This report presents the proposed process plant design for the Arctic Project, updated from the 2020 Arctic Feasibility Study Technical Report (2020 FS) and based on verification testwork conducted by ALS in 2022 and process optimization using Ausenco's benchmark database.
Report context
This technical report is dated January 20, 2023, and is titled "NI 43-101 Technical Report on Feasibility Study" for the Arctic Project. The report documents a feasibility study for the processing of MS and SMS ores from the Arctic deposit, hosted in the Ambler Sequence within a volcanogenic massive sulphide (VMS) belt. The deposit mineralisation occurs as stratiform SMS to MS beds within graphitic chlorite schists and quartz mica schists.
Processing route
Overview and Plant Configuration
The process plant design is based on a robust metallurgical flowsheet developed for optimum recovery. The plant will operate two 12-hour shifts per day, 365 days per year, with an overall plant availability of 92%. The process will produce three concentrates: copper concentrate, zinc concentrate, and lead concentrate. Gold and silver are expected to be payable at a smelter and are recovered in both the copper and lead concentrates.
Due to significant levels of talc contained in the mined materials (2.92% in the plant feed), a talc flotation circuit is required to remove the mineral before base metal flotation.
Crushing and Grinding
Run-of-mine ore will be trucked to a crushing station and dumped into a 200-t receiving bin protected with a 1,000-mm-aperture stationary grizzly. Ore will be reclaimed with an apron feeder and scalped of fines with a 75-mm-aperture vibrating grizzly. The grizzly oversize will pass to a primary jaw crusher operating with a closed side setting of 100 mm. Crushed material together with grizzly undersize, with a P80 of 80 mm, will be conveyed to a single covered conical coarse ore stockpile with a live capacity of 5,000 t and total capacity of approximately 20,000 t.
The grinding circuit will consist of a SAG mill followed by a ball mill arranged in closed circuit with a hydrocyclone cluster (SAB configuration). The SAB circuit will reduce the crushed ore particle size from a P80 of 80 mm to 70 µm. The SAG mill will be a grate discharge type with 12 mm apertures and no pebble ports. The nominal feed throughput of the circuit will be approximately 453 t/h.
Talc Pre-Flotation
The ball mill hydrocyclone overflow will feed the talc rougher circuit, composed of rougher and cleaner flotation stages. The rougher flotation will be performed in conventional forced-air cells and the cleaner flotation in a Jameson cell. The talc cleaner concentrate will be pumped to final tailings.
Bulk Copper-Lead Flotation and Regrinding
Talc pre-flotation tailings will be pumped to copper/lead bulk flotation conditioning tanks where copper and lead mineral collectors will be added. Conditioned slurry will undergo rougher flotation in conventional tank flotation cells. The bulk rougher concentrate will be reground in a 600 kW regrind ball mill configured in reverse, closed circuit with hydrocyclones, reducing to a particle size of 80% passing 40 µm. The reground concentrate will be further upgraded by two stages of cleaner flotation. The 1st bulk cleaner and cleaner scavenger flotation will be conducted in conventional tank cells. The 2nd bulk cleaner flotation will be performed in a Jameson cell.
Copper and Lead Separation
The bulk 2nd cleaner concentrate will be pumped to the copper-lead separation flotation conditioning tank, where sodium cyanide and lime will be added to suppress copper minerals. Lead flotation will be conducted at a pH ranging from 9.0 to 9.5. The lead rougher concentrate will be further upgraded in three stages of cleaner flotation to produce the final lead concentrate. Tailings from the 1st cleaner flotation will be combined with tailings from the lead rougher flotation to produce the final copper concentrate.
Zinc Flotation and Regrind
Copper-lead bulk rougher tailings and copper-lead bulk cleaner scavenger tailings will be processed to recover zinc. Tailings from the copper-lead flotation circuit will be conditioned with lime (to a pH above 10.5, to depress pyrite) and copper sulphate (to activate zinc minerals). Zinc rougher concentrate will report to a regrinding circuit with a 355 kW regrind ball mill configured in closed circuit with hydrocyclones. The zinc concentrates will be reduced to a particle size of 80% passing 40 µm. The zinc cleaner circuit will operate at a pH of 11 or above to reject pyrite, with two stages of cleaner flotation. The 2nd cleaner flotation will use a Jameson cell.
Concentrate Dewatering
Copper, lead, and zinc concentrates will report to separate high-rate thickeners. Thickened slurries will be dewatered using pressure filters to a design moisture content of 6%. Two identical tower press filters are recommended: one common unit for lead and zinc concentrates dewatering, and another unit dedicated to dewatering the copper concentrate.
