The N'chwaning mine (or N'Chwaning mines) are located in the

Northern Cape Province The Northern Cape ( ; ; ) is the largest and most sparsely populated province of South Africa. It was created in 1994 when the Cape Province was split up. Its capital is Kimberley. It includes the Kalahari Gemsbok National Park, part of the Kga ...

South Africa South Africa, officially the Republic of South Africa (RSA), is the Southern Africa, southernmost country in Africa. Its Provinces of South Africa, nine provinces are bounded to the south by of coastline that stretches along the Atlantic O ...

. N'chwaning has one of the largest

manganese Manganese is a chemical element; it has Symbol (chemistry), symbol Mn and atomic number 25. It is a hard, brittle, silvery metal, often found in minerals in combination with iron. Manganese was first isolated in the 1770s. It is a transition m ...

reserves in

having estimated reserves of 323.2 million tonnes of manganese ore grading 42.5% manganese. There are three shafts, designated as N'Chwaning, N'Chwaning II and N'Chwaning III. The majority of the major mineral finds documented originate from the N'Chwaning II shaft. N'Chwaning is considered a single vertical hoist shaft. N'Chwaning II is a vertical skip shaft, currently still in production with an underground crushing facility. N'Chwaning III has two main shafts - A vertical personnel shaft and a decline shaft. N'Chwaning III additionally has seven underground silos for storing different grades of ore. N'Chwaning is known to produce high-quality mineral specimens of

rhodochrosite Rhodochrosite is a manganese carbonate mineral with chemical composition Manganese(II) carbonate, MnCO3. In its pure form (rare), it is typically a rose-red colour, but it can also be shades of pink to pale brown. It Streak (mineralogy), streak ...

manganite Manganite is a mineral composed of manganese oxide-hydroxide, MnO(OH), crystallizing in the monoclinic system (pseudo-orthorhombic). Crystals of manganite are prismatic and deeply striated parallel to their length; they are often grouped togethe ...

ettringite Ettringite is a hydrous calcium aluminium sulfate mineral with formula: . It is a colorless to yellow mineral crystallizing in the trigonal crystal system, system. The prismatic crystals are typically colorless, turning white on partial dehydratio ...

inesite Inesite is a hydrous calcium manganese silicate mineral. Its chemical formula is Ca2Mn7Si10O28(OH)2•5(H2O). Inesite is an inosilicate with a triclinic crystal system. It has a Mohs hardness of 5.5 to 6, and a specific gravity of 3.0. Its name ...

, jouravskite and other minerals. The N'Chwaning mine is located on the farm N'Chwaning 267, from which the name is derived. The license area also includes what was formerly known as the Black Rock mine area, and is situated in the

ores of the Kalahari Manganese Fields.

History

The ore body was discovered in 1940 by Assmang, and led to the acquisition of a manganese outcrop. The properties on which the ore is situated were subsequently acquired by Assmang, and led to the 1975 commissioning of the Gloria mine (medium grade carbonated ore) as well as the later commissioning in 1972, 1981 and 2004 respectively of the N'Chwaning I, I and III shafts.

Geology

The N'Chwaning mines are situated in the Kalahari Manganese Fields, with the primary ore hosted in the Hotazel Formation of the Griqualand West Sequence, forming part of the

Proterozoic The Proterozoic ( ) is the third of the four geologic eons of Earth's history, spanning the time interval from 2500 to 538.8 Mya, and is the longest eon of Earth's geologic time scale. It is preceded by the Archean and followed by the Phanerozo ...

Transvaal Supergroup. The ore body shows extreme

faulting In geology, a fault is a planar fracture or discontinuity in a volume of rock across which there has been significant displacement as a result of rock-mass movements. Large faults within Earth's crust result from the action of plate tectonic ...

and

hydrothermal Hydrothermal circulation in its most general sense is the circulation of hot water (Ancient Greek ὕδωρ, ''water'',Liddell, H.G. & Scott, R. (1940). ''A Greek-English Lexicon. revised and augmented throughout by Sir Henry Stuart Jones. with th ...

upgrading, responsible for the formation of a large majority of the mineral species described from the Kalahari Manganese Fields. Zoning exists within the ore body both in the vertical and horizontal sense, where horizontal zoning is fault related and shows high grade

hausmannite Hausmannite is a complex oxide, or a mixed oxide, of manganese containing both Divalent, di- and Trivalent, tri-valent manganese. Its chemical formula can be represented as , or more simply noted as , or , as commonly done for magnetite (), the co ...

ore, intermediate areas show a very complex mineral assemblage (including

braunite Braunite is a silicate mineral containing both di- and tri- valent manganese with the chemical formula: Mn2+Mn3+6 SiO4 Common impurities include iron, calcium, boron, barium, titanium, aluminium, and magnesium. Braunite forms grey/black tetragon ...

and

jacobsite Jacobsite is a manganese iron oxide mineral. It is in the spinel group and forms a solid solution series with magnetite. The chemical formula is (Mn,Mg)Fe2O4 or with Redox, oxidation states and substitutions: (Mn2+,Fe2+,Mg)(Fe3+,Mn3+)2O4.

), while distal areas have a lower grade ore consisting predominantly of braunite and

kutnohorite Kutnohorite is a rare calcium manganese carbonate mineral with the formula in the dolomite group of minerals. It forms a solid solution with the other group members dolomite and ankerite. The mineral was originally spelt "kutnahorite" but "kut ...

. Vertical zoning in the orebody is shown by high iron and low manganese concentrations at the contacts, with an increase in manganese grade towards the centre of the body. Two seams are mined - the No.1 seam is on average 6 metres thick, with a depth of 400 metres at the N'Chwaning mine and a depth of 200 metres at the Gloria mine. The No.2 seam is stratigraphically placed above the No.1 seam, with ongoing mining using the N'Chwaning II infrastructure.

References

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History

Geology

See also

References