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-trending long axis of 60 km and a short axis of 27 km.

The rocks of the Sudbury Structure, and specifically rocks of the SIC and Whitewater Group, are affected by several fault sets and by ductile and brittle deformation associated with these faults. The Sudbury Structure is cut by a number of regional and local mafic dyke swarms. Archean footwall rocks on the North Range are crosscut by north-south trending dykes of the ~2.454 Ga Matachewan swarm.

Northwest-trending olivine tholeiitic dykes of the Sudbury swarm, dated at 1.238 Ga, crosscut the SIC and all rock units within and surrounding the Sudbury Structure.

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 exceptions being at the Quadra FNX Mining Ltd. McCreedy West Mine and the Xstrata Nickel Strathcona Mine.

South Range contact-type Ni-Cu deposits are similar to those of the North Range. They occur at the base of the SIC in the sub-layer and include the Creighton Mine and Stobie Mine orebodies, Murray Mine Main Orebody and the Blezard Main Orebody. The South Range Footwall Breccia underlies the sub-layer and is derived from melanocratic metasedimentary rocks and metavolcanic rocks. Ni-Cu mineralization occurs as disseminated to massive sulphide within the sub-layer. These deposits are generally zoned from massive ore at the footwall to disseminated sulphide ore toward the hangingwall. The PGE-Au content of the contact deposits is generally low. Similar to North Range contact deposits, Ni-Cu mineralization occurs within bodies of footwall breccia with minor amounts of quartz diorite. Massive sulphide Cu-PGE-Au footwall mineralization is also found in the South Range deposits but is not abundant (Creighton Mine).

Significant economic Ni-Cu-PGE-Au mineralization occurs within quartz diorite offset dykes at Copper Cliff Mine offset orebodies and the Totten Mine orebodies. They can extend for many kilometres into the Sudbury Structure wall rock, and may be radial or concentric to the contact of the SIC with distinct, sharp contacts. Quartz diorite is the main component of South Range offsets, and of distal (>3 km from sic contact) portions of North Range offsets. Footwall breccia also occurs here as sheets and discontinuous lenses concentrated along the lower contact of the SIC, and as a major component of some of the offset dykes.

Mineralization consists of zones of disseminated blebby and massive Ni-Cu-PGE-Au sulphide that is spatially associated with inclusion-rich phases of quartz diorite, as well as with local structural complexities of the dykes. Ni-Cu-PGE-Au deposits have longer dip lengths then strike length and contain at least 5% sulphide. Areas between orebodies consist of barren quartz diorite or weakly mineralized inclusion-rich quartz diorite.

The mining methods used at the Ontario Operations include cut-and-fill mining (CAF), mechanized cut-and-fill mining (MCAF), underhand cut-and-fill mining (UCAF), Post Pillar CAF (PPCAF), Sublevel Cave (SLC), Blasthole Stoping (BS), Vertical Retreat Mining (VRM) and Uppers Retreat Mining (URM). Underground mining is composed of both remnant pillar extraction in older mining blocks and new mining zones.

The underground mining method selection is based primarily on deposit geometry but also on a number of other factors including available infrastructure, geotechnical constraints and experience at the mine. The primary mining methods used at Coleman Mine are PPCAF in the massive contact orebodies and MCAF in the narrow vein footwall orebodies. For mining sill pillars in the Coleman main orebody (MOB) and the 150 orebody, BS and/or UCAF methods are used. The Copper Cliff Mine uses VRM, BS (slot-slash variation) for the bulk of the production. Sill pillars are recovered using URM. The Copper Cliff Mine LOMP also makes provision for limited use of MCAF. Creighton Mine employs BS (slot-slash variation), URM and MCAF mining methods. The primary mining methods used at Frood and Stobie mines are SLC, VRM and URM. Garson Mine uses slot-slash variation and URM mining methods. The mining methods planned at Totten Mine include VRM, URM, BS and MCAF.

"We plan to cease processing Voisey’s Bay feed in Sudbury during the year of 2017.

In the second half of 2017, we will convert our two-furnace operation in Sudbury into a single furnace. As a result of this change, we expect to increase the proportion of production of copper concentrate to total copper production from the current rate of 45% to 70% in 2017 and to 80% in 2018, maximizing the smelter capacity for nickel. In addition, we plan to cease production of copper anode and increase production of copper matte. By 2018, we expect that about 10% of our copper production will be sold in the form of copper matte. We plan to renovate one of the operational furnaces from March 2017 to June 2017, followed by the immediate decommissioning of the other furnace. The rebuilt furnace will have its capacity increased, but due to the single furnace operation, the overall production of refined nickel and copper in the long term will decrease by approximately 30%."

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