Geometallurgy of the Tenke-Fungurume sediment-hosted copper-cobalt district, D.R. Congo

This paper presents and analyzes the geometallurgy of ores at the Tenke-Fungurume district, a major global source of Cu and Co. Ores at depth are mainly Cu, Cu-Fe, and Cu-Co sulfides (chalcocite group, chalcopyrite, bornite, carrollite, pyrite) hosted in variably silicified dolomite and shale layers. Within roughly 200 m of the surface the sulfides are overprinted by malachite, heterogenite, brochantite, pseudomalachite, and chrysocolla. A mixed zone at intermediate depth contains metals as cobaltoan dolomite, sphaerocobaltite, cuprite, and native copper in addition to sulfides and oxides (sensu lato).

Geometallurgical properties are highly variable and anisotropic due to the wide unit-to-unit variation in lithology and alteration. Average crusher work index varies from 6.3 to 8.6 kWh/t across units. Average grinding Bond work index ranges from 10.8 kWh/t in the basal argillaceous conglomerate to 15.4 kWh/t in the overlying, variably silicified dolomitic shales. In these dolomitic shales, both work indices correlate strongly with rock uniaxial compressive strength. The same correlation is present in an unlaminated silicified algal dolomite, in which abrasion index also correlates with quartz content. There are no other observed correlations among comminution characteristics, geomechanical properties, and mineralogy.

Flotation tests show average recoveries of 87% Cu and 61% Co in the sulfide stage, 61% Cu and 40% Co in the oxide stage. Highest recoveries came from the variably silicified dolomitic shales, the lowest from the extremely phyllosilicate-rich basal unit. The main losses in flotation are of oxide minerals and some chalcocite. Apart from the rejection of cobaltoan dolomite, most flotation problems are due to muscovite, biotite, and chlorite, which report to concentrate and may cause sliming and other sources of loss.

Leach test recoveries for Cu and Co show strong inverse correlations with the fraction of metal hosted in sulfides. Oxide-dominated ores are generally 80–90 % leachable, with Cu recoveries < 20 % for primary sulfides other than chalcocite. In leach testing, Co recoveries exceed Cu recoveries in the same samples, though ultimate Co recovery in practice is lower due to more locking and minor Co hosted in insoluble chlorites. Acid consumption is a function of dolomite concentration and varies from a low of 226 kg/t in a slightly dolomitic shale to a high of 435 kg/t in a laminated dolomite. Acid consumption by other gangue minerals is undetectable over the timescale of testing.

Ores are divided into one of six types at the mine: sterile; leached; oxide; sulfide; oxide-dominant mixed; and sulfide-dominant mixed ores. The first two of these are below cutoff grade and contain few or no Cu or Co minerals. Higher-grade material is subdivided into the last four categories based on results from quick-leach testing and 1-hour acid-soluble Cu analysis, along with logged mineralogy. Overall, the main controls on geometallurgical behavior are (1) depth below surface, which influences grade and determines ore mineral type and leachability, and (2) rock type, which affects comminution and flotation characteristics and acid consumption. Many of the results highlight the need for geometallurgical characterization to include as much textural and geological information as possible to aid in correlating geological features with metallurgical outcomes.