Copper Mine Tour

On March 9th we drove south of Tucson to the ASARCO Mineral Discovery Center in Sahuarita, AZ to tour an open pit copper mine.  The guided tour took us to the edge of the open mine pit, then back to the plant to see how the ore is processed and copper removed from the waste rock. At this mine, every ton of ore produces about 13 pounds of copper.  But, for every ton of ore approximately 3 ton of rock has to be processed.
 Rock is first blasted to fracture it into material that can be loaded onto the huge trucks and hauled to a crusher.  The primary crusher reduces the rock to about 8 inch size pieces. A secondary gyratory crusher breaks those pieces even smaller.  From there the rock travels through large rotating mills that contain 8 inch diameter steel balls which pulverize the rock into a powder. The powder is mixed with water, lime, and other chemicals to create a slurry which goes to a flotation tank. Air is bubbled in, the extracted copper attaches to the air bubbles and is separated, dried and forms a fine powder which is now 28% copper.  At this point the powder is shipped to another site for smelting and refining.
   Huge amounts of electricity and water are needed for this process.  Much of the water is reclaimed and reused, which helps in this state with so little water resources.  Some byproducts of the copper separation process, small amounts of silver and gold, can be sold to help pay for electricity.  Some mines like this are evaluating the use of solar panels to help supplement the energy requirement.  The open pits are very controversial due to the environmental impact they have.  There are some efforts being made to reclaim the damaged earth and initiate native plants and animals to come back.  One way of doing this is to introduce grazing cattle into the area, hoping as they feed they will spread grasses and seeds over the earth.