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Chromatographic separation of the platinum-group elements, gold, base metals and sulfur during degassing of a compacting and solidifying igneous crystal pile

Publication ,  Journal Article
Boudreau, AE; Meurer, WP
Published in: Contributions to Mineralogy and Petrology
January 1, 1999

The major platinum-group elements (PGE) concentrations in layered intrusions are typically associated with zones in which the sulfide abundance begins to increase. In a number of layered intrusions, there is also a distinct stratigraphic separation in the peak concentrations of the PGE from those of the base metals, gold and sulfur through these zones. These stratigraphi"offsets" are characterized by a lower, typically S-poor, Pt- and Pd-enriched zone overlain by a zone enriched in the base metals, S and Au. The separations amount to a few decimeters to several tens of meters. In some instances, the high Pt and Pd concentrations are associated with trivial amounts of sulfide. Theoretical considerations suggest that these offsets can be modeled as chromatographic peaks that develop during an infiltration/reaction process. Using Pd as a typical PGE and Cu as a typical base metal, a numeric model is developed that illustrates how metal separations can develop in a vapor-refining zone as fluid evolved during solidification of a cumulus pile leaches sulfide and redeposits it higher in the crystal pile. The solidification/degassing ore-element transport is coupled with a compaction model for the crystal pile. Solidification resulting from conductive cooling through the base of the compacting column leads to an increasing volatile concentration in the intercumulus liquid until it reaches fluid saturation. Separation and upward migration of this fluid lead to an upward-migrating zone of increasingly higher bulk water contents as water degassed from underlying cumulates enriches overlying, fluid-undersaturated interstitial liquids. Sulfide is resorbed from the degassing regions and is reprecipitated in these vapor-undersaturated interstitial liquids, producing a zone of relatively high modal sulfide that also migrates upward with time. Owing to its strong preference for sulfide, Pd is not significantly mobile until all sulfide is resorbed. The result is a zone of increasing PGE enrichment that follows the sulfide resorption front as solidification/degassing continues. In detail, the highest Pd concentrations occur stratigraphically below the peak in S and base metals. The high Pd/S ratio mimics values conventionally interpreted as the result of high (silicate liquid)/(sulfide liquid) mass ratios ("R" values). However, in this case, the high Pd/S ratio is the result of a chromatographic/ reaction front enrichment and not a magmatic sulfide-saturation event. © Springer-Verlag 1999.

Duke Scholars

Published In

Contributions to Mineralogy and Petrology

DOI

ISSN

0010-7999

Publication Date

January 1, 1999

Volume

134

Issue

2-3

Start / End Page

174 / 185

Related Subject Headings

  • Energy
  • 4019 Resources engineering and extractive metallurgy
  • 3705 Geology
  • 3703 Geochemistry
  • 0499 Other Earth Sciences
  • 0403 Geology
  • 0402 Geochemistry
 

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Boudreau, A. E., & Meurer, W. P. (1999). Chromatographic separation of the platinum-group elements, gold, base metals and sulfur during degassing of a compacting and solidifying igneous crystal pile. Contributions to Mineralogy and Petrology, 134(2–3), 174–185. https://doi.org/10.1007/s004100050477
Boudreau, A. E., and W. P. Meurer. “Chromatographic separation of the platinum-group elements, gold, base metals and sulfur during degassing of a compacting and solidifying igneous crystal pile.” Contributions to Mineralogy and Petrology 134, no. 2–3 (January 1, 1999): 174–85. https://doi.org/10.1007/s004100050477.
Boudreau, A. E., and W. P. Meurer. “Chromatographic separation of the platinum-group elements, gold, base metals and sulfur during degassing of a compacting and solidifying igneous crystal pile.” Contributions to Mineralogy and Petrology, vol. 134, no. 2–3, Jan. 1999, pp. 174–85. Scopus, doi:10.1007/s004100050477.
Journal cover image

Published In

Contributions to Mineralogy and Petrology

DOI

ISSN

0010-7999

Publication Date

January 1, 1999

Volume

134

Issue

2-3

Start / End Page

174 / 185

Related Subject Headings

  • Energy
  • 4019 Resources engineering and extractive metallurgy
  • 3705 Geology
  • 3703 Geochemistry
  • 0499 Other Earth Sciences
  • 0403 Geology
  • 0402 Geochemistry