Project Background

The Canyon City Mill began operation in 1986. The owner of the site, at the time of operation, was Charlie Stoll. Robert Graham, the owner of Canyon City Mill, was subleasing the site from Stoll. The site was used for a cyanide leaching process to extract gold from mined ore from underground gold mines near Oatman, Arizona. One source of the ore was the Minneapolis Mine. No mining was done at the site. Operations ceased in 1991 after 90,000 gallons of cyanide solution was spilled on the property. The operation used three 30,000-gallon tanks to store sodium cyanide solution, which was sprayed or dripped onto piles of crushed ore in the leach field. As the cyanide passed over the ore, the gold formed complexes with the cyanide solution, forming the pregnant leach solution (PLS). Carbon in the form of cinders was used to absorb the gold from the cyanide-gold complexes for recovery. The cyanide was recycled back to the cyanide solution tanks. Figure 1 to the right shows the 30,000 gallon cyanide solution holding tanks.