Age and primary architecture of the Copperton Zn-Cu VMS deposit, Northern Cape Province, South Africa

The Prieska Copper Mine (Copperton) deposit, located in the Northern Cape Province of South Africa, exploited from 1972 to 1994 a very large (ca. 47 Mt pre-mining resource) massive sulphide lens containing on average ca. 1% Cu and 2% Zn. The orebody occurred as a stratiform/stratabound tabular lens hosted by the subvertically dipping Copperton Formation, which is part of the intensely deformed and highly metamorphosed Areachap Group. The latter represents a 1.3-1.24 Ga continental volcanic island arc that was accreted onto the western margin of the Kaapvaal Craton during the initial stages of the 1.2-1.0 Ga Namaquan Orogeny. The present contribution is aimed at resolving important uncertainties surrounding the architecture, age and origin of this world class base metal deposit. Despite intense deformation and high-grade metamorphism the original architecture of the deposit is found to be unusually well preserved, with a stratabound zone of intense hydrothermal alteration below, and a series of characteristic cap rocks above the massive sulphide orebody. Geochemical data and radiometric ages for host rocks and massive sulphide ores lead to the conclusion that the Copperton deposit comprises a very large chimney-type volcanogenic massive sulphide deposit that formed at 1.28-1.29 Ga. The deposit meets many of the criteria of the bimodal-siliciclastic or bimodal-felsic types of VMS deposits. (C) 2011 Elsevier B.V. All rights reserved.