Insights from 3-D Structural and Lithological Geomodeling of K.O.V. Mine, Kolwezi Region, Democratic Republic of the Congo: Olistostromes in an Evolving Lufilian Arc Foreland Basin

Abstract

The Kolwezi area of the Democratic Republic of the Congo hosts world-class stratabound Cu-(Co) and U-(± Cu-Ni-Co-Pb-Zn) mineralization within large fragments (écaille) of Lower Roan Group units that are hosted in the regional Roan breccia. Long-debated genetic models for the development of these types of deposits include the development of tectonic mélanges, friction breccias, sedimentary mélanges, olistostromes, and halokinesis or salt tectonics. Compiled historical data and new data at K.O.V. mine, which is an amalgamation of the Kamoto-East, Oliveira, and Virgule mines, situated in the Kolwezi “klippe” or subbasin, has been reanalyzed and used in the construction of a new, fully constrained, implicit 3-D model of lithologies and major structures. This data, which spans approximately 80 years, includes diamond and reverse-circulation drilling, new structural and lithological mapping data, downhole televiewer data, and macrostructural logging. In-pit observations, combined with these new, fully constrained, implicit 3-D models, provide new insights into the geometry and genesis of these deposits and their encompassing volume. The Kolwezi subbasin, characterized by K.O.V. mine, resulted from gravity-driven mass transport processes, concomitant with sedimentary deposition within a progressively folded foreland basin during orogenesis. The final geometry of fragments is due to (1) features that were inherited from the fold-and-thrust belt in the hinterland; (2) features caused by incorporation and dismemberment of fragments throughout a regional Roan breccia, as they were shed into the foreland basin; and (3) large-scale juxtaposition and impingement of fragments, complicated by late-kinematic tightening of the Kolwezi subbasin, further dewatering of the pile, and possibly further remobilization of fluids and metals. Collectively, these features, typified by K.O.V. mine, indicate that the Kolwezi subbasin, the Tombolo subbasin, and book similar regions in the foreland constitute the localized, preserved remnants of an olistostrome that was deposited within a previously much larger foreland basin, ahead of an advancing, thin-skinned fold-and-thrust system, and against the Nzilo block on the western margin of the Lufilian arc.