TY - JOUR

T1 - Experimental constraints on gold and silver solubility in iron sulfides

AU - Pal'Yanova, Galina

AU - Mikhlin, Yuri

AU - Kokh, Konstantin

AU - Karmanov, Nick

AU - Seryotkin, Yurii

PY - 2015/7/27

Y1 - 2015/7/27

N2 - Experiments were performed to determine crystallization of Fe,S-melts (pyritic and troilitic with molar ratio S/Fe ratios of 2 and 1, respectively) containing traces of gold and silver at (Ag/Au)wt ratios varying from 10 to 0.1. The solid products were studied by optical microscopy, scanning electron microscopy, X-ray powder diffraction (XRD), microprobe analysis, and X-ray photoelectron spectroscopy (XPS) in order to reveal the concentration limits of "invisible" gold and silver in magmatic iron sulfides, and to determine the influence of sulfur on forms of precious metals in the Fe-S system with different Ag/Au ratios. Au-Ag phases do not form inclusions but instead concentrate on the grain boundaries in the synthetic pyrrhotite and troilite, while pyrite comprises micro- (1-5 μm) and macroinclusions of Au-Ag alloys and Au-Ag sulfides. In "pyritic" systems, the fineness of alloys increases from 650 to 970‰ and the composition of sulfides changes from acanthite (Ag2S) to uytenbogaardtite (Ag3AuS2) and petrovskaite (AgAuS) as the Ag/Au ratio decreases. The concentrations of "invisible" precious metals revealed in troilite were 0.040 ± 0.013 wt.% Au and 0.079 ± 0.016 wt.% Ag. Measured concentrations in pyrite and pyrrhotite were <0.024 wt.% Au and <0.030 wt.% Ag. The surface layers of iron sulfides probed with XPS were enriched in the precious metals, and in silver relative to gold, especially in the systems with Fe/S = 1, probably, due to depletion of the metallic alloy surfaces with gold. Au- and Ag-bearing iron sulfides crystallized primarily from melts may be the source of redeposited phases in hydrothermal and hypergene processes.

AB - Experiments were performed to determine crystallization of Fe,S-melts (pyritic and troilitic with molar ratio S/Fe ratios of 2 and 1, respectively) containing traces of gold and silver at (Ag/Au)wt ratios varying from 10 to 0.1. The solid products were studied by optical microscopy, scanning electron microscopy, X-ray powder diffraction (XRD), microprobe analysis, and X-ray photoelectron spectroscopy (XPS) in order to reveal the concentration limits of "invisible" gold and silver in magmatic iron sulfides, and to determine the influence of sulfur on forms of precious metals in the Fe-S system with different Ag/Au ratios. Au-Ag phases do not form inclusions but instead concentrate on the grain boundaries in the synthetic pyrrhotite and troilite, while pyrite comprises micro- (1-5 μm) and macroinclusions of Au-Ag alloys and Au-Ag sulfides. In "pyritic" systems, the fineness of alloys increases from 650 to 970‰ and the composition of sulfides changes from acanthite (Ag2S) to uytenbogaardtite (Ag3AuS2) and petrovskaite (AgAuS) as the Ag/Au ratio decreases. The concentrations of "invisible" precious metals revealed in troilite were 0.040 ± 0.013 wt.% Au and 0.079 ± 0.016 wt.% Ag. Measured concentrations in pyrite and pyrrhotite were <0.024 wt.% Au and <0.030 wt.% Ag. The surface layers of iron sulfides probed with XPS were enriched in the precious metals, and in silver relative to gold, especially in the systems with Fe/S = 1, probably, due to depletion of the metallic alloy surfaces with gold. Au- and Ag-bearing iron sulfides crystallized primarily from melts may be the source of redeposited phases in hydrothermal and hypergene processes.

KW - "Invisible" gold and silver

KW - Ag-Au alloys

KW - Au-Ag sulfides (acanthite, uytenbogaardtite, petrovskaite)

KW - Iron sulfides (pyrite, pyrrhotite, troilite)

UR - http://www.scopus.com/inward/record.url?scp=84937845338&partnerID=8YFLogxK

U2 - 10.1016/j.jallcom.2015.07.131

DO - 10.1016/j.jallcom.2015.07.131

M3 - Article

AN - SCOPUS:84937845338

VL - 649

SP - 67

EP - 75

JO - Journal of Alloys and Compounds

JF - Journal of Alloys and Compounds

SN - 0925-8388

ER -