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

Grigore Simon, Hui Huang, James E. Penner-Hahn, Stephen E. Kesler and Li-Shun Kao
Oxidation state of gold and arsenic in gold-bearing arsenian pyrite
American Mineralogist (August 1999) 84 (7-8): 1071-1079


XANES measurements on gold-bearing arsenian pyrite from the Twin Creeks Carlin-type gold deposits show that gold is present as both Au (super 0) and Au (super I+) and arsenic is present at As (super I-) . Au (super 0) is attributed to sub-micrometer size inclusions of free gold, whereas Au (super I+) is attributed to gold in the lattice of the arsenian pyrite. STEM observations suggest that As (super I-) is probably concentrated in angstrom-scale, randomly distributed layers with a marcasite or arsenopyrite structure. Ionic gold (Au (super I+) ) could be concentrated in these layers as well, and is present in both twofold- and fourfold-coordinated forms, with fourfold-coordinated Au (super I+) more abundant. Twofold-coordinated Au (super I+) is similar to gold in Au (sub 2) S in which it is linearly coordinated to two sulfur atoms. The nature of fourfold-coordinated Au (super I+) 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. Au (super I+) was probably incorporated into arsenian pyrite by adsorption onto pyrite surfaces during crystal growth. The most likely compound in the case of twofold-coordinated Au (super I+) was probably a tri-atomic surface complex such as S (sub pyrite) -Au (super I+) -S (sub bi-sulfide) H or Au (super I+) -S-Au (super I+) . 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.

ISSN: 0003-004X
EISSN: 1945-3027
Serial Title: American Mineralogist
Serial Volume: 84
Serial Issue: 7-8
Title: Oxidation state of gold and arsenic in gold-bearing arsenian pyrite
Affiliation: University of Michigan, Department of Geological Sciences, Ann Arbor, MI, United States
Pages: 1071-1079
Published: 199908
Text Language: English
Publisher: Mineralogical Society of America, Washington, DC, United States
References: 61
Accession Number: 1999-066013
Categories: Economic geology, geology of ore depositsMineralogy of non-silicates
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 2 tables
N35°00'00" - N42°00'00", W120°00'00" - W114°04'60"
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2018, American Geosciences Institute.
Update Code: 199922
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