Management of residual pyrite in mine tailings

At a mining property located in central Idaho, tailings with a residual pyrite content of approximately one percent are susceptible to oxidation if deposited within drained and unsaturated areas of the tailings disposal facility. A study was conducted to evaluate tailings management options to alleviate current oxidation and the potential for future development of acid rock drainage. Operational modifications proposed for control of tailings oxidation include addition of a flotation circuit to separate a portion of the residual pyrite from the whole tailings stream. During modified operations, two tailings products will be produced; inert tailings with a low potential for acid generation and pyrite concentrates. Separate management of the resulting tailings products is proposed. Inert tailings will be deposited through the existing tailings delivery system and placed in all areas susceptible to oxidation, effectively capping existing pyrite bearing tailings with an inert cover. The pyrite concentrate will be deposited in the tailings pond where subaqueous conditions will be maintained and encapsulation within inert tailings will occur. Unsaturated flow and oxygen diffusion modeling of existing conditions, and conditions following modified operations, indicated that the placement of an inert tailings cover over the existing drained and unsaturated pyrite bearing tailings will reduce oxygen availability and the rate of oxidation. Based on oxygen diffusion modeling of conditions within the proposed pyrite concentrate disposal area, the oxidation of pyrite concentrate deposited subaqueously and encapsulated within inert tailings was predicted to occur at a rate that will not result in measurable impact to water quality during operations or following facility closure and reclamation.