Phelps Dodge drills confirm extension of Morenci mine

Phelps Dodge (TSE), the free world’s second largest copper producer, has identified an interesting-looking extension to the main orebody at its Morenci copper mine in Arizona. Vice-President Thomas Foster says the company has known for some time that a substantial amount of oxidized copper mineralization existed in an area to the northwest of an open pit deposit containing roughly 127 million tons of grade 0.72% copper.

But it wasn’t until a new solvent extraction-electrowinning (SX-EW) plant was installed at Morenci that the “extension zone” became interesting, Foster told The Northern Miner recently.

The largest of Phelps Dodge’s three U.S. copper mines, the Morenci is held 85% by Phelps Dodge and 15% by the U.S. subsidiary of Japan’s Sumitomo Metal Mining Co. Concentrate production from an open pit operation is expected to be 675 million lb. in 1990. In 1989, roughly 150,000 tons of concentrates were produced at Morenci via conventional milling methods and 175,000 tons by the SX-EW process.

According to Phelps Dodge, 60 holes drilled in the extension zone area northwest of the mine have identified chalcocite mineralization that is continuous over the project area.

Known as the Coronado deposit, the mineralized zone is more than 800 ft. thick in some areas and averages 430 ft.

The chalcocite deposit is overlain by leachable copper oxide mineralization averaging 300 ft. thick and based on drilling so far combined sulphide and oxide preliminary reserves stand at 150 million tons grading 0.7% copper.

Metallurgical testing demonstrates that the deposit is amenable to copper recovery by flotation and by heap leaching using the SX-EW recovery method, the company says. “There is almost no overburden to speak of,” added Foster.

In a bid to identify new mineralization in the extension area, Phelps Dodge will continue drilling.