Duncan Lake PEA Plans a 113,000 t/d Magnetite Concentrator With Three SAG Mills and a 135 km Slurry Pipeline to a James Bay Pellet Plant

Century Iron Mines and Augyva Mining Resources' May 2013 preliminary economic assessment for the Duncan Lake iron property in Québec targets 11.55 Mt a year of 67.6% Fe concentrate from Deposits 3 and 4.

The NI 43-101 Technical Report, Preliminary Economic Assessment of the Duncan Lake Iron Property, James Bay, Québec, was prepared for Century Iron Mines Corporation and Augyva Mining Resources Inc. with an effective date of March 22, 2013 and an issue date of May 6, 2013. The magnetite concentrator would sit between Deposits 3 and 4, closer to Deposit 3, which has the better tonnage and grade. It would crush, grind, magnetically separate and thicken the ore. Its concentrate would be pumped by pipeline to a port near Stromness Island, where a pellet plant would also be built.

Critical Data

Overview

Trucks deliver run-of-mine ore to two gyratory crushers. The crushed ore goes to a covered 120,000 t stockpile with one day of storage, and a 60,000 t uncovered ROM stockpile sits by the crushing plant. Three SAG mills grind the ore and screen it at 3.36 mm. Cobber magnetic separators reject non-magnetic gangue. Six ball mills regrind the cobber concentrate to 85% passing 75 µm, and low-intensity magnetic separation produces the final concentrate. The grind size was selected from Davis Tube testwork on Deposit 3 ore, and up to 29% Deposit 4 ore was considered acceptable in the blend. Non-magnetic hematite and a little magnetite are lost to tailings with the gangue.

Key Process Stages

Crushing and reclaim. Two identical gyratory crushers with hydraulic rock breakers are housed in an enclosed building with two ROM pockets, producing P80 198 mm. Apron feeders, conveyors and trippers fill the covered stockpile, and six apron feeders in a concrete tunnel reclaim to the SAG mills.

Primary grinding. Each 12.2 by 7.9 m SAG mill has a 22,000 kW gearless motor and runs at 72% solids. A 25 by 12 mm discharge grate and an 8 mm trommel with pocket lifter return oversize to the mill. Trommel undersize is pumped to 3.36 mm vibrating screens, whose oversize also returns to the mills.

Cobbing. Cobber magnetic separators reject about 10% of the feed as liberated non-magnetic gangue, which goes to a hydroclassifier and then tailings. The cobber concentrate goes to secondary grinding.

Secondary grinding. Six 7 by 13.5 m ball mills of 9,300 kW run in parallel and closed circuit with hydrocyclones, at 47.5% solids in the pump boxes. Cyclone overflow at 85% passing 75 µm goes to the finisher magnetic separators.

Magnetic separation. Six LIMS trains, each with six triple-drum separators fed at about 25% solids, produce the final concentrate. The non-magnetic tails go to two tailings thickeners.

Thickening and pipeline. The concentrate thickener takes the concentrate to 65% solids. Large variable-speed, positive-displacement pumps under the thickener then send it about 135 km along the road to Chisasibi and the La Grande River to the pellet plant. Tailings thickener and hydroclassifier underflows are pumped to the tailings pond at 55% solids.

Additional Interesting Data and Summary

Thickener overflows drain by gravity to an insulated, below-grade concrete process water reservoir, which holds 20 minutes of plant demand to allow a quick restart after a power failure. Water from the tailings pond is also returned for reuse. Standby diesel generators would run critical equipment, including the pipeline pumps, during outages. The report notes that pipeline testwork on the concentrate is still needed to size the pumps and line, and that thickener testwork without flocculant is still to be done.

In summary, the 2013 Duncan Lake PEA is a very large magnetite flowsheet, with three 22 MW SAG mills, cobbing, six ball mills and LIMS finishing, that turns 24.8% Fe ore into 11.55 Mt a year of 67.6% Fe concentrate, delivered by a long slurry pipeline to a coastal pellet plant.

Key Processes

• Twin gyratory crushing and covered stockpile
• SAG milling with trommel and 3.36 mm screening
• Cobber magnetic separation
• Ball milling with hydrocyclones to 85% passing 75 µm
• Low-intensity magnetic separation (six trains)
• Concentrate and tailings thickening
• Long-distance slurry pipeline to a pellet plant

Source: NI 43-101 Technical Report, Preliminary Economic Assessment of the Duncan Lake Iron Property, James Bay, Québec, Canada, Century Iron Mines Corporation and Augyva Mining Resources Inc., effective date March 22, 2013.