Arizona is nicknamed “The Copper State” because of the great deposits of copper that Nature has placed here.  If Arizona was a country, it would be the second largest producer of copper in the entire world.  Only Chile produces more copper than Arizona.The star on the Arizona state flag is copper-colored because the red metal is so important to the state’s economy.  A miner is even depicted on the state seal.Asarco currently operates three copper mine properties in Arizona:

  • The Ray Complex mine and mill, between Hayden and Superior, Arizona
  • The Silver Bell mine and SX/EW plant, northwest of Tucson, Arizona
  • The Mission Complex mine and mill, south of Tucson

The Mineral Discovery Center is located at the Mission Complex, and tours of that facility are available between 9:30 a.m. and 3:30 p.m. on days that the Center is open (see the Home Page for more information).

 Mine_at_workThe Mission Mine Ore Body
The ore body at the Mission Mine has an average grade of about 0.67 percent copper, which means every ton (2,000 pounds) of ore produces about 13 pounds of copper. But for every ton of ore, about three more tons of waste rock must be removed. Only the enormous scale and efficiency of an open-pit mining operation can make such a low-grade deposit economically viable.Geologists and Mining Engineerscomposite_geology
Mining engineers rely on information collected by mine geologists to develop a computer model of the copper deposit.  Sophisticated interactive graphical computer programs are used to carefully plan and track the progress of the mining operation on a daily, weekly, monthly, and annual basis.When the Mission Mine was being planned almost 50 years ago, it took several engineers working several months to develop a single mine plan.  In that period of time, the price of copper could have changed significantly, thus making the mine plan inappropriate.With current computer technology, changes to the mine plan can now be made in a few days by one mining engineer.  A number of mine plans based on different metal prices can be developed to help the mine better respond to changing market conditions.  When the price of copper is high, lower-grade ore can be cost-effectively mined along with the better grade ore. When the price is low, the mining operations can focus on the higher grade ores.
 Drilling and Blasting Crew
 mine_blastBlast holes are drilled in a pattern partially determined by the hardness of the rock. The goal is to fracture the rock enough that the large shovels can load it in the haul trucks without encountering big unbroken boulders that would be too large for the throat of the primary crusher.The holes are loaded with a mixture of ammonium nitrate and fuel oil (ANFO). Safety is the highest priority at the Asarco Mission Complex, so the blasting crew detonates the charge during shift change when no one is in the pit.Blasting technology has steadily improved, and mine blasts may not seem as dramatic as in the past.  This is because now more energy goes into fracturing the rock in place, so not as much rock and dirt gets thrown into the air.
 Big Trucks and Big Shovels
 big_equipmentThe large electric shovel pictured here can fill a 240-ton capacity haul truck in only three passes!  The Mission mine has several big shovels and a whole fleet of large trucks — some with a carrying capacity of 320 tons each!The shovels are powered by 4,160 volts of electricity carried to each one by an “extension cord” more than two inches thick (and of course those are copper wires in that cable!).  The mine electricians make sure the pit operations have safe and reliable electrical service.
 Truck Dispatch SystemDispatch
A central high-speed, computer system keeps track of every truck and shovel.  It “looks ahead” to determine when a shovel will need a truck to load and then which truck will be in that vicinity at that time.  This system reduces the time a truck will wait in line at a shovel to be loaded, as well as the time a shovel is waiting for a truck to arrive.The Dispatch system was developed here in Tucson by Modular Mining Systems, Inc. and is used in mines all over the world.  Dispatch also monitors truck vital signs like oil pressure and temperature, which helps identify equipment problems before they cause a breakdown.
 Dust Control
 water_truckMine roads are kept damp by spraying them with 10,000-gallon water trucks that are almost as big as the haul trucks.  This effectively reduces the amount of dust kicked up by the haul trucks and other traffic on the mine roads.Water jets in the crushers and at the ends of conveyor belts also serve to keep wind-blown dust to a minimum.
You can stand right at the south rim of the Mission open-pit copper mine and watch the mining operation in progress when you visit the Mineral Discovery Center.  If you start your tour about a half-hour before the 4:00 p.m. shift change, you might get to see an actual mine blast.