANES spectra are characteristic for Cu+. Since there is no evidence for coupled substitution involving a monovalent element, we propose that Ge4+ substitutes for (Zn2+, Fe2+) with vacancies in the structure to compensate for charge balance. This study shows the utility of synchrotron radiation combined with electron beam micro-analysis in investigating low-level concentrations of minor metals in common sulfides.",
keywords = "Germanium, Oxidation state, Sphalerite, Synchrotron radiation, XANES spectroscopy (Ge; Fe; Cu K-edges)",
author = "Cook, {Nigel J} and Barbara Etschmann and Ciobanu, {Cristiana L} and Kalotina Geraki and Howard, {Daryl L} and Timothy Williams and Nick Rae and Allan Pring and Guorong Chen and Bernt Johannessen and Joel Brugger",
year = "2015",
doi = "10.3390/min5020117",
language = "English",
volume = "5",
pages = "117--132",
journal = "Minerals",
issn = "2075-163X",
publisher = "MDPI",
number = "2",

}

Cook, NJ, Etschmann, B, Ciobanu, CL, Geraki, K, Howard, DL, Williams, T, Rae, N, Pring, A, Chen, G, Johannessen, B & Brugger, J 2015, 'Distribution and substitution mechanism of Ge in a Ge-(Fe)-bearing sphalerite', Minerals, vol. 5, no. 2, pp. 117-132. https://doi.org/10.3390/min5020117

Distribution and substitution mechanism of Ge in a Ge-(Fe)-bearing sphalerite. / Cook, Nigel J; Etschmann, Barbara; Ciobanu, Cristiana L; Geraki, Kalotina; Howard, Daryl L; Williams, Timothy; Rae, Nick; Pring, Allan; Chen, Guorong; Johannessen, Bernt; Brugger, Joel.

In: Minerals, Vol. 5, No. 2, 2015, p. 117-132.

Research output: Contribution to journalArticleResearchpeer-review

TY - JOUR

T1 - Distribution and substitution mechanism of Ge in a Ge-(Fe)-bearing sphalerite

AU - Cook, Nigel J

AU - Etschmann, Barbara

AU - Ciobanu, Cristiana L

AU - Geraki, Kalotina

AU - Howard, Daryl L

AU - Williams, Timothy

AU - Rae, Nick

AU - Pring, Allan

AU - Chen, Guorong

AU - Johannessen, Bernt

AU - Brugger, Joel

PY - 2015

Y1 - 2015

N2 - The distribution and substitution mechanism of Ge in the Ge-rich sphalerite from the Tres Marias Zn deposit, Mexico, was studied using a combination of techniques at μm- to atomic scales. Trace element mapping by Laser Ablation Inductively Coupled Mass Spectrometry shows that Ge is enriched in the same bands as Fe, and that Ge-rich sphalerite also contains measurable levels of several other minor elements, including As, Pb and Tl. Micron- to nanoscale heterogeneity in the sample, both textural and compositional, is revealed by investigation using Focused Ion Beam-Scanning Electron Microscopy (FIB-SEM) combined with Synchrotron X-ray Fluorescence mapping and High-Resolution Transmission Electron Microscopy imaging of FIB-prepared samples. Results show that Ge is preferentially incorporated within Fe-rich sphalerite with textural complexity finer than that of the microbeam used for the X-ray Absorption Near Edge Structure (XANES) measurements. Such heterogeneity, expressed as intergrowths between 3C sphalerite and 2H wurtzite on [110] zones, could be the result of either a primary growth process, or alternatively, polystage crystallization, in which early Fe-Ge-rich sphalerite is partially replaced by Fe-Ge-poor wurtzite. FIB-SEM imaging shows evidence for replacement supporting the latter. Transformation of sphalerite into wurtzite is promoted by (111)* twinning or lattice-scale defects, leading to a heterogeneous ZnS sample, in which the dominant component, sphalerite, can host up to ∼20% wurtzite. Ge K-edge XANES spectra for this sphalerite are identical to those of the germanite and argyrodite standards and the synthetic chalcogenide glasses GeS2 and GeSe2, indicating the Ge formally exists in the tetravalent form in this sphalerite. Fe K-edge XANES spectra for the same sample indicate that Fe is present mainly as Fe2+, and Cu K-edge XANES spectra are characteristic for Cu+. Since there is no evidence for coupled substitution involving a monovalent element, we propose that Ge4+ substitutes for (Zn2+, Fe2+) with vacancies in the structure to compensate for charge balance. This study shows the utility of synchrotron radiation combined with electron beam micro-analysis in investigating low-level concentrations of minor metals in common sulfides.

AB - The distribution and substitution mechanism of Ge in the Ge-rich sphalerite from the Tres Marias Zn deposit, Mexico, was studied using a combination of techniques at μm- to atomic scales. Trace element mapping by Laser Ablation Inductively Coupled Mass Spectrometry shows that Ge is enriched in the same bands as Fe, and that Ge-rich sphalerite also contains measurable levels of several other minor elements, including As, Pb and Tl. Micron- to nanoscale heterogeneity in the sample, both textural and compositional, is revealed by investigation using Focused Ion Beam-Scanning Electron Microscopy (FIB-SEM) combined with Synchrotron X-ray Fluorescence mapping and High-Resolution Transmission Electron Microscopy imaging of FIB-prepared samples. Results show that Ge is preferentially incorporated within Fe-rich sphalerite with textural complexity finer than that of the microbeam used for the X-ray Absorption Near Edge Structure (XANES) measurements. Such heterogeneity, expressed as intergrowths between 3C sphalerite and 2H wurtzite on [110] zones, could be the result of either a primary growth process, or alternatively, polystage crystallization, in which early Fe-Ge-rich sphalerite is partially replaced by Fe-Ge-poor wurtzite. FIB-SEM imaging shows evidence for replacement supporting the latter. Transformation of sphalerite into wurtzite is promoted by (111)* twinning or lattice-scale defects, leading to a heterogeneous ZnS sample, in which the dominant component, sphalerite, can host up to ∼20% wurtzite. Ge K-edge XANES spectra for this sphalerite are identical to those of the germanite and argyrodite standards and the synthetic chalcogenide glasses GeS2 and GeSe2, indicating the Ge formally exists in the tetravalent form in this sphalerite. Fe K-edge XANES spectra for the same sample indicate that Fe is present mainly as Fe2+, and Cu K-edge XANES spectra are characteristic for Cu+. Since there is no evidence for coupled substitution involving a monovalent element, we propose that Ge4+ substitutes for (Zn2+, Fe2+) with vacancies in the structure to compensate for charge balance. This study shows the utility of synchrotron radiation combined with electron beam micro-analysis in investigating low-level concentrations of minor metals in common sulfides.

KW - Germanium

KW - Oxidation state

KW - Sphalerite

KW - Synchrotron radiation

KW - XANES spectroscopy (Ge; Fe; Cu K-edges)

UR - http://www.mdpi.com/2075-163X/5/2/117/pdf

U2 - 10.3390/min5020117

DO - 10.3390/min5020117

M3 - Article

VL - 5

SP - 117

EP - 132

JO - Minerals

JF - Minerals

SN - 2075-163X

IS - 2

ER -