Minera Los Pelambres, Chile
The Los Pelambres deposit, located 200km north of Santiago and 45km east of Salamanca in Choapa Province, was discovered by one of Chilean copper's founding fathers, William Braden, in the 1920s. Today's project, the world's fifth-largest copper mine, was started by Antofagasta Holdings in the 1990s.
In late 1997, Antofagasta sold a 25% stake in Minera Los Pelambres to one Japanese consortium and a 15% holding to another. With partner project finance loans secured, mine development started immediately, and production began in December 1999. Fresh water supply is drawn from three mountain streams but is carefully recycled. Electricity is taken from the grid via a dynamically controlled DC-link.
Antofagasta plc now owns 60% and manages the operation, which employs 521 people, via Antofagasta Minerals SA. One partner consortium comprises Nippon Mining and Metals Co. Ltd (15%), Marubeni Corp. (8.75%) and Mitsui & Co. Ltd (1.25%), while Mitsubishi Materials Corp. (10%) and Mitsubishi Corp. (5%) make up the other. Nippon Mining & Metals and Mitsubishi Materials planned to take delivery of approximately half the concentrate output.
Los Pelambres reserves
Porphyry copper mineralisation – chalcopyrite, chalcocite, bornite, covellite and molybdenite – makes up a resource of 3,000Mt grading 0.65% Cu and 0.014% molybdenum. By end-2005, the reserves figures were: proven – 831Mt grading 0.68% Cu, 0.019% Mo, 0.034g/t Au and 1.2g/t Ag; probable – 655.9Mt grading 0.67% Cu, 0.016% Mo, 0.032g/t Au and 0.93g/t Ag; and possible – 525.2Mt at 0.59% Cu, 0.0138% Mo, 0.033g/t Au and 0.57g/t Ag.
By 2008, a two-stage exploration programme to identify additional reserves was completed. The drilling programme identified an additional 1.9 billion tons of resources.
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The mine is an open pit sized 2.5km x 2.2km at surface, which is at an altitude of 3,100m above sea level (asl). Three Ingersoll-Rand electric rotary rigs drill blastholes, the initial two P&H 4100AS mining shovels and a LeTourneau L-1800 wheel loader, plus a 4100XPB shovel added later, work with a haulage fleet of five 329t-capacity Caterpillar 797 haul trucks to shift waste and ore in equal proportions. The mine works two 12-hour shifts.
Trucks feed an FFE Minerals 60in x 110in primary gyratory crusher and a sophisticated overland conveyor system engineered by ThyssenKrupp takes the ore 13km to the stockpile at the concentrator, which is down at 1,620m asl.
Two 17,000hp FFE Minerals 36ft x 19ft SAG mills work with four 9,500hp FFE Minerals 21ft x 33.5ft ball mills, giving a throughput of about 85,000t/d. In 2001 Los Pelambres decided to install pebble crushing to improve the SAG mill performance, and Bechtel designed an upgrade programme to raise the throughput to 114,000t/d. FFE supplied a redesigned SAG discharge system for this project. The pebble crusher was installed in August 2003 and had an immediate positive effect.
Concentration and separation involves two steps, carried out in a bulk flotation plant and a molybdenum plant. Bulk flotation involves rougher, scavenger and cleaner flotation with associated concentrate regrind stages and is optimised by the Metso Minerals VisioFroth system. Bulk copper-moly concentrate goes to a thickener prior to treatment in the molybdenum plant. Flotation tails go to tailing thickeners. About 70% of process water is recycled.
The concentrate slurry is piped via Salamanca and Illapel to the purpose-built port of Los Vilos (Punta Chungo) where it is dewatered for shipment. Los Pelambres treats the water extracted for use in irrigating a nearby eucalyptus plantation.
In April 2004, the Chilean government approved an Environmental Impact Statement covering a second tailings disposal site, Mauro. Construction would allow Los Pelambres to mine an additional 2,000Mt over the life of mine and extend that life from 22 to 47 years at the current processing rate of 114,000t/d. Alternatively, the concentrator capacity could be increased to 175,000t/d, possibly in stages. Construction of the Mauro tailings dam was completed in December 2008 at a cost of $600m.
In its first full year, 2000, Los Pelambres processed 34Mt of ore to produce 298,900t of copper-in-concentrate and 5,450t of molybdenum. In 2003, the plant treated an average of 113,300t/d of ore grading 0.91% copper, with average recovery 89.9%, to produce a total of 826,500t of concentrate grading 40.9% copper. Payable copper-in-concentrate totalled 326,700t and payable molybdenum, 8,700t.
2004 saw a 7.3% increase in output to 350,600t payable copper-in-concentrate despite a lower average ore grade of 0.88% Cu, mainly because of the pebble crusher added to the grinding circuit during 2003. However, the payable moly tonnage fell to 7,900t. In 2005, the copper ore grade fell again to 0.80% and payable copper-in-concentrate output dropped to 322,800t as the mine focused on maximising moly production, which rose to the 2003 level of 8,700t.
A $192m expansion project that was completed in 2007, boosting production capacity of the mine to 130,000t/d. By the end of 2008, the mine produced 136,000t of ore per day, graded at 0.76% ore.
A plan for further plant expansion was approved in July 2008. The expansion will boost copper production to 90,000t a year from early 2010. By June 2009, the project was 47% complete and within the allotted $1bn budget.