Geology of gold deposits in the Southern Marginal Zone of the limpopo belt and adjacent Sutherland Greenstone Belt, South Africa: Klein Letaba

The Klein Letaba gold deposit is situated within the Hout River Shear Zone which separates the Southern Marginal Zone (SMZ) of the Limpopo Belt in the north from the Sutherland greenstone belt of the Kaapvaal Craton in the south. Ultramafic lithologies and their sheared (tremolite/actinolite schist) and altered (tourmaline-plagioclase-tremolite schist and quartz-biotite-amphibole schist) equivalents dominate the mine area. Metamorphic mineral assemblages in subordinate metapelitic lithologies, which include kyanite, sillimanite, staurolite, anthophyllite, garnet, and biotite, suggest that the mine area was subjected to high-temperature metamorphism under middle to higher amphibolite facies conditions. Similar high-grade assemblages also characterize the gold mineralized zone, which strikes N85'E and dips 80' to the north. This zone, which forms an integral part of the Hout River Shear Zone, consists of nine north-dipping auriferous shear structures arranged en echelon from the southwest to the northeast. Gold occurs in sulphide-quartz veins and in sheared and altered quartz-biotite-amphibole schist in the ductile shear zones. Gold particles with an average grain size of 5 - 10 microns are closely associated with sulphides and also occur along amphibole grain boundaries and included in quartz and amphibole. Geological constraints, including the observation that sulphides are often concentrated in the pressure shadow tails of porphyroclasts in mylonite, demonstrate a syntectonic origin for the gold mineralization in the Klein Letaba mine. The mineralization was associated with the late stages of a regional high temperature K₂O-metasomatic event related to ductile shearing along the Hout River Shear Zone, close to 2600 Ma.