An expanded program for the assessment, monitoring and remediation of water inflow and subsidence is under way at the Goldex mine, according to Agnico-Eagle Mines Ltd. Despite deteriorating ground conditions, the mine and mill continue to run at capacity. During the third quarter, the Goldex mill processed an average of 8,222 metric tons per day (mt/d), compared with 8,448 mt/d during the second quarter of 2011. Goldex produced 40,224 oz during the third quarter, down from 41,998 oz in the second quarter. The decrease, according to the company, was largely due to the slightly lower throughput combined with slightly lower grades.
Goldex continues to grout a weaker, fractured, volcanic rock unit in the eastern end of the hanging wall of the deposit. The grouting program is expected to reduce a water inflow to the underground mine, which has caused subsidence issues at the mine site as previously saturated soils are draining into the mine and lowering the water table. Movement on the surface has been observed in the mill building and at the headframe. However, water flow rates have been controlled as remediation continues.
While the company’s underground instrumentation shows that the volcanic rock mass above the Goldex orebody is stable, it has received an opinion from a rock mechanics consultant that suggests water inflow has negatively impacted the integrity of the rock mass. As a result, the company is undertaking further assessment of the stability of the rock mass and is increasing its efforts to decrease water inflow and the potential negative effects of the water on the rock mass.
The grouting and monitoring program includes drilling from the surface and underground. Miners are drilling from the surface to investigate the area around the eastern end of the deposit for water flow and possible rock subsidence. Underground, miners are drilling into the volcanic rock unit to determine whether additional fracturing and movement in the rock mass has occurred. They are grouting with six larger drills, targeting the rock between 80 m and 100 m below surface over an area at the eastern end of the deposit to stop or reduce the water inflow.
The mine is also installing additional instrumentation to monitor for any soil and rock movements. They currently have excess pumping capacity to ensure that increased water flows can be dealt with, should the need arise. Agnico-Eagle said the program will be reassessed on a three month basis to determine whether additional remediation work or changes in the mining plan are warranted.
The initial budget for remediation of this subsidence issue was C$20 million through 2011. The company now anticipates 2011 expenditure will increase to C$25 million. It also believes it will have to spend an additional C$20 million in 2012.