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The Zandrivier Deposit, Pietersburg Green Belt, South Africa: an Auriferous Tourmalinite

P O Box 6084 Pietersburg North, 0750, South Africa, e-mail: steffen{at}mweb.co.za

J. M. Barton, Jr.

Department of Geology, Rand Afrikaans University, P.O. Box 524, Auckland Park, 2006, South Africa, e-mail: jmb{at}na.rau.ac.za

The Zandrivier Mine on Mount Mare in the Pietersburg Greenstone Belt exploited a gold-bearing, arsenical tourmalinite that formed during episodes of ductile and brittle deformation associated with D₂ tectonism along the Snymansdrift Shear Zone. The deposit is unusual for an Archaean mesothermal gold lode in southern Africa with respect to the abundance of tourmaline rock that hosts large quantities of auriferous arsenopyrite. Some ore is preserved within strain shadows of a resistant quartz mica schist horizon, while fluid focussing and sulphide deposition were enhanced by the competence contrast between the overlying quartz mica schist and chert with a mudstone-derived, chlorite phyllonite in the footwall. Mineralisation appears to have commenced with barren pyrrhotite-siderite veining under a high strain regime with subsequent gold and arsenopyrite being deposited under brittle-ductile conditions associated with progressively decreasing strain. Although mineral elongation lineations and S-C duplexes in the quartz mica schist and phyllonite generally indicate oblique reverse movement with a dextral component, other kinematic indicators reflect elements of possibly earlier sinistral and normal motion. The deficiency of other major gold deposits in the Mount Mare section of the Pietersburg Greenstone Belt may be due to lack of balance between critical factors such as a favourable strain regime, relatively brittle host rocks, and conduits to an auriferous fluid source.