Robots are not needed to mine Cigar Lake uranium

The Saskatchewan Mining Development Corp. has submitted a mining proposal to federal regulators in Ottawa to approve the start of a test mine entry at about this time next year on the high-grade uranium deposit at Cigar Lake, Sask.

The plan calls for extracting 40 cu m of rich uranium ore grading 12% U3O8 over a 2-ye ar period to evaluate a number of underground mining alternatives for full production to start, probably in 1993. Three mining systems using existing technology, are being considered.

“Our competitors say we’ll never be able to mine it,” Vice-president of Mining and Engineering, John E. Tosney told 180 delegates at the Automation in Mining Symposium in Sudbury. “But our partners (Cogema Canada, 32.62% and Idemitsu Uranium Exploration Canada, 12.87%) ask how are we going to mine it. I think that with the collaborative resources of the mining industry behind us we’ll be able to make it work”

At such remarkable grades only 4-5 truckloads will suffice to feed a world-class milling operation that could produce 12 million lb of yellowcake per year — an output equal to that of Key Lake, the world’s largest single producer.

Although the task of mining the deposit will not be easy, new robotic mining methods, still in the development stage, will not be necessary. Shielded, semi-automated remote control and containerized haulage units equipped with air filtration for the operator’s cab, workplace monitoring of alpha and gamma radiation, personal dosimetry, stringent training and hygiene programs, and special ventilation design methods in routine use today would suffice.

The deposits lie 425 m below the surface.

The biggest challenge, Mr Tosney says, may be the unconformity which exists between the barren Athabasca sandstone and the basement gneiss complex where the deposit occurs. Classical bench testing of core for rock strength and the measurement of in-situ field stresses indicate that the strength of the highly altered clay zone is insufficient to allow a mine opening to stay open.

Current thinking is to precondition the ground by freezing. Lab tests on clay strength relative to temperature are under way.

The high clay content also means build-up of this material will likely occur on the walls of bins, chutes, haulage units and at ore transfer points. Special decontamination procedures, wash down of equipment and gamma probing of high maintenance units are envisioned. Special slimes settling and water treatment facilities will also be needed.

The three most likely mining systems are:

* Raisebore mining — This non-entry type of mining uses conventional technology currently used for driving ore and waste passes. Operators would work from work stations in the barren waste rock and ore would be removed by remote control haulage units from a lower mining level.

* Undercut and fill mining — Remotely controlled road header mining machines and loading equipment could be used in conjunction with shotcrete and freezing for ground support.

* Hydromilling — This technique would use a remote controlled piling excavation machine developed by Soletanche which uses two cutting drums to excavate a hole 1.5 m by 2.5 m. Ore would be removed in slurry form. Concrete could be used as backfill.

Bench-scale test work is also under way on in-situ leaching. But the complex chemistry of the deposit and the low horizontal permeability of the host rock could adversely affect ground conditions.