Tailings Disposal
Final flotation tailings consist of the talc flotation concentrate, zinc rougher flotation tailings, and zinc cleaner scavenger flotation tailings. These will be directed to a 32 m diameter high-rate thickener. Thickener underflow with a solid density of 47% will be pumped to the tailings storage facility. Thickener overflow will be delivered to the Process Pond for distribution to the plant.
Reagent Handling
Various chemical reagents will be added to the grinding and flotation circuits. Reagents include sodium isopropyl xanthate (SIPX), collector 3418A, MIBC frother, lime, flocculant, sodium cyanide, sodium metabisulphite (SMBS), zinc sulphate, and copper sulphate.
Power and Water Supply
Plant power will be generated on site using diesel generator sets, with four operating and one on standby. Each generator will be rated 13.8 kV, 5.5 MW, with a total power output capacity of 21.6 MW excluding the redundant unit. The total connected load for the plant will be 25.9 MW with a normal operating load of 21.0 MW.
Three separate water supply systems will be provided: a fresh water system, a Waste-Rock Control Pond (WRCP) water supply system, and a process water supply system. The total water usage for the process plant is 42,240 m³/d.
Key reported parameters
| Parameter | Unit | Value | Basis |
|---|---|---|---|
| Plant Design Capacity | t/a | 3,650,000 | Design |
| Plant Design Capacity | t/d | 10,000 | Design |
| Operating Availability – Crushing | % | 65 | Design |
| Operating Availability – Grinding and Flotation | % | 92 | Design |
| Operating Availability – Concentrate and Tailings Filtration | % | 84 | Design |
| Process Plant capacity, nominal @ 92% availability | t/h | 453 | Design |
| ROM Specific Gravity | – | 3.25 | Design |
| Plant Feed Grade – Copper, Design | % | 3.00 | Design |
| Plant Feed Grade – Lead, Design | % | 0.74 | Design |
| Plant Feed Grade – Zinc, Design | % | 4.20 | Design |
| Plant Feed Grade – Gold, LOM Average | g/t | 0.47 | Design |
| Plant Feed Grade – Silver, LOM Average | g/t | 35 | Design |
| Plant Feed Grade – Talc, LOM Average | % | 8 | Design |
| Crushing Feed Size, 80% Passing | mm | 504 | Design |
| Crushing Circuit Product Size, 80% Passing | mm | 80 | Design |
| Bond Ball Mill Work Index, Design | kWh/t | 11.6 | Design |
| Bond Abrasion Index, Design | g | 0.038 | Design |
| A x b, design | – | 109 | Design |
| Grinding Circuit Product Size, P80 | µm | 70 | Design |
| Regrinding Circuit Product Size, 80% Passing – Bulk Rougher Concentrate | µm | 40 | Design |
| Talc Pre-Flotation Stage Recovery to concentrate, mass | % flotation feed | 21.5–25.7 | Testwork |
| Talc Pre-Flotation Stage Recovery, talc | % | 88.6 | Testwork |
| Copper-Lead Bulk Rougher Stage Recovery to concentrate, mass | % flotation feed | 12.7–15.0 | Testwork |
| Copper-Lead Cleaners Stage Recovery, Copper | % | 92.1 | Testwork |
| Copper-Lead Cleaners Stage Recovery, Gold | % | 52.0 | Testwork |
| Copper-Lead Cleaners Stage Recovery, Silver | % | 32.5 | Testwork |
| Lead Cleaners Stage Recovery, Lead | % | 61.3 | Testwork |
| Lead Cleaners Stage Recovery, Gold | % | 21.6 | Testwork |
| Lead Cleaners Stage Recovery, Silver | % | 48.6 | Testwork |
| Zinc Cleaners Stage Recovery, Zinc | % | 88.5 | Testwork |
| Zinc Cleaners Stage Recovery, Gold | % | 3.3 | Testwork |
| Zinc Cleaners Stage Recovery, Silver | % | 5.7 | Testwork |
| Total connected load | MW | 25.9 | Design |
| Normal operating load | MW | 21.0 | Design |
| Total water usage | m³/d | 42,240 | Design |
Project website: https://trilogymetals.com/properties/arctic/
Technical qualifications
This report presents a feasibility study design. No historical operating data are available as the Arctic Project has not yet been constructed or operated. All process design criteria for the flotation plant were determined from testwork conducted by ALS Metallurgy, described in Section 13 of the original report. The process plant design is updated from the 2020 Arctic Feasibility Study Technical Report (2020 FS) by considering verification testwork conducted by ALS in 2022, along with process optimization based on Ausenco's benchmark database. The report does not include actual plant performance data, as the facility is in the design phase. No information on project economics, ownership, current status, or external links is included in this processing overview.
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Source: Arctic Project, NI 43-101 Technical Report on Feasibility Study, January 20, 2023, Sections 17.1–17.5.
