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Will the project create acid mine drainage?

No, Sandfire has carefully designed the Black Butte Copper Project to protect all water resources and prevent any acid mine drainage. Acid mine drainage, by definition, happens when water flows over or through sulfur-bearing materials that is exposed to oxygen, it then can oxidize, becomes acidic, and carries toxic materials to surface water ways. To prevent this, Sandfire has designed our underground mine so that all entrances are close to 200 feet above the ground water level and over 300 feet above the underground mine workings in the copper deposit. Water cannot run uphill out of the mine so nothing can ever drain/flow out of the mine. This ensures that terrible accidents like the one on the Animas River in Colorado cannot happen at our Black Butte Copper Project.

To ensure no acid mine drainage occurs above ground, Sandfire will leave no mill tailings (finely ground rock left after removal of the copper minerals) lying directly on the surface at the end of mine life. Sandfire’s mining plan includes returning about ½ of the mill tailings underground by mixing them with cement and piping them into the underground mined cavities they originally came from. This happens continually during mining so only a small amount of mined area is open and exposed to the air at any given time. Once mining is completed, there are no large open spaces left underground in the mined cavities and thus no room for underground water reservoirs. The cemented tailings are hard, like concrete, and have very low permeability so water does not pass through them, just like the surrounding rock. Because the tailings filled mine lies below the water table there is no available oxygen to allow oxidation and subsequent liberation of metals into the groundwater.

Sandfire will also add cement to the other ½ of the tailings and pipe them into a double lined cemented tailings facility where it sets up as a, non-flowable material. A pumping system in a sump will pump all water (squeezed from the tailings as they harden and/or from precipitation that falls on the facility) out of the facility and into a process water pond with a high pH, where any acidity is quickly neutralized. As a further precaution, Sandfire will pump every drop of water touched by the mining and concentrating processes, including precipitation falling on the mine site, through a reverse osmosis (RO) water treatment system to meet Montana’s strict non-degradation standards for ground water. The operation will return this water directly back to the groundwater system from where it came by an underground infiltration system consisting of perforated piping buried 6 to 8 feet underground in highly permeable ground.