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DIAMONDS IN AFRICA

DEMOCRATIC REPUBLIC OF CONGO

The age of the kimberlites of the Kasai and the North of Angola

It has not been made radiometric dating to my knowledge on the kimberlites of Kasaï (nor those of the North of Angola).
But the age of their setting could be exactly situated by stratigraphic considerations that have been put well in evidence by J. LEPERSONNE (1960): "After the Wealdien (or Neocomien, base of the Lower Cretaceous) took place the tectonic movements, radial faults and warpings and a certain erosion created a discordance under the Aptien... During the same period, or little earlier, intruded the kimberlites of Kasaï and Northern Angola and took place the surface of erosion that separate, in these regions, the set the Kwango Formation (likely Albien and partially superior Aptien and base of the Cenomanien) of the Loïa Formation (Wealdien) at the base"... "In Bakwanga... the kimberlites... intrude the Loïa Formation, and on the other hand in Western Kasaï and in Angola the base of Kwango Formation conceals diamonds that come from the destruction of these kimberlites".

The setting of the kimberlites and their erosion dates therefore between the Wealdien and the Albien (110/120 MY). It would have been therefore a little more precocious in the Central Africa that in the South and Northwest where the phenomenon appears to be dated during the Superior Cretaceous (Turonien in Sierra-Leone).

OTHER OCCURRENCES OF DIAMOND IN CONGO

In the Democratic Republic of Congo (DRC), outside of the rich deposits of Tshikapa and Bakwanga, a lot of other diamond occurrences exist that only caused little or not at all interest because of their economic, real or inferred lack of value.

If one tries to classify them, one can distinguish:
1° the deposits bound to the cretaceous cover of the southern border of the Congo pan.
2° those of the northern border on the Oubanguien Shield that is like types knew in the east of the Central African Republic.
3° the indications of the east (Maniema) enigmatic enough.
4° the kimberlites of the Kundelungu to the north of the Katanga Province.

I. CONGO PAN

The Congo pan is in short a very big syncline of a circular shape and 1,300 km of diameter, this structure is probably fairly old because under a Cenozoic, Mesozoic and Palaeozoic cover of the deep drilling encounter the horizontal Precambrian, or older, beds of the Katanga Formation.

On the edge of the pan, and in particular in the south, the extension of the Mesozoic and Cenozoic sediments is big. As one saw it for Tshikapa the cretaceous Kwango formation collected and scattered the diamonds but the size of this phenomenon that followed a period of an intense of post-kimberlitique erosion, is actually enormous and extends considerably beyond the only field of Tshikapa. Not only it spreads toward the west in the region said of the Kwango, to the south in Angola (Lunda), and also to the east, but the recent research by a French team in Brazil shows its likely extension to the west of Minas Geraes until the approach of Bolivia! However the intercontinental adjustment Africa - Brazil shows that this display of the cretaceous diamantiferous deposits constitutes a more than 4,000 km long belt. The continents being readjusted its orientation presents a slant (toward the west) at 10° on the present equator in Africa, and of 33° (toward the east) on the present equator in Brazil.

It is probable that this orientation translates, in the former Gondwana continent, a sub latitudinal direction, because one finds the same climatic conditions in the successive deposits on both sides of the ocean.

Deposits of Kwango

This partially diamantiferous region spreads on close to 500 km large to the west of the field of Tshikapa and 400 km from south to north. It is drained by a succession of rivers, taking their sources in Angola and flowing South-North toward the River Kasaï that throws himself in Congo River, 150 km above Kinshasa (ex Leopoldville). There the fossils of Kwango Formation defined its age as Cenomanien or Turonien (J. LEPERSONNE). The top is limited by the erosion of the end of Cretaceous under the shape of fossilized polymorphous sandstone of Palaeogene age. The kimberlites sources has been discovered lately close to the sources of Kwango River in Angola and even to the south of the Congo's border the conglomerate of Calonda is diamantiferous.

It seems that DUNCAN SMITH has discovered the existence of diamonds since 1922-24, and the region was re-prospected since. The mineralized zones known are:
- on the lower course of the Luange River in Tetetshi at the confluent with the Tobi River (140 km. NNW of Tshikapa) the deposits little important of tiny diamonds (40 stones/ct) and poor enough be of any importance.
- On the Kwenge River traces of diamond exist 40 km upstream from Kikwit, and on the Wamba River to the S.E. of Kitinda (on the 7° parallel) are found alluviums with a diamond grade of 0,52 ct/m3 and others higher toward Panzi. Finally, on the Kwango River, 450 km to the W and NW of Tshikapa, of the alluvial exploration by EKL (1961-62) had delimited four distinct sections on 500 km. of river course from the Angolan border. The most upstream (region of the Guillaume and François-Joseph Falls) doesn't have any gravels. The second (region of the Yonzos River and Cuilo River) would present some interest with good contents on a 30 km long stretch. Then after 100 km of flats covered of sand (non sampled?) the important mineralized alluvial flats are found between Kingushi and Takundi (to the north of the 5th parallel), but with variable grades. It is likely that there were some exploitation, quickly enough abandoned. The diamonds were generally small what would remove some interest in these deposits. I ignore if there is any artisanal mining in this vast region.

South-East of the Congo Pan (Lomami)

The superior basins of the Lukemies River and Lomelas River (Long. 23/24° E. Lat. 3° S) contain small diamonds of unknown origin. These stones, rather small, resemble those from Tshikapa, therefore could not come from Bakwanga that is located 300 to 400 km. to the southwest, but are of another unknown source.

Diamond Geology [ 1  India  3  4  5  6  7  8  Brazil  10  11  12  13  14  15  16  17  18  19  20  Borneo  22   South Africa  24  25  26  27  28  29  30  31  32  33  34  35  36  37  38  39  40  Venezuela, Guyana  42  Australia  44  Argyle  Congo  46  47  48  49  50  51  52  53  54  55  Angola  57  58  59  Guinea  ]


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Rafal Swiecki, geological engineer email contact

This document is in the public domain.

March, 2011