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PRECISE AGE OF THE PLATINIFEROUS MERENSKY REEF, BUSHVELD COMPLEX, SOUTH AFRICA, BY THE U-Pb ZIRCON CHEMICAL ABRASION ID-TIMS TECHNIQUE^*

James S. Scoates and Richard M. Friedman

Pacific Centre for Isotopic and Geochemical Research, Department of Earth and Ocean Sciences, University of British Columbia, 6339 Stores Road, Vancouver, British Columbia V6T-1Z4, Canada

Corresponding author: e-mail address, jscoates{at}eos.ubc.ca

The Bushveld Complex, South Africa, is the world’s largest layered intrusion and host to the majority of the known resources of platinum group elements, chromium, and vanadium. Despite intensive study, determining the precise crystallization age of the Bushveld Complex has proven to be difficult. In this study, zircon and rutile were identified in thin section and separated from a sample of pegmatitic feldspathic orthopyroxenite from the PGE-rich Merensky reef, West mine (Townlands shaft), Rustenburg section. Low U (21–105 ppm) zircon occurs with interstitial biotite and is locally in direct contact with sulfide. Rutile occurs mainly as inclusions within or overgrowths on chromite, especially in the chromitite stringers that bound the reef, and also as acicular grains with biotite. A U-Pb crystallization age of 2054.4 ± 1.3 Ma was determined from single-crystal chemical abrasion ID-TIMS U-Pb dating of zircon, and multigrain fractions of rutile yielded a U-Pb cooling age of 2055.0 ± 3.9 Ma. Integration of the Merensky reef crystallization age with existing U-Pb age determinations for intrusions that pre- and postdate emplacement and crystallization of the layered rocks of the Bushveld Complex indicate that magmatism occurred at ca. 2054 Ma and is contemporaneous with related magmatic activity across the northern Kaapvaal craton of South Africa and Botswana.

This article has been cited by other articles:

				A. J. Naldrett, A. Wilson, J. Kinnaird, and G. Chunnett PGE Tenor and Metal Ratios within and below the Merensky Reef, Bushveld Complex: Implications for its Genesis J. Petrology, April 20, 2009; (2009) egp015v1. [Abstract] [Full Text] [PDF]