Lac, Cambior to double mill capacity at Doyon

There’s going to be a lot more ore coming from the Doyon gold mine in northwestern Quebec, the underpinning of two major mining companies, so management has decided to spend $16 million to double milling capacity.

That will bring to $56 million the amount the partners, Lac Minerals and Cambior Inc., are spending at the open pit mine. They are already about three- quarters of the way through a $40-million, 3-year underground development program expected to be completed by the end of 1987.

The mill expansion is over and above the cost of that development program with the cost to be shared equally. While Lac is operator of the mine, a management committee with three members from each company oversees operations.

Increased mill capacity will have little impact on total gold production, estimated to be about 210,000 oz in 1986 compared to 169,420 oz in 1985. Less than half the ore mined at the Doyon is currently milled on site, the rest being shipped to Lac’s East Malartic mill with some being shipped to Noranda’s Horne smelter where it is used as flux material.

The expanded mill will, in effect, allow all of the mine’s ore to be processed on site.

The Doyon mill now has a rated capacity of 1,650 tons per day using conventional cyanidation and Merrill Crowe processes. The expanded mill will be able to handle 3,300 tons per day and is expected to be in operation by November, 1987.

At the end of 1985 the mine was producing 3,443 tons of ore per day. The changeover to underground mining from the current open pit operations, which has started and is expected to be completed by 1988 when open pit reserves are depleted, could result in lower production due to hoisting capacity.

A preliminary report earlier this summer indicates annual production of 137,000 oz of gold in 1989 and 119,000 oz in 1990, but those are very conservative estimates based on the present 1,650-ton- per-day mill and the absence of operating results from underground mining in the main zone.

Present hoisting facilities can handle 2,700 tons a day, but one of the shaft’s four compartments could be used as a second hoisting compartment. If the second hoist is installed (the headframe is designed to handle it) hoisting capacity could be significantly increased.

The Doyon is Canada’s largest open-pit gold mine. The shift to underground mining is well under way, however, with the timbered shaft having reached its target depth of 2,150 ft in March. By the end of 1986 the two companies expect to have spent more than $36 million in the $40-million development program.

There are actually two zones currently being mined, the Main zone and the West zone. The open pit mine that accounted for production prior to 1986 was on the Main zone. That open pit has been extended to include the upper portion of the west zone.

Underground mining has started on the main zone and will be augmented with production from the west zone.

Proven and probable ore reserves at the end of 1985 were as follows:

Grade

Tons (oz per ton)

OPEN PIT

Main zone 2,772,000 0.14

West zone 553,000 0.18

UNDERGROUND

Main zone 7,030,000 0.16

West zone 997,000 0.34

TOTAL 11,352,000 0.17 The mine accounts for almost a third of Lac’s gold production (not including the Page-Williams mine at Hemlo, Ont.). It is Cambior’s only source of gold production. Located seven miles west of Cadillac, the mine has been operating since March, 1980. It expects to pour its millionth ounce of gold on Oct 7.

Operating cost per oz of gold produced at the mine in 1985 was $312(Cdn), including depreciation and amortization.