Cassiar mine running on new feed

Although block caving operations at the Cassiar asbestos mine in northern British Columbia have encountered some problems with oversize material, the average ore grade has been considerably higher than expected. Princeton Mining (TSE), owner of the Cassiar mine, began underground mining operations in early November after spending three years developing the McDame deposit.

The McDame is the downward extension of the asbestos deposit mined by open pit at the site since the early 1950s and exhausted in 1989. Ore delivered from underground to date has averaged 9.2% fibre, compared with the 5.6% fibre grade anticipated in the feasibility study.

Bill Zemenchic, mine manager, said drill hole data used for the study is being reviewed to determine if the overall grade might be higher than expected. He noted that aside from the oversize problems, mining operations have gone very smoothly.

The mine utilizes a relatively unusual mining method known as blockcaving. The method involves developing heavily supported drawpoints below a column of ore and undercutting the column by blasting. As the blasted ore is pulled from the drawpoint,the ore above, which is characteristically highly fractured and sheared, naturally caves. The rate of caving is controlled by the rate of extraction.

The feasibility on the McDame deposit anticipated the caved ore to be no more than 12 inches, but in practice the operation has encountered boulders measuring up to three feet.As a result, operations have been temporarily suspended while a feeder-breaker system is installed above the ore pass in order to break material down to 12-inch passing.

Zemenchic said the feeder-breaker should be up and running soon.

Based on a 5.6% average fibre grade, the mine is expected to produce about 94,000 tons of fibre for 1991.

The price of asbestos fibre has continued to make gains, adding a further 5-6% for the various asbestos grades over last year, according to Lianne Gulka, spokesman for Princeton.

Although Princeton does not publish information on its fibre prices and product mix, the 1989 annual report showed asbestos revenue of $70.7 million from total sales of about 120,000 tons.

With copper prices nudging the US$1-per-lb. level, off from more than US$1.30 per lb. in 1990, Princeton is implementing a revised mine plan at its

Similco operation in an attempt to decrease operating costs.

Princeton owns and operates the Similco open copper mine near Princeton, B.C., and recently announced a layoff of 47 employees as well as a change in the operation’s general manager. The company plans to begin mining the Virginia deposit which was outlined during a $2-million exploration program last year.

The layoffs are being made in light of a lower mining rate for the new deposit. As a result of a lower stripping ratio on the Virginia compared with current operations, the mining rate will drop to 45,000 tons per day from 65,000 tons per day.

Jim O’Rourke, president, said the stripping ratio has been running well above the 5-year average of about 0.83-to-1 and the new mining plan will bring it back below 1-to-1.

O’Rourke declined to disclose current operating costs but did say the revised mine plan will bring costs down to the US90 cents range.

Copper production is expected to remain unchanged at about 60 million lb. per year.