The Buffelsfontein Gold Mine, situated about 160km southwest of Johannesburg in the Free State, South Africa, ranks among the world’s largest gold mines with estimated reserves of 11.02 million ounces of gold. Owned by Simmer & Jack, this underground operation includes both gold and uranium resources, anticipating an annual production of 318,000 ounces by 2014.
However, the mine faced a setback on May 4, 2010, when an accident led to the closure of the Number Five shaft. The incident occurred during a routine inspection on level 27, causing the ground to cave in and resulting in the tragic death of three miners. This shaft, previously closed after a seismic event in March 2005, remained shut pending further investigation into the 2010 incident.
Buffelsfontein’s proven and probable reserves are substantial, with estimates of 5.7 million ounces of gold and 27.32 million tons of uranium. The grades are reported at 6.12g/t for gold and 0.24lb/t for uranium. Despite challenges, the mine holds significant potential for continued production and exploration in the future.
Buffelsfontein Gold Mine Geology
The Buffelsfontein gold mine is situated within the Klerksdorp gold field in the renowned Witwatersrand Basin, known for its late Archean-aged gold deposits. The basin comprises a 6km thick sequence of sedimentary rocks, extending up to 300km laterally northeast to southwest and 100km northwest to southeast on the Kaapvaal Cratonne. The western, southern, and eastern sections of the basin are overlain by 4km of volcanic and sedimentary rocks from various periods.
Gold is primarily found within the Vaal Reef, a laterally extensive conglomerate dominating the mine. The Vaal Reef consists of quartzite packages and oligomictic conglomerates concentrated on non-conformities, divided into eight geozones. Unique facies within the reef exhibit distinct grade characteristics, containing crystalline and nodular pyrite, uraninite, gold, and carbonaceous material within a less-than-2m-thick quartz pebble conglomerate horizon.
The structural geology of the Hartebeestfontein Mine, forming the north division, is marked by a 20° average strike and dip. Fault displacements, attributed to dykes, place the Vaal Reef between 800m and 2,500m deep. The north division shares its boundary with the geologically complex south division, characterized by 800m to 1,000m fault displacements and a 25° dip towards the southeast. The central zone exhibits a triplicated reef due to the impact of a complex thrust fault, adding further geological intricacy to the mining area.
Gold mines in South Africa