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Minerals 2016, 6(1), 20; doi:10.3390/min6010020

Chemical Environment of Unusually Ge- and Pb-Rich Willemite, Tres Marias Mine, Mexico

1
Department of Geosciences, North Dakota State University, Fargo, ND 58108, USA
2
Chair of Geology and Economic Geology, Peter-Tunner-Straße 5, Leoben 8700, Austria
3
Karlsruhe Institute of Technology, Institute for Synchrotron Radiation, Hermann-von-Helmholtz-Platz 1, Eggenstein-Leopoldshafen D-76344, Germany
These authors contributed equally to this work.
*
Author to whom correspondence should be addressed.
Academic Editor: Raymond M. Coveney
Received: 30 December 2015 / Revised: 8 February 2016 / Accepted: 23 February 2016 / Published: 9 March 2016
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Abstract

The Tres Marias carbonate-hosted Zn-Ge deposit in Chihuahua, Mexico contains willemite [Zn2SiO4] with unusually high concentrations of minor and trace elements (e.g., Pb, Ge, As, P, V); Pb concentrations are as high as 2 wt %, and Ge may reach 4000 ppm (average 900 ppm). Electron microprobe analyses and synchrotron X-ray fluorescence maps show that Zn and Ge, as well as Zn and Pb are negatively correlated, whereas Ge and Pb are positively correlated across zoned willemite crystals. In cathodoluminescence (CL) images, those areas of willemite having high trace element concentrations have no, or low CL intensities, whereas zones low in trace elements (except for P) display bright blue CL colors. X-ray absorption fine structure (XAFS) spectroscopy was used to characterize the chemical nature of Ge and Pb in willemite. Comparisons to reference spectra of natural and artificial substances points to the presence of Ge4+ and Pb2+ in Tres Marias willemite. No evidence for Pb4+ was detected. Oscillatory zonation reflects trace element incorporation into willemite from the oxidation of primary Ge-bearing sphalerite and galena (PbS) by siliceous aqueous fluids. View Full-Text
Keywords: XAFS; XANES spectroscopy (Ge, Pb); germanium; lead; willemite; Zn2SiO4; Tres Marias XAFS; XANES spectroscopy (Ge, Pb); germanium; lead; willemite; Zn2SiO4; Tres Marias
This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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MDPI and ACS Style

Saini-Eidukat, B.; Melcher, F.; Göttlicher, J.; Steininger, R. Chemical Environment of Unusually Ge- and Pb-Rich Willemite, Tres Marias Mine, Mexico. Minerals 2016, 6, 20.

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