Chapter 26 - Tectonometamorphic Controls on Archaean Gold Mineralization in the Barberton Greenstone Belt, South Africa

Abstract

The New Consort gold mine in the Paleo- to Mesoarchaean Barberton greenstone belt, South Africa, forms one of the oldest shear-zone hosted gold deposits on Earth. In contrast to the mainly greenschist facies gold deposits in the west-central parts of the Barberton greenstone belt, the mine is situated in upper greenschist to amphibolite facies wall rocks in the structural hanging wall of an exhumed gneiss dome along the northern margin of the belt. The structural controls and tectonic setting, but also the conditions and timing of the mineralisation and the fluid sources are controversial and far from being resolved. A detailed evaluation of the currently available structural, petrological, and geochronological data indicates a complex tectono-metamorphic evolution and polyphase mineralization over a protracted period of time, with the main phase of gold mineralization occurring very late in the overall tectonic evolution of the belt. Gold deposition occurred during a series of hydrothermal events related to the late-stage and, on a regional scale, rather cryptic evolution of the belt. The large time gap of almost 200 Ma between the main phase of accretionary tectonics at ca. 3230 Ma and the main episodes of gold mineralization remains somewhat enigmatic and distinguishes the Barberton-type mineralization from most other shear zone hosted deposits.