The magmatic copper-nickel sulphide deposits at Sudbury are part of the Paleoproterozoic Sudbury Structure which comprises the Sudbury Igneous Complex (SIC); breccias, mudstones siltstones and wackes of the Whitewater Group which occupy the centre of the Sudbury Basin; and a ring of brecciated and shockmetamorphosed Archean and Paleoproterozoic footwall rocks which surrounds the SIC. All rocks defined as footwall to the Sudbury Structure are cut by occurrences of Sudbury Breccia. This breccia occurs as small veins, irregularly shaped patches and large, laterally extensive, crudely tabular bodies, which may extend for many kilometres along strike. The rocks of the SIC, dated at 1.85 Ga, are exposed within an elliptical or beanshaped ring with a NE-rending long axis of 60 km and a short axis of 27 km.

North Range contact-type Ni-Cu deposits occur at the base of the SIC in association with a noritic to gabbroic inclusion-bearing contact phase termed the sub-layer, and within the metamorphic textured footwall breccia/granite breccia below the sub-layer in embayment features. These deposits include the Coleman Mine (formerly McCreedy East), Main, West and East orebodies.

The sub-layer inclusions consist of footwall and mafic to ultramafic rocks with the volumetric distribution of the sub-layer controlled by the shape and morphology of the basal contact of the SIC. Sulphide mineralization within the sub-layer consists of disseminated to massive sulphide generally zoned from massive sulphide at the footwall to disseminated sulphide ore towards the hangingwall. The PGE-Au content of the contact deposits is variable but low.

The bulk of the economic North Range Ni-Cu occurs within the granite breccia. This footwall breccia consists of fragments of country rock, exotic ultramafic inclusions and rare sub-layer and mafic norite xenoliths in a metamorphic-textured quartzo-feldspathic matrix. Mineralization occurs as blebby disseminations and fragments of sulphide, veins and stringers, and as accumulations of massive sulphide within bodies of footwall breccia. A transition zone exists between the footwall breccia and non-brecciated footwall rock with the greatest amount of sulphide found at the base of the footwall breccia.

Two types of footwall deposits have been defined in the North Range. These are massive stockwork style sulphide Cu-PGE-Au deposits (Coleman Mine 153 and 170 orebodies) and disseminated low sulphide high PGE-Au zones and deposits (Coleman 148 Zone and lenses within the 153 Orebody). Footwall mineralization is highly fractionated compared to the contact mineralization and is emplaced within or near thermally metamorphosed Sudbury Breccia into dilatant fractures. A physical connection between the contact sulphide and footwall sulphide is not always preserved or recognized.

The primary mining methods used at Coleman Mine are Post Pillar cut-and-fill mining in the massive contact orebodies and mechanized cut-and-fill mining in the narrow vein footwall orebodies. For mining sill pillars in the Coleman main orebody (MOB) and the 150 orebody, Blasthole Stoping and/or underhand cut-and-fill mining methods are used.

Ore is transported from the Ontario Operations mines and third party ore suppliers by rail and/or truck to Clarabelle Mill where it is blended together. The ore is crushed and ground, with the majority of the pyrrhotite removed through magnetic separation and sent to a designated waste storage area in the Copper Cliff tailings impoundment area. The remaining ore undergoes selective flotation to produce a bulk nickel and copper concentrate grading 14% Ni equivalent and approximately 8.5% Cu and 11% Ni. The concentrate is dewatered, mixed with custom concentrate feed and high-grade silica flux and conveyed to the smelter. The rock tailings are used for mine backfill, building dams in the Tailings area, or disposed of in the Copper Cliff tailings impoundment area.

Concentrate produced from the flotation process is used to generate a high copper concentrate by depressing the pentlandite, thus allowing the copper to float. The concentrate is then filtered to produce a filter cake with approximate grades of 33% Cu and 0.4% Ni. This process currently generates ~500 tonnes per day of final marketable copper concentrate production and reduces the copper units sent to the smelter. This process also allows the Clarabelle Mill to accept higher copper to nickel ratio ores from the mines.

