Mine Closure and Reclamation

The Kennecott Ridgeway Mine in South Carolina, used waste rock in construction of the tailings impoundment, with compaction and encapsulation. Development of two pits allowed partial backfilling of one during mining of the other. Lime softening was used, to buffer acid generated by the pit walls, backfill and contact runoff water from the site. To close the tailings impoundment, the deposition system was graded to created positive drainage and tailings were coverd quickly by placing the cover as a slurry.

Black Pine Mining, Inc. (BPMI) contracted in 1995 with WESTEC, Inc. (whose operations were merged with SRK Consulting in 1998) to prepare a closure plan for their 34-million ton heap leach facility located in the south-eastern corner of Idaho, USA. The heap, a valley fill design, had 50 million gallons of solution in process containing cyanide and other constituents in concentrations greater than safe drinking water standards.

Though the Escondida deposit has reserves sufficient for an additional 40 to 50 years of mining, Minera Escondida Limitada (MEL) is making plans now to regularly set aside funds for closing the mine and related facilities – an approach expected to pay significant dividends later. The Escondida deposit is 3,100 m above sea level in the Atacama desert of northern Chile. Mining started in late 1990. Recent estimates put reserves at about 1,800-million tons of ore, with an average 1.59% copper. The current mining rate is about 127,000 tpd.

Closing orphaned zinc mines: Faro, Vangorda and Grum mines, Yukon The 100 million tonnes of sulphide-rich tailings from the closed Faro mill is damaging the environment by generating acid and releasing zinc metal. SRK was hired to assist in the development of a closure plan, and is now part of a Technical Advisory team to guide all aspects of the site closure. Coordinating with other consultants and government representatives, SRK developed and implemented early remediation measures such as creating fish-friendly habitat near the fresh water supply dam.

Controlling arsenic trioxide dust: Giant gold mine, Yellowknife, NWT Chambers of the now-closed underground Giant mine, in what was originally thought to be permafrost ground, were used to store 237,000 tonnes of arsenic trioxide dust captured from roaster emissions over a 50-year period. SRK was initially chosen as Technical Advisor to review all possible long term management options, which culminated in developing a plan that included innovative passive ground freezing to manage the arsenic trioxide areas.

Mine closure: Red Dog Mine, Brooks Range, Alaska Red Dog is the largest zinc-lead mine in the world, with a projected life beyond 2030. SRK and SENES have developed a draft closure and reclamation plan that is intended to satisfy the State regulatory requirements for the solid waste permit amendment and negotiation of the reclamation security.

Britannia Mine, BC, Canada, once the biggest producer of copper in the British Commonwealth, produced about 800,000 tonnes of Cu metal between 1904 & 1974. Open workings allowed 5 million cubic metres of mine water containing over 200 tonnes of dissolved metals to flow into Howe Sound each year. We engineered a surface water diversion that cut mine inflows by about 10% and contributed to a treatment system that precipitates metals into a high density sludge, which is deposited into the original pits and glory holes. Results: Reduction of 500,000 cubic metres of mine water annually; discharge of treated effluent to Howe Sound with full compliance of current environmental standards.