Nchwaning Manganese Mine

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This mine is owned and managed by Assmang and it's rights include the entire Nchwaning Farm #267 which is this boundary and it also includes the former Black Rock Mine area. The manganese ores of the Kalahari Manganese Field are contained within sediments of the Hotazel Formation of the Griqualand West Sequence, a subdivision of the Proterozoic Transvaal Supergroup. The Nchwaning deposit consists of a gently dipping and regular strata bound body of high-grade ore (+48%Mn), which has undergone a hydrothermal upgrading associated with faulting. The combined high metal content and low impurities make this an exceptional smelting ore.

The mine was originally established in 1972, with the Nchwaning No.2 shaft coming into production in 1981. This shaft is still active and ore is mined, and then crushed underground prior to being hoisted up a 450m vertical shaft. This shaft has a capacity of +/- 120000tpm.

A new shaft complex, Nchwaning No.3 was recently completed in order to provide access to high quality ore for decades to come. Production from this complex commenced in May 2004 and became fully operational in February 2006. This new mining operation is serviced by two shafts; a vertical personnel shaft to a depth of 350m and a decline shaft equipped with conveyors, which is the main hoisting shaft. Hoisting capacity is +/- 200000 tons per month.
Ore Processing:

The existing plant has been upgraded and now treats the ore from both Nchwaning No.2 and No.3 mines. Ore is crushed, washed and screened to various sizes and then is stacked according to size and grade. These stacks have nominal capacities of 280 to 320 tons each and are numbered and sampled. This allows extremely accurate grade control for all shipments made from the mine.
Ore Quality:

Typical analyses of manganese ore grades

Element 47% fines 48% lumpy
Mn % 48.0 49.0
Fe % 11.4 10.5
SiO2 6.0 4.5/6.0
P % 0.05 0.05
S % 0.19 0.17
AI2O3 0.39 0.35
CaO 5.0 4.9
MgO 0.7 0.7
K2O <0.1 <0.1
Na2O <0.1 <0.1

Sizing:
Lumpy minus 75 millimetres plus 9 millimetres
Fines minus 9 millimetres
Rail and port facilities:
Railroads

Underground loading.

Manganese ore produced at Nchwaning and Gloria mines is transported by private rail to Hotazel where the trucks are transferred to the Hotazel-Port Elizabeth railway line. The railing takes approximately 30 hours for the +/- 1100km distance from the mines to the Port Elizabeth harbour.

At the harbour the train is split up into 25 or 50 trucks and shunted into the ore terminal marshalling yard. Here various truck loads are split up per grade and shunted to the truck tippler where the ore is channelled to the storage bins or directly to the ship by means of conveyor belts.
Port Elizabeth harbour

The port facilities at the Port Elizabeth harbour consist of a two-line interconnecting conveyor belt system. From the tippler, the ore is carried either by one or both lines to the storage bins where it is deposited by means of one or two stacker-reclaimers, or directly to the vessel.

There are four bins with a total capacity of 460 000 tons. When required for loading, the reclaimers are positioned alongside the required grades and extract the ore from the bins back onto the conveyor belts to the outloaders for shipping.

A brief history

Extensive prospecting work from the early 1920s led to the discovery of manganese deposits and subsequent mining in the late 1920s on farms between Sishen and Postmasburg in the Northern Cape. Associated Manganese of South Africa, renamed Assmang Limited in 2001, was formed in 1935 to amalgamate various small operations and was listed on the JSE in 1936. Rail infrastructure was duly developed to transport the bulk ores, and the first ship was dispatched from Durban harbour in March 1936.

Following the Company’s acquisition of the Black Rock deposit in 1940, a number of other large properties underlain by ore were subsequently found and acquired in the area. Manganese operations were extended and today include the Nchwaning and Gloria underground mines.
Manganese mining at Black Rock
Nchwaning Mine

Nchwaning Mine was originally established in 1972, with a single vertical hoisting shaft. A second shaft, the Nchwaning No. 2 vertical skip shaft, was commissioned in 1981. At the still-active No. 2 shaft, ore is mined and crushed underground prior to being hoisted up the 450m vertical shaft. This shaft has a capacity of approximately 120 000 tonnes per month.

Construction on a new shaft complex, Nchwaning No. 3, began in 2004 and was completed in 2006. The new mine is serviced by two shafts: a vertical personnel shaft to a depth of 400m, and a decline shaft equipped with conveyors. Hoisting capacity from this shaft is approximately 200 000 tonnes per month. “At Nchwaning No. 3, we have seven underground silos which are used to store different grades of ore. Underground processing and storage allow us to change the mix of product we send to the surface as demand arises,” says General Manager Sechaba Letaba.

“We are also proud to have the only underground workshop of its kind in the country,” says Letaba. “In it we carry out services, do pick repairs – you name it – and save time and costs by maintaining equipment close to where it is used.”

Over R500 million was recently invested in constructing a new processing plant at Nchwaning to expand the mine’s processing capacity from 3 million to 6 million tonnes per annum. “The new plant, which was commissioned in June 2010, is capable of processing 900 tonnes per hour of manganese ore from both Nchwaning 2 and Nchwaning 3 shafts,” says Letaba.

At Nchwaning Mine, manganese ore is crushed, washed and screened to various sizes, then stockpiled according to size and grade in stacks ranging in capacity from 280 to 320 tonnes each.


Reference for information:
www.assmang.co.za/o/manganese/nchwaning.asp
www.mining-technology.com/projects/assmang/
www.ambriefonline.com/nov_dec10%20cover.html