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).
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:
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:
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.
Rafal Swiecki, geological engineer email contact
This document is in the public domain.