Metallum Resources' October 2021 feasibility study for the Superior project east of Thunder Bay, Ontario sizes a 327,600 t/y concentrator that makes copper and zinc concentrates by sequential flotation and returns all tailings underground as paste.
The Superior Zinc and Copper Project lies in north-western Ontario, about 180 km east of Thunder Bay, and Metallum Resources Inc. is redeveloping it. DRA Global prepared the NI 43-101 Technical Report and Feasibility Study with an effective date of September 15, 2021 and a report date of October 13, 2021. The recovery section draws on the Superior Lake Bankable Feasibility Study prepared by Primero for Superior Lake Resources in 2019. The processing facilities are based upon the sequential flotation of underground ore from the Pick Lake deposit to produce separate copper and zinc concentrates. The plant has a nominal capacity of 327,600 t/y at 44 dry t/h, with a plant feed grade of 0.78% copper and 16.25% zinc. Concentrates travel in sealed containers to a rail siding about 30 km away at the town of Schreiber.
Critical Data
| Parameter | Value | Unit | Notes |
|---|---|---|---|
| Annual ore throughput | 327,600 | t/y | 44 dry t/h, 85% utilization |
| Feed grade | 0.78% Cu | Not applicable | 16.25% Zn |
| Copper recovery | 78.4 | % | Concentrate grade 18.6% Cu |
| Zinc recovery | 93.9 | % | Concentrate grade 51.0% Zn |
| Crushed product | 134 | mm P80 | Third-party contractor |
| Surge bin | 440 | t | Overflow forms a dead stockpile |
| ROM pad | 6,000 | t | Up to 14 days of buffer |
| Grind | 75 | µm P80 | Closed circuit single-stage SAG |
| Copper regrind | 25 | µm P80 | Copper flotation at 34% solids |
| Zinc regrind | 38 | µm P80 | Zinc flotation at 27% solids |
| Copper / zinc filter area | 20 / 160 | m3 | Horizontal plate and frame, 75% utilization |
| Filter cake moisture | Below 10 | % | Transportable limit for copper 12% |
| Paste plant feed cake | 17 | % moisture | Paste at about 78% solids |
| Mine life | 8.5 | years | Underground |
Overview
A third-party contractor operates a mobile, modular multi-stage crushing and screening circuit. Crushed ore goes to a surge bin and a single-stage SAG mill with cyclones. The flotation circuit floats copper first, then zinc from the copper scavenger tailings, with a concentrate regrind in each. Concentrates are thickened, filtered and loaded into 20 t top-fill sea containers. Tailings are thickened and sent to a paste backfill plant, with a pump-to-TSF option if the paste plant is offline.
Key Process Stages
ROM pad and crushing
The ROM pad holds up to 6,000 t of stockpiled ore to blend feed and buffer the mine for up to 14 days of suspended mining. A contractor operates the mobile crushing and screening circuit, fed and cleared by front-end loader. Crushed ore reaches the surge bin by a conveyor with an overhead magnet that removes magnetic tramp material. A variable-speed hydraulic apron feeder withdraws ore onto the mill feed conveyor, and surge bin overflow forms a dead stockpile that the loader reclaims to feed the mill when the crusher is offline.
Milling and classification
A single-stage SAG mill reduces the crushed product to a nominal 75 µm P80, with an A*b value of 32.4. Cyclones classify, and underflow returns to the SAG mill by gravity. Cyclone overflow passes a vibrating single-deck trash screen, and the underflow feeds an agitated flotation feed surge tank, from which slurry is pumped at a constant rate to remove fluctuations in flotation feed.
Copper flotation
A conventional circuit has roughing and scavenging at 34% solids, followed by cleaning, cleaner scavenging and recleaning. The scavenger tailings are the feed to zinc flotation. A regrind mill brings the copper concentrate to a nominal 25 µm P80, which testwork showed to be optimal for maximizing copper grade while minimizing penalty elements.
Zinc flotation
The zinc circuit has roughing and scavenging at 27% solids, cleaning and cleaner scavenging, and two stages of recleaning. The regrind brings zinc concentrate to 38 µm P80 for the same reasons.
Concentrate handling
Dedicated high-rate thickeners bring each concentrate to 60% solids, and the underflow is screened before an agitated filter feed tank with 24 hours of residence time for surge capacity. Horizontal plate and frame pressure filters finish the dewatering. Each filter discharges onto a stockpile in a concentrate building with two days of storage, and a loader batch loads 20 t containers that are weighed before leaving. The site holds four days of container storage.
Tailings and paste backfill
A high-rate tailings thickener produces a 60% solids underflow, and all thickened tailings are expected to go to the paste plant. The agitated paste filter feed tank has 12 hours of residence time. Two ceramic disc filters make a cake of about 17% moisture, which a conveyor carries to a paste mixer with binder. Paste leaves the hopper at about 78% solids and is pumped underground.
Additional Interesting Data and Summary
The plant runs 365 days a year, 24 hours a day, with moderate instrumentation and automation to limit the operator requirement. The design follows well-proven and conservative practice for copper and zinc flotation. All processing equipment is new, and the flowsheet shows historical testwork and the testwork program in the report's metallurgy section.
The copper filter is sized at 20 m3 and the zinc filter, which handles the larger tonnage, at 160 m3, with copper concentrate produced at about 1.0 t/h and zinc concentrate at 12.8 t/h. Both thickeners use an assumed specific settling rate of 0.35 t/m2/h. The plant is described as a mineral processing flotation concentrator with associated services and ancillaries, designed to take run-of-mine ore from the underground mine and upgrade the copper and zinc minerals into two concentrates and a barren tail. Design copper concentrate filtration uses a specific rate of 0.085 t/m2/h.
Key Processes
- Contractor mobile crushing and screening
- Single-stage SAG milling with cyclones
- Sequential copper then zinc flotation with regrinding
- Concentrate thickening and plate and frame filtration
- Container loadout for rail transport
- Tailings thickening and paste backfill
Source: Superior Zinc and Copper Project NI 43-101 Technical Report – Feasibility Study, October 13, 2021.
