The Renard kimberlites were emplaced into granitic and gneissic host rocks, and contain diamonds of economic interest. The bodies comprise a late Neo-Proterozoic to Cambrian kimberlite field in Québec (Girard, 2001; Moorhead et al., 2002; Letendre et al., 2003).

To date, nine kimberlite pipes have been identified over a 2 km2 area in the Renard Cluster (Renard 1 to Renard 10; with Renard 5 and Renard 6 forming one body, referred to as Renard 65). The kimberlite pipes are typically spaced between 50 m and 500 m from each other. Geophysical data and drill information from delineation and bulk sampling programs indicate that, in general, most of the Renard kimberlites are irregular and elliptical in plan view. Surface areas of the kimberlite portion of the pipes range from 0.1 ha to 2.0 ha. Two laterally extensive kimberlite dyke systems, known as the Lynx and Hibou dykes, have been identified to the west and northwest of the pipe cluster, respectively (Figure 7.3). Portions of both dykes are included in the mineral resource estimation. Additional dyke like kimberlites have been discovered elsewhere on the property. These are not included in the mineral resource estimation but may warrant additional work at a later date.

A mine plan has been developed to extract the Indicated Mineral Resources of the Renard Project. The Renard 2 and Renard 3 kimberlite pipes will be mined through a combination of open pit and underground mining methods, whereas the Renard 65 kimberlite pipe will be mined by open pit mining method only and the Renard 4 pipe will be mined by underground method only. Open pit and underground Mineral Reserves were estimated independently based on criteria specific to each method.

The Renard 2 and Renard 3 open pit excavations result in a single pit at surface with two pit bottoms centered on the respective orebodies. The excavation is therefore treated as a single pit and is referred to as the R2/R3 OP.

The underground mine will be developed while mining the R2/R3 OP, and following its depletion, the underground mine will be extended to surface through the pit floor.

Waste rock from the open pit will be placed into the Renard 2 and Renard 3 underground stopes via the open pit to provide support for the stope walls during mining. Waste Waste material to support the Renard 4 underground stopes will be backfilled through backfill raises from surface.

Four underground mining methods were shortlisted and evaluated, including blasthole shrinkage (BHS), sublevel retreat (SLR), long hole panel mining with backfill (LHP), and blasthole shrinkage with pillars (BHSP). Based on this study, the blasthole shrinkage (BHS) mining method was selected to mine the underground portions of the Renard 2, Renard 3 and Renard 4 kimberlite pipes.

The BHS method consists of drilling and blasting the ore with long large-diameter blastholes, and extracting the ore at the base of the stopes from drawpoints. During the blasting phase, ore is left in the stope to support the walls until the complete stope has been blasted. Since ore expands when blasted due to the voids in the broken rock, it is necessary to draw out this swell on an ongoing basis, approximately 35% of the total in situ ore. Thus, with this method, there is a continual supply of ore production throughout the blasting period, and once the blasting is complete, the remaining broken ore can be drawn from the stope – generally at a very high rate with few restrictions.

With the BHS method, the kimberlite in a panel is blasted in successive vertical lifts over the height of the panels, in a benching fashion. One or two slot raises will be excavated over the height of the stope to provide initial free faces from which to initiate the blasting. These slot raises will be excavated during the drilling phase using a “Machine Roger” ITH drill head attached to an ITH drill rig. While the panel is being blasted, sufficient blasted ore will be left in the stope (shrinkage) to provide support to the walls and limit the extent of sloughing or caving from the back if that should be experienced.

The blasting and production phase will start by blasting the undercut drawcones from the drawpoint level and advance in a retreat blasting and mucking sequence. After each blast, sufficient ore will be drawn (mucked out) to provide for a free face and ample void before proceeding with the next blast. The blasting strategy will be to blast out the drawcones below each panel before beginning the blasting of the downholes.

The downholes are typically 60 m long, drilled from the drill level above. Blasting will be done by vertical benching, initiated towards a central slot raise, in vertical lifts. Following each blast, the blasted ore will be mucked out from the drawpoints below, until the void or gap at the top of the blasted ore to the back is sufficient for choke blasting the next lift. During the blasting phase, 35% of the ore will be drawn from the stope through drawpoints to accommodate the swell of broken ore.

Once the crown pillar of the North panel of the 290 mining zone is blasted, the Renard 2 pipe will be open to surface and, at this point, production mucking in this panel can be ramped up to the full production rate. As blasting of the other panels progresses towards the South, the opening in the pit bottom will get bigger until the crown pillar of the last panel is blasted.

As the blasting inside the South panels of 290 Lis nearing completion, the blasting sequence can progress in the North panels of the 470L. The mass blasting of the 470L mining zone residual pillar (pillar below the 290L drawpoint level) will include not only the pillar, but also the underside of the drawpoint troughs on the 290L. Detailed modelling will confirm the thickness of the pillar to be kept in situ between the above mucking horizons and the blasted stope below. Mucking directly above the panel will have to be completed before the sill/crown pillar of the panel below can be removed. After this blast, the drawpoints on 290L will have been destroyed and mucking from the North panel on 470L can be ramped up to full production. This sequence will be repeated for each individual panel as mining progresses towards the South on this level. The blasting sequence on 590L and 710L will be the same as on 470L.

