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In fact, the Forminière was the specialized entrepreneur prospecting and mining for the account of the other companies. From1912 to 1961 the whole production of the Kasaï was achieved therefore by only the Forminière, that extracted from the Kasaï about 24 millions karats between 1909 and 1961.

The record number has been reached in 1932 with 867,585 karats.
The cut-off grade has been estimated then at 0.7 ct/m3. The Forminère estimated that on June 1st, 1966, the reserves were of about 5 millions m3 at 0.73 ct/m3. It excluded the big rivers deposits (the active channels and flats). One estimates the cut-off grade of artisan exploitations to be at 0.3 ct/m3.

The semi-mobile washing plants with big pans of 8 feet followed the overburden stripping by about 150 m jumps.

In 1957 there were 53 mines: 7 in flats and terraces, 42 in creeks and 4 on tailings. In 1960 this number had fallen to 37 spread on 22 rivers.

Among the last industrial exploitations, one can mention:
The terrace of Tshisaka on River Tshikapa had a thick gravel (up to 5 m) "in dome" on the hill. The sterile overburden was removed by monitoring; the gravel was mined by hand with an output of 5,000 m3 per month having the content of 0.3 to 0.5 ct/m3.
The 12-km long Ramona Creek. The average grade content was of 3 ct/m3 with thin thickness of gravel (0.3 to 0.7 m), but had beautiful potholes in the Lualaba sandstone with enormous grades.
The terraces of Tshitala on the Kasaï River had the sterile overburden thick of 10 m and the gravel of 3 to 4 m. The average grade content of 1 ct/m3 can be considered as good.

In 1959, was excavated 3,425,161 m3 of which 2,656,049 m3 of the sterile overburden and 769,112 m3 of pay-gravel with a production of 657,906 cts for a grade content of 0.86 ct/m3 in gravel or 0.19 ct/m3 in total excavated.
In River Lumembe numbers of stones was from 7 to 8 per karat, with 18.75% of the stones bigger than a karat and the average grade of 0.67 ct/m3.
In Longatshimo numbers of stones was from 10 to 11 per karat, with 12.5% of the stones bigger than a karat and the average grade of 0.61 ct/m3.
In Tshikapa numbers of stones was of 13 by karat, with 8.65% of the stones bigger than a karat and the average grade of 0.92 ct/m3.

One can observe that the quantity of the diamonds becomes richer toward the downstream (the higher average grades) and at the same time becomes impoverished in quality (the smaller stones). This phenomenon has been noted elsewhere and it is maybe a general rule.

The proportion of the European workers was very small, in January 1960 only 56 Europeans (0.85%) for 6,566 Congolese.

Future of the Kasaï
One estimates that in 1966, the reserves in small rivers were about 5 millions m3, to the content of 0.73 ct/m3 or 30 millions m3, to the content of 0.3 ct/m3.

In the alluviums of the big rivers the reserves could be about 8 millions karats. To the difference of the deposits of the tributaries that has been prospected carefully, those of big rivers are known badly. The big rivers flow on the Precambrian floor and not on sandstone and have by this fact bigger flats and bedrock more auspicious to the dredging. Therefore one day the industrial exploitations will reappear as big river dredges.

Flats of Kasai River in Kasai District of Congo


(Also called of Lubilash or Bushimaïe)

The group of deposits of Bakwanga in the south Kasaï constitutes the biggest accumulation of diamonds - and at the same time the more "concentrated" with Kimberley - that is known on the surface of the globe.

By the end of 1966, 330,000,000 carats had already been mined. The likely reserves, that are not unveiled, represent 25 maybe to 30 years of life at the present fantastic rhythm of 12 to 15 millions carats per year.

Not only the volume of alluvium gravels and especially of exploited up to now eluvions, is enormous, but also the grades are also very high. This quantitative wealth comes, it is true, to compensate the big mediocrity of the product extracted, constituted, one will see, essentially by the boart - and of the fragile enough boart, whose sales value is weak, US$2 to 3 by carat only, and even less - because overproduction in part illegal, tends to break a market already saturated.

Its primary layers of cretaceous age, or the initial accumulation of diamonds at the immediate vicinity of the kimberlites is relatively little scattered thanks to a very particular local coincidence. It gives to the group of Bakwanga its character of extreme concentration: close to one billion of carats were probably united on few square kilometres at the confluent of the Bushimaïe and the Kanshi. A new rich zone was, it is true, discovered since about thirty kilometres to the southwest.


The first diamonds were found in abundance (8,840 stones) in December 1916 by the English geologist YOUNG in the River Bushimaïe in Lukulenge downstream of Bakwanga, then more upstream. Although very rich, these layers offered less appeal for long time to FORMINIÈRE that those of the region of Tshikapa because of the lower quality of their diamonds that found few buyers. The considerable stocks of boart that had accumulated were used very quickly at the time of the 2nd World War, especially in the U.SA., and since the mines of Bakwanga took the head extensively in the world production, while achieving in 1961 the fantastic number of 18,010,568 carats.

Until 1960 the Mining of the Bécéka, subsidiary of the Railroad of the Low Congo Katanga that possessed the concessions, didn't work there herself, but through the intermediary of the FORMINIÈRE. The mines are exploited today by the MIBA (Mining Company of Bakwanga), operating company of the SIBEKA that followed the BECEKA.

Toward 1948, the works of professor DE MAGNÈE lead to a discovery of the primary deposit that was searched for in vain for years. These kimberlites were covered and surrounded of very big eluvial deposits that were explored to uncover important reserves of high-grade pay-gravel. In 1956, a new zone of pipes was found in Tshibua, about thirty kilometres to the southwest.

In 1959, the mechanization already advanced made a new jump forward. But the unrests consecutive to the independence of Congo and to the secession of the South Kasaï - which become for some time an autonomous State - provoked the massive departures of European workers and a decrease of production that seem to have stopped very soon after.

The strong structures of the big mining companies of the ex-Belgian Congo - and this one comes second behind the Mining Union of the Katanga - were more or less the only ones to have resisted (no without some damages it is true) in the middle of the storm that disrupted then this new and too vast State of Central Africa. Fortunately, it has since recovered its balance and its cohesion.

Geographical situation
Long. 23° 40' E. / Lat. 6° 10' S.
Long. 23° 30' E. / Lat. 6° 25' S.

The concessions of the Miba inherited from the of Railroad Company of BCK cover 60,000 km2 between the parallel of Lusambo (about 5°) to the north and the one of Luiza (7° 10') to the south, and the meridians of Grandjika to the east and in the Luebo to the west.
It is a region of undulating plateaus at the altitude of 700 m, drained by a dense hydrographic network.

The northwards drainage toward the Congo Basin is: to the East by the Bushimaïe River and the Luilu River, affluents of the Lubilash River that bending west as is taking the name of Sankuru then throw itself in the Kasaï River at Port-Francqui, and to the west by the Lubi River and the Lukula River that join the Sankuru River.

The country, of wooded savannah, is cultivated here and there and very populated, especially by Balubas that, with the unrests, immigrated from the Katanga or West Kasaï. In 1962, Bakwanga counted in 320,000 inhabitants, and Miabi, neighbouring centre, more of 200, 000. It means that there is no problem with men-power that is abundant and of good quality.

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Rafal Swiecki, geological engineer email contact

This document is in the public domain.

March, 2011