Comparative Study of the Kimberlites of Bakwanga (North Group) and Bakwa-Kalonji (South Group) In East Kasai, Democratic Republic of Congo.

Abstract

The presence of kimberlites in the Democratic Republic of Congo has been known since buttgenbach reported a typical ‘yellow ground’ in Katanga as early as 1908, and prospecting work before and after 1914 had already identified twenty-four pipes in the province. In eastern Kasai, the local Kimberlite, which crosses the entire Precambrian (Socle and its overburden) as well as the sandstone Mesozoic and is covered by the Tertiary, is found in two groups, namely the Northern Group, also known as the Bakwanga Kimberlites, and the Southern Group, known as the Bakwa-Kalonji Kimberlites. With the same age, dated to the Cretaceous and quantified at 71.3 million years, a comparative scientific study of the two groups of kimberlites in East Kasai is of interest in order to gain an insight into the primitive magmatism that created them. To this end, we have set ourselves the objective of taking stock of geochemical knowledge of the Bakwanga and Bakwa-Kalonji kimberlite massifs (accessible to our sampling) in order to better interpret and compare, from a petrological point of view, the genesis, composition and nature of these kimberlite intrusions.Based on our studies, we found that the Kimberlitic formations studied (Bakwanga and Tshibwe Kimberlite) are all characteristic of ultrabasic (or silica-undersaturated), mafic and not ultramafic, hyperalkaline, ultrapotassic, volatile-rich (H2O and CO2) magmatism of the lamproite or orangite group, showing clear crustal alteration or contamination and originating in the upper mantle. These two groups differ in terms of the lithology of the host rock (limestone and/or dolomite for the northern group and sandstone for the southern group). In terms of the proportion of xenoliths in the respective kimberlites, there is a total absence of sedimentary xenoliths, particularly limestone and dolomite, and incidentally sandstone, in the southern kimberlites. Gabbro-dioritic xenoliths are more abundant in the southern group than in the north, and xenoliths from basement rocks are more abundant and dominant in the north than in the south.)