N'Chwaning Mines, Kuruman, Kalahari manganese field, Northern Cape Province, South Africa
|Latitude & Longitude (WGS84):||27° 7' 45'' South , 22° 51' 56'' East|
|Latitude & Longitude (decimal):||-27.12944,22.86556|
|Other regions containing this locality:||Kalahari Desert, Africa|
|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
Ore: Rhodochrosite (carbonate) and olmiite (silicate)
Gangue: Oyelite and calcite.
(Sources: Cairncross et al & Messner.)
Mineral ListMineral list contains entries from the region specified including sub-localities
86 valid minerals. 8 (TL) - type locality of valid minerals.
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.
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0 - 66 Ma