Metallurgical testwork and flowsheet design for the Marathon Project support a split copper-PGM flotation circuit with fine grinding and multiple cleaning stages, processing 5 Mtpa in years 1–5 and expanding to 8 Mtpa from year 6 onward.
Report context
The Marathon Property Pre-Feasibility Study (PEA) technical report was prepared by P&E Mining Consultants Inc. for Generation Mining Limited and is dated 2019. The report presents a process plant design based on extensive bench-scale metallurgical testing conducted over several years at multiple laboratories, including crushing, grinding, batch, cycle, and mini pilot-scale froth flotation testing. The most recent tests focused on confirming circuit stability, maximizing concentrate grade, and representing a split Cu-PGM flowsheet with fine grinding and multiple cleaning stages in each flotation circuit.
Processing route
Primary crushing and stockpiling
Run-of-mine mineralized material is hauled by 221 t haul trucks from the open pit and dumped directly into a gyratory primary crusher (Metso 54/75 inch, 450 kW installed power) that reduces material from less than 1,000 mm to a product size of P80 150 mm. The crusher has an operating capacity of 1,750 tph and is scheduled to operate 8.5 hours per operating day to process 5 Mtpa. Crushed material drops into a surge bin, onto an apron feeder, and is transported by a 100 m conveyor to a covered stockpile. The stockpile is contained under a permanent unheated conical dome to prevent snow and rain intrusion and has a capacity of approximately 100,000 tons (about 7 days).
Grinding circuit (Phase 1)
Stockpiled material is reclaimed by four apron feeders (in two pairs) and conveyed to a SAG mill. The SAG mill is nominally 9.7 m diameter by 4.3 m long with 7,460 kW installed power, oversized for 5 Mtpa but suitable for 8 Mtpa. The SAG mill discharges over a vibrating screen with 76 mm openings; oversize pebbles are returned to the SAG feed after crushing in a short head cone crusher (2.3 m × 2.5 m × 2.6 m, 315 kW) to 15 mm. Undersize feeds a ball mill (6.7 m diameter by 9.1 m long, 7,460 kW) operating in closed circuit with cyclones at a circulating load of up to 250%. Cyclone overflow targets P80 of 200 µm (212 µm per design criteria) and flows to copper rougher flotation.
Copper flotation circuit
The copper rougher circuit comprises two rows of four 50 m³ Outotec e50 flotation cells (eight cells total in Phase 1) with 20 minutes residence time. Reagents include potassium amyl xanthate (PAX) and MIBC frother, with milk-of-lime slurry added for pH control. Copper rougher concentrate is re-ground in a VertiMill (Metso VTM-800-EB) to P80 of 20 µm in closed circuit with cyclones. Re-ground concentrate feeds a 4-stage cleaner circuit: three 10 m³ Outotec e10 first cleaner cells, two 10 m³ e10 cleaner-scavenger cells, four 4 m³ Metso DR24 second cleaner cells, and two 10 m³ column cells in series for third and fourth cleaning. Copper cleaner-scavenger tailings are sent to the PGM re-grind circuit.
PGM flotation circuit
Copper rougher tailings are re-ground in a ball mill (6.7 m diameter by 9.1 m long, 7,460 kW) in closed circuit with cyclones to produce a PGM rougher feed of P80 100 µm. PGM rougher flotation uses two banks of four 50 m³ Outotec e50 cells (eight cells total in Phase 1) with 20 minutes residence time. PGM rougher concentrate is re-ground to P80 of 10 µm using either two VertiMills (one operating, one standby) or a horizontal stirred mill such as an IsaMill with ceramic grinding media. The ground concentrate undergoes four stages of cleaning: 20 minutes residence time in three 10 m³ Outotec e10 first cleaner cells, followed by three 10 m³ e10 first cleaner-scavenger cells, four 4 m³ Metso DR24 second cleaner cells, and two column cells (0.45 m diameter by 10 m high, 10 m³ each) for third and fourth cleaning.
Concentrate handling
Copper and PGM concentrates are combined in a concentrate thickener (14 m diameter) where feed slurry is mixed with flocculant and thickened to 60% solids. Thickened concentrate is pumped to plate and frame pressure filters, reducing moisture to 10% or less (target 8%). If moisture exceeds 10%, a Holoflite-type dryer may be considered. Concentrate can be shipped in bulk during mild weather; for winter shipment, heated containers or bagging in 1-tonne lots is proposed.
Residual sulphide flotation
PGM rougher tailings feed a conditioner tank (over 10 minutes retention) where depressed sulphides are reactivated by pH adjustment and/or carbon dioxide addition. Up to five 50 m³ flotation cells produce a moderately enriched sulphide concentrate that becomes Type 2 process solids (potentially acid generating). Sulphide flotation tailings become Type 1 process solids (non-acid generating). Both streams are thickened to approximately 50% solids before separate pumping to the process solids management facility.
