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assmang manganese mines, northern cape province, south africa - mining technology | mining news and views updated daily

assmang manganese mines, northern cape province, south africa - mining technology | mining news and views updated daily

The Kalahari Manganese field is located in the Northern Cape Province, 700km south-west of Johannesburg, South Africa. It contains approximately 80% of the worlds known high-grade manganese ore reserves. The district yields four million tonnes per annum (Mtpa), which is mined mainly by two companies: Samancor and Assmang.

Originally established in 1935, Assmang is jointly owned and managed by African Rainbow Minerals and Assore. The company wholly owns the Nchwaning and Gloria manganese mines, near the Black Rock area of the Kalahari Manganese field.

In early 2000, Assmang announced an expansion involving the development of a new shaft complex at Nchwaning to add 2Mtpa of run-of-mine ore capacity. The expansion made Nchwaning the worlds lowest-cost underground manganese mine and extended its lifetime by 30 years.

In 2014, an expansion project was undertaken at both the Gloria and Nchwaning underground mines to increase the mining capacity from 3.2Mtpa to 4.6Mtpa. The expansion project involved refurbishments, upgrades and new installations, in addition to the sinking of a 167m-deep ventilation shaft with a 5.5m diameter at the Gloria underground mine.

Assmang secured approval from environmental authorities for an expansion of the Gloria manganese mine in September 2018. The project will upgrade the rock handling infrastructure and surface processing plant at the mine, as well as related infrastructure to reduce water and energy consumption. The project is expected to be completed in late 2021.

At Black Rock, near the northern end of the basin, the Transvaal System rocks lie 300m from the 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 Volwater Formation at the top of a sequence of Transvaal System rocks. As well as being faulted, the horizons are folded.

Nchwaning has two manganese seams. Seam one is six-metre thick and situated approximately 400m underground while seam two is located above seam one at Nchwang 2. Seam two can be accessed through the Nchwaning 2 shaft. Gloria manganese seam one is estimated to contain 35.44Mt of mineral reserves. Mineral reserves of 3.85Mt were identified at Nchwaning Seam two in 2013, where mining started in 2014.

As of 2019, Nchwanings total measured and indicated resources were 303.95Mt, while proven and probable reserves were 177.86Mt. Glorias measured and indicated resources were 65.99Mt, while proven and probable reserves were 115.04Mt.

Both mines are underground operations, using the room-and-pillar method. Nchwaning started with one vertical hoisting shaft, with the 450m-deep No 2 vertical skip shaft added and the plant upgraded in 1981.

The established areas use Boart Longyear hydraulic drilling rigs and Wagner load-haul-dump (LHD) machines and trucks to transport the ore to storage silos, primary crushers and screens that feed the hoisting systems. Roofs are scaled using a modified three-wheeled loader.

For the new area, Assmang requested a three-boom rig fitted with two rock drills for face work plus one for roof-bolting, so the mine can drill holes for roof bolts and face-blast holes from the same set-up.

Shaft complex Nchwaning 3 provides access to high-quality ore. 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 varies 200,000t a month.

The existing plant was upgraded and treats the ore from both Nchwaning 2 and 3 mines. The run-of-mine ore is crushed, washed and screened, with no other processing needed. After the ore has passed through the plants, it is stacked according to size and grade. The capacities of the stacks vary between 280t and 320t each, and are numbered and sampled.

Exports travel by the main South African Railways route to Port Elizabeth on the Indian Ocean. Lesser tonnages are directed to the domestic steel industry. The feasibility study for exporting manganese through the Saldanha Port was completed in 2012.

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