Denver — After a rough year at the helm of the El Abra copper mine in northern Chile,
The open-pit mine failed to meet the expectations placed on it when Phelps Dodge bought a 51% interest in the mine, as part of the Cyprus Amax Minerals acquisition, of late 1999. The remaining stake is held by Chilean state-owned Corporacion Nacional del Cobre de Chile (Codelco).
Bottlenecks in the ore-delivery system held down production, while a mix-up in ore control resulted in sulphide mineralization being sent to the leach pad during the second quarter of 2000. The impact of the ore-control mistake proved significant: a loss of 6 million lbs. of copper production, increased cash costs of 0.6 per lb. across the whole company, and US$4 million in lost earnings.
The situation forced Phelps Dodge to take a harder look at the mine, beginning first with a review of the orebody model at El Abra that improved the ability to distinguish between leachable oxide mineralization and non-leachable sulphide mineralization in the pit.
El Abra is a typical Andean copper porphyry, though complex structural geology accounts for an irregular transitional zone between the overlying oxide and underlying sulphide mineralization. The dominant oxide minerals are chrysocolla and brochantite; absent is atacamite, a predominant mineral found at Codelco’s nearby Radimiro Tomic and Chuquicamata mines.
In July, Phelps Dodge also initiated an infill-drilling program that will delineate reserves beyond the mine plan initially laid out by Cyprus.
Part of the work entailed re-evaluating the vast conveyor system that brings ore 9 miles to the processing plant. No drastic changes were made, though the company found that systematic maintenance helped keep the conveyors working at 118,000 tons of ore per day. The company is hoping to increase that to 120,000 tons per day.
Phelps Dodge started third-phase stripping in the northern and eastern parts of the open pit in 1999 and is already seeing production from the underlying reserves. In all, the company moves 260,000 tons of rock at the mine each day.
In addition, Phelps Dodge set out on another program that will allow the mine to reach the goals the company set for it. The run-of-mine project will contribute production from lower-grade ore. In all, Phelps Dodge has outlined 260 million tons of lower-grade mineralization not classified as reserves, averaging 0.31% copper. West of the open-pit, the company has been stockpiling the material in Quebrada Ichuno for a valley-fill leach facility.
The company has awarded the engineering contract to Fluor Daniels, and has already received the environmental permits. The first solution should be applied early in 2002.
Phelps Dodge’s re-invention of El Abra is already beginning to show positive results. Performance was up in the fourth quarter of 2000, to 55,600 tons of electrowon copper. In 2000, the mine produced 217,400 tons of copper, turning in its best performance since it began operating, in December 1996.
Phelps Dodge expects 2001 to be even better. The mine should exceed 250,000 tons of copper, surpassing its design capacity for the first time in its short history.
The company says, as a policy, it will not release cash operating costs for individual mines.
Proven and probable reserves at the end of 2000 stood at 852 million tons averaging 0.45% copper, enough for many more years of operation. Meanwhile, the company is evaluating other satellite deposits for additional oxide reserves.
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