10
AngloGold Ashanti Supplementary Information: Mineral Resources and Ore Reserves 2007
South Africa operations: overview
The Vaal River operations consist of Great Noligwa, Kopanang, Tau
Lekoa and Moab Khotsong mines. The primary reefs in this region are
the Vaal Reef (VR) and the Ventersdorp Contact Reef (VCR) and the
secondary reef mined is the Crystalkop Reef (C Reef).
The West Wits operations are made up of Mponeng, Savuka and
TauTona and these mines are situated near the town of Carletonville.
The primary reefs mined are the Carbon Leader Reef (CLR) and VCR.
All seven operations are 100% owned by AngloGold Ashanti. In
addition, the Vaal River Surface and West Wits Surface operations
consist of the reprocessing of waste rock dumps and tailings dams
resulting from the mining of the primary and secondary reef horizons.
The South African operations are all located in the rocks of the famous
Witwatersrand Basin, which is regarded as the greatest gold-bearing
repository on Earth.
Geology of the Witwatersrand Basin
The Witwatersrand Supergroup (deposited in the area often described
as the Witwatersrand Basin) comprises a six-kilometre thick sequence
of predominantly argillaceous and arenaceous sediments that extend
laterally for some 300km north-east/south-west and 100km north-
west/south-east on the Kaapvaal Craton. The upper portion of the
sequence contains the laterally-extensive, gold-bearing quartz pebble
conglomerate horizons or reefs.
Further west, south and east the basin is overlain by up to four
kilometres of Archaean, Proterozoic and Mesozoic volcanic and
sedimentary rocks. The Witwatersrand Basin is late Archaean in age
and is considered to be around 2.7 billion to 2.8 billion years old.
The reefs, which are generally less than two metres thick, are widely
considered to represent laterally extensive braided fluvial deposits.
Separate fan systems were developed at different entry points and
these are preserved as distinct goldfields with local geological
variations. AngloGold Ashanti operates in two of these goldfields,
known as the Carletonville (West Wits) and Klerksdorp (Vaal River)
Goldfields.
There is still much debate about the origin of the gold mineralisation in
the Witwatersrand Basin. Gold was generally considered to have been
deposited syngenetically with the conglomerates, but increasingly an
epigenetic theory of origin is being supported. Nonetheless, the most
fundamental determinant of gold distribution in the basin remains the
sedimentary features, such as facies variations and channel directions.
Gold generally occurs in native form often associated with pyrite and
carbon, with quartz being the main gangue mineral.
West Wits (Mponeng, Savuka and TauTona operations)
Two reef horizons are exploited at the West Wits operations: the VCR,
located at the top of the Central Rand Group, and the CLR near the
base. The separation between the two reefs increases from east to
west, from 400m to 900m, due to the non-conformity of the VCR with
Vaal River Operations
Great Noligwa
Kopanang
Tau Lekoa
Moab Khotsong
West Wits Operations
Savuka
TauTona
Mponeng
Operations
Johannesburg
North West
Gauteng
Free State
Eastern Cape
SOUTH AFRICA
Welkom
Carletonville
Klerksdorp
Durban
Cape
Town
Bloemfontein
0
400km
Orkney
The South African operations
comprise seven underground mines
which are located in two
geographical regions on the
Witwatersrand Basin; known as the
Vaal River and West Wits operations.