Platinum-group element micronuggets and refertilization process in Lherz orogenic peridotite (northeastern Pyrenees, France)

Jean Pierre Lorand*, Olivier Alard, Ambre Luguet

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

129 Citations (Scopus)

Abstract

Highly siderophile elements (Platinum-group elements, Au and Re) are currently assumed to reside inside base metal sulfides (BMS) in the convecting upper mantle. However, fertile lherzolites sampled by Pyrenean orogenic peridotite massifs are unexpectedly rich in 0.5-3 μm large micronuggets of platinum-group minerals (PGM). Among those, sulfides from the laurite-erlichmanite series (Ru, Os(Ir)S(As)2), Pt-Ir-Os alloys and Pt-Pd-Te-Bi phases (moncheite-merenskyite) are predominant. Not only the BMS phases but also the PGM micronuggets must be taken into account in calculation of the PGE budget of orogenic fertile lherzolites. Laurite is a good candidate for equilibrating the whole-rock budget of Os, Ir and Ru while accounting for supra-chondritic Ru/IrN. Textural relationships between PGMs and BMS highlight heterogeneous mixing between refractory PGMs (laurite/Pt-Ir-Os alloys) inherited from ancient refractory lithospheric mantle and late-magmatic metasomatic sulfides precipitated from tholeiitic melts. "Low-temperature" PGMs, especially Pt-Pd bismuthotellurides should be added to the list of mineral indicators of lithosphere refertilization process. Now disseminated within fertile lherzolites, "lithospheric" PGMs likely account for local preservation of ancient Os model ages (up to 2 Ga) detected in BMS by in-situ isotopic analyses. These PGMs also question the reliability of orogenic lherzolites for estimating the PGE signature of the Primitive Silicate Earth.

Original languageEnglish
Pages (from-to)298-310
Number of pages13
JournalEarth and Planetary Science Letters
Volume289
Issue number1-2
DOIs
Publication statusPublished - 15 Jan 2010
Externally publishedYes

Keywords

  • highly siderophile elements
  • orogenic peridotites
  • platinum-group minerals
  • upper mantle

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