Polymet mine plan cuts cost projection (June 21, 2005)

A new conceptual mine plan for Polymet Mining’s (POM-T) NorthMet copper project in Minnesota says the deposit could be put into production at a significantly lower cost than had been estimated in earlier studies.

Sydney-based consulting firm Australian Mine Design & Development estimated that a 25,000-tonne-per-day operation would have mining costs around US$1 per tonne. Processing costs would probably run near US$6 per tonne to float a sulphide concentrate, autoclave it, and produce copper by solvent extraction and electrowinning. The plant would also produce nickel and cobalt hydroxides and a precious-metal-bearing sludge as byproducts.

In an agreement with steelmaker Cliffs Erie, Polymet has optioned a mothballed taconite mill about 15 km southwest of the pit, which has a grinding capacity of 100,000 tonnes per day. The company expects a considerable reduction in capital cost estimates as a result.

A revised resource estimate, by Australian consulting firm Hellman & Schofield, puts NorthMet’s inferred resource (above the 152-metre elevation) at 215 million tonnes grading 0.31% copper, 0.09% nickel and 0.007% cobalt, with 0.3 gram palladium, 0.08 gram platinum and 0.04 gram gold per tonne. Another 110 million tonnes, grading 0.32% copper, 0.08% nickel, 0.006% cobalt, 0.3 gram palladium, 0.1 gram platinum and 0.05 gram gold per tonne, are inferred.

Initial pit-optimization studies suggest the economic pit depth is around 195 metres, so not all that material would ultimately be available to convert to reserves.

More feasibility work is planned.