Here is an interesting discussion of underground disposal of tailings at the Doris North Project in Nunavut:

Tailings is often disposed of in underground mines as backfill to provide ground or wall support. This naturally decreases the above ground storage requirements and simultaneously stabilizes mined-out areas. For tailings to provide adequate backfill strength it has to have a high permeability, low compressibility, and the ability to rapidly dewater. The tailings must thus contain a large sand fraction. This often results in the tailings being separated using a cyclone with the coarse sand fraction being used as backfill and the fines fraction being sent to a conventional tailings deposition site.

Placement of the mill tailings underground was considered as an attractive option but there is not enough room to dispose all the Doris North Project tailings. The maximum tailings volume that can be stored underground is approximately 25% of the solids volume. This is only 8% of the total tailings slurry feed, and therefore an additional SATD or LBTD facility would still be required. The use of the mine waste rock as backfill and the swell factor contribute to this space deficiency, and since the tailings is less geochemically active than the waste rock, it makes more sense to store the waste rock underground than the tailings. Furthermore, early in the mine life there will no mined out workings in which the tailings could be placed, which would require an interim storage area on surface.

During the development of the Doris North Project feasibility, MHBL examined the possibility of utilizing mining voids as an alternative tailings storage area in addition to a primary LBTD or SATD facility.

Several alternate means of delivering tailings underground were examined. These were as a thickened slurry and as a low moisture filter cake. The introduction of a conventional or thickened slurry into the underground workings was rejected. As the mine lies within permafrost and conditions are expected to remain at -10oC year round the free draining water contained within the slurry would create significant operating problems underground. Water draining out of the slurry would enter the main haulage ramps and freeze. To counter this, operations would have to add significant quantities of calcium chloride which would be prohibitively expensive and problematic.

Under the proposed operations the mine is expected to be a net consumer of water (no generation combined with minor losses to the ore), the introduction of a large volume of water would require major pumping installations throughout the mine. Pumping back large volumes of high chloride water to the mill would create a corrosive environment within the mill increasing maintenance and mill down time.

Placing filter cake underground was also rejected for the following reasons:

  • Placing all of the filter cake underground is not possible.
  • Placement of fill underground is not a continuous process. Only after lifts have been mined out is the stope available for fill. This would require significant surface storage of filter cake fill. At 15% moisture this filter cake would freeze during winter months making digging near impossible without blasting.
  • Bateman’s assessment of the capital indicated that filtering tailings would increase capital costs by over one million dollars. Operating costs would be expected to increase by $3 per tonne due to increased power, labor and maintenance.

It is acknowledged that underground placement of a portion of the tailings generated would be a positive step. Given the specific site conditions encountered within the Doris North Project it is impossible to predict how much tailings could be placed underground; however, during operations MHBL will generate a coarse tailings product using a DSM screen which could be trucked underground as fill is required. If no fill is required this product would be recombined with the main tailings stream for disposal.

I am not sure of the current status of this mine that has a two-year life. The website of the owner Miramar is pretty absent any information I can find. There is a fun presentation from April 2007 at this link on the mine.

In a June 8, 2007 news report I read this:

After more than three years of waiting, Miramar Mining Corp. is preparing for the construction of its Hope Bay Doris North gold mine in Nunavut. At least 20 workers are on site 140 kilometers south of Cambridge Bay, quarrying rock that will be used to build a kilometer-long road and a gravel pad for equipment and construction material. Later this month, work will begin on the 100-metre jetty that will stretch out into Roberts Bay. The company expects it will obtain all the permits and licenses it will need for constructing buildings by the end of this year.

"It's the culmination of a long environmental assessment process. The project has been well scrutinized through a public assessment process and we're quite happy to see things finally coming to fruition," said Larry Connell, Miramar's environment manager. "We look forward to actually going into operation in 2008 and starting to become a productive member of the community of Nunavut." Connell said the company received a land-use license from the Kitikmeot Inuit Association to do the quarrying and roadwork.

The incoming construction material is being trucked to Hay River, N.W.T., where it will be loaded on 13 barges for the trip to the western Nunavut site. Miramar wants to extract about 300,000 ounces of gold from a deposit at the north end of Doris Lake. Once in production, it could pump around $136 million into the territorial economy over a two-year period starting next year.

In September of 2007, CBC reported:

Five years into the review process, Miramar Mining Corp. came one step closer to opening its Doris North gold mine, after the Nunavut Water Board approved the company's water license. Indian and Northern Affairs Minister Chuck Strahl still has to approve a six-year license covering construction, operation and post-production reclamation of the mine site, located 125 kilometers southwest of Cambridge Bay in west central Nunavut.

It took Miramar five years to reach this point in the review process for a mine that is only supposed to run for two years. "It's been frustrating to take so long. I don't think any of us predicted that going in," environment manager Larry Connell said. "It's a new process. Nunavut is a new territory. And so everyone is learning as we go. Hopefully as each project goes through, this process will get more and more streamlined, and people will get more and more used to how it's going to work, and the timelines will improve," he said.