N'Chwaning Mines, Joe Morolong Local Municipality, John Taolo Gaetsewe District Municipality, Northern Cape, South Africai

Regional Level Types
N'Chwaning Mines	Group of Mines
Joe Morolong Local Municipality	Municipality
John Taolo Gaetsewe District Municipality	District Municipality
Northern Cape	Province
South Africa	Country

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The N'Chwaning mines term is used to group together three manganese mines located in the Northern Cape Province of South Africa. These mines (or shafts) are known as N'Chwaning I (est. 1972), N'Chwaning II (production started in 1981) and N'Chwaning III (became fully operational in 2006).

The N'Chwaning mines comprise one of the largest manganese reserves in South Africa, having estimated reserves of 323.2 million tonnes of manganese ore grading 42.5% manganese.

Apart from their ore producing significance, the N'Chwaning mines are notable and famous among the mineral collecting community for producing high-quality mineral specimens of rhodochrosite, manganite, ettringite, inesite, jouravskite and other minerals. The majority of the major mineral finds documented originate from the N'Chwaning II shaft.

The N'Chwaning mines derive their name from the farm they are located, namely farm N'Chwaning 267. The license area also includes what was formerly known as the Black Rock mine area, and is situated in the manganese ores of the Kalahari Manganese Fields.

Mine Type/Method: Room & Pillar. N'Chwaning 1 was originally established in 1972, with a single vertical shaft. The 450 m 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 350 m and a 2.2 km 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 crystals) overlying volcanic glass breccias and lavas of the Ongeluk Formation. The banded iron-formation units grade into microcrystalline kutnohoritic ovoid-rich braunite rock. The kutnohorite in this area is concentrated in ovoids, which represent partially compacted, early diagenetic concretions 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 45 m thick. This is the major ore unit of the Kalahari manganese field, with a manganese content varying between 20 and 48 weight percent. The middle manganese-bearing unit (cycle 2) is a maximum of 2 m thick and is not economically viable. The top manganese orebody was mined in previous years. It rarely exceeds 5m thickness. Grey hematitic and manganese minnesotaite rocks are found between the lower and the middle manganese orebodies.

About 1300 million years ago a widespread hydrothermal event occurred 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 hydrothermal event is of great significance from the collectors' point of view, as a wide range of rare as well as unusual mineral combinations were produced.

The manganese orebodies in the north-western part of the Kalahari manganese field (Wessels, Black Rock, and N'Chwaning Mines) have been termed Wessels-type ore. These orebodies contrast markedly to the primary Mamatwan-type ore. The ore has been hydrothermally altered and metamorphosed. This resulted in a manganese ore with a coarser grain size with higher manganese 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 minerals such as tephroite and rhodochrosite as well as aegirine (in the iron formation above the ore layers)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 percent 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]

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

(Sources: Cairncross et al. & Messner.)

Commodity List

This is a list of exploitable or exploited mineral commodities recorded from this region.

Mineral List

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

94 valid minerals. 9 (TL) - type locality of valid minerals.