of deposition of gold, silver and other base metals. Copper and molybdenum sulfide minerals are dispersed in the intruded stock and in the adjoining carbonate sedimentary skarns. The main stratigraphic rocks in Bingham Canyon are Upper Pennsylvanian sandstones, quartzites, and limestones known as the Bingham Mine Formation in the Oquirrh Group. The central porphyry ores formed from mantle hydrothermal circulation while the outer vein and deposits in the sedimentary rocks formed at lower temperature when magmatic and meteoric waters mixed. Recovery process The extracted ore is treated at the Kennecott smelter at nearby Magna, Utah. The ore is run through a concentrator, where grinding mills reduce it to the consistency of face powder. Flotation then separates the gangue from the metalliferous particles, which float off as a 28-percent concentrate of copper along with lesser amounts of silver, gold, lead, molybdenum, platinum and palladium. A selective flotation step separates the molybdenite (molybdenum disulfide) from the chalcopyrite. The filtered concentrate slurry is piped to the smelter, where it is dried, and then injected along with oxygen into a flash smelting furnace to oxidize the iron and sulfur. The oxidized iron is skimmed off, while the sulfur dioxide gas is captured and sent to an on-site acid plant for conversion to valuable sulfuric acid – a million tons of it each year. Left behind is a molten copper sulfide called matte. The 70-percent-copper matte is water-quenched to form a sand-like solid, then injected, with oxygen, into a flash-converting furnace that produces molten, 98.6-percent-pure copper. This copper is then cast into anode plates and shipped by rail to the refinery. At the refinery, the anode plates are pressed flat and interleaved with stainless steel cathode blanks. Automated robotic vehicles place the prepared anodes in cells containing an acidic electrolyte. When the cells are electrified, the anodes slowly dissolve, freeing copper ions that are deposited on the cathode as 99.99-percent-pure copper. Impurities and precious metals settle to the bottom of the electrolytic cells as anode slimes. A chlorination leaching process recovers the gold and silver, which is melted in induction furnaces. Operations Kennecott's Bingham Canyon Mine is the largest artificially made excavation in the world, and is visible to the naked eye from an orbiting space shuttle. Employing some 2,000 workers, of material are removed from the mine daily. Electric shovels can carry up to or of ore in a single scoop. Ore is loaded