Gold solubility and partitioning between sulfide liquid, monosulfide solid solution and hydrous mantle melts: Implications for the formation of Au-rich magmas and crust–mantle differentiation

Gold solubility and partitioning between sulfide liquid, monosulfide solid solution and hydrous... The solubility of Au in sulfur-free vs. sulfide-saturated melts and its partitioning behavior between sulfide liquid (SL), monosulfide solid solution (MSS) and hydrous basanite melt at variable Au activities was investigated in a fO2 range of FMQ−2 to FMQ+1.6 at 1200°C/1.5GPa using piston cylinder apparatus. Gold solubility in sulfur-free (<100μg/g S) melt is low (0.6–1.6μg/g) and increases with fO2 in a manner consistent with Au dissolution as AuO1/2, whereas in sulfide-saturated melts it is high (13.6±1.7μg/g) and independent of fO2. Variations in the chlorine content of sulfide-saturated melts (0.2–1.2wt% Cl) had no measurable effect on Au solubility. Gold partition coefficients between sulfide liquid and silicate melt (DAuSL/SM) are very high, ∼10,000±3000, which is at the upper end of values reported in previous studies. Gold partition coefficients between MSS and silicate melt (DAuMSS/SM) are much lower, 60±10, which is at the lower end of previous values. Both DAuSL/SM and DAuMSS/SM are independent of fO2. The new Au partition coefficients were used in conjunction with previously published Cu and Ag partition coefficients to investigate the role of MSS versus SL during partial melting in the source region of primitive potassic magmas and during crust–mantle differentiation.The high Au content of ore deposits associated with potassic magmas has commonly been explained by the dissolution of Au-rich sulfide liquid, either during partial melting in the mantle source or during partial re-melting of sulfide-bearing cumulates at the crust–mantle boundary. We argue that MSS is the dominant sulfide phase in the mantle source region of these magmas, and thus that their high Au content is a consequence of low MSS–silicate melt partition coefficients rather than of sulfide exhaustion or partial re-melting of sulfide-bearing cumulates.Continental crust is depleted in Au, Ag and Cu relative to mantle melts, which was thought to be due to removal of sulfide liquid at the crust–mantle boundary. However, based on sulfide phase relations at high-pressure and high-temperature and corresponding sulfide–silicate melt partition coefficients we come to the conclusion that sulfides precipitated at the crust–mantle boundary are dominated by MSS rather than sulfide liquid, and thus have a much lower capability to sequester Au, Ag and Pb than in the case of sulfide liquid. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Geochimica et Cosmochimica Acta Elsevier

Gold solubility and partitioning between sulfide liquid, monosulfide solid solution and hydrous mantle melts: Implications for the formation of Au-rich magmas and crust–mantle differentiation

Loading next page...
 
/lp/elsevier/gold-solubility-and-partitioning-between-sulfide-liquid-monosulfide-3HWI4cbb0S
Publisher
Elsevier
Copyright
Copyright © 2013 Elsevier Ltd
ISSN
0016-7037
eISSN
1872-9533
D.O.I.
10.1016/j.gca.2013.05.014
Publisher site
See Article on Publisher Site

Abstract

The solubility of Au in sulfur-free vs. sulfide-saturated melts and its partitioning behavior between sulfide liquid (SL), monosulfide solid solution (MSS) and hydrous basanite melt at variable Au activities was investigated in a fO2 range of FMQ−2 to FMQ+1.6 at 1200°C/1.5GPa using piston cylinder apparatus. Gold solubility in sulfur-free (<100μg/g S) melt is low (0.6–1.6μg/g) and increases with fO2 in a manner consistent with Au dissolution as AuO1/2, whereas in sulfide-saturated melts it is high (13.6±1.7μg/g) and independent of fO2. Variations in the chlorine content of sulfide-saturated melts (0.2–1.2wt% Cl) had no measurable effect on Au solubility. Gold partition coefficients between sulfide liquid and silicate melt (DAuSL/SM) are very high, ∼10,000±3000, which is at the upper end of values reported in previous studies. Gold partition coefficients between MSS and silicate melt (DAuMSS/SM) are much lower, 60±10, which is at the lower end of previous values. Both DAuSL/SM and DAuMSS/SM are independent of fO2. The new Au partition coefficients were used in conjunction with previously published Cu and Ag partition coefficients to investigate the role of MSS versus SL during partial melting in the source region of primitive potassic magmas and during crust–mantle differentiation.The high Au content of ore deposits associated with potassic magmas has commonly been explained by the dissolution of Au-rich sulfide liquid, either during partial melting in the mantle source or during partial re-melting of sulfide-bearing cumulates at the crust–mantle boundary. We argue that MSS is the dominant sulfide phase in the mantle source region of these magmas, and thus that their high Au content is a consequence of low MSS–silicate melt partition coefficients rather than of sulfide exhaustion or partial re-melting of sulfide-bearing cumulates.Continental crust is depleted in Au, Ag and Cu relative to mantle melts, which was thought to be due to removal of sulfide liquid at the crust–mantle boundary. However, based on sulfide phase relations at high-pressure and high-temperature and corresponding sulfide–silicate melt partition coefficients we come to the conclusion that sulfides precipitated at the crust–mantle boundary are dominated by MSS rather than sulfide liquid, and thus have a much lower capability to sequester Au, Ag and Pb than in the case of sulfide liquid.

Journal

Geochimica et Cosmochimica ActaElsevier

Published: Oct 1, 2013

References

You’re reading a free preview. Subscribe to read the entire article.


DeepDyve is your
personal research library

It’s your single place to instantly
discover and read the research
that matters to you.

Enjoy affordable access to
over 12 million articles from more than
10,000 peer-reviewed journals.

All for just $49/month

Explore the DeepDyve Library

Unlimited reading

Read as many articles as you need. Full articles with original layout, charts and figures. Read online, from anywhere.

Stay up to date

Keep up with your field with Personalized Recommendations and Follow Journals to get automatic updates.

Organize your research

It’s easy to organize your research with our built-in tools.

Your journals are on DeepDyve

Read from thousands of the leading scholarly journals from SpringerNature, Elsevier, Wiley-Blackwell, Oxford University Press and more.

All the latest content is available, no embargo periods.

See the journals in your area

Monthly Plan

  • Read unlimited articles
  • Personalized recommendations
  • No expiration
  • Print 20 pages per month
  • 20% off on PDF purchases
  • Organize your research
  • Get updates on your journals and topic searches

$49/month

Start Free Trial

14-day Free Trial

Best Deal — 39% off

Annual Plan

  • All the features of the Professional Plan, but for 39% off!
  • Billed annually
  • No expiration
  • For the normal price of 10 articles elsewhere, you get one full year of unlimited access to articles.

$588

$360/year

billed annually
Start Free Trial

14-day Free Trial