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The Formation of Stratiform PGE Deposits in Layered Intrusions

  • A. J. Naldrett
  • G. Cameron
  • G. von Gruenewaldt
  • M. R. Sharpe
Part of the NATO ASI Series book series (ASIC, volume 196)

Abstract

The principle stratiform platinum group element deposits are the Merensky Reef and UG-2 chromitite of the Bushveld and the J-M Reef of the Stillwater Complexes. In the Bushveld Complex, cryptic variation in the MgNo of bronzite and in the An and Sr content of plagioclase within the Merensky cyclic unit, the apparent crossing of the plagioclase cotectic by the magmareponsible for this and other units, and variations in 87Sr/86Sr initial ratio, and, in the Stillwater Complex, the change in the order of liquidus phases, point to the involvement of at least two different magmas in each intrusion.

In each deposit the PGE are closely associated with base metal sulfides. Despite the presence of volatiles and some evidence of hydrothermal mobilization of PGE in most deposits, it is concluded, from the constancy of sulfide composition within stratigraphic layers and the variability between these layers, that the sulfides and host rocks were deposited simultaneously.

It is proposed that the cyclic units are the consequence of periodic influx of new, primitive magma, that the sulfides segregated in response to magma mixing during influx, and that turbulent convection within the influxes gave the sulfides the opportunity to equilibrate with, and thus concentrate PGE from, a very large mass of magma, thus accounting for the high PGE tenor of these deposits. In the case of deposits within massive chromitite, the PGE, Ni and Cu tenors were likely upgraded as a result of the loss of FeS.

Keywords

Layered Intrusion Platinum Group Mineral Bushveld Complex Econ Geol Cyclic Unit 
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

© Springer Science+Business Media Dordrecht 1987

Authors and Affiliations

  • A. J. Naldrett
    • 1
  • G. Cameron
    • 2
  • G. von Gruenewaldt
    • 3
  • M. R. Sharpe
    • 3
  1. 1.Centre de Recherches sur la Synthese et Chimie des MinerauxG.I.S., B.R.G.M — C.N.R.SOrleans, CedexFrance
  2. 2.Department of GeologyUniversity of TorontoTorontoCanada
  3. 3.Bushveld Research InstituteUniversity of Pretoria HillcrestPretoriaSouth Africa

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