Trent Weatherwax, a Masters student at the University of British Columbia, sent me a copy of his paper, A Conceptual Design of a Backfill System for Underground Preconcentration Facility. His co-authors are B. Klein and R. Pakalnis (his supervising professors at UBC) and D. Proudfoot of Xstrata Nickel.

This paper was published at the CIM MINEFILL2007 Montreal, Quebec. Unfortunately the paper is heavily copyrighted, so you will have to contact the authors for a copy. Here is my brief review of the paper augmented by discussions at lunch with Trent.

Trent has just about completed his thesis which is the basis of the paper, and he has accepted a position with Barrick in Toronto. He will be dealing with the use of paste tailings as backfill in the local mines and when he is expert he will be involved in implementing similar approached at Barrick’s Nevada mines.

Trent’s paper’s abstract (which I am allowed to quote in full by CIM) reads:

Ongoing research is being undertaken at UBC to develop pre-concentration and waste disposal systems for underground base metal mines. The base case pre-concentration system consists of dense media separation, which yields a coarse reject material. For waste disposal, several conceptual designs have been developed - the most appropriate design depends on a number of factors, including mining depth, location, fill strength requirements, and metallurgy. A test program was carried out for nine ore types from four different Xstrata Nickel mines in Ontario to assess the amenability to pre-concentration and characterize the waste for backfill. This paper presents the results of this study and proposes mine-fill options for the underground processing system.

Here are the primary points from the study that supports Trent’s thesis and paper:

  • Samples were collected from nine orebodies representing four of Xstrata Nickel’s mines in Ontario, including the Craig, Fraser, and Thayer Lindsley mines in the Sudbury Basin and the Montcalm mine near Timmins.
  • Dense media separation (DMS) tests were conducted on each of the ore samples to assess their amenability to pre-concentration.
  • The waste products were then characterized geotechnically in preparation for their use as fill.
  • Thayer Lindsley mine is the smallest of Xstrata’s Sudbury mines and utilizes long-hole open-stoping and cut and fill methods. Currently, the uncemented rock fill, in the form of development waste and crushed -90 mm ballast, is used to provide confinement for the post-pillars in cut and fill mining and to maintain the overall stability of the mine.
  • The Montcalm mine is the only mine in this study not currently using some form of backfill. Mining is done using open stoping methods. Ore is crushed on surface and then hauled 100km to the Kidd Creek Metallurgical complex for processing. At the indicated 30% rejection rate, 260,000 tons of DMS rejects a year would be produced.
  • Located near the Strathcona mill in Onaping, the Fraser and Craig Mines would have easy access to flotation tailings, making composite fill an attractive option for both mines.
  • By showing how the coarse rejects from a preconcentration process can be incorporated into a mine’s backfill system, another link is made in the step towards an integrated underground mining and processing system.

We will watch these ideas develop in practice with interest.