The Ruashi ore body is a stratiform, sediment-hosted copper deposit (“SSC”) located in the Central African Copper belt. The Copper belt forms one of the world’s greatest metallogenic provinces containing over a third of the world’s cobalt reserves and a tenth of the world’s copper reserves. The Central African Copper belt is second only to the Chilean Porphyry belt in terms of copper endowment but lags significantly in terms of production.

The Ruashi copper-cobalt ore bodies are situated within a 24 km long by 2 km wide, northwest to southeast trending fold structure. The Lukuni-Ruashi Etoile trend consists of a recumbent, synclinal fold, Ruashi on the southern limb and Etoille on the northern limb. The flanks are made up of Roan rocks and the core by the Mines Group, all occurring to the southwest of a prominent regional northwest to southeast trending thrust fault. A local thrust fault dipping to the south, locates within the RAT formation immediately south of the Ruashi ore bodies. A listric fault-breccia pattern separates the ore bodies from one another.

Three ore bodies have been identified at the Ruashi Mine, namely Ruashi I, Ruashi II and Ruashi III.

Ruashi I, the largest of the three, is located in the northwest of the mining area. The lateral extent of Ruashi I measures approximately 900 m in a northwest to southeast direction and 350 m across strike. In cross-section, the oxide zone extends to approximately 130 m below surface, whilst sulphide mineralisation has been intersected to depths of more than 300 m below surface. The Ruashi I ore body terminates against a brecciated shear zone on the north-western and south-eastern edges of the pit.

Ruashi II is a smaller fragment, extending along strike for approximately 200 m and 250 m across strike. It terminates against listric shear zones to the north-west and south-east. Currently, a flat lying thrust fault terminates the ore body in depth. Exploration is planned to confirm the lack of, or existence of a mineralised ore body below the thrust fault. A large gap of approximately 200 m of brecciated Lower Kundelungu strata separates Ruashi II from Ruashi I.

Ruashi III occurs at the south-easterly end and has a strike length of approximately 650 m and a cross strike width of 200 m. Unlike Ruashi I and II, the copper orebody is buried by 30 m to 80 m of cover rocks. A HG cobalt zone or “cap” with low grade copper starts at a depth of approximately 12 m below surface in the west. Ruashi III is structurally controlled within a complex fold structure. The oxide zone extends to a depth of 300 m in the east. Drilling during the latter part of 2010 exposed malachite mineralization some 200 m beyond the previous eastern limits of the ore-body, down to depths of 300 m. Artisanal mining on Ruashi III has not been as extensive as at Ruashi I and II, and was restricted to the upper near surface cobalt zone 10 to 20 m below surface.

Oxide copper minerals at Ruashi include malachite (see Figure 3.8), chrysocolla, native copper, cuprite, cornetite and azurite. Other oxide minerals include magnetite and specularite. The dominant cobalt mineral in the oxide zone is heterogenite. Trace quantities of oxidised uranium minerals have been observed but are very uncommon.

Chalcopyrite and diginite dominate the copper minerals in the sulphide zone (up to 96%). Bornite is found in minor quantities. Cobalt sulphides in the form of linnaeite and carrollite are irregularly distributed in intimate mixtures with the copper sulphides, with sporadic abnormal concentrations. Extremely high quantities of cobalt may occur in veins dominated by cobalto-calcite. Disseminated pyrite is found in all the formations and occurs as small amorphous masses in the grey RAT (Roches Argileuses Talceuse).

Abundant pyrite mineralization occurs in the graphitic shales of the SDS zone. Chalcocite together with malachite occurs below the water table in the transition zone as replacement rims on primary bornite and chalcopyrite sulphides. Cobalt sulphides generally decrease with depth beyond the transition zone.

Ruashi Mine is an open cast mining operation and the deposit is mined by conventional open-pit mining methods using truck and excavator combinations. It has an annual production capacity of approximately 38.5 kt of copper and 5 kt of cobalt.

Ruashi I is largely mined out up to a depth of approximately 52 m below surface (1 240 amsl). The design extends another 28 m down to the 1 205 level. However, a southern pushback is planned to access additional ore at depth. The pit is accessed by a ramp from the north, with the north-western and south-eastern parts being serviced by ramps branching off from the existing northern ramp.

