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Minerals 2015, 5(2), 117-132;

Distribution and Substitution Mechanism of Ge in a Ge-(Fe)-Bearing Sphalerite

School of Chemical Engineering, University of Adelaide, Adelaide, SA 5005, Australia
School of Geosciences, Monash University, Clayton, VIC 3800, Australia
South Australian Museum, North Terrace, Adelaide, SA 5000, Australia
Diamond Light Source, Harwell Science and Innovation Campus, Didcot, Oxon OX11 0QX, UK
Australian Synchrotron, 800 Blackburn Rd., Clayton, VIC 3168, Australia
The Monash Centre for Electron Microscopy, Monash University, Clayton, VIC 3800, Australia
School of Chemical and Physical Sciences, Flinders University, GPO Box 2100, Adelaide, SA 5000, Australia
Key Laboratory for Ultrafine Materials of Ministry of Education, School of Materials Science and Engineering, East China University of Science and Technology, Shanghai 200237, China
Author to whom correspondence should be addressed.
Academic Editor: Mostafa Fayek
Received: 3 February 2015 / Revised: 6 March 2015 / Accepted: 16 March 2015 / Published: 24 March 2015
Full-Text   |   PDF [14591 KB, uploaded 24 March 2015]   |  


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 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. View Full-Text
Keywords: synchrotron radiation; XANES spectroscopy (Ge; Fe; Cu K-edges); sphalerite; germanium; oxidation state synchrotron radiation; XANES spectroscopy (Ge; Fe; Cu K-edges); sphalerite; germanium; oxidation state

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Cook, N.J.; Etschmann, B.; Ciobanu, C.L.; Geraki, K.; Howard, D.L.; Williams, T.; Rae, N.; Pring, A.; Chen, G.; Johannessen, B.; Brugger, J. Distribution and Substitution Mechanism of Ge in a Ge-(Fe)-Bearing Sphalerite. Minerals 2015, 5, 117-132.

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