Meeting uranium mining’s `challenge of the decade’

Official figures put the total contained uranium in the underground orebody at 385 million lb of U3O8 That’s enough to supply the energy requirements of Saskatchewan (at current levels) for another 1,600 years. There are two distinct sections of ore: the main pod containing 285 million pounds of U3O8 at an average grade of 12% and the western extension containing another 100 million lb of 4% grade. In contrast, the Elliot Lake, Ont., uranium mines’ average grade is roughly 0.1%. The high grade of the Cigar Lake find means that gamma radiation will be one of the greatest obstacles to successful mining.

The project owners — Cameco (48.75%), Cogema Canada (32.625%), Idemitsu Uranium Exploration (12.875%), Corona Grande (3.75%), and Korea Electric Corp. (2%) — face more obstacles than just radiation hazard. Along with radioactivity comes radon gas emissions and a proper ventilation system is needed to solve that problem.

In addition, a halo of clay surrounds the orebody, which will require extensive ground control measures. Pre-excavation support, such as freezing the ground, may be required. Shotcreting all underground openings should prevent ground movement. But the clay within the ore also poses ore handling challenges. Regular ore passes might become clogged and the ore can’t be allowed to sit long at drawpoints (if drawpoints are used).

Cigar Lake has proposed three test mining methods and perhaps a fourth in its quest to extract the uranium. Standard raise-boring with development openings above and below the orebody will be tried first. Project General Manager George Peebles told The Northern Miner that if the method proves workable, the consortium will go ahead with development without testing the remaining methods.

Undercut-and-fill using remote control equipment and the application of a surface-proven technique called blind boring (that is, boring from a development heading above the ore without a similar opening below) are also on the drawing board. As well, Peebles mentioned that box-hole boring from a bottom level up into ore was a candidate test method.

At another underground test project about 100 km northeast, the Midwest Joint Venture is testing a similar high grade uranium deposit. There, project operators will test blind boring first. The Midwest deposit, owned 45% by Denison Mines (TSE), 20% by Bow Valley Industries (TSE), 20% by Uranerz Exploration and Mining, and 15% by PNC Exploration, hosts 56 million lb U3O8 at an average grade of 1.25%.

At Midwest, a shaft has reached the bottom-most level and contractor Thyssen Mining Construction of Canada is driving a development drift toward ore. By the end of June, test mining should be under way, said senior mine geologist and site supervisor Larry Richardson.

At Cigar Lake, the shaft is more than halfway to the 510-vertical-ft target. Drifting and test mining should be well advanced by mid-1990.

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