The process plant design capacity is 2,160,000 tpa (dry solids basis). The plant overall utilization is estimated to be 78%, equivalent to an operating time of 6,833 hours per year or 315 tph and 6,000 tpd. Stornoway expects to increase the plant throughput to 323 tph, already within initial plant equipment capacity, and increase the plant availability to 83.5% by optimizing plant maintenance sequences. Once the plant achieves sustainable nameplate throughput, further optimization work will be conducted focusing on liberation, diamond breakage and increasing the overall plant utilization. The ore processing system will liberate, concentrate and recover diamonds from 45 mm to 1mm. Taking the above into consideration by July 2018, Stornoway expects the plant will operate at a throughput of 7,000tpd at an overall plant utilization of 83,5%.

The ore processing system will liberate, concentrate and recover diamonds from 45 mm to 1mm.

Once the plant achieves sustainable nameplate throughput, further optimization work will be conducted focusing on liberation, diamond breakage and increasing operating plant utilisation.

Liberation design will use stage crushing where each crusher will operate with a large crushing gap to protect against potential diamond breakage. ROM material will be crushed, washed and sized at various stages to produce -45 mm ore, before all liberated diamonds are recovered within either a Dense Media Separation (DMS) or Large Diamond Recovery (LDR) concentration process. All rejected material larger than 6 mm from these processes is re-crushed within a High Pressure Grinding Roll (HPGR) crusher to maximize the liberation of trapped diamonds. The HPGR product is then returned to the scrubber circuit to wash and de-agglomerate the HPGR product. The HPGR promotes interparticle crushing used for tertiary crushing and is the principal diamond liberator generating a product size of 60% smaller than 6 mm. The majority of the unwanted fines (-1 mm) are separated from the ore in these circuits and then pumped to the thickening circuit for dewatering.

A surge bin with a capacity of 240 tonnes decouples the DMS from the ore preparation circuit. The process plant will produce a DMS and LDR concentrate which will be treated in a secure diamond recovery facility that uses diamond differentiation techniques based on magnetic, X-ray, laser Raman and ultra-violet technologies, with hand sorting as final de falsing step to produce a nominally 98% diamond product.

Recovered diamonds will be processed through the cleaning facility and then prepared for valuation within the recovery facility. The diamond plant is expected to have a diamond recovery efficiency of not less than 97% by mass and 99% by value of liberated diamonds. Liberation design uses three stages of crushing where each crusher operates with a large gap to protect against diamond breakage. Primary crushing is performed by a jaw crusher, which reduces the size of Runof-Mine (ROM) ore to less than 220 mm. Secondary crushing is performed by a cone crusher to reduce ore to less than 45 mm.

Two 200 tph DMS circuits concentrate -19/16 +1 mm feed by separating liberated diamonds and heavy minerals from lighter kimberlite and waste constituent minerals, in a density controlled ferrosilicon medium. DMS rejects are sized into two streams; -19/16 +6 mm, which is combined with fresh feed reporting to the HPGR, and the -6 +1 mm, which is mixed with dewatered fines and discarded as dry stackable material to the processed kimberlite containment area.

Concentrate surge bins with a capacity of 60 tonnes decouples the recovery plant from the DMS circuits. The recovery plant is capable of processing at a maximum rate of 7.2 tph.

Concentrate fed to the recovery plant is sized into 3 size fractions, -3+1mm (fines), -8+3mm (middles) and -19/16 +8mm (coarse). The fines and middles size fraction are fed to a two stage magnetic separation stage. The non magnetic material will then be sent via jet pump to the two stages of X-ray sorting and the magnetic material will flow to the rejects sump. X-ray concentrate is stored prior to the reconcentration circuit where the concentrate will be dried and fed to the Recon X-ray machines. The concentrate from the Recon X-ray will then be transfered to the Raven single particle sorting machines. The “super” concentrate (98% diamond by weight) will then be transferred to the sorthouse for further de falsing. The rejects from the Recon X-ray, Raven and sorthouse (waste) will be collected and sent through to the auditing stream (scavenging) and processed through an UV Osprey machine. The coarse size fraction will transfer directly to a two stage X-ray sorting stage. The concentrate will transfer directly to the sorthouse and the rejects will be transferred and combined with the fines and middles rejects at the rejects sump. The recovery rejects will be jet pumped to a tails screen where the coarser fraction (-45+8mm) will be sent to the HPGR for further liberation and the -6+1mm will combine with the DMS tails for PK disposal.

Final diamond recovery is achieved by hand sorting diamonds from waste in a secure glove box, located within the sorthouse in the recovery plant. The diamonds will be chemically cleaned before preliminary valuation and export.