Sedimentological evaluation of Pb-Zn exploration potential of the Precambrian Griquatown fault zone in the northern Cape Province, South Africa

The Griquatown Fault Zone (GFZ) is a major target for Pb-Zn exploration in South Africa. The sedimentary, structural and thermal history of the fault zone are evaluated. The fault zone experienced a synsedimentary period of activity between 2550 and 2500 Ma and a major post-Postmasburg Group (less than 2223 Ma) episode of mainly vertical movements. Possible source rocks for generation of metalliferous brines are abundant along the southwestern margin of the Kaapvaal craton and shales southwest of the GFZ are time correlative to a thick peritidal stromatolitic carbonate sequence in the northeast. Fluids driven by compaction and orogenic pressure migrated across the GFZ, via the carbonates, towards the east. Metamorphic overprint south of the GFZ, based on illite crystallinity, and fluid inclusions north of the fault zone are above the oil window. Metamorphic peaks south of the fault zone are at 1750 Ma and 1213 Ma and the intensity of metamorphic overprint decreases from west to east. Because of high temperatures of metamorphic and orogenic overprint and possible remobilisation of fluids, Mississippi-Valley-Type (MVT) ore deposits are unlikely to be found within the Griquatown Fault Zone, but are expected, rather, to the northeast of it. Higher temperature, remobilised vein-related deposits could, however, occur in the GFZ itself.