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 Ontario Operations use conventional bulk stoping or narrow vein cut-and-fill mining methods, depending on the mine and geological setting. Mines are Owner-operated, and use conventional equipment.

Vale has technical guidelines and procedures in place to ensure that valid geotechnical data are collected and interpreted using appropriate methods, and that existing or planned risk mitigation measures that support mine designs are based on those data and interpretations. Geotechnical data collection and rock mass characterization are used to define geotechnical domains.

For each domain, ground support designs are specified that take into account geotechnical conditions, excavation service life and geometry, proximity to present and future openings, personnel exposure, local historical experiences, and local regulations. Geotechnical recommendations for vertical development, lateral development, and mining stopes, are provided. Legacy workings and drill holes with respect to mine plans are considered to ensure these hazards are mitigated.

All underground mines must have an effective Ground Control Management Plan, also referred to as the “Mine Design Package”, which is a single coherent document that must be developed through application of sound geotechnical engineering practices, conform to local mining regulations, and be aligned with Vale’s safety standards. Within the mine design package of each seismically active mine, there is a Seismic Management Plan. Five mines are seismically active at the Report effective date, consisting of the Coleman, Creighton, Copper Cliff, Garson and Totten Mines.

Either sand or mill tailings are used as a hydraulic backfill, with the type of fill materials dependent on the proximity of a mine to the Clarabelle Mill, and the availability of proximal alluvial sand sources. High-density (paste) backfill is only used at the Main zone of the Garson Mine.

Hydrological planning relies on historical norms and information. Most of the water that reports to the underground operations is from three sources: pumped in, surface runoff and ground water. A large percentage of a mine’s process water is pumped in (approximately 50–70%); about 30–50% is derived from surface depending on the season, and, other than the Garson Mine, only minor amounts are contributed from ground water.

Mines are accessed using a combination of shafts, declines, and internal ramps.

Several mining methods are used across the Ontario Operations: open stoping (longitudinal, transverse, slot–slash); post-pillar cut-and-fill; narrow vein cut-and-fill; vertical retreat; uppers retreat and mechanized cut-and-fill. Each mine has a substantial history of which mining methods work best under various geological and geotechnical conditions. This production record is considered when selecting the mining method.

The ore and waste handling system varies at each mine. Ore can be transported using load–haul–dump vehicles to a central loading area or ore pass, and then trucked to an underground crusher, from where it is hoisted to surface; or, if the mine has decline access, it is trucked to surface. Most of the waste rock is used underground as fill, although some rock hoisting of rock can occur.

Each mine has a ventilation system in place. Some ventilation circuits are shared with Glencore operations.

Each mine has a production schedule that incorporates production and cost information for each producing area within the mine, based on mineral reserve estimates. Production schedules were limited by process and infrastructure constraints such as ventilation, drift development, LHD/haulage, backfilling, and muck circuit/storage. The assemblage process activities were used to derive costs based on a combination of historical and budgeted rates. These plans were collated into an overall production schedule for the Ontario Operations. Based on this schedule, the forecast mine life is 22 years (2022–2043).

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The process plant design was based on a combination of metallurgical testwork and familiarity gained during historical processing. The Clarabelle Mill was originally built in 1971 and subsequently underwent a number of major modifications. The hourly design throughput of the plant was based on a yearly throughput of approximately 8 M tons. The utilization calculation was that the plant would operate 350 days per year, with an availability of 92%, for a net utilization of 88.2%. In 2017, the crushing plant and rod mill circuit was put on care and maintenance and the Clarabelle Mill became a SAG-only operating plant. The yearly throughput based on SAG-only operation is approximately 6.0 Mt.

At the concentrator, the ore is crushed and ground and fed to the froth-flotation cells. The multistaged froth flotation separates the sulphide minerals into a nickel concentrate and a copper concentrate. The tailings are disposed of in tailings ponds. The nickel concentrate typically aver ........