|PROF. STEVE RICHARDSON|
|Department of Geological Sciences||Kimberlite Research Unit|
|Louis Ahrens Building, Library Road||Kaapvaal Craton Project|
|University of Cape Town|
|Rondebosch, 7701, RSA|
|ph: #27 (0)21 650 2916/2659|
|fax: #27 (0)21 650 3783|
Archean cratons contain a major share of the world's precious metal and diamond mineralization. In particular, the Kaapvaal craton hosts not only the largest known gold and platinum deposits, the ca. 2.9 Ga Witwatersrand Basin and the 2.05 Ga Bushveld Complex, but also some of the economically most significant diamond deposits in surrounding kimberlite pipes. Sulfide and silicate inclusion-bearing diamonds entrained by these kimberlites present a unique opportunity to characterize the lithospheric mantle encountered by Bushveld magmas en route to emplacement in the crust.
Sulfide inclusions in ca. 2.0 Ga diamonds from Venetia and Premier show initial Os isotope ratios even more radiogenic than those of Bushveld platinum group element (PGE) sulfide ore minerals. When combined with the Sm-Nd and Rb-Sr isotope compositions of garnet inclusions and macrocrysts, this suggests that continental mantle harzburgite and eclogite components, in addition to an original convecting mantle component, most likely contributed to the genesis of both the diamonds and the Bushveld Complex. This multi-component subcontinental lithospheric mantle (SCLM) contamination model may also apply to other PGE-enriched intrusions, given the harzburgitic and eclogitic affinities of the ultramafic versus tholeiitic (or anorthositic) parental magma types variously recognized in the 2.7 Ga Stillwater Complex (Wyoming craton), 2.5 Ga Great Dyke (Zimbabwe craton) and 1.3 Ga Muskox Intrusion (Slave craton). Indeed, SCLM contamination may be a general feature of continental mafic magmatism and will be the focus of ongoing research.
Richardson SH, and Shirey SB (2008) Continental mantle signature of Bushveld magmas and coeval diamonds.
Nature 453, 910-913.
Westerlund, KJ, Shirey, SB, Richardson, SH, Carlson, RW, Gurrney, JJ and Harris JW (2006) A subduction wedge origin for Paleoarchean peridotitic diamonds and harzburgites from the Panda kimberlite, Slave craton: evidence from Re-Os isotope systematics. Contributions to Mineralogy and Petrology 152, 275-294.
Richardson, SH, Shirey SB, and Harris JW (2004) Episodic diamond genesis at Jwaneng, Botswana, and implications for Kaapvaal craton evolution. Lithos 77, 143-154.
Shirey, SB, Harris, JW, Richardson SH, Fouch, MJ, James, D, Cartigny, P, Deines, P, Viljoen, F (2002) Diamond genesis, seismic structure, and evolution of the Kaapvaal-Zimbabwe craton. Science 297, 1683-1686.
Richardson, SH, Shirey, SB, Harris, JW, Carlson, RW (2001) Archean subduction recorded by Re-Os isotopes in eclogitic sulfide inclusions in Kimberley diamonds. Earth Planet Sci Lett 191, 239-248.
Richardson, SH and Harris, JW (1997) Antiquity of peridotitic diamonds from the Siberian craton. Earth Planet Sci Lett 151, 271-277.
Richardson, SH, Harris, JW and Gurney, JJ (1993) Three generations of diamonds from old continental mantle. Nature 366, 256-258.
Richardson, SH, Erlank, AJ, Harris, JW and Hart, SR (1990) Eclogitic diamonds of Proterozoic age from Cretaceous kimberlites. Nature 346, 54-56.
Richardson, SH (1986) Latter-day origin of diamonds of eclogitic paragenesis. Nature 322, 623-626.
Richardson, SH, Gurney, JJ, Erlank, AJ and Harris, JW (1984) Origin of diamonds in old enriched mantle. Nature 310, 198-202.