Misima to give Place Dome 210,000 oz a year

VANCOUVER — Determined to maintain its position as North America’s largest gold producer, Placer Dome has announced yet another mine development — this time at its Misima gold property in Papua New Guinea. Earlier this month (N.M., Dec 7/87) the company gave the go-ahead for its Big Bell project in Western Australia which will be another major gold producer.

Construction work at Misima will begin in January and plant commissioning is scheduled for July, 1989. Gold output during the first 14 months (which includes a 2-month commissioning period for the mill) should total 400,000 oz along with 2.6 million oz silver. However, average annual production during the estimated 10-year life of the mine is projected to be 210,000 oz.

W. Anthony Triggs, senior vice- president project developments for Placer Dome, explains to The Northern Miner that a higher grade portion of the Misima orebody will be mined initially. This is the reason for the above-average gold output early on. Also, the near-surface oxide ore is softer, which will allow the plant to handle more volume.

Plant capacity is 16,500 tons per day and the mill will use a semi- autogenous grinding circuit followed by conventional cyanidation. Gold and silver will be recovered by carbon adsorption in a carbon- in-pulp circuit and recoveries are expected to be 90% for gold and 60% for silver.

Misima Island is located 150 miles off the southeast tip of New Guinea and 580 miles northeast of Cairns, Australia. Mineral exploration and mining have been carried out there almost continuously since 1888 and Placer Dome optioned the property in 1977. Extensive studies Extensive engineering, metallurgical, and environmental studies were completed in 1986 and a feasibility study was presented to the Papua New Guinea government in February, 1987. Triggs notes that project logistics at Misima are much better than the company’s high grade Porgera deposit in the Western Highlands which is also quite refractory.

The Misima plant will be constructed at tidewater and the mine site a few miles inland. The plant site would also contain a power station, company offices and maintenance facilities. Other infrastructure, including an airstrip and employee accommodation, will be located 2.5 miles east of the plant site near Bwagaoia, the island’s only town and administration centre.

The Misima orebody contains 61.7 million tons of reserves grading 0.04 oz gold and 0.6 oz silver. The waste-to-ore ratio is 1.28:1 and very little production stripping is required. Triggs concedes the plant might be able to operate above capacity but he says it hasn’t been specifically designed to.

The government of Papua New Guinea has elected to purchase a 20% interest in the mine and it will put up its pro-rata share of capital costs. Placer Dome’s interest in Misima Mines will be 60.6%. A subsidiary, Placer Pacific, will have an 80% interest in the venture. Its costs will be funded by an $80 million(A) private placement completed last July, $20 million(US) from the sale of gold warrants, and from funds borrowed through a bank multi- option credit facility or additional sales of gold warrants.

Placer Dome has two other gold projects under way: Dona Lake in northwestern Ontario and the Big Bell in Western Australia. With these three properties coming on-stream in 1989, its share of production in the Placer Dome group will exceed 1.1 million oz gold per year. A production decision at Porgera is expected in 1988 so gold production should climb even higher the year after.