Personnel from Mexico's Federal Attorney's Office for Environmental Protection visited the San Dimas mine to evaluate the extent of the damage caused by a cyanide spill that reached the nearby Piaxtla river.
San Dimas, located in the northwestern Durango state, is owned by Canada's Primero Mining (TSX:P). The project consists of five ore blocks contained within a 22,500 hectares contiguous property. San Dimas uses long-hole stoping and mechanized cut-and-fill underground mining methods and all its ore is processed at the closeby Tayoltita mill, which uses conventional crushing/grinding coupled with cyanidation and zinc precipitation for recovery of gold and silver.
The recent spill took place on March 11 and was immediately reported, but only this week were officials able to visit the site. According to the information provided to them by the company, 200 litres of effluent were released into the environment due to an oversight in the closing of the valve of a pipe that carries remnants of cyanide solution. By leaving the valve open, the pipe exhausted its fuel reserves and, since it's located on sloping terrain, the solution started to leak out until it reached the river.
The solution is said to have traveled some 250 metres downstream, reached a concentration of 100-180 mg/l of cyanide, and killed an undetermined number of fish, most of them juveniles measuring between 1 to 5 centimetres. "In response to the emergency, the company removed the dead fish and implemented a wildlife monitoring program around the Piaxtla river," the government agency explained in a press release that preceded the visit.
According to local media, the Attorney's Office now has to file a post-inspection report and, if it deems it necessary, execute an administrative procedure against the miner.