DIAMONDS IN AFRICA
DEMOCRATIC REPUBLIC OF CONGO
II. NORTHERN BORDER
The diamonds of the "Oriental Province" on the North edge of the pan have been found in exploitations of gold. One can mention three favourable zones:
1° Region of Bondo (Long. 23° 45' E. - Lat. 3° 45' N.). There were exploited some auriferous alluvials on the old crystalline granitic basement that includes some metamorphic shreds in particular in the basin of the Bili River. Curiously everywhere are found diamonds the basic rocks, dolérites, gabbros are also found (ex Concession Baraka). Bondo is on the big Uelé River that gave its name to this region of big forest.
2° Region of Aketi (Long. 23° 45' E. - Lat. 2° 40' N.). 120 km to the south of Bondo are found auriferous-diamantiferous alluviums in the basin of the Telé River, East of Aketi, and on 150 km until Andudu to the SE of Buta. This would be in part in the Roan Formation and in the group of Lindi (?) based on the old crystalline basement.
3° Region of Poko (Long. 26° 45' E. - Lat. 3° 05' N.). It is on the old basement, and the FORMINIÈRE had a big concession there between the Ueré and the Poko Rivers. More to the East (toward the Ituri-Kidali) one would lose the trace of the diamonds.
It is necessary to note that the stones of very good quality and big enough (record 16 cts) would resemble to those of the Oubangui. In the exploitation of gold by sluice a lot of the small diamonds had to be lost, what would appear to valorize such indications. It is not necessary to delude oneself however too much because if one takes into account the very big volumes of gravel cleaned, the grade of diamond can be actually very weak: it is what an experience made at Etéké in Gabon in similar conditions showed. Seen the quality of the stones the topic is not all the same deprived of interest.
III. THE REGION OF THE MANIEMA
The Maniema in NE of the Congo is known for its tin. On the periphery of stanniferous alluviums some flats exist with zones of exploitable diamond grade.
The origin of this mineralization, which seems not to have a report with the deposits of the Congolese pan, is unknown. Some had suggested a Precambrian origin while making the relation with the indications of diamond in Uganda that could drift from conglomerates and sandstone of the Karagwe-Angkole Formation. Some also invoke the glacial deposits of the Karoo. The FORMINIÈRE, which detained the monopoly of the diamond mining in the ex Belgian Congo, was too richly endowed in the Kasaï region to worry about these peripheral and probably marginal deposits.
IV. THE KIMBERLITES OF THE KUNDELUNDU (KATANGA)
The kimberlites in Katanga have been first discovered by the Belgians 40 years before those of Bakwanga. It is a rare example where these rocks, generally little visible, have been found directly and not from indications of diamonds (their mineralization is besides very weak). The big dimension of these bodies, those of Tabala (50 ha) and Kambali (26 ha) are among the biggest of the world, had to present a very obvious outcrops.
Tanganyika Concession Ltd. (TCL), in 1907, did the first researches and found the first diamond on the Mutendele River, the left affluent of Lualaba River (4). H. BUTTGENBACH, in1908, determined the first sample of kimberlite. Ten pipes were seen, very quickly, it seems, in the basins of the Luizi River and the Lushipuka River to the west.
In 1910, the Committee of Exploration of Kundelungu Lualabas was formed by the TCL and the CSK (Special Committee of Katanga). SIMKAT (Belgian Industrial and Mining Co. of Katanga) achieved deepened prospecting until 1913 and later in 1926 under the direction of V. BRIEN. In 1960 the CSK tempted more geo-chemical prospecting for Ni-Cr (5). 24 pipes have been listed and probably all sampled (20 for sure). The grades being very weak and the diamonds of little value, it has been concluded to the lack of interest in these primary deposits. A project of new research has been prepared, in 1966, by geologist N. KORETZKY to whom I am indebted of a lot of information. In a very distinct zone, 250 km. NW (80 km. NE of Kamina), could exist other indications of kimberlitic pipes maybe in relation with the diamonds of Lomami.
The kimberlites are localized close to the edges east and west of the Kundelungu at 180 km. NNE of Elisabethville (Long. 27° 40' to 28°E., Lat. 10° to 10° 20' S). 200 km. long, south to north, and 50 km. large, this 1,800 m of altitude mesa suddenly ends by high abrupt cliffs on its two east and west faces. The rivers that take their sources on the plateau clear the edges by deep gorges and falls: the one on the Lofai River, 340 m. high, would be one of the highest waterfall in Africa. Lufira River (basin of the Lualaba River) drains the west side, and Luapula River the east side.
The plateau is constituted by the horizontal sedimentary layers of the Superior Kundelungu Formation of Katangien age (630 MY). The lower part, where the feldspathic sandstone then the mica shales rest on a pudding of base, is not represented. The superior part, thick of 600 to 700 m, understands some calcareous quartzites then feldspathic and sandstone at the summit. (L. CAHEN - The Geology of Belgian Congo). The surface of the plateau is concealed by a thick enough layer of recent sand, with a lot of intercalations of rolled pebbles witnesses of a former hydrographic network much different of the present one (N. KORETZKY). This superficial mask and the intervention of a former drainage come to disrupt the research of kimberlites by concentrations of heavy minerals. Is it for this reason that one doesn't know any pipes that are not close to the more dissected edges? Are these edges the preferential zones corresponding to longitudinal fractures, which limit to the east and to the west a horst dominating the two depressed zones of the Lakes Moero and Lualaba? However, in these depressions one doesn't find lowered Kundelungu Formation and the cliffs maybe are due solely the erosion? It is curious that such ambiguousness is found elsewhere, for example, in Kenieba (Mali), at the Tambaoura cliff, in Vargem Bonita in Brazil and in La Sierra de Canastra, etc.
(4) Therefore it seem to be before JANOT found diamonds in the Kasaï, who would not have been therefore the first finder of diamond in Congo.
(5) CSK - VAN DE STEEN (March 1960) - The State of Advancement of Geo-chemical Research in Katanga.
Rafal Swiecki, geological engineer email contact
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