At the Copper Cliff Smelter, the nickel-copper bulk concentrate is dried and processed through two flash furnaces and five or six converters. The smelter produces a bulk matte, sulphur dioxide and slag. The sulphur dioxide from the flash furnaces is fixed in the Acid and Liquid SO2 Plants, and sold as sulphuric acid and liquid sulphur dioxide, while the lower-strength stream from the converters is vented to the stack. The slag from the furnaces is a waste product.

The converter matte is slow-cooled to produce a coarse crystal structure. It is then crushed, ground, and separated into metallics, nickel sulphides and copper sulphides by magnetic separation and flotation in the Matte Separation Plant.

All of the precious metal-bearing metallic, and some of the nickel oxide, are sent to the Copper Cliff Nickel Refinery. The remaining nickel sulphide is roasted in fluid bed roasters. The resulting nickel oxide is processed in the Copper Cliff Nickel Refinery or the Clydach Nickel Refinery, and a portion is marketed directly as nickel oxide sinter 75.

Copper sulphide from Matte Separation is treated in the MK reactor, where sulphur dioxide, as well as molten metal, is produced. The sulphur dioxide is fixed as sulphuric acid. Additional impurities are removed from the molten metal in finishing converters, producing blister copper and a nickel oxide residue. The small amount of sulphur dioxide evolved in the finishing converters is vented to the stack. The molten blister copper is transferred to anode furnaces and cast into anodes, which are then sold to or processed by others.

Nickel Refinery Process Description
The processes at Copper Cliff Nickel Refinery represents the final stage in the recovery of metallic products from mined ore before shipment to market. There are three main facilities at the Nickel Refinery – the Nickel Refinery Converter (NRC) Plant, the Inco Pressure Carbonyl (IPC) Plant and the Electrowinning Building.

At the NRC, feed input (nickel sulphide crudes, metallics, nickel oxides, precious metal baring intermediates and refinery intermediates) are charged into two Top Blown Rotary Converters (TBRCs), and melted using natural gas-oxygen lance burners. Once the temperature of the bath has reached approximately 1600ºC, petroleum coke is added to reduce the oxygen content of the bath (called reduction). High pressure oxygen is occasionally blown into the bath to desulphurize it if the sulphur content is too high. The melted product is transferred to a teeming ladle and poured through high velocity water jets (called granulation). The resultant granules are dewatered, dried in a gas-fired kiln and conveyed to the IPC.

At the IPC, the granules are batch-reacted with carbon monoxide at temperatures up to 180ºC and pressures up to 1000psi, in three 150-ton rotating reactors. Nickel and iron are extracted as carbonyl vapours, while copper, cobalt, precious metals and other impurities are retained in the residue. This residue is milled and pumped to the Electrowinning Plant. The carbonyl vapour is liquefied, purified in two parallel distillation columns and sent to decomposers. In the (eighteen) decomposers, nickel deposits from the carbonyl stream onto a stream of pre-heated nickel pellets. The remaining nickel carbonyl vapour is decomposed to produce pure nickel powder. The iron-nickel carbonyl is condensed, stored, re-vaporized and decomposed to ferronickel pellets.

At the Electrowinning Building, the IPC Residue is treated in an oxidative acid leach circuit to remove nickel, cobalt, iron, arsenic and other minor element contaminants. A second leaching circuit is used to dissolve copper, selenium and tellurium from the first leach solid residue. The slurry is filtered and the residue is sent to Port Colborne to extract the precious metals. The filtrate is pumped into tanks and an electrical current is applied through titanium cathodes and lead anodes. The copper plates onto the cathode over a two week period. The copper sheets are removed from the cathodes and sent to market. The first stage leach solution is fed to the iron/arsenic removal circuit and then through a copper clean-up circuit. The nickel and cobalt are precipitated from the solution with soda ash. The resultant carbonate stream is thickened and sent to Port Colborne.