Platinum-Group Elements and Au Distribution in Ni Arsenide-Chromite Veins from the Rifo-Betic Lherzolite Massifs (Morocco—Spain)

  • M. Leblanc
  • F. Gervilla-Linares

Abstract

In the lherzolite massifs distributed along the Western Mediterranean Alpine belt from Southern Spain (Carratraca, Ojen, Ronda) to Northern Morocco (Beni-Bousera) there are about 50 veins of a very peculiar Ni-Cr mineralization including an association of niccolite and Zn-V-rich chromite with accessory arsenides, sulphoarsenides, sulphides and graphite; the gangue minerals are orthopyroxene or cordierite. They are associated with pyroxenite dikes related to the late stages of upwelling and partial melting of the mantle peridotites. Mineral association and textural relations have led Oen (1973) to propose a high temperature magmatic segregation of an immiscible oxyarsenide liquid for the origin of these veins.

Ten samples of Cr-Ni ores from Morocco and Spain were analysed by fire-assay and neutron activation (XRAL, Don Mills, Ontario). They contain from 0·7 to 5·2ppm platinum-group elements (PGE) with up to 1.5ppm of Pt and of Pd. They have high gold contents (3·5–18ppm) and there is a positive correlation between Au-Ni-As and PGE.

These Cr-Ni ores exhibit flat PGE patterns with an Os depletion. They show a large range of values from the Ni-poor ores, which have only 10 times the values obtained for mantle peridotites, to the Ni-rich ores which have chondritic values. However the PGE patterns are similar to those of their primitive mantle source rock, suggesting that they were unfractionated during the concentration processes.

From a single sample (Beni-Bousera) separated chromite displays a PGE pattern with a strong negative slope whereas the corresponding niccolite exhibits a strong positive slope. The chromite pattern closely resembles podiform chromitites, but Os-Ir values are 10 times higher; the niccolite pattern is similar to the trend of the Merensky Reef. Thus there was a partitioning of PGE in the magma between chromite (Os-Ir) and niccolite (Pt-Pd). PGE minerals have not yet been observed.

A chromite pod and a spinel layer (Ronda) were analysed. The PCE trend of the chromite displays an Os depletion and a moderate negative slope, intermediate between the field of the podiform chromitites and the flat trend of the Ni-Cr ores. The spinel has a PGE trend characterized again by a negative slope from Os to Pd (330–30ppb) but shows a strong Pt enrichment (230 ppm).

The authors feel that these rocks represent a new type of PGE and gold mineralization in mantle peridotites. The concentration of PGE, up to chondritic values, is ascribed to the segregation of an immiscible oxyarsenide liquid from a magma resulting from the partial melting of a mantle diapir.

Keywords

Mantle Peridotite Garnet Lherzolite Magmatic Sulphide Mantle Diapir High Gold Content 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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Copyright information

© Elsevier Science Publishers Ltd 1988

Authors and Affiliations

  • M. Leblanc
    • 1
  • F. Gervilla-Linares
    • 2
  1. 1.Centre Géologique et GéophysiqueUniversité des Sciences et Techniques du LanguedocMontpellierFrance
  2. 2.Departamento de Mineralogia-PetrologiaUniversidad de GranadaGranadaSpain

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