Bedrock at the Ekati Project is dominated by Archean granitoids, intruded by metagreywackes of the YK Supergroup and transected by Proterozoic mafic dykes. No younger cover sediments are preserved. Bedrock is overlain by Quaternary glacial deposits which are generally less than 5 m thick.

The 45 to 75 Ma kimberlites, part of the Lac de Gras kimberlite field, intrude both the granitoids and metasediments. The kimberlites are mostly small pipe-like bodies (surface area predominantly <3 ha but can reach as much as 20 ha) that typically extend to projected depths of 400–600 m below the current land surface. Kimberlite distribution is controlled by fault zones, fault intersections and dyke swarms.

The kimberlites are made up almost exclusively of volcaniclastic olivine-rich volcaniclastic kimberlite (VK), with lesser mud-rich, resedimented volcaniclastic kimberlite (RVK) and primary volcaniclastic kimberlite (PVK). In rare cases (e.g. Pigeon), pipes are dominated by or include significant proportions of magmatic kimberlite (MK). Economic mineralization is mostly limited to olivine-rich resedimented volcaniclastic and primary volcaniclastic types.

Diamond grades are highly variable. Estimated average grades for kimberlites that have been bulk sampled range from less than 0.05 cpt to more than 4 cpt.

Koala is mined as a sub-level/incline cave (SLC), similar to a block cave. Both Pigeon and Misery open pits have commenced production. The Lynx open pit started pre-stripping in 2015 and production is scheduled for early 2017. The Sable open pit is scheduled to start pre-stripping in 2018 and production in 2019. The Jay open pit is scheduled to start pre-stripping in 2021 and production in 2022.

The kimberlite pipes at Ekati are approximately circular in plan view and are generally located within granite, a competent host rock. The ore-waste boundary is abrupt and is readily distinguished by rock type. Ultimate vertical mining depths are 300 m at Misery, 190 m at Pigeon, 300 m at Sable, 140 m at Lynx, and 360 m at Jay.

The open pits are currently mined using conventional truck-shovel operations and are developed in benches that are typically 10 m high. The Jay pit, due to the presence of overburden and significant resedimented kimberlite, will have double bench (30 m) configuration in granite and metasediment, single bench (15 m) configuration in kimberlite, and single bench (10 m) configuration in the overburden. Sable is planned on triple benches (3 x 10 m).

The main truck loading and haulage equipment currently in use are diesel hydraulic shovel/excavators with a bucket capacity of 12 m3 and 90 t capacity off-road haul trucks. The Jay mine plan assumes 225 t capacity off-road haul trucks for ore and waste haulage. The main loading units selected for Jay were 17 m3 loaders and 34 m3 shovels.

The Koala mine was developed with sub-levels spaced 20 m apart vertically and 5 m x 5 m draw points on a 14.5 m spacing (centre to centre). The highest elevation production sub-level is located at 2050L, approximately 160 m below the base of the former Koala open pit. Ore production from the draw points is a combination of the blasted kimberlite and caved kimberlite that lies above the blasted zone through to the pit. As production proceeds, the top of the cave zone below the pit is constantly being drawn down, and the level and profile of the surface expression of the cave zone is closely monitored. Below sub-level 1850L the mine transitions to an incline cave, with the lowest production level located at 1810L.

Kimberlite is transported from the mines via a 1.37 m wide conveyor system hung via chain from the back of the conveyor ramp. The system consists of four main underground conveyor sections plus a surface “stacker” conveyor, with a transfer arrangement between each conveyor. All production mucking is carried out using load haul dump (LHD) vehicles, tramming to the remuck bays or loading 45 t capacity diesel haulage trucks. Ore is dumped into an ore pass system, and fed to a 500 t/h primary mineral sizer before loading onto the 2.4 km long conveyor system from Koala to the process plant. On surface, the radial stacking conveyor discharges to an 8,000 t surface stockpile.

The Ekati processing plant had an original design capacity of 9,000 dmt/d. Through various efficiency improvements, the current capacity and budgeted operating rate is 10,800 dmt/d with an overall equipment efficiency (OEE) of 83.4% (FY 2017). FY18 (2017) planned capacity is 11,250 tpd at an OEE of 83.4%. This will be achieved by various efficiency improvements including the screen panel change out and the introduction of the Fines DMS circuit. Further efficiency improvements are planned to achieve 12,000 dmt/d in conjunction with the Jay project.

The recovery of diamonds from the processing of the host kimberlite ore at the Ekati Diamond Mine includes (Figure 17-1):
* Primary crushing—redundancy with primary, secondary, and reclaim sizers;
* Stockpiling—used as a buffer between plant and crushing;
* Secondary crushing (wet cone crusher);
* Tertiary crushing and re-crushing for further diamond liberation;
* Sizing, de-gritting, and desanding;
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