Assmang Manganese Mines, South Africa

The Kalahari Manganese Field, located in Northern Cape Province, about 700km southwest of Johannesburg, contains around 80% of the world's known high-grade manganese ore reserves. The district yields about 4Mt/y, mined mainly by Samancor and Assmang.
Originally established in 1935 and now jointly owned and managed by African Rainbow Minerals and Assore, Assmang wholly owns two mines near the community of Black Rock. Assmang commissioned Nchwaning in 1972 while the Gloria mine, to the south, started production in 1978. Each had a plant nominally rated to treat 1Mt/y ore.
Early in 2000, Assmang announced an expansion involving the development of a new shaft complex at Nchwaning to add about 2Mt/y of run-of-mine ore capacity, to make Nchwaning the world’s lowest-cost underground manganese mine, and to extend its lifetime by about 30 years.
The expansion, including additional treatment capacity, was commissioned in May 2004 and was completed in May 2005 at a capitalised cost of R780m. Assmang operates three eight-hour shifts per day from Monday to Friday, as well as a single shift on Saturday, employing a total of 2,510 people at its various operations.
Assmang announced recently a capital expenditure programme of R748m to more than double manganese production by 2010. Assmang mines more than 1.5 million tons of manganese ore from the Nchwaning and Gloria mines in the same region.
The company also produces manganese alloys at its Cato Ridge works in KwaZulu Natal. Assmang currently produces more than 200,000 tons of manganese alloys per year. Recently the company said it would like to build a new manganese alloy plant near the mine.
GEOLOGY AND RESERVES
The Kalahari Manganese Field lies within a large structural basin that extends approximately 40km south to north and 5km to 15km east to west, dipping gently northwest. At Black Rock, near the northern end of the basin, the Transvaal System rocks lie about 300m from surface, beneath Kalahari Formation sands and calcretes, Karroo System tillites and Waterberg System shales and quartzites.
The sub-horizontal stratabound manganese ore horizons occur in banded ironstone of the Voëlwater Formation at the top of a sequence of Transvaal System rocks. As well as being faulted, the horizons are folded.
The ore is massive and averages 48% manganese; at Nchwaning it is particularly low in phosphorus while Gloria has a higher manganese-to-iron ratio. At the end of 2006 Assmang's reserves totalled 192Mt with mineral resources of 428.4Mt.