Ni-Cu-Co-PGE mineralisation is located at or near the base of subvolcanic mafic-ultramafic intrusive complexes referred to as the “Raglan Formation”. Resources are generally determined at a 1.5% Ni cut-off and are composed of disseminated, net-textured, and massive pyrrhotite-pentlandite-chalcopyrite rich sulphides contained within 134 individual sulphide lenses, extending from surface to more than 900m vertical depth. The size of these high-grade sulphide lenses varies significantly from 0.01Mt to 6.1Mt, averaging 0.2Mt.

Several mining methods can be encountered in underground mines. The choice of the mining method depends mainly on the mechanical properties of the bedrock. At Raglan Mine, two mining methods are used to extract the ore from lenses: the cut and fill method and the long hole method. Cut and fill mining is a selective method of mining in which horizontal cuts (slices of ore) are removed advancing upwards. Upon completion, the cut is filled back to the access ramp with backfill material, which is often composed of waste material excavated from ramps and drifts. Another drift is driven on top of the filled cut. This process continues until the top of the stope is reached.

At Raglan Mine, the cut and fill method is used at the bottom of the lens, when the dip of the lens is low and prevents the use of the long hole method. A small proportion of each lens is operated by this technique, the rest of the lens is operated by long hole method. The proportion between the two methods varies from one lens to another. It depends on the characteristics of the lens and also on the selected cut-off grade. It is important to know the proportion of each lens to be operated by each mining method given that their production rates differ greatly: the long hole mining method has a much higher production rate than the cut and fill mining method.

Mining seldom recovers all resources present in an ore deposit. The amount of ore actually extracted from a deposit is referred to as the mining recovery rate and is expressed as a percentage. In addition, a certain amount of waste is usually mixed in with the ore during mining. Waste mixed in with ore is called dilution and is usually expressed as the dilution factor. Finally, the amount of nickel in the ore cannot be recovered at 100% at the processing plant. A recovery factor at the processing plant should also be considered to more accurately estimate the amount of extracted nickel. The mining recovery rate, the percentage of dilution, and the processing plant recovery rate that we used in our MIP model were those provided by the engineering team at Raglan Mine.

As mentioned before, the stopes must be backfilled. This is because when a stope is excavated, the void left by the excavation creates pressure on the rock that surrounds it and this may cause subsidence. To do the backfilling, the engineers use waste rock from the excavation of ramps and drifts as backfill material. During a year, if more waste is extracted than ore, the surplus that is not used for backfilling stopes must be transported to the surface. Conversely, if more ore was extracted in a year, waste material stored on surface will have to be descended into the mine to compensate for the lack of backfill material. Both operations raise operational costs, and these costs must be considered in the MIP model for each year of the planning.

Raglan Mine facilities include four active underground mines, a concentrator, power plant, administrative and accommodation facilities, a fresh water supply source and fuel tanks.

The ore extracted from Raglan Mine is crushed, ground and processed on-site to produce a nickel-copper concentrate, which is then sent to the Sudbury Smelter for further processing. The concentrator treats approximately 1.3 million tonnes of ore yearly, resulting in more than 39,000 tonnes of nickel-in-concentrate annually.