Three mine closings forge Noranda’s policy on shutdowns

With two operations recently closed and a third mine shutdown imminent, Noranda (TSE) is bringing into play its environmental management system that has been developed during the last several years to keep pace with the expanding environmental legislation.

The three operations are the Brenda Mines (TSE) and Bell Copper open-pit mines in British Columbia, and the Mattabi-Lyon Lake underground mines in the Sturgeon Lake area of northwestern Ontario. Brenda was shut down last year and Mattabi-Lyon Lake this year.

The mill at Brenda’s open pit copper-molybdenum mine started in 1970 at 20,000 tons per day; it was brought up to 24,000 tons per day within months and to 30,000 tons in 1985, at which level it remained until final closure in June, 1990. The mine was one of the lowest grade in the country, averaging 0.16% copper and 0.035% molybdenum. Tonnage milled amounted to 201 million tons.

The surface expression of the finished pit is about 3,500 ft. by 3,500 ft. with high and low walls of 1,300 ft. and 800 ft.

The mine is located in an environmentally sensitive area and only 17 miles by road from one of B.C.’s best known tourist regions, Okanagan Lake, with its valley of irrigated fruit farms.

Brenda’s host rock is chemically basic and does not generate acid. Nor does soluble copper cause difficulties, but minute quantities of molybdenum leach from the rock and that is a matter of concern.

Molybdenum is not known to be harmful to humans but can be harmful to cattle and sheep if ingested in high enough concentrations over long periods. Thus, grasses and common field fodder absorb and concentrate molybdenum carried in the irrigating water, and in the dry country of the Okanagan, irrigation is the usual source of moisture. A number of procedures for removing the molybdenum are being examined.

Brenda’s extensive rock dumps are being profiled to lower, more stable slopes and fine material distributed over coarse rock wherever it is available. The seeding of various grasses and legumes is under way and shrubs and trees are also being planted.

The provincial government has been paid $5 million and rehabilitation is expected to be completed in five years. Monitoring and testing will continue until the entire area has stabilized, but even with the relatively trouble-free characteristics of Brenda, this work could extend into the next century.

The Bell Copper open pit mine is in no less a sensitive area. It is situated a little more than a mile from Babine Lake, claimed to be one of the richest salmon spawning lakes in B.C. The lake is estimated to produce more than 100 million salmon fry each year.

Bell Copper’s 10,000-ton-per-day mill first turned over in late 1972. Its capacity was increased to 17,000 tons in 1980 and continues at the same rate to the present time. Ninety million tons have been milled to date. Ore grade has averaged 0.54% copper and 0.007 oz. gold per ton. Final pit dimensions will be about 3,200 ft. by 2,560 ft. and 680 ft. deep.

The mine was originally scheduled for closure in the fall of 1992 but if ongoing studies are positive, the operation could see up to a 15-year extension of its life.

The acid generating potential of the waste rock varies from nil to low with the low values originating from patchy and sporadically distributed sulphides in the waste rock. Mill tailings are chemically neutral. The tailings starter dams were constructed, in part, from the sporadically mineralized rock noted above and testing is now under way to quantify seepage volumes and their heavy metal content.

Preliminary talks have taken place with the provincial government regarding environmental bonding, but no decisions will be made until Bell’s de-commissioning plan, scheduled for July, 1992, is complete.

The plan will include analysis of acid generation scenarios, biological and biochemical response to the mine’s seepage and runoff and examination of the several options available for handling contaminants, including open pit storage and wetlands detoxification.

In comparison with the environmentally benign Bell and Brenda operations, Noranda’s 60% owned Mattabi Mines and 100% owned Lyon Lake mine in northwestern Ontario worked massive sulphide ores hosted within pyritic wall rocks.

Mattabi was worked as both an open pit and underground operation from 1972 until late-1988; 12.3 million tons grading 7.5% zinc, 0.8% copper, 0.9% lead and 3.5 oz. silver per ton passed through the 3,000-ton-per-day mill.

Lyon Lake was brought into production in 1986 and the ore trucked five miles to the Mattabi mill. Its several but relatively small orebodies were forecast for exhaustion in late-1991 but low metal prices forced an earlier closure in May of this year. This was a wholly underground mine and about 1.3 million tons were milled of a grade similar to that of Mattabi. About 800,000 tons of developed ore grading 7.5%-8% zinc are being left underground but it is unlikely the material will ever be recovered. The mine is being allowed to flood and all equipment is being sold.

There are two large areas requiring environmental consideration, an open pit waste pile and the mill tailings.

Environmental proposals, currently at an advanced stage, are being prepared by Noranda and its consultants. When completed, the data will form the basis for discussion with the provincial government and other interested parties. The information gathered will also establish the terms and dollar amount of the environmental bonding agreement.

One of the crippling ironies facing Mattabi and a score of operations like it is that the production of acid runoff from rock piles and tailings dumps will take a hundred years or more. The volume of runoff is more than enough to cause environmental damage for a lengthy period but the volume is too small and the heavy metal content too low to make commercial recovery worthwhile.