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PGE-bearing mafic-ultramafic sills in the floor of the eastern Bushveld Complex on the farms Blaauwboschkraal, Zwartkopje, and Waterval

Centre for Research on Magmatic Ore Deposits, Department of Geology, University of Pretoria, Pretoria 0002, e-mail: wdmaier{at}scientia.up.ac.za

J. Sliep

ISCOR Ltd., PO Box 450, Pretoria 0001

Sarah-Jane Barnes

Sciences de la terre, Université du Québec, Chicoutimi G7H 2B1, Canada, e-mail: sjbarnes{at}uqac.uquebec.ca

S.A. de Waal

Centre for Research on Magmatic Ore Deposits, Department of Geology, University of Pretoria, Pretoria 0002, e-mail: sadw{at}scientia.up.ac.za

C. Li

Department of Geological Sciences, University of Indiana, Bloomington, IN 47405, USA, e-mail:cli{at}indiana.edu

Mafic-ultramafic sills of up to 450m in thickness occur near the contact between sedimentary and volcanic rocks of the Silverton Formation, Transvaal Supergroup, on the farms Blaauwboschkraal, Zwartkopje and Waterval, some 10km north of Waterval Boven in the Mpumalanga Province. The sills consist of peridotite, harzburgite, pyroxenite and gabbro, and may locally contain up to about 10% Ni-Cu-PGE sulphides. Metal contents of the rocks reach 0.7% Cu, 0.8% Ni, and 2 ppm PGE. Sulphides are found at variable levels within the intrusions and are interpreted to have precipitated from distinct surges of magma streaming through a conduit. This model is analogous to that proposed for the Uitkomst Complex, which hosts sulphides of broadly similar composition to the present bodies and which consists of broadly similar lithologies, apart from the presence of chromitite in the latter. The lithological and compositional similarities between the intrusions raise the possibility of undiscovered economic sulphide concentrations in the present bodies. However, olivines in most of the ultramafic rocks are undepleted in Ni, suggesting that either sulphide segregation was minor and localized, or that any metal-depleted magmas were flushed out of the conduit by undepleted magma.

This article has been cited by other articles:

				A. Kerr and A. M. Leitch Self-Destructive Sulfide Segregation Systems and the Formation of High-Grade Magmatic Ore Deposits Economic Geology, March 1, 2005; 100(2): 311 - 332. [Abstract] [Full Text] [PDF]