Ruashi II is the smallest of the three ore bodies. The design extends up a depth of 90 m below surface (1 195 amsl). The pit has a diameter of roughly 400 m on surface. A single ramp provides access to all the levels in both Pit II and Pit III. The current pit floor is 41 m below surface.

Ruashi II is the smallest of the three ore bodies. The design extends up a depth of 90 m below surface (1 195 amsl). The pit has a diameter of roughly 400 m on surface. A single ramp provides access to all the levels in both Pit II and Pit III. The current pit floor is 41 m below surface.

Ruashi III is the largest ore body with the highest overburden stripping requirement. The pit floor of phase I stripping is now at 25 m below surface and the BOMZ horizon containing HG cobalt ore is exposed in the northern portion of the pit. The pit has a designed depth of 190 m with the lowest bench on the 1 095 m elevation and is accessed by a dual ramp system. However, the poor geotechnical qualities of the weathered RAT unit on the southern pit walls preclude the presence of permanent ramps. The ramp configuration is largely a function of the separate mining stages on the southern and northern side of the pit.

The mining equipment is owned and maintained by MCK, the mining contractor. The majority of material can be loaded without drilling and blasting. Loading is carried out by diesel powered hydraulic excavators. Waste and ore is hauled by 40 t ADTs.

Ruashi Mining commenced stockpile mining operations in June 2005 for processing through the Ruashi Phase I oxide flotation concentrator plant. Phase I involved the construction of a concentrator plant to treat the oxide stockpiles that were left untreated by Union Minière and Gécamines with the concentrate being transported to the SX-EW facility owned by Sable Zinc in Zambia where copper cathode and cobalt carbonate were produced. Phase II of the project commenced in March 2007 and involved the development of the Ruashi Mine opencast orebody and the construction of an expanded crushing and milling section, the new acid leaching section and SX-EW plant for the production of copper cathode and cobalt hydroxide on site from ore mined from the Ruashi Mine orebody. Open-pit mining operations at the Ruashi Mine commenced in October 2007. Stockpile reserves were depleted and the Phase I concentrator plant was placed on care and maintenance in March 2009. All copper and cobalt have been produced from the Phase II plant since then.

At the copper plant the feed undergoes four processes: (1) leaching (copper and cobalt), (2) leach counter current decantation, (3) tailings neutralization, and (4) copper SX-EW. First, copper and cobalt metal in the ore is dissolved using sulphuric acid in a leach solution. The Metorex Group has constructed a sulphuric acid plant on site at the Ruashi Mine to produce sulphuric acid and sulphur dioxide and has commissioned the sulphur dioxide section of the plant in the first half of 2013. Solids are then separated from the leach solution using the leach counter current decantation. At the tailing neutralisation stage, the remaining acidic solution is neutralised. Copper is then extracted into a copper sulphate solution. Finally, the solution goes to the electrowinning stage, where it is electrochemically purified and produces copper cathode (LME A Grade). The copper cathode plates are then cleaned, separated and packed for dispatch.

Solution containing cobalt from the solvent extraction process is processed at the cobalt plant. Impurities such as iron and aluminium are first removed from the solution. A cobalt product is then precipitated and further purified as a result of the removal of magnesium. The resultant cobalt salt is dried, packed, and prepared for dispatch. The cobalt hydroxide produced is exported from the Ruashi Mine to Johannesburg.

The primary crusher consists of a ramp for tipping of RoM ores, vibrating grizzly, a feed-bin, a jaw crusher and feeders for discharging material.

The mill feed belt conveyor delivers the crushed ore to the Semi Autogeneous Grind (“SAG”) mill. Water is added to the mill. The milled ore then gravitates to the mill discharge sump. From the sump the mix is pumped to a bank of four cyclones (of which one is currently a stand by unit). The cyclone overflow from the mill circuit reports to the Pre-Leach-Thickener.

The Leach circuit is the first step in the refining process of copper. The aim of Copper Leaching is to leach copper and cobalt metal from the feed ore with minimal dissolution of other impurities. Sulphuric acid is used to achieve copper and cobalt dissolution.

