This 2023 Preliminary Economic Assessment describes a proposed 15,000 tpd copper concentrator using an SABC grinding circuit, primary and secondary flotation, two-stage cleaner flotation with columns, regrind to 20 µm, and conventional concentrate dewatering. The flowsheet design references a 1991 White Pine mill memorandum.
Report context
The PEA, effective July 12, 2023 and issued September 7, 2023, was prepared by G Mining Services Inc. for White Pine Copper LLC. The process design section (Section 17) forms the basis of this profile. The report cover identifies it as a Preliminary Economic Assessment, while internal page headers reference a Feasibility Study; this profile treats the source as a PEA. The flowsheet draws on a historical White Pine Column Cell Conversion memorandum dated 1991 from the former mill superintendent, but the PEA states that additional metallurgical testwork will be required to confirm flotation stage numbers, cell versus column selection, residence times, flowsheet configuration and reagent schemes.
Processing route
Crushing, stockpiling and grinding
Underground mineralized material is conveyed to surface and deposited into a single 4,000 live‑ton stockpile. Two apron feeders regulate feed to the SAG mill via a weight-scale conveyor. The grinding circuit is a SABC configuration: a variable‑speed SAG mill (Ø10.4 m × 5.6 m EGL, 12,000 kW) in closed circuit with a trommel screen, followed by a fixed‑speed ball mill (Ø6.1 m × 9.3 m EGL, 6,000 kW) in closed circuit with cyclones. Trommel oversize pebbles from the SAG mill are recirculated to the SAG mill feed conveyor. Cyclone overflow, at a target P₈₀ of 105 µm, passes through a trash screen and reports to flotation. Cyclone underflow returns to the ball mill. Grinding media is added via a kibble. Two vertical sump pumps serve the grinding area.
Primary flotation and secondary flotation
Flotation feed enters a rougher conditioner tank where frother and other reagents are added. Primary flotation comprises four 200 m³ forced‑air tank cells in series. Primary concentrate flows to the regrind cyclone feed hopper. Primary flotation tailings are pumped to a desliming cyclone cluster; the underflow reports to four 50 m³ forced‑air secondary flotation tank cells in series. Secondary concentrate is combined with primary concentrate at the regrind cyclone feed hopper. Secondary tailings gravitate to the flotation tails pump box. A distribution system allows stage addition of collector and frother along both flotation trains.
Regrind circuit
Combined primary and secondary concentrate is pumped to a regrind cyclone cluster. Cyclone underflow gravitates to an overflow horizontal ball mill (Ø6.1 m × 10 m EGL, 7,000 kW) fitted with a trommel screen. The regrind mill operates in closed circuit with cyclones targeting a product P₈₀ of 20 µm. Water and lime (if required) are added to achieve desired milling density and pH. Cyclone overflow reports to the cleaner conditioner tank.
Cleaner flotation (two stages)
The PEA describes two stages of cleaning, in contrast to an executive‑summary reference to three stages. This profile follows the Section 17 wording.
Regrind cyclone overflow enters a cleaner conditioning tank for additional reagent addition. First cleaner flotation consists of seven 50 m³ trough cells in series. First cleaner concentrate is pumped to the second cleaner stage. First cleaner tailings are returned to the rougher flotation circuit.
Second cleaner flotation uses a single column, 5 m diameter by 15 m high. Frother is added to the column feed box. Column concentrate is collected in a pump box and pumped to the concentrate thickener. Column tailings gravitate to a pump box and are sent to the slime cyclone cluster.
The PEA notes that the final arrangement for recirculation of cleaning streams, including recirculation of first cleaner scavenger concentrate to the regrind/first cleaner circuit and its tailings to the rougher last cells, will be determined by additional testwork.
Concentrate thickening and filtration
Final concentrate is pumped to a high‑rate thickener. Flocculant is diluted to 0.25 % w/w with process water in an in‑line mixer before addition. Thickener underflow at approximately 60 % solids w/w is pumped to an agitated filter feed tank with 12 hours surge capacity. A filter press dewaters the concentrate to a target moisture of approximately 9 % w/w using pressing and air‑blowing steps. Filter cloth is washed with raw water between cycles. Filtrate returns to the thickener by gravity.
Concentrate is discharged directly to the floor of the concentrate shed. A front‑end loader transfers it to a 542‑t storage area and subsequently to a loadout hopper. A conveyor with a weight scale loads concentrate trucks.
Tailings handling
Slimes cyclone overflow and secondary (scavenger) tailings are combined in a mixing box, sampled by an on‑stream analyzer, and then join intermittent reagent sump pump streams in the flotation tailings pump box. Final flotation tailings are pumped to the Tailings Disposal Facility (TDF).
Water and reagents
Process water is sourced from concentrate thickener overflow and TDF decant water, with raw water makeup as required. Anti‑scalant is added to the process water tank. Raw water is used for filter cloth wash, reagent makeup and cooling. Filtered decant water serves low‑pressure gland water and the on‑stream analyzer.
