EXPLORATION ’93 — SX-EW gaining prominence at `stand-alone’

Solvent extraction-electrowinning (SX-EW) has long served as a secondary source of copper for large U.S. producers, but the process is also gaining prominence among so-called stand-alone operations.

In the first nine months of last year, at its Yerington mine, 80 miles southeast of Reno, Nev., Arimetco International (TSE) produced about 6.3 million lb. using the leach technology.

Now Arimetco is set to start up its 50%-owned MacArthur mine, adjacent to Yerington. The two projects combined are to produce about 24 million lb. in 1993.

Engineers are studying the possibility of constructing a plant to process sulphide ore from Yerington as well as from the Ann Mason deposit, which contains about 483 million tons at 0.4% copper.

Arimetco also owns the Johnson copper mine, 60 miles east of Tucson, Ariz. The 30,000 lb.-per-day operation, which began in 1990, produced about 6.1 million lb. in the first nine months of 1992.

Production from Johnson in 1993 is projected to be about 10 million lb. Partners Western Copper Holdings (TSE) and Thermal Exploration (ASE) are planning a leaching operation at their Williams Creek oxide copper-gold open pit, near Carmacks, Y.T.

Diluted pit reserves of the Number One zone, to a depth of 600 ft., are estimated at 13.6 million tons grading 1.07% copper and 0.014 oz. gold per ton.

A 25-million-lb.-per-year plant is planned, and the company will complete a bankable feasibility study by late July and permitting before year-end. Arimetco also has an option to acquire a 100% interest in the Copper Basin property, 30 miles south of Needles, Calif. Reserves there are estimated at 12.5 million tons grading 0.55% copper.

Although the company is focusing on Williams Creek this year, about $100,000 is budgeted for Copper Basin. The work will entail metallurgical work to test leachability of the copper mineralization.

Kookaburra Resources (VSE) hopes to develop a SX-EW plant at its Santa Fe project, 25 miles east of Hawthorne, Nev.

The company outlined preliminary reserves of about 16.1 million tons grading 0.55% copper and is completing metallurgical testing. A prefeasibility study will follow. Prefeasibility is also planned for the Chaucha copper project in Ecuador. Kookaburra can earn up to a 65% interest in the property from AG Armeno Resources (VSE).

A recent study of Chaucha estimates a 14,000-ton-per-day SX-EW plant would produce about 33 million lb. of cathode copper per year. Those figures are based on an estimated minable reserve of 60 million tons grading 0.46% copper at a 0.83-to-1 strip ratio.

The project would cost about US$63.6 million, including $6.75 million in working capital but excluding $17 million for engineering procurement, construction management and contingency.

Azco Mining (VSE) is evaluating three large copper oxide projects for their solvent extraction potential, including two in Mexico and a third, more advanced, project in Arizona.

Azco is raising capital to develop its Sanchez project, near Safford, Ariz. Sanchez contains an estimated 168 million tons grading 0.34% copper at a strip ratio of about 1.08-to-1.

About 12 million tons would be leached annually to produce 56 million lb. of cathode copper per year at a cash cost of about US49 cents per lb. Estimated capital cost: US$75 million.

Azco Chairman Anthony Harvey hopes to have financing in place for construction to begin this summer.

Azco recently completed a drilling program at its Piedras Verdes project in Mexico, where, last year, a new zone of higher-grade copper was encountered to the west of the main zone. The company has yet to compile a reserve estimate but will likely proceed with feasibility work this summer, Harvey said.

Cambior (TSE) acquired an option last October to earn a 50% interest in Azco’s third oxide copper project, the Suaqui Verde in northern Mexico. To earn the interest, Cambior must complete a bankable feasibility and spend at least US$800,000 in the first year.

Among the high-grade copper oxide projects being developed in Chile is Cerro Colorado, which owner Rio Algom (TSE) expects will produce about 88 million lb. per year over 23 years.

Even larger, with a projected annual output of about 200 million lb., is the Zaldivar project of Placer Dome (TSE) and Outokumpu Copper Resources. Teck (TSE) and associated companies Cominco (TSE) and Cominco Resources International (TSE) plan to use SX-EW at their Quebrada project in Chile.