Abstract:

The Kakula deposit is a high-grade sedimentary-rock-hosted copper deposit (349 Mt, 3.23% at<br/>1% cut-off) closely associated with the world-class Kamoa deposit (752 Mt, 2.67% Cu at 1%<br/>cut-off) in the central African copperbelt, Democratic Republic of Congo. Copper-sulphide ore at<br/>Kamoa-Kakula is predominantly in the matrix of the Sturtian “grand conglomérat” ( 715 Ma),<br/>which is thought to have represented a redox front that was vital for copper-sulphide<br/>precipitation from oxidized metalliferous fluid. Understanding the fine-grained Kakula diamictite<br/>matrix components is critical to understanding the timing and movement of copper-bearing fluids<br/>relative to deposition, diagenesis, later alteration, and deformation of the host succession. A<br/>provisional paragenesis for the matrix has been produced and scanning electron microscope<br/>chemical analyses were used to compare composition in different stratigraphic levels and in areas<br/>of “aligned” versus “non-aligned” matrix. Diamictite deposition from subaqueous sedimentgravity-<br/>flows was followed by a protracted series of events recorded in the matrix paragenesis.<br/>In chronological order, as demonstrated by relative-dating relationships among matrix<br/>components, these events include dolomite overgrowth, diagenetic pyrite precipitation, chlorite<br/>recrystallization and replacement, copper-sulphide mineralization (chalcopyrite – bornite –<br/>chalcocite), hematization, and potassium alteration (muscovite ± biotite; K-feldspar). Finely<br/>crystalline copper-sulphide grains are ubiquitously disseminated in the matrix of the host<br/>interval, and are commonly enclosed by well-developed muscovite crystals, suggesting that ore<br/>mineralisation may have been relatively early. Compositional analyses show a decrease in copper<br/>concentration moving up-section as well as substantially lower copper concentrations in<br/>“aligned” versus “non-aligned” matrix at a given stratigraphic level. The compositional data and<br/>provisional paragenesis provide an important framework for evaluating: (a) the timing of<br/>mineralisation and possible remobilisation; (b) the influence of matrix characteristics on the<br/>copper mineralizing event; (c) the influence of the copper mineralizing event on the matrix, and;<br/>(d) the different ore characteristics at Kakula versus Kamoa.