Waste and Tailings

The ore that will be mined at both the Birch Lake and Maturi sites is sulfide-bearing ore, which means sulfur-containing minerals carry the copper-nickel-PGMs values present in the rock.  The sulfur must be separated from the metals order to retrieve the metals.  Technically, this defines the project as sulfide mining.  Sulfide mining carries the potential to create acid mine drainage if sulfur-bearing minerals in ore, waste rock, or tailings are exposed to both air and water, creating sulfuric acid.  The environmental fear is that acid could somehow find its way to the Lake and Boundary Waters.  Sulfide mining has, in the past, created major issues in mining operations world-wide.

However, at the Birch Lake Project, sulfide levels are dramatically lower than in the many mineral deposits in the Western U.S. and elsewhere.  In addition technology and engineering have evolved to enable Franconia to responsibly control the potential for acid mine drainage.

The waste rock that will be excavated during construction and development of the underground mines will be limited compared to the hundreds of millions of tons of waste rock often generated in large open pit mines.  The waste, part of which may be sulfur-bearing, will initially be stored at the surface in an engineered facility designed to control air and water exposure.  Later, during operations, part or all may be placed underground.

The tailings that remain during processing of the ore will be treated in the same manner as the waste rock.  After the flotation concentration stage of processing, the tailings left will contain the sulfur level about that of everyday rock (.05% – .08 %) and be non-acid generating.  After the metals are separated from the sulfur, in the hydrometallurgical process, the sulfur will be oxidized to sulfate and neutralized with lime or limestone to form gypsum, the material used in wallboard.  The gypsum and small amount of other processing wastes will be deposited in an engineered facility or placed underground.

The empty underground mine rooms can be backfilled with waste material, isolating it from air or water to inhibit acid generation.  The backfilled material will also provide structural strength to the mined-out areas to assure no surface subsidence.

The surface disposal facility or facilities will be engineered to minimize potential for air and water exposure, and potential for seepage or drainage should infiltration occur.  The site will be monitored during operation and after closure to assure that potential drainage, if it occurs, is promptly treated as necessary.  All of the technology and engineering will be subject to the most rigorous environmental regulatory controls.