Metallogeny of the Chrome Ores of the Xerolivado-Skoumtsa Mine, Vourinos Ophiolite, Greece: Implications on the genesis of IPGE-bearing high-Cr chromitites within a heterogeneously depleted mantle section

Evangelos Tzamos, A. Kapsiotis, Anestis Filippidis, A. Koroneos, G. Grieco, A. Ewing Rassios, N. Kantiranis, A. Papadopoulos, P. N. Gamaletsos, A. Godelitsas

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Abstract

Chrome ore deposits comprise less than 1% of the volume of a pervasively serpentinized dunite body (∼3.5km3) that constitutes the Xerolivado-Skoumtsa Mine of the Vourinos Ophiolite in northwestern Greece. Ores have been examined to aid determination of their geological mode of occurrence, their mineralogy and mineral chemistry (Cr-spinel and olivine), and platinum-group element (PGE) geochemistry. The ore bodies are highly deformed and of the schlieren type, where Cr-spinel-rich and serpentine (after olivine)-rich layers (1-20cm thick) alternate. The Cr-spinel displays a limited range in Cr# [100×Cr/(Cr+Al)] atomic ratio (77-85) and TiO2 content (0.05-0.22wt%). The Mg# [100×Mg/(Mg+Fe2+)] of Cr-spinel shows a wider variation (52-74) indicating that subsolidus (Mg Sp -Fe2+ Ol ) re-equilibration occurred. Remnant fresh olivine in the serpentine-rich layers is typical forsterite [Fo#: 100×Mg/(Mg+Fe2+)=93-95]. The Cr-rich chromitite ores have total PGE and Au abundances that range between 74.3 and 205ppb: they show a general enrichment in Ir and Ru over PPGE (Rh, Pt and Pd) resulting mostly in a negatively-sloping C1 chondrite-normalized PGE profile with a quite strong Ru peak. Field observations indicate that the schlieren banding of the deformed ore bodies is a tectonometamorphic feature acquired within ductile deformation of the ophiolitic slab. Geochemical calculations demonstrate that the parental melts of the Xerolivado-Skoumtsa high-Cr chromitites were boninitic. Their high Ru content and variation in Cr# Sp values indicate a polygenetic origin from geochemically similar, but spatially distinct melt inputs. These melts originated within a hydrated mantle wedge beneath a forearc basin within an evolving lithospheric slab. We emphasize that the PGE budget of the Xerolivado-Skoumtsa chromitites was not inherited from interactions of the migrating melts with their parental harzburgites, but it is an intrinsic feature of the deep-seated and heterogeneously depleted mantle source of these magmas.
Original languageEnglish
JournalOre Geology Reviews
ISSN0169-1368
DOIs
Publication statusPublished - 2017
Externally publishedYes

Keywords

  • Chromian spinel (Cr-spinel)
  • Chromitites
  • Greece
  • Ophiolites
  • Platinum-group elements (PGE)
  • Vourinos

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