Placer Dome’s Sigma mine mixes nostalgia with high-tech

Second in longevity among the troika of classic mines started by Dome Mines and Campbell Red Lake Mines in eastern Canada, the Sigma mine in Val d’Or, Que., is a creature of contrasts. The Placer Dome (TSE) property is a major mine, massive in the extent of its workings, yet operated on a human scale.

Without being old-fashioned, Sigma retains, like an Indiana Jones film set, the flavor of years gone by. Individual miners work in