Archean and Proterozoic mineralization and tectonics at the Renco Mine (northern marginal zone, Limpopo Belt, Zimbabwe)

Abstract

Gold mineralization at the Renco mine occurs within the northern marginal zone of the Limpopo belt along east-northeast-trending structures that formed in the Late Arehean (2.6 Ga Pb-Pb step leach age on syntectonic garnet) under granulite facies. The mineralization is hosted by a massive enderbite which intruded at 2.57 Ga (U-Pb zircon age). North-northeast-trending pyroxenite dikes were intruded around 2.4 Ga (Pb-Pb step leach age of garnet and pyroxene), probably associated with the intrusion of the Great Dyke and satellites. The northern marginal zone had been exhumed to crustal levels corresponding to greenschist facies by this time. The major gold-bearing pyrrhotite-chalcopyrite + or - bismuth mineralization occurred under greenschist facies conditions (<400 degrees C). This occurred at approximately 2.0 Ga as deduced from cooling of biotite associated with mineralization (1.88 Ga Rb-Sr age). This ca. 2.0 Ga age of the mineralization implies a link with the important Early Proterozoic tectono-thermal event in the Limpopo belt during which shearing occurred under greenschist facies conditions in the Triangle shear zone. The Reneo deposit is not, as formerly suggested, a high-grade mineralization, although there is some evidence for a precursory, high-grade phase of mineralization in the Late Archean. Its genesis is quite distinct from most of the greenstone-associated deposits of the Zimbabwe craton, which are known or inferred to be Late Archean in age.