An 8in pipeline carrying a mixture of mine tailings and cement has ruptured at Pogo Gold mine in Alaska spilling cement-like material in to the surrounding area.
Around 90,000-gal of backfill containing one to three parts-per-million of cyanide spilled from the pipeline.
The rupture also caused a valve inside a pump house to break.
The material is said to be combination of mine tailings and cement that hardens in to concrete, used to fill-in tunnels created by the underground mining process.
Alaska Department of Environmental Conservation (DEC) state on-scene coordinator Tom DeRuyter said that the pH level of the slurry was enough to neutralise the cyanide.
According to DeRuyter, the paste will be allowed to solidify at the mine site before being removed by personnel with the help of heavy equipment and hand tools.
The DEC will continue to monitor Pogo mine's response and review its plans for cleaning up affected gravel in the area.
Pogo mine, which is owned by Japan's Sumitomo Metal Mining, is carrying out an investigation to determine the cause of the spill.
The mine is located about thirty miles north-east of Delta Junction, and has estimated reserves and resources of 4.87 million troy ounces of gold.