Second only to McArthur River,
With proven and probable ore reserves of 551,000 tonnes grading 19.06% U3O8, representing 231 million lbs., it’s a relatively small orebody — but one that is incredibly rich in grade and high in value. The deposit sits 40 km inside the eastern edge of the Athabasca basin, 660 km north of Saskatoon, Sask.
On behalf of its joint-venture partners,
According to Scott Bishop, chief mine engineer, who spoke at this year’s Mineral Exploration Roundup in Vancouver, the project is on track to begin production in 2007. Cameco is constructing surface and underground facilities to support an operation that is expected to produce 18 million lbs. U3O8 annually for at least 15 years during the first phase of production. The go-ahead decision was based on a projected payback period of about eight years.
“That’s enough nuclear fuel to power twenty-eight 1,000-megawatt nuclear reactors every year,” Bishop said. “Twenty-eight thousand megawatts represents about twenty-five per cent of Canada’s total energy demand, or approximately one hundred per cent of Ontario’s load.”
The property is accessible by either road or air. A single-track road into the property has recently been widened to an all-season, double-lane road. The site is connected to the provincial electricity grid.
Initially, the Cigar Lake uranium ore will be processed at Cogema’s McClean Lake operation, 70 km northeast. As Cigar Lake production ramps up to full capacity, just over half of final uranium processing will be completed at Cameco’s Rabbit Lake mill. It’s anticipated that the ramp-up period could take up to three years before Cigar Lake reaches full production.
Discovered in 1981 by Cogema, Cigar Lake is a typical Athabasca basin unconformity type uranium deposit. It occurs at depths ranging from 410 to 450 metres below surface at the contact between metamorphic basement rocks of the Wollaston Group and overlying sandstones of the Athabasca Group. The setting is analogous to the Key Lake, McClean Lake and Collins Bay deposits.
The Cigar Lake deposit is distinguished by its size, its very high grade and the high degree of associated hydrothermal clay alteration. The deposit is flat-lying, 1,950 metres long, ranging from 20 to 100 metres wide, and up to 16 metres thick. It has been defined by some 200 holes representing 92,000 metres of core drilling from surface. Individual intercepts grade up to 60% uranium.
The joint-venture partners have had to overcome some major technical challenges concerning the project’s development, which included ground stability, ground water control, radiation exposure, and ore handling and storage. Starting with the sinking of the no. 1 shaft in 1988-1989, a decade-long test mining program resulted in the selection and validation of “jet boring,” a non-entry mining method. Horizontal development was advanced on two levels and test mining in previously frozen ground, involved box-hole boring and high-pressure water-jet boring.
A tunnel-boring machine was designed and successfully tested to allow development in the weak and highly variable rock under the deposit.
“The ground conditions can change very quickly,” Bishop explained. The custom-designed boring machines incorporate both rock-cutting bits and soil-cutting picks. With a 4.25-metre inside diameter, the tunnel-boring machines are capable of advancing 4-6 metres per day, though Bishop noted that they have achieved an advance rate up to 8 metres per day. Once a cavity has been mined out, it will be backfilled with rock.
These are enclosed systems, which allow for the containment of dust and radon, while providing shielding against gamma rays. Operators never enter the orebody or have direct contact with the ore.
Ground freezing is required to safely develop through some of the clay zones and to mine out the uranium orebody that has water-saturated sandstones directly above it. This will serve to improve ground conditions, prevent water inrush and stop radon migration. The ground is frozen by pumping brine that has been cooled to minus 40 Celsius through a pattern of drill holes spaced at 2-metre intervals.
“With the water and clay, the only way we can develop the mine through some of this ground is to actually freeze it,” Bishop explained. “We started freezing in September and we have got some of our temperature profiles that are already down to minus fifteen degrees Celsius.”
About 160 freeze holes have been completed to date.
Additional ground support includes conventional bolting and screening, shotcreting of various thicknesses, steel arches and concrete tunnel liners.
Cigar Lake is being developed in two phases. The phase-1 orebody is the thickest, widest, highest-grade portion of the deposit. “It will support our first fifteen to twenty-five years of production,” Bishop said. A lower-grade and thinner second-phase part of the deposit will support production for another 15 years at a reduced operating rate. Additional inferred resources are estimated at 317,000 tonnes averaging 16.9% U3O8, or 118 million lbs.
The initial processing of the uranium ore will take place underground at Cigar Lake. The ore will be crushed, ground and slurried underground, pumped to surface and loaded into specialized containers for transport to the McClean Lake and Rabbit Lake mills for further processing. Wastes from the Cigar Lake ore will be processed and managed at the two mill sites.
“We are on target to start construction of our underground mill in May of this year,” Bishop said.
Pre-construction activities started in 2003, with the sub-collar construction of the no. 2 headframe and hoist. The no. 2 shaft will be used for ventilation and access. Official construction began in early 2005 and is expected to take about 27 months to complete, with production scheduled for 2007. The no. 2 shaft is being sunk to 500 metres depth. It is currently down to the 390-metre level.
To support the underground mining operation, surface facilities are being added, including the construction of a permanent 250-person residence, ore loading facilities, waste pile components and other related infrastructure. The new camp should be inhabitable by April 2006. The workforce during the construction phase of the project has averaged about 300 people over the past year, peaking at slightly over 500.
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