Age and origin of the Earth's oldest carbonate-hosted Pb-Zn-(F) deposits

Pb-Zn deposits hosted by dissolution collapse breccias in dolostones of the Neoarchaean Transvaal Supergroup in Griqualand West, South Africa are regarded as the Earth's oldest examples of MVT deposits. This association is based on numerous lines of geological, mineralogical-textural and geochemical similarities. K-Ar ages of 2.038 +/- 0.040 Ga and 2.059 +/- 0.041 Ga for hydrothermal illite intergrown with ore-forming sphalerite has provided the first accurate age constraints for these deposits. These ages are within error of the intrusive age of the Bushveld Complex as well as the age of stratabound fluorite deposits in the dolostones of the Transvaal Supergroup in the Transvaal region. Based on these results, a metallogenetic model is proposed that identifies the intrusion of the Bushveld Complex as the driving mechanism for long-lived hydrothermal systems active on a subcontinental scale. These systems gave rise to fluorite deposits in dolostones proximal to the intrusion, where fluids had a distinct magmatic contribution. Fluorite-poor Pb-Zn deposits, in contrast, formed in the distal tectonic foreland of the Bushveld intrusion, reflecting the migration of pre-existing aqueous fluids and brines along suitable basement aquifers.