STRATIGRAPHY AND DIAGENESIS OF THE PALEOPROTEROZOIC BUSHY PARK ZINC-LEAD DEPOSIT, SOUTH AFRICA

The Bushy Park zinc–lead deposit is located in the Northern Cape Province, South Africa. The sulfides are hosted by karst related breccias which were formed in carbonate shelf-deposits of the Paleoproterozoic (2.5 Ga) Campbellrand Subgroup. These rocks are completely dolomitized and partly silicified but have not undergone major metamorphism and display remarkable preservation of depositional fabrics. The interval includes the Papkuil and Klippan Formations, a >150m sequence of cyclic microbial laminates interbedded with domal and columnar stromatolites that display possible evidence of evaporites. The Klippan is distinguished from other units by heavy silicification and brecciation. These strata are overlain by the Kogelbeen Formation consisting of 200m of interbedded columnar stromatolites and oolites.

Replacive dolomite ranges from relatively fine crystalline planar texture, typical of early diagenetic dolomitization, to coarse crystalline nonplanar texture suggestive of epigenetic dolomitization and/or neomorphism of pre-existing dolomite. The nonplanar dolomite is associated with coarse crystalline dolomite and calcite cements, that are paragenetically related to quartz cement, abundant pyrobitumen, Zn, Cu, Pb, and Fe sulfide minerals, and intense brecciation. A distinctive cathodoluminescent microstratigraphy, observed in the carbonate cements, indicates a paragenesis involving multiple stages of cementation and mineralization. This suggests a complex fluid history which includes the emplacement of petroleum.

These data indicate that the Bushy Park deposit underwent depositional, diagenetic, and epigenetic processes similar to Paleozoic and younger Mississippi Valley-type deposits world-wide and share many characteristics in common with deposits found in the Appalachian Region of North America.