Marathon Palladium & Copper Project — 2021 Feasibility Study (Section 17)

Section 17 of the March 2021 feasibility study describes the proposed process plant design to produce a copper-PGM flotation concentrate from the Marathon Palladium & Copper Project in Ontario, Canada.

Report context

This feasibility study (FS) dated March 2021 presents the process design for the Marathon Palladium & Copper Project. The process plant is designed to process 25,200 t/d (9.2 Mt/y) at average life-of-mine feed grades of 0.21% copper and 0.63 g/t palladium to produce a copper-PGM flotation concentrate. The plant operating schedule is based on two 12-hour shifts per day for 365 days per year, with 70% availability for the crushing circuit, 92% for grinding and flotation circuits, and 85% for the concentrate filter.

Processing route

Primary crushing

Run-of-mine ore will be delivered to a primary gyratory crusher dump pocket by 216-t haul trucks or by front-end loader. The dump pocket has a capacity of approximately 580 t with dual side dumping. A hydraulically operated rock breaker will fracture oversize material. Crushed ore is withdrawn by a variable speed apron feeder and transferred to the primary crusher discharge conveyor, then to a 1.4 km overland conveyor feeding the coarse ore stockpile. A metal detector and magnet are located on the discharge conveyor for tramp metal protection.

Coarse ore stockpile and reclaim

Coarse ore feeds a single conical covered stockpile with total storage capacity of approximately 75,000 t. Nominal live capacity is 27% of total tonnes (18 hours retention). Remaining capacity can be recovered using a bulldozer or excavator. Two belt feeders, each capable of design throughput, transfer material to the SAG mill feed conveyor.

Grinding and pebble crushing

The grinding circuit consists of a single SAG mill (10.36 m diameter x 5.79 m effective grinding length, 15 MW twin pinion drives) followed by a single ball mill (7.92 m diameter x 11.28 m effective grinding length, 15 MW twin pinion drives) operating in closed circuit with a primary cyclopak. The SAG mill operates in closed circuit with a double deck screen and a pebble crusher. Screen undersize flows to the cyclone feed pump box. Pebble crusher discharge is recycled to the SAG mill feed conveyor. Primary cyclone overflow is the flotation feed with a target 80% passing size of 106 microns.

Rougher flotation and cleaner circuit

Primary cyclone overflow reports to the rougher flotation head tank. The rougher bank consists of ten direct flotation reactor cells. Rougher concentrate undergoes regrinding in two parallel HIG mills (5,500 kW each) to a target P80 of 18 μm. Reground concentrate reports to an iron sulfide aeration tank (30 minutes residence time) for pyrrhotite suppression at pH 11 prior to cleaning.

The cleaner circuit comprises three stages of flotation using DFR cells. First cleaner has six cells, second cleaner has six cells, and third cleaner has five cells. Cleaner scavenger flotation with four cells treats first cleaner tailings, with scavenger concentrate recycled to the rougher concentrate regrind circuit. Third cleaner concentrate is the final Cu-PGM concentrate.

Tailings coarse regrind and PGM scavenger flotation

Rougher tailings are classified by sand/slime cyclones. The coarse fraction (P80 +53 μm) is reground in two open-circuit HIG mills (5,500 kW each) to a product P80 of 38 μm. Reground material reports to PGM scavenger flotation comprising five DFR cells. PGM scavenger concentrate returns to the rougher concentrate regrind circuit. The fine fraction combines with PGM scavenger tailings as low-sulfide, non-PAG tailings directed to the tailings thickener.

Concentrate thickening and filtration

Final concentrate from the third cleaner is thickened in a single high-rate thickener (unit area thickening rate 0.28 m²/t/d) to 55-60% w/w solids underflow. Thickened concentrate is pumped to an agitated filter feed tank with 12 hours surge capacity, then to a single Outotec Larox PF 60/72 horizontal pressure filter producing cake at 10-13% w/w moisture. Filtrate returns to the concentrate thickener.

Concentrate storage and load out

Filter cake discharges by gravity to a concrete storage bunker with capacity for up to 7 days at nominal production rates. Concentrate is loaded by front-end loader into a chute feeding a belt conveyor for truck loading. Transport trucks are weighed on a load-out scale at site.

Tailings thickening and storage

Combined rougher tailings fine fraction and PGM scavenger tailings are thickened in a single 65 m diameter high-rate thickener (unit area thickening rate 0.12 m²/t/d) to 55-60% w/w solids. First cleaner scavenger tailings are pumped separately to designated sub-aerial locations within the tailings storage facility to mitigate oxidation and acid generation. Thickener underflow reports to the TSF by gravity or centrifugal pumping.

Reagents

Potassium amyl xanthate (PAX) is used as collector in rougher and cleaner flotation, delivered as pellets in bulk bags and mixed to 15% w/w solution. Cytec Aero 3501 acts as PGM collector, delivered as liquid in totes. Methyl isobutyl carbinol (MIBC) provides froth, delivered as liquid in totes. Carboxymethyl cellulose (CMC) is used as depressant in the cleaner circuit to improve final concentrate grades by depressing talc. Two flocculant mixing systems serve the concentrate and tailings thickeners. Quicklime is delivered in 30 t trucks for slaking, with lime slurry used primarily in the concentrate regrind circuit.

Water systems

Fresh water is supplied from the Water Management Pond or Storm Water Management Pond. Process water is sourced from tailings thickener overflow, concentrate thickener overflow, concentrate filtrate, return water from the TSF, and fresh water make-up. A dedicated firewater reserve of 400 m³ is contained in the fresh water tank.

Key reported parameters

Technical qualifications

The process design is based on information and metallurgical test results summarized in Section 13 of the report. Bench scale testing completed during 2020 applied conventional flotation cell technology. The evaluation of Woodgrove DFR cells during 2020 Phase 1 and Phase 2 metallurgical test programs supports a 20% decrease in baseline mass pull in the rougher and cleaner circuits relative to conventional flotation technology, with no change in metal recovery. Process mass balances for the FS applied the higher baseline mass pull for equipment sizing. Initial design concepts for the FS have excluded Cu-PGM concentrate magnetic separation. Determination of predictive recovery curves was established with the 2020 metallurgical testing programs, with estimated metal recovery defined in equations for the GeoMet model including the PGM-scavenger flotation circuit.

Source: Marathon Palladium & Copper Project Feasibility Study, March 2021, Section 17: Recovery Methods.