Reserves, grade up at Windy Craggy

Because of a boost in both the quantity and quality of reserves at the huge Windy Craggy massive sulphide deposit, owner Geddes Resources (TSE) is more confident than ever of a long life for its proposed mining venture in northwestern British Columbia. The Vancouver-based junior recently filed its Stage I report with the British Columbia government in which it outlined plans for an open pit copper mining operation starting in 1994. The proposed mine, in a rugged and remote area near the Alaska-Yukon border and inaccessible by road, is expected to produce for at least 20 years at a rate of at least 20,000 tonnes per day and account for about 1% of world copper production.

After incorporating results from its 1989 exploration program, Geddes is reporting geological reserves in proven, probable and possible categories of 165.4 million tonnes averaging 1.89% copper, compared with 118.8 million tonnes at the same copper grade in August, 1989. The new calculation was made by the company’s consultant Derry, Michener, Booth and Wahl, using a 1% copper cutoff grade.

Gerald Harper, president of Geddes, said the constancy of the average grade of copper despite the addition of 46 million tonnes to reserves “is a dramatic demonstration of the magnitude and consistency of this world-class deposit.”

Gold and cobalt grades remained consistent but Geddes reported the average silver grade increased by 0.5 grams per tonne to 3.9 grams per tonne, reflecting higher silver grades encountered in the northern portion of the North zone as defined in the last quarter of 1989.

The 1989 drilling program also allowed 32.9 million tonnes grading 2.12% copper, 0.16 grams gold, 3.30 grams silver and 0.083% cobalt to be defined as proven. Much of this reserve is near the 1400-metre exploration adit level and in the South zone where drill spacing is close.

When combined with probable reserves of 110.2 million tonnes, the grade of the 143.17 million tonnes of proven and probable reserves is 1.69% copper, 0.20 grams gold, 3.40 grams silver and 0.084% cobalt.

If a 0.5% copper cutoff grade is used, reserves in all categories now exceed 200 million tonnes, including both the massive sulphide deposit and adjacent volumes of stringer or disseminated mineralization.

Geddes will be continuing to drill the deposit in the 1990 work season with the objective of upgrading the portion of reserves near surface that will provide the early years of production from an open pit in the North zone.

Geddes’ preliminary mining plan includes two open pits, the North and South, with an average stripping ratio of 3.2-to-1 waste to ore.

Metallurgical test work to date indicates that a 28% copper concentrate can be produced with recovery of 88% of the copper although fine grinding will be required to liberate the chalcopyrite from pyrite and pyrrhotite in four stages of flotation. (Geddes does not expect to achieve significant byproduct production of cobalt, gold, or silver, although it projects that zinc may be recoverable in certain portions of the zone.)

The conventional flow sheet incorporates semi-autogenous grinding followed by ball milling, high intensity conditioning, flotation and dewatering. Power will be supplied by large diesel generators at both the plant and mine sites.

The mine plans incorporate measures to protect the environment during operations and after closure from any potential acid generation in the pit, waste dumps and tailings impoundment.

The British Columbia government is expecting a great public interest in the proposed 100-km access road linking the property to the Haines Hwy. and the year- round port of Haines, Alaska, as the road at one point crosses the Tatshenshini Valley.

“Because the region has important economic development as well as recreational values, government has already given partial funding to study road options and environmental impacts,” said British Columbia Mines Minister Jack Davis.

The Windy Craggy project is expected to provide 500 jobs during the three years of development and construction, plus 638 jobs during operation. Two major companies, Northgate Exploration (TSE) and Cominco (TSE), each has equity interests in Geddes although Northgate is the larger shareholder.