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N'Chwaning Mines, Kuruman, Kalahari manganese field, Northern Cape Province, South Africa

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Latitude & Longitude (WGS84): 27° 7' 45'' South , 22° 51' 56'' East
Latitude & Longitude (decimal): -27.12944,22.86556
GeoHash:G#: ke0m8m4pw
Other regions containing this locality:Kalahari Desert, Africa
Locality type:Group of Mines
Köppen climate type:BSh : Hot semi-arid (steppe) climate

Mine Type/Method: Room & Pillar. N'Chwaning 1 was originally established in 1972, with a single vertical shaft. The 450m N'Chwaning 2 shaft with an underground crushing station came into production in 1981. N'Chwaning 3 became fully operational in 2006 and is serviced by two shafts; a vertical personnel shaft to a depth of 350m and a 2.2km main hoisting decline conveyor shaft.

Geology: 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 N'Chwaning deposit consists of a gently dipping and regular strata bound body of high-grade ore, which has undergone a hydrothermal upgrading associated with faulting.

The base of the Hotazel Formation consists of a bright-red banded iron-formation bed (varying from massive to fine-grained specularite and/or euhedral magnetite cystals) overlying volcanic glass breccias and lavas of the Ongeluk Formation. The banded iron-formation units grade into microcrystaline kutnohoritic ovoid-rich braunite rock. The kutnohorite in this area is concentrated in ovoids, which represent partially compacted, early diagenetic concreations in hematite and braunite rock. The braunite rock bed of the lower section of the lowest of the three sedimentary cycles present in the Hotazel Formation, is between 5 and 45m thick. This is the major ore unit of the Kalahari manganese field with an manganese content varying between 20 and 48 weight per cent. The middle manganese-bearing unit (cycle 2) is a maximum of 2m thick and in not economically viable. The top manganese ore body was mined in previous years. It rarely exceeds 5m thickness. Grey hematitic and manganese minnesotaite rocks are found between the lower and the middle maganese ore bodies

About 1300 million years ago a widespread hydrothermal event occured in the north-western portion of the Kalahari manganese field which reached temperatures up to 450°C in the Wessels, N'Chwaning and Black Rock Mines. This event decarbonated and desilicated portions of the Hotazel Formation to the north-west and thus upgraded the manganese content of the ore. Furthermore the hydrothermic event is of great significance for from the collectors point of view as a wide range of rare as well as unusual mineral combinations where produced.

The manganese ore bodies in the north-western part of the Kalahari manganese field (Wessels, Black Rock and N'Chwaning Mines) have been termed Wessels-type ore. These ore bodies contrast markedly to the primary Mamatwan-type ore. The ore has been hydrothermically alterd and metamorphised. This resulted in a manganese ore with a coarser grain size with higher manganes content. This ore is braunite-rich and contains other major minerals such as braunite II, bixbyite, hausmannite, marokite and hematite together with minor amounts of calcite. The overall carbonate content of the Wessels-type ore is lower than that of the Mamatwan-type ore. Andradite and barite are common gangue minerals. Additionally minor minerls such as tephroite and rhodochrosite as well as aegirine (in the iron formation above the ore layors)are associated with this ore type. Most of the Wessels, Black Rock, N'Chwaning II and parts of N'Chwaning I ores are of this type.

The Hotazel outlier is situated in a graben to the east of Black Rock and contains a very high grade ore (60 to 70 per cent average). Hausmannite with lesser amounts of other minerals and a very low carbonate component are the main constituents of the Hotazel supergrade ores. Although the ore is found typically in the Hotazel Mine, parts of the Langdon Annex and N'Chwaning I Mines also contain this ore-type[1]

Ore: Rhodochrosite (carbonate) and olmiite (silicate)
Gangue: Oyelite and calcite.

(Sources: Cairncross et al & Messner.)

Mineral List

Mineral list contains entries from the region specified including sub-localities

86 valid minerals. 8 (TL) - type locality of valid minerals.

Regional Geology

This geological map and associated information on rock units at or nearby to the coordinates given for this locality is based on relatively small scale geological maps provided by various national Geological Surveys. This does not necessarily represent the complete geology at this locality but it gives a background for the region in which it is found.

Click on geological units on the map for more information. Click here to view full-screen map on Macrostrat.org

Quaternary - Tertiary
0 - 66 Ma

ID: 3185837
Cenozoic sedimentary rocks

Age: Cenozoic (0 - 66 Ma)

Lithology: Sedimentary rocks

Reference: Chorlton, L.B. Generalized geology of the world: bedrock domains and major faults in GIS format: a small-scale world geology map with an extended geological attribute database. doi: 10.4095/223767. Geological Survey of Canada, Open File 5529. [154]

0 - 66 Ma

ID: 2233217
Kalahari Group

Age: Cenozoic (0 - 66 Ma)

Stratigraphic Name: Kalahari Group

Description: Superficial deposits comprising gravels, clays, sandstone, silcrete, calcrete and aeolian sand

Reference: Council for Geoscience. Geologic map of South Africa, 1:1M. National Science Councils of South Africa. [41]

Pleistocene - Paleogene
0.0117 - 66 Ma

ID: 3306660

Age: Cenozoic (0.0117 - 66 Ma)

Lithology: Sedimentary

Reference: Thiéblemont, D. (ed.). New edition of the 1:10,000,000 geological map of Africa. CGMW-BRGM. [190]

Data and map coding provided by Macrostrat.org, used under Creative Commons Attribution 4.0 License

Localities in this Region
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South Africa

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Hochleitner, R. (1986): Neufund von Gaudefroyit-Kristallen in Südafrika. LAPIS 11 (6), 19-20.
Cairncross, B. and R. Dixon (1995) Minerals of South Africa.
Gutzmer, J. (1996). Genesis and alteration of the Kalahari and Postmasburg manganese deposits, Griqualand West, South Africa (Doctoral dissertation, Rand Afrikaans University).
Cairncross, B., Beukes, N. and Gutzmer, J. (1997): The Manganese Adventure – The South African Manganese Fields. Associated Ore & Metal Corporation Limited, Johannesburg, Republic of South Africa.
Cairncross, B., Beukes, N. (2013) The Kalahari Manganese Adventure – The Adventure Continues. Associated Ore & Metal Corporation Limited, Johannesburg, Republic of South Africa.

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