This technical report describes the process flowsheet, plant design, and ore-specific processing considerations for the Ekati Mine kimberlite processing facility in the Northwest Territories, Canada.
Report context
This NI 43-101 technical report for the Archon Minerals Limited Buffer Zone Joint Venture, Ekati Mine, Northwest Territories, Canada, is dated March 2015. The report documents the recovery methods employed at the Ekati process plant, which has been in operation since commissioning at the end of 1998 and reached full production in 1999. The plant was originally designed by Fluor Daniel Wright Signet in 1995.
Processing route
Primary Crushing
The plant flowsheet begins with primary crushing, where run-of-mine ore is fed to a dump pocket by truck or front-end loader and crushed using a primary MMD1300 mineral sizer. A second MMD1000 mineral sizer operates in parallel to meet target throughput. Run-of-mine ore is reduced to approximately -300 mm by primary crushing.
Stockpile and Secondary Crushing
A stockpile serves as a buffer between the plant and crushing operations. Secondary crushing uses a cone crusher to reduce primary crusher product to -75 mm.
Tertiary Crushing
High pressure grinding rolls liberate locked diamonds from the ore undamaged and in the critical feed size range of -75 +1.2 mm.
Scrubbing and De-gritting
Crushed ore undergoes primary and secondary wet scrubbing and screening to produce clean, suitably sized material for further size reduction (-75 +1.2 mm) and concentration by heavy media separation (-25 +1.2 mm). Primary and secondary de-gritting separates unwanted fines (-1.2 mm) from the ore.
Heavy Media Separation
Two heavy media separation modules separate washed and sized feed (-25 +1.2 mm) on the basis of density into diamond-bearing concentrate and a processed kimberlite stream. The processed kimberlite stream is discarded to the processed kimberlite stockpile area, while the diamond-bearing concentrate reports to the recovery plant.
Re-crush Loop
An optional re-crush loop allows -28+8 mm heavy media separation floats to be re-crushed with the high pressure grinding roll to further liberate locked diamonds. Automated diverter gates for on-the-fly toggling of the re-crush loop were added in 2014. The re-crush option is used when there is sufficient capacity in the high pressure grinding roll and heavy media separation circuits.
Diamond Recovery
Diamonds are extracted from heavy media separation concentrates using a combination of sizing screens, wet high intensity magnetic separation, wet X-ray sorting, drying, dry single particle X-ray sorting, grease tables, and hand sorting. Plus 1 mm recovery plant rejects are recycled to the high pressure grinding roll, while -1 mm recovery plant rejects are routed to the primary scrubbing circuit.
Product Handling
Daily drops from X-ray and grease table streams are collected and brought to the weighing room. Visual sorting is performed on +6 mm X-ray concentrate to remove non-diamond material. Every two to three days, concentrate from each stream is collected into parcels, weighed, sealed in labeled bags, and twice weekly shipped to the Sorting Valuation Facility in Yellowknife.
At the Sorting Valuation Facility, parcels are re-weighed and received into the diamond management tracking system database. The -6 mm X-ray concentrate and grease table concentrate are visually sorted using high intensity magnetic separation to aid in separating non-magnetic diamonds from magnetic and paramagnetic non-diamond material. Diamonds from X-ray streams are batched, sieved, and weighed by size fraction, while diamonds from grease table streams are batched, sieved, and weighed separately.
Fines and Coarse Rejects Disposal
The -0.5 mm slimes fraction is thickened and pumped to the Long Lake Containment Facility area. The grits fraction (-1.2 +0.5 mm) is combined with the heavy media separation processed kimberlite (-25+1.2 mm or -8+1.2 mm with re-crush loop enabled) and conveyed to a stockpile before being loaded and trucked to a coarse processed kimberlite facility.
Energy and Water
Approximately 31 MW of primary power generating capacity is available from seven 4.4 MW Caterpillar diesel generator sets. The site typically operates five generating units in winter and four in summer, with an additional four 0.75 MW auxiliary units as standby capacity. Process water is sourced from the site water reclaim system, with raw water tank capacity of 475,000 gallons, of which approximately 185,000 gallons is reserved for firefighting emergencies. Chemicals including coagulant, flocculant, and salt are used to settle material in thickeners prior to discharge.
Key reported parameters
| Parameter | Value | Basis |
|---|---|---|
| Plant design capacity | 15,500 t/d | Design specification |
| Current/budgeted throughput | 12,320 dmt per operating day (without planned maintenance) | Operating data |
| Primary power generating capacity | 31 MW | Design specification |
| Generators | Seven 4.4 MW Caterpillar diesel generator sets; four 0.75 MW auxiliary units | Design specification |
| Raw water tank capacity | 475,000 gallons | Design specification |
| Firefighting reserve | 185,000 gallons | Design specification |
| Pigeon plant feed period | 2015 through 2019 | Proposed mine plan |
| Pigeon maximum throughput (100% feed) | 12,000 dmt/day (at 1.2 mm screen) | Testwork |
| Pigeon recovery (bulk sample test) | 95.6% | Testwork |
| Jay ore processing start | 2020 | Proposed mine plan |
| Pigeon heavy mineral concentrate | 3% compared to 1.3% normal blended feed | Testwork |
| Misery processing period | 2001 to 2007, blend 10-25% of feed | Historical operating data |
Project website: https://cabinradio.ca/247508/news/yellowknife/nwt-firm-hopes-to-rapidly-turn-newly-acquired-deposit-into-mine/
Technical qualifications
The report contains the following specific qualifications regarding recovery methods. There are 17 years of production history allowing reasonable assessment of plant performance in a production setting. No data or assumptions in the Mineral Reserves mine plan are significantly different from previous plant operating experience, previous production throughputs and recoveries, or the Ekati Project background history.
The current process facilities are appropriate to the kimberlite types that will be mined from various domains outlined in the Mineral Resource and Mineral Reserve block models. The flowsheet, equipment, and infrastructure are appropriate to support the mine plans.
As there are a number of kimberlite sources being treated, the plant will produce variations in recovery due to changes in kimberlite type and domains being processed. These variations are expected to trend to the forecast recovery value for quarterly or longer reporting periods.
Granite, clay, and tramp metal content of material sent to the plant requires monitoring, and a blending strategy is typically used. Material from the Pigeon open pit will need monitoring to ensure limited impact from sediments, fines, and heavy mineral content on the plant.
Processing of the Jay kimberlite will require minor modifications to the process plant. Due to expected high clay content in the upper portion of the Jay kimberlite pipe, combined with limited blending options available during initial processing stages for Jay, plant upgrades are being considered to better handle the sticky material and expected reduction in overall process utilization.
Reagent consumptions and process conditions are based on both test work and production data. The operating costs associated with these factors in the Mineral Reserves mine plan is considered appropriate given the nature of the kimberlites to be processed. There are sufficient processed kimberlite storage options available to support the mine plans.
On-going operation of the process plant, together with additional data collected from a small bulk sample plant, has resulted in mitigation of most processing issues. The residual list of key issues that are monitored includes risks from treatment variables such as clay behaviour and material sources yet to be sampled and characterised in detail.
A sample plant located next to the process plant building is used to regularly check diamond recovery and grade control.
Source: Archon Minerals Limited Buffer Zone Joint Venture, Ekati Mine, Northwest Territories, Canada, NI 43-101 Technical Report, March 2015, Section 17 Recovery Methods.
