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American Mineralogist

Journal of Earth and Planetary Materials

Ed. by Baker, Don / Xu, Hongwu / Swainson, Ian


IMPACT FACTOR 2017: 2.645

CiteScore 2017: 2.31

SCImago Journal Rank (SJR) 2017: 1.440
Source Normalized Impact per Paper (SNIP) 2017: 1.059

Online
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1945-3027
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Volume 84, Issue 7-8

Issues

Oxidation state of gold and arsenic in gold-bearing arsenian pyrite

Grigore Simon
  • Department of Geological Sciences, University of Michigan, 2534 C.C. Little Building, Ann Arbor, Michigan 48109, U.S.A.
  • Shell International Exploration and Production B.V., Carel van Bylandtlaan 16, The Hague, The Netherlands.
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/ Hui Huang
  • Department of Chemistry, University of Michigan, 930 North University Avenue, Ann Arbor, Michigan 48109, U.S.A.
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/ James E. Penner-Hahn
  • Department of Chemistry, University of Michigan, 930 North University Avenue, Ann Arbor, Michigan 48109, U.S.A.
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/ Stephen E. Kesler
  • Department of Geological Sciences, University of Michigan, 2534 C.C. Little Building, Ann Arbor, Michigan 48109, U.S.A.
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/ Li-Shun Kao
  • Department of Geological Sciences, University of Michigan, 2534 C.C. Little Building, Ann Arbor, Michigan 48109, U.S.A.
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Published Online: 2015-11-13 | DOI: https://doi.org/10.2138/am-1999-7-809

Abstract

XANES measurements on gold-bearing arsenian pyrite from the Twin Creeks Carlin-type gold deposits show that gold is present as both Au0 and AuI+ and arsenic is present at AsI-. Au0 is attributed to sub-micrometer size inclusions of free gold, whereas AuI+ is attributed to gold in the lattice of the arsenian pyrite. STEM observations suggest that AsI- is probably concentrated in angstrom-scale, randomly distributed layers with a marcasite or arsenopyrite structure. Ionic gold (AuI+) could be concentrated in these layers as well, and is present in both twofold- and fourfold-coordinated forms, with fourfold-coordinated AuI+ more abundant. Twofold-coordinated AuI+ is similar to gold in Au2S in which it is linearly coordinated to two sulfur atoms. The nature of fourfold-coordinated AuI+ is not well understood, although it might be present as an Au-As-S compound where gold is bonded in fourfold coordination to sulfur and arsenic atoms, or in vacancy positions on a cation site in the arsenian pyrite. AuI+ was probably incorporated into arsenian pyrite by adsorption onto pyrite surfaces during crystal growth. The most likely compound in the case of twofold-coordinated AuI+ was probably a tri-atomic surface complex such as Spyrite-AuI+-Sbi-sulfideH or AuI+-S-AuI+. The correlation between gold and arsenic might be related to the role of arsenic in enhancing the adsorption of gold complexes of this type on pyrite surfaces, possibly through semiconductor effects.

About the article

Received: 1998-09-14

Accepted: 1999-02-13

Published Online: 2015-11-13

Published in Print: 1999-07-01


Citation Information: American Mineralogist, Volume 84, Issue 7-8, Pages 1071–1079, ISSN (Online) 1945-3027, ISSN (Print) 0003-004X, DOI: https://doi.org/10.2138/am-1999-7-809.

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© 2015 by Walter de Gruyter Berlin/Boston.

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