Reagents include:
- Frother (glycol): dosed at 0.037 kg/t (primary float feed), 0.004 kg/t (primary float mid), 0.008 kg/t (secondary float head), 0.0016 kg/t (secondary float mid), 0.003 kg/t (column cell sparger water).
- SIBX collector: dosed at 0.029 kg/t (ball mill feed), 0.037 kg/t (primary float feed), 0.009 kg/t (primary float mid), 0.009 kg/t (secondary float mid), 0.0012 kg/t (cleaner float mid), 0.014 kg/t (regrind mill feed), 0.0008 kg/t (Cu bleed conditioner). Delivered as pellets, dissolved in water. Tank ventilation removes carbon disulphide gas.
- Sodium silicate: dissolved in raw water and dosed via diaphragm pumps.
- N‑Dodecyl Mercaptan: dosed neat to the primary flotation circuit.
- Flocculant: powdered, mixed to 0.25 % w/v, then diluted to approximately 0.025 % w/v before addition to the concentrate thickener.
- Hydrated lime: not planned because the ore is essentially barren of pyrite and flotation is carried out at natural pH; space is reserved if needed.
- Anti‑scalant: dosed neat to the process water tank.
On‑stream analysis and air supply
An OSA system monitors percent solids, copper, iron and silver assays on nine process streams including flotation feed, primary/secondary/cleaner/column concentrates, cleaner and column tailings, regrind cyclone overflow, and final tailings. Cumulative shift samples are collected for laboratory analysis.
High‑pressure air (700 kPa g) is supplied by two compressors in lead‑lag configuration, dried and distributed for plant and instrument air. Rougher flotation air is supplied by two low‑pressure blowers; cleaner flotation air by two separate low‑pressure blowers.
Key reported parameters
| Parameter | Units | Value | Basis |
|---|---|---|---|
| Nominal plant throughput | tpd (dry) | 15,000 | Design |
| Plant availability | % | 92 | Design |
| Annual operating time | h | 8,060 | Design |
| Head grade (life‑of‑mine) | % Cu | 1.0 | Design |
| Head grade – silver | g/t Ag | 11 | Design |
| Crushing work index (CWi, 85th percentile) | kWh/t | 11.8 | Testwork |
| Bond ball mill work index (85th percentile) | kWh/t | 14.4 | Testwork |
| Primary grind size (cyclone overflow P₈₀) | µm | 105 | Design |
| Regrind product size (P₈₀) | µm | 20 | Design |
| Primary flotation conditioning time | min | 5 | Design |
| Primary flotation residence time | min | 15 | Design |
| Secondary flotation residence time | min | 5 | Design |
| Cleaner 1 residence time | min | 5 | Design |
| Target concentrate grade | % Cu | 30.5 | Target (design) |
| Target overall recovery | % Cu | 88 | Target (design) |
| Concentrate filter cake moisture | % w/w | ~9 | Target (design) |
| Concentrate thickener underflow solids | % w/w | ~60 | Design |
| SAG mill dimensions (EGL) | m | Ø10.4 × 5.6 | Selected equipment |
| SAG mill installed power | kW | 12,000 | Selected equipment |
| Ball mill dimensions (EGL) | m | Ø6.1 × 9.3 | Selected equipment |
| Ball mill installed power | kW | 6,000 | Selected equipment |
| Regrind mill dimensions (EGL) | m | Ø6.1 × 10 | Selected equipment |
| Regrind mill installed power | kW | 7,000 | Selected equipment |
| Primary flotation cells – number and volume | – / m³ | 4 × 200 | Selected equipment |
| Secondary flotation cells – number and volume | – / m³ | 4 × 50 | Selected equipment |
| First cleaner flotation cells – number and volume | – / m³ | 7 × 50 | Selected equipment |
| Second cleaner column – diameter × height | m | 5 × 15 | Selected equipment |
| Concentrate storage capacity | t | 542 | Design |
Project website: https://www.highlandcopper.com/projects/white-pine-north-project/
Technical qualifications
This profile is based solely on the process design section (Section 17) of the 2023 Preliminary Economic Assessment for the White Pine North Project. The PEA states that additional metallurgical testwork is required to confirm the number of flotation stages, the use of flotation cells versus columns, residence times, flowsheet configuration and reagent adjustments. The flowsheet design references a 1991 White Pine mill memorandum but does not present new pilot‑plant or locked‑cycle test results to support the selected stage recoveries, overall recovery or concentrate grade targets. The target overall recovery of 88 % and concentrate grade of 30.5 % Cu are design targets, not demonstrated by the testwork described in Section 17. The report cover identifies the document as a PEA; internal page headers inconsistently refer to a Feasibility Study. This profile treats the source as a PEA and does not claim that the proposed design represents current or historical operations.
Source: *Preliminary Economic Assessment – White Pine North Project, Michigan, USA*, prepared by G Mining Services Inc. for White Pine Copper LLC, effective date July 12, 2023, issue date September 7, 2023. of Section 17 (Process Design).