Phase 2 expansion (year 6 onward)
From production year 6 to end of life-of-mine, the process plant treats 8 Mtpa. Expansion includes: primary crusher operation increasing from 8.5 to 13.5 hours per day; addition of a secondary cone crusher (Metso HP800 or equivalent) with a screen deck for 75 mm material; installation of a second ball mill; and additional flotation cells (10 Outotec e50 rougher cells for copper, 10 for PGM; larger cleaner circuits). Ramp-up to 8 Mtpa is estimated at 85% in Q1 of year 6, then 100% thereafter.
Key reported parameters
| Parameter | Unit | Phase 1 (Years 1–5) | Phase 2 (Years 6+) | Basis |
|---|---|---|---|---|
| Nominal annual input | dry tpa | 5,000,000 | 8,000,000 | Design |
| Operating days per year | days | 350 | 350 | Design |
| Nominal daily input | dry tpd | 14,300 | 22,900 | Design |
| Primary crusher type | , | Metso 54/75" gyratory | Metso 54/75" gyratory | Design |
| Primary crusher installed power | kW | 450 | 450 | Design |
| Primary crusher feed F80 | mm | 500 | 500 | Design |
| Primary crusher closed side setting | mm | 150 | 150 | Design |
| Secondary crusher | , | , | Metso HP800 | Design |
| SAG mill dimensions (dia. × EGL) | m | 9.7 × 4.3 | 9.7 × 4.3 | Design |
| SAG mill installed power | kW | 7,460 | 7,460 | Design |
| SAG mill product P80 | mm | 2.5 | 2.5 | Design |
| Ball mill dimensions (dia. × EGL) | m | 6.7 × 9.1 | , | Design |
| Ball mills – number | No. | 1 | 2 | Design |
| Ball mill installed power | kW | 7,460 | TBD | Design |
| Primary grinding P80 | µm | 200 | , | Design |
| Copper rougher residence time | min | 20 | 20 | Design |
| Copper rougher cell volume | m³/cell | 50 | 50 | Design |
| Copper rougher cells (2 lines) | No. | 8 | 10 | Design |
| Copper rougher conc. regrind P80 | µm | 20 | 20 | Design |
| PGM rougher residence time | min | 20 | 20 | Design |
| PGM rougher cell volume | m³/cell | 50 | 50 | Design |
| PGM rougher cells (2 lines) | No. | 8 | 10 | Design |
| PGM rougher conc. regrind P80 | µm | 10 | 10 | Design |
| Concentrate thickener diameter | m | 14 | 14 | Design |
| Concentrate filter cake moisture | % | 10 | 10 | Design |
| Abrasion Index (AI) | kWh/t | 0.396 | 0.4 | Micon (2008) |
| Bond Ball Mill Work Index | kWh/t | 16 | 16 | Micon (2008) |
| Copper recovery (years 1–5) | % | 92 | , | Testwork-based PEA estimate |
| Copper recovery (years 6+) | % | , | 90 | Testwork-based PEA estimate |
| Palladium recovery | % | 82.9 | 82.9 | Testwork-based PEA estimate |
| Platinum recovery | % | 74.5 | 74.5 | Testwork-based PEA estimate |
| Gold recovery | % | 73.2 | 73.2 | Testwork-based PEA estimate |
| Silver recovery | % | 71.5 | 71.5 | Testwork-based PEA estimate |
Project website: https://genmining.com/news/2025/generation-mining-expands-its-land-package-at-the-marathon-district/
Technical qualifications
The process plant recoveries for this PEA were determined by P&E to be as stated above, based on metallurgical testwork. The flowsheet design and equipment selection are derived from bench-scale testing and preliminary engineering; all major equipment items are subject to detailed review and adjustment following advanced engineering studies. The PGM circuit detailed design (e.g. for a Feasibility Study) requires consideration of opportunities for economic expansion to 8 Mtpa, including scheduled changes in feed grade, scale-up of flotation, grinding, pumping, and thickening capacities, supplemented by metallurgical performance experience during the first years. Fine grinding methodology and grinding media type require additional testwork. The use of reclaim water is assumed not to adversely affect flotation performance, with minor treatment or fresh-water addition as contingency. The report notes that HPGR technology was considered by previous studies but was not selected for this PEA; P&E suggests that a conventional SAG-ball mill combination presents lower risk for northern Canadian operations.
*Source: Marathon Property, 2019 Pre-Feasibility Study, Generation Mining Limited, P&E Mining Consultants Inc. Report No. 367, Sections 1.14, 1.15, 17.1–17.16.*
