Morenci is a porphyry copper open pit mine and processing facility located at Morenci in Greenlee County, southeast Arizona. Morenci is one of North America's largest producer of copper and one of the largest open-pit mines in the world. It is one of the world's largest producers of copper cathode from SX/EW. Its operations pioneered the use of GPS system technology and computer-controlled dispatching in its haul trucks, shovels and other heavy equipment
The mine is located at Morenci, Arizona in Greenlee County, Southeast Arizona, about 50 miles northeast of Safford. It encompasses approximately 21826 hectares comprising 19, 263 hectares of patented mining claims and other fee lands, 2,393 hectares of unpatented mining claims, and 170 hectares of land held by state or federal permits, easements and rights-of-way. The Coronado deposit is part of the Morenci pit.
Property - Morenci is a porphyry copper-molybdenum deposit. Both sulphide and oxide ores occur, with pyrite and chalcocite being the main sulphide minerals, and chrysocolla and malachite the predominant oxides. Molybdenite, galena and sphalerite are also present.
The Morenci mine is developed on a porphyry copper deposit that has leachable oxide and secondary sulfide mineralization, and millable primary sulfide mineralization.
The predominant oxide copper mineral is chrysocolla; chalcocite is the most important secondary copper sulfide mineral and chalcopyrite the dominant primary copper sulfide.
There is a predominately quartz monzonite magma intruded on the regional limestone and shale to create a porphyry deposit about 1400 x 900 m and averaging 250 m thick, with chalcocite grains, and pyrite, chalcopyrite, and sphalerite veins beneath a capping layer about 80 m thick.
Supergene enrichment in the Morenci porphyry copper deposit was the result of erosion, chemical weathering and mineralization. Low-grade primary chalcopyrite and pyrite mineralization was deposited as a result of Laramide magmatic and hydrothermal processes, initial unroofing and erosion removed approximately 1.8 km of rocks overlying the deposit and shed detritus to the north, the deposit was preserved under 640 to 950 meters of volcanic rocks as a result of mid-Tertiary extension and volcanism.
Most of the supergene copper enrichment at Morenci appears to have been formed as a result of Basin and Range deformation between ~13 and ~4 Ma. Iron oxidizing bacteria and sulfate reducing bacteria contributed to leaching and enrichment of copper. Destruction of the current enriched blanket accompanied base-level drop and stream incision as a result of progressive drainage integration in southern Arizona in the late Pliocene and Pleistocene.
Mining & Operations
The Morenci complex in southeastern Arizona comprises an open-pit mine, a concentrator, four solution extraction facilities and three electrowinning tankhouses. Ore is mined using open pit methods from two open pits (the Morenci and Metcalf Pits) which are located on two sections of the same deposit. The ore is crushed in the pit and transported out using a conveyor system. Solvent extraction-electrowinning (SX-EW) and concentrate/precipitate are the main copper production methods. The operation also produces by-product silver, gold and molybdenum.
Morenci operates continuously and has a workforce of 2000 plus employees, producing 840 million pounds of copper per year.
Morenci mines 830,000 tons of rock per day. Horizontal benches are 50 feet high. Currently two open pits (the Morenci and Metcalf Pits) which are located on two sections of the same deposit are in operation. Ore is crushed in three in-pit crushers and removed by conveyor. High-grade ore is conveyed to leach pads within the pit, the bulk of the primary crusher output (63,500t/d of ore) is secondary crushed and conveyed to a dump-leaching site. The Morenci pit is currently being backfilled, and utilized as a leach pad.
Mining equipment includes electric rotary rigs, mainly made by Bucyrus, drill blastholes; 13 P&H 4100 and 2800 series electric rope shovels load the truck fleet. The trucks include more than 60 Caterpillar units, both 793 (218t capacity) and 797 (272t) models.
Morenci was an early adopter of GPS technology and computer-controlled dispatching in its haul trucks, shovels and other heavy equipment. A cooperative agreement with Morenci allowed NIOSH and system manufacturers to test radar and GPS systems on Caterpillar model 793 and 797 dump trucks used in mine production. Development continued over a 2 year period resulted in a mine-ready system in April 2002. The real-time positioning software works on all open pit mining equipment, trucks, shovels, drills, dozers, and conveyors.
Morenci uses Series II Advanced Equipment (AE) mining equipment simulator software and hardware developed by Phelps Dodge and Immersive Technologies. The AE simulators are used to train new operators and re-train experienced operators.
Morenci has four solution extraction facilities and three electrowinning tankhouses. The copper production method is SX-EW. Two concentrators are currently on care-and-maintenance. The mine produces 370,000 tonnes of copper cathode per year at full capacity, with silver, gold and molybdenum by-products.
Morenci's first SX/EW plant was commissioned in 1987. Morenci's concentrators suspended operations in 2001 when the property made the transition to 100-percent SX/EW production.
The ore currently being leached is a portion of the sulfide ore now being mined. In addition, four major sulfide waste dumps from previous operations are now being leached. These dumps collectively contain over one billion tons of low-grade copper ore. Copper in the low-grade dumps was previously considered waste and would have been unrecoverable by smelting. Morenci is the largest producer of copper from SX/EW.
Environment and Community
Morenci is a "zero-discharge" operation. Virtually all of the water used at Morenci is recycled, some of it many times over. Morenci is registered for ISO 14001 certification.