MINING:
Geology: The Skorpion ore body is unique and comprises of an oxide deposit due to intense weathering of previous zinc sulphide ore minerals. L imestone is inter-fingered with the zinc-oxides to form a very complex body. Integrated grade control is required for selective mining. The resource contains > 20 million tonnes of zinc ore at a grade of 11%, resulting in ± 2.2 million tonnes of zinc.

Survey: Pre & post the mining activities surveying is conducted to report on drill & loading plans and mining & stockpile progress.

Mining: The essential grade control requires regular liaison between Mining and the Refinery. The mine will extract on average 1,5 million tonnes of ore per annum from the open pit with 10m bench heights. A combination of blasting and hydraulic excavation is used to expose the ore for hauling with a fleet of 5x tipper trucks. The final shape of the pit is to be 1km long x 800m wide. T he entire mining fleet is maintained on site.

REFINERY: The Skorpion Zinc Refinery has several major plant sections and these are listed below:

Comminution & Tailings: There are two input streams from mining being the zinc ore and the limestone streams. Ore and limestone are fed into the crusher tip from a series of stockpiles at Mining and these tip storages are fed forward into separate crushing circuits. After being crushed to about 8mm for ore and 10mm for limestone, the ore is fed into a stacker reclaimer unit for blending purposes and limestone into a silo. From here the streams both fed forward into separate mills where it is milled to size. The products are then thickened for feeding into the leach and neutralisation circuits respectively. The residue from the Refinery process is sent by conveyor belt in a cake form to the tailings dump some 3 km away.

Leaching & Purification: The milled and thickened ore product from Comminution is sent to a leaching circuit where sulphuric acid is added to dissolve the zinc. The neutralisation circuit follows where milled and thickened limestone is added to precipitate impurities. The slurry is then thickened and the underflow solids report to the residue belt filters. Here the slurry is filtered and the remaining solution is sent back into the process. The residue belt product being a relatively dry cake is sent to the tailings dump.The thickener overflow solution containing zinc (pregnant leach solution – PLS) is fed to the solvent extraction plant as required. A Cu/Ni cementation circuit receives a portion of the PLS and using zinc dust removes contained copper. The residue belt remnant solution reports to the Basic Zinc Sulphate circuit (BZS) where BZS is formed and sent back to leach, the zinc free solution is re-used. An effluent treatment plant receives plant spillages and precipitates any metals to produce a solution for re-use in the plant.

Acid Plant: The sulphuric acid plant is a sulphur burning plant, producing two types of acid i.e. industrial and chemically pure acid. The waste heat generated from the acid plant is used to produce steam and keep the Refinery at temperature. There are also two 14MW electrode boilers to produce steam if the acid plant is down at any time.

Solvent Extraction: The PLS from the leach is treated in an aqueous/organic set of circuits through mixer settlers where the first circuit extracts the zinc from the aqueous to the organic phase. The zinc diminished solution, called raffinate, is sent back to the leach to collect more zinc. The second circuit both chemically and mechanically washes impurities out of the solution and ensures that a clean solution reports to the third stripping circuit. Here electrolyte is used to strip the zinc off the organic and into an acidic zinc solution called loaded electrolyte. HCl is used to regenerate the organics which are re-used. A reverse osmosis plant provides demineralised water.

Electrowinning: This section uses large amounts of electrical power (90MW) to plate zinc out of the loaded electrolyte solution and onto solid cathodes. The cathodes produced are of special high grade quality (99,995% pure zinc).

Cast House: The zinc cathode sheets stripped out of electrowinning are fed into melting furnaces. From here ingots or jumbo forms are cast for sale to the international markets. The zinc products are transported by truck to Luderitz where they are stored before shipment.

Technical/metallurgical services: This department provides technical focus, consultation and insight on metallurgical projects and test work. The production metallurgist will rely on the technical metallurgist for advice and consultation to ensure production is optimally met and improved upon at all times. Special test work is conducted and a comprehensive laboratory is operated on site. Metallurgical accounting is also collated here.