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 exploratio n in South Africa. The sedimentary, structural and thermal history of the fault zone are evaluated. The fault zone experienced a synsediment ary period of activity between 2550 and 2500 Ma and a major post-Postm asburg Group (less than 2223 Ma) episode of mainly vertical movements. Possible source rocks for generation of metalliferous brines are abun dant along the southwestern margin of the Kaapvaal craton and shales s outhwest of the GFZ are time correlative to a thick peritidal stromato litic carbonate sequence in the northeast. Fluids driven by compaction and orogenic pressure migrated across the GFZ, via the carbonates, to wards the east. Metamorphic overprint south of the GFZ, based on illit e crystallinity, and fluid inclusions north of the fault zone are abov e the oil window. Metamorphic peaks south of the fault zone are at 175 0 Ma and 1213 Ma and the intensity of metamorphic overprint decreases from west to east. Because of high temperatures of metamorphic and oro genic overprint and possible remobilisation of fluids, Mississippi-Val ley-Type (MVT) ore deposits are unlikely to be found within the Griqua town Fault Zone, but are expected, rather, to the northeast of it. Hig her temperature, remobilised vein-related deposits could, however, occ ur in the GFZ itself.