There were fears that capping the shaft could possibly stall the GAG inertisation unit, which has run for a week and is continuing to operate this morning.
But conditions at the mine improved during the weekend.
A New Zealand Police spokesman told ILN gas emissions from the shaft became more stable and weather conditions improved enough to allow the capping operation to go ahead yesterday.
Two 170-kilogram, semi-circular steel plates were separately airlifted in by helicopter, then bolted together and placed on top of the ventilation shaft, with sandbags securing the completed cap.
This operation was completed shortly after 2pm.
Not to be confused with Australian underground coal fire fighting specialist Dr David Cliff, who also is at the scene, police superintendant Dave Cliff provided an update yesterday.
“We're hopeful the cap will help to improve the effectiveness of the GAG engine, and stabilise conditions inside the mine," he said.
At the time Cliff said gas levels would be monitored for several hours after the capping, but the police spokesman said oxygen levels are still being monitored this morning.
Once the environment is stable enough, teams plan to shut down the GAG engine for temporary maintenance and add more concrete to bolster the sealing at the portal.
"From that point it will be a case of maintaining a stable atmosphere inside the mine," Cliff said.
"With the cap in place the GAG may not need to run continuously, and we will only operate it as oxygen levels rise.
"Monitoring will continue over the coming week while we plan to introduce a nitrogen-generation unit. This will pump nitrogen into the mine to maintain an inert environment and reduce the temperature."
Air Liquide is arranging transport of its Floxal Coal Mine AMSA Unit to the mine in conjunction with NZ Police.
“The AMSA unit has been diverted from its previous intended purpose of inerting a mine in Australia with the cooperation of the customer,” the company said this morning.
Australian and NZ staff from the company will commission the unit and operate it during this mission.
The mobile Floxal unit is the smaller version of the inertisation unit, which is increasingly used in Australia’s underground coal sector.
