DIAMONDS IN AFRICA
DEMOCRATIC REPUBLIC OF CONGO
Based on the information provided by geologist Marcel Guillaume Bardet.
In quantity the RDC was the biggest producer of diamond in the world: 18,072,000 cts for the year 1961. This number has been achieved on the only one but enormous deposit of Bakwanga, in the region of Bushimai, which almost detained the monopoly of the "crushing boart". After the independence of 1st. July 1960 Congo dove in the socio-economic mess that stopped practically the organized statistics of production.
The RDC also possesses the alluvial fields of the Kasaï that were very rich, and of which the extension in Angola is in exploitation, mainly by artisanal mining, and achieves more than 1,000,000 cts per year.
Other occurrences of diamond have been signaled in this vast country, although it was not the subject of exploitation.
Fields of the Kasaï (Tshikapa)
The diamantiferous fields of Kasaï, the most formerly exploited in Central Africa, spreads between the parallels 8°30' and 5° South and the meridians 20° and 22°30' East. Its southern part is in Angola, and the Congolese sector stops about at the 7° parallel. Nevertheless, it covers more than 20,000 km2 around the mining centre of Tshikapa, that is 650 km to the ESE of Kinshasa, in a flat region at about 600 m of altitude.
The fields of the Kasaï are solely alluvial. The diamantiferous sedimentary layers date from the Cretaceous. The diamonds are found in the lower part of the Bokungu Formation.
The diamonds of the Kasaï are small but of a beautiful quality with up to 65% of jewelery stones.
The platform of the region of Tshikapa rests on the old very folded and metamorphic crystalline Kasaï Shield of 2 to 2.7 billions of years old, that hardly shows on the surface. It is only exposed at the bottom of river valleys.
The floor consists of the granites, gneiss and migmatites, syenites, of the metamorphic rocks: quartzites, amphibolites, itabirites, 2 micas schists, pegmatites and the old basic intrusions: uralitized dolerites and ophitic gabbros.
On this floor rests in discordance the following sub-horizontal formations:
The Lukuga formation (Permian) (Karoo inf.) (Equivalent to the Lutoë formation in Angola)
A mudstone-sandstone formation of light brown to yellow colour composed from the bottom to the top:
This formation never is diamantiferous in Congo or in Angola. In Kasaï, one finds it as a rare outcrops in South in the depressions of Precambrian floor.
Overlaying the Congolese Basin are Jurassic and Cretaceous sediments of the "Continental Inset".
It is necessary to distinguish 3 layers currently in the formations known as Lualaba-Lubilash:
The Loïa layer in Kasaï is formed from the bottom up:
The Kwango layer (Equivalent to the Lunda formation in Angola) made of sandstones and conglomerates is diamantiferous. Its purplish colour contrasts well with the bottom part of Lualaba-Lubilash formation while its thickness varies from 0 to 200m. In Kasaï, the Kwango layer starts as a conglomerate of deltaic origin. This conglomerate has the aspect of a lateritic crust often forming small irregular lentils with intercalations of thin layers of nodules of argillite. The agates are very frequent and there is a large assortment of heavy minerals.
Cenozoic The system of Kalahari rests on the applanation of the end of Cretaceous and is previous to the applanation of the superior Pliocene.
One distinguishes two sets of deposits:
The doleritic intrusions
Rafal Swiecki, geological engineer email contact
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