Leaching is performed in four leach tanks arranged in series (6 hours total residence time) under acidic and reducing conditions. The optimum acidity and oxidation/reduction potential conditions in the leach tanks are maintained by the addition of sulphuric acid (to all four leach reactors) and sulphur dioxide gas (as sulphur burner gas, to the last two reactor only) respectively.

Milled ore in the form of slurry is received by the leach stock tanks from the reduction circuit. These tanks serve to hold the ore to prevent large fluctuations of feed into the leach tanks. The slurry is pumped from these tanks to the first of four agitated leach tanks. Here the slurry is mixed with sulphur dioxide (“SO2”) or Sodium meta bi-sulphate (“SMBS”) solution and acidified raffinate. Sulphuric acid dissolves the copper and cobalt, removing the metals from the solid ore and creating a leach solution. The SMBS is used as an alternative to SO2 gas.

The thickener feed tank feeds into the thickener feed well where it is mixed with flocculent. During the thickening process the solids from the leach slurry separate by gravity from the liquids. The result is that the heavier solids make up most of the underflow, which reports to the Leach Counter Current Decantation Circuit (“CCDs”). The lighter liquid fraction overflows from the thickener and reports to the Pinned Bed Clarifier where remaining suspended solids are removed. The liquid product is then stored in the High Grade Pregnant Leach Solution (“PLS”) Storage Pond.

The CCD process involves the separation of solids by way of a cascade of thickeners for continuous counter-current washing of the solids. The result is a concentrated pregnant leach solution (PLS) discharging from the cascade on the one end of the train and washed solids on the other.

Following the CCD process, residue slurry reports to Tailings Neutralisation. The aim of this process is to neutralise residue slurries and precipitate any base metals left in these slurries before disposal to the tailings dam. Slurry is received from the CCDs and as well as from the Fe/Al and Magnesium Removal processes that form part of the Cobalt circuit.

The SX process involves the extraction of copper from a leach solution.
The copper SX is arranged as a split circuit (HG SX and LG SX) in order to reduce the acid and lime requirements of the plant. The HG SX treats the bulk of the copper in solution (75%) and therefore generates large amounts of acid, which is recycled back to the leach circuit. The LG SX treats the balance of the leached copper (25%) and therefore generates lower acid tenors in its raffinate stream and is therefore suitable for sending to the cobalt circuit where the acid is neutralised.

Both the HG SX and LG SX sections comprise a two stage extraction, a one stage washing and a one stage stripping circuit. The extraction, washing and stripping equipment are conventional mixer-settlers.

The HG SX raffinate, containing ~1 200 mg/l Cu and 20 gpl sulphuric acid, is recycled to the leach circuit to make use of the free acid. The LG SX raffinate, containing ~150 mg/l Cu and ~8 gpl sulphuric acid, is forwarded to the cobalt plant.

The final step of the copper purification process is filtration of the advanced solution through Multi-Media Filters (“MMF”) in order to remove entrained organic so that an impurity-free, copper-rich aqueous solution reports to Electro-winning.

An auxiliary process in SX is crud treatment. Crud forms in the settlers for a number of reasons and it is required to be treated in order to maintain settler capacity as well as to reduce loss of organic. Crud is processed in a centrifuge and both the organic and aqueous salvaged from this treatment process are returned to the SX circuit.

Cobalt Plant.
Iron is precipitated in three reactors arranged in series under oxidative conditions using milk of lime (“MOL”) and the introduction of a dilute SMBS/air mixture with the pH profile in the reactors being progressively increased. Aluminium is precipitated in a further reactor at a higher pH. Approximately 15% of the manganese in the bleed is taken down together with the iron and aluminium. Slurry from the final reactor reports to the Iron/Aluminium Removal Thickener, where a flocculent is added.

Cobalt is precipitated using magnesia and caustic in four precipitation reactors arranged in series such that overflow from one reactor will report via gravity to the next reactor. Magnesia is added to Tank 1 at MgO:Co ratio of 1:1. Caustic is added to tanks 2 and 3. Precipitation is performed at a pH~ 8.2.