Conference Proceedings (Earth Sciences)

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Genesis of the stratiform BH-t Swartberg Cu-Pb-Zn-Ag deposit, Northern Cape, South Africa
(Geology Applied to Mineral Deposits, 2013) Rudnick, Tarryn-Kim; Rozendaal, Abraham
Swartberg is a metamorphosed Broken Hill- type Cu-Pb-Zn-Ag deposit in the north-west of South Africa. The mineralogy and stratigraphy closely resemble that of the nearby Broken Hill, Deeps and Gamsberg deposits. Swartberg is the least-studied of these and this and ongoing studies aim to complete the picture of the district by providing a clearer understanding of the deposit. It comprises two discrete, stacked stratiform orebodies, both of which are deformed by a recumbent, isoclinal F2 fold and refolded by an open F3 fold. The orebodies were deposited in a northeast-southwest trending basin, hinged to the northwest by a hydrothermal feeder fault. Both the upper orebody (UOB) and lower orebody (LOB) formed as syngenetic exhalatives, with the LOB representing an early, precursor exhalation stage to the more extensive stage that formed the UOB. The UOB displays a clear gradation from vent-source proximal chemogenic sediments in the F2 fold hinge, deposited under hotter, more reducing conditions, to distal material formed under cooler, oxidizing conditions. After deposition, the basin underwent several episodes of deformation and metamorphism to medium grades (pressure < 4.5kbar), during which the sulphides underwent limited mobilization into the F2 hinge zone.