The mineral resource and reserve for the Diavik Diamond Mine consists of four diamondbearing kimberlite pipes located under water in Lac de Gras. The pipes are relatively small, each having surface expressions less than 200 m in diameter, but they are high in grade. The kimberlite pipes that underpin the present mining plan are named A154S, A154N and A418. The fourth pipe, A21, is fully permitted for mining and in November 2014 received corporate approvals to commence the stages of construction toward its development as an addition to the mine plan.

Diamonds are generally included as xenocrysts in kimberlite magma as it is formed and ascends through the upper mantle and crust. As the earth’s surface is approached, the kimberlite magma, which is rich in volatiles such as CO2, erupts explosively to form the characteristic root-shaped pipe structure. Abundant kimberlite is erupted as pyroclastic ejecta and falls both within and adjacent to the pipe. The pipe is filled with a combination of pyroclastic kimberlite, hypabyssal kimberlite, and country rock that slumped back into the pipe. At Lac de Gras, the tops of the pipes were removed by continental glaciation. The kimberlites are softer than the surrounding rocks so that depressions were formed after the glaciers retreated and filled with water to become lakes. When the pipes occur under larger lakes, such as Lac de Gras, the pipes typically lie beneath small depressions on the lake bottom.

The Diavik Diamond Mine operates 24 hours per day, 365 days of the year. Crews at this remote site are resident on site while they work 12-hour shifts for 14 days, then rotate home for 14 days of rest. Four rotating crews cover 12-hour dayshifts, 12-hour nightshifts, on-site and offsite rotation.

Mine design, planning and scheduling is based on 5 m intervals.

Benches in the two completed open pits and the future A21 open pit are 10 m high. Catchment berms in the final walls are located every three benches, and the ‘triple-benched’ 30 m walls are pre-sheared (pre-split) in a single 30 m pass. The combined A154-A418 open pit operation was designed to supply 1.5 million tonnes per annum (Mtpa) of kimberlite and exceeded this soon after 2003 start-up, peaking at 2.4 Mtpa sustained during 2006–2008. Waste-to-ore ratios were comparatively high, averaging 10-to-1 over the life of the pits. Total ore and waste mining peaked at more than 31 Mtpa and averaged between 20–25 Mtpa for most of the combined two-pit life. The A21 open pit will have a similarly high waste-to-ore ratio and is expected to deliver between 0.2 to 1.0+ Mtpa, averaging around 0.6 Mtpa, from 2018 to 2023.

Underground, blast-hole stopes are planned 25 m high and sub-level retreat stopes are also 25 m. Both mining methods take place simultaneously and multiple faces are in production from more than one level. Production ramp-up to the targeted steady-state output of 1.5–1.8 Mtpa ore took three years (2010–2012) as mine development in the granitic host rock pushed ahead to access additional ore faces. For 2013, Diavik’s first full year underground, the mine produced 1.9 Mt of ore and, with ore stockpiled from the open pit, processed 2.1 Mt. For 2014, 2.1 Mt of underground ore was mined and, with stockpiled ore, nearly 2.3 Mt was processed. Subsequent underground operating performance to the end of 2016 has been at similar levels.

For each of the pipes, pre-production stripping was carried out to remove lake-bottom sediments and glacial till (collectively referred to as overburden) that covered the bedrock and kimberlite pipe. Indistinguishable in the field and therefore mined as a single unit, the overburden was placed in a designated area so that it can be accessed and used in future for mine closure work.

Underground ore and waste is brought to surface at one of three portal entrances by underground haulage trucks and dumped on the ground in designated piles. The “portal muck” is then picked up by front-end loader and put onto surface haulage trucks (kept in service after the end of open pit mining) to be hauled either to the waste-rock dump (if waste rock) or to the ore processing plant.

Cemented rock-fill (“CRF”) is used as backfill underground. It is back-hauled into the mine (A154N only) from the nearby backfill plant by empty underground haulage trucks on their return trips.

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Diamond ore processing uses no chemicals to separate diamonds from kimberlite. The gravitybased methods used rely on the relatively heavier weight of diamonds to separate them.

Since 2015, two streams have been added to the coarse diamond fraction in recovery. In October 2014, a grease table was added to the -12 +6mm fraction that scavenged the rejects from the primary free-fall machines. In October 2016, an additional x-ray machine was installed that allowed the scavenging of the -30mm +6mm fractions (the entire range) of the primary freefall x-ray rejects.

In the recovery section of the plant, the diamonds are separated from the waste minerals using x-rays that trigger the unique characteristic of diamonds to glow. This triggers photo-electric sensors that direct strategicallyplaced air blasts to blow the diamonds into collection receptacles. Waste material is re-crushed if it is greater than a specific size otherwise the material is considered rejects and is stockpiled with a possibility to be reprocessed in future. The recovered stones then move through a series of sorters to the bottom of the processing plant where — under stringent security surveillance — an authorized employee measures and records the weight of the stones and also removes any non-diamonds.

Total recovery of all stones larger than the screen aperture has been the goal as small diamonds are economically viable for Diavik to recover. Grease tables have been incorporated into the recovery plant to support this. The screen size was 1 mm initially but has since been reduced to 0.85 mm. Nominal screen size is reported as 1 mm to provide a small allowance for wear.

The recovered diamonds are stored in a secured vault while waiting to be flown to Yellowknife for further cleaning and sorting. The diamonds are separated and packaged by size, weighed and stored in a special suitcase for shipping. The diamonds are flown discreetly but under security escort to the Diavik Diamond Mine’s product splitting facility (“PSF”) in Yellowknife where it is “split” by size and value into respective shares for the two Diavik Joint Venture entities. The PSF’s quality management system is ISO 9001 certified.