Cameco Corp announced that it has temporarily suspended remediation work at the No.1 shaft at its Cigar Lake uranium project, which flooded in 2006, due to an increase in the rate of water inflow to the mine.
Cigar Lake (Image: Cameco)
In October 2006, a rockfall in the underground production area of the mine led to flooding. Mine operator Cameco expected that closing bulkhead doors would contain the water inflow and protect mine shaft No.1, the future processing area, pumps, a refuge station and a heat exchanger for ore freezing.
Unfortunately one of the doors did not seal properly, allowing water to enter the processing area while worker attempts to fully seal the door were unsuccessful. Furthermore, the rate of water ingress far exceeded the speed water could be pumped out. Finally, Cameco managers decided there was no option but to allow the water to overtake the mine. All staff were evacuated with no injuries and there was no impact on the environment.
Cameco began a five-phase remediation programme in early 2007 to remove water from the Cigar Lake mine. The company had expected to complete dewatering No.1 shaft in the second half of 2008. Cameco said that shaft had been pumped down to 430 metres below the surface when the increase in water flow, to 600 cubic metres per hour, was reported yesterday. Such an inflow rate "is beyond the range that can be managed while sustaining work in the shaft," the company said.
Tim Gitzel, Cameco's chief operating officer, said: "Remediation and dewatering of the No.1 shaft has been progressing smoothly up to this point." He added, "An inflow at this rate is disappointing but our remediation plan, as approved by our joint venture partners, recognised the risk and included specific actions to be taken at various levels of inflow." These actions include additional grouting from the surface and ground freezing if necessary.
In a statement Cameco said, "Work in the shaft has been suspended while the situation is assessed to determine the source and characteristics of the inflow, implications for planned remediation work and the impact, if any, on our planned production date."
"Our current plan is to allow the water level in the shaft to rise to approximately 100 metres below surface," Cameco said. "This will allow additional data to be gathered from instruments used to monitor groundwater conditions. As the water level rises, the rate of inflow will naturally diminish. This information will be analyzed to determine next steps. After this is complete, the water will be allowed to return to the natural equilibrium level."
Cigar Lake is one of the world's most promising uranium deposits, with estimated reserves of 113 million pounds of U3O8 at grades as high as 20.7%. Led by Cameco, holding 50% of the project, a consortium of Areva Resources Canada (37%), Idemitsu Canada Resources (8%) and Tepco Resources (5%) has been developing the deposit in the north of Canada's province of Saskatchewan. Originally, the mine was expected to begin operating in early 2008. In July, Cameco said that the start of production at Cigar Lake was anticipated for 2011 "at the earliest."