The two tumbler barrels seen along side the building on a platform are filled with water and steel balls the size of softballs. As the barrels rotate the cooled slag from the slag pots (containing approximately 2% copper content) is fed into the tumblers and crushed by the tumbling steel balls. After being crushed to a fine sand consistency it is slurried to precipitate out the remaining copper producing a very moist concentrate averaging between 22% to 37% copper content. From there it is sent to the Filter Plant (image 264)