Highland Eying 25-year Mine Life for White Pine North

Highland Copper has reported the results of a preliminary economic assessment (PEA) that support development of an underground mine at its White Pine North project on Michiganís Upper Peninsula, producing an average of 40,000 metric tons per year (mt/y) of copper and 1.3 million ounces per year (oz/y) of silver over a 25-year mine life.

The past-producing White Pine mine operated by Copper Range Co. is located on the property and was in production from 1953 through 1995. The current project is an extension of the historical mine. The PEA considers White Pine North as a stand-alone project and utilizes existing infrastructure to minimize initial capital expenditures. The PEA and mineral resource estimate were prepared by G Mining Services Inc.

Initial capital expenditures to develop White Pine North are estimated at $457 million, net of preproduction revenue of $56 million. Life-of-mine cash costs are estimated at $1.40/lb of copper, including royalties. Mineral resources included in the mine plan total 121.4 million mt grading 0.98% copper and 11.80 g/mt silver, containing 2.6 billion lb of copper and 46.1 million oz of silver.

Mining would be by a conventional room-and-pillar method. Mine access is planned as a new covered box-cut to establish a portal at the western side of the deposit followed by a decline to the orebody. The preproduction period requires 41,512 m of development. Ground conditions are expected to be good to excellent, similar to the historical White Pine mine. The production schedule is based on mining a fixed target of 5.4 million mt/y. To achieve this annual production, seven to fourteen production panels would be in production simultaneously.

The PEA envisions a process plant design based on the historical White Pine metallurgical flowsheet to produce copper concentrate, with a nominal throughput of 15,000 mt/d and a planned availability of 91.3%. The flowsheet consists of crushing, grinding in closed circuit with a ball mill targeting a primary grind of 100 microns, rougher flotation with concentrate regrind, cleaner flotation using three stages of cleaning, concentrate thickening, filtration, and tailings disposal. Copper recovery is estimated at 88% in a concentrate grading 30.5% copper. Silver recovery is estimated at 76%. Studies show that copper recovery might be further increased by concentrate grade and reagents optimization.

Highland Copper envisions building a new natural-gas-fired power generation plant, with capacity estimated at 30 megawatts. The existing tailings disposal facility would be utilized to deposit tailings from the White Pine North project, which would require dam raises over the life-of-mine. Water supply is available from an existing Lake Superior pump station. A new 2-km access road to the project processing and administrative complex is planned from Michigan highway M-64.

As featured in Womp 2019 Vol 11 - www.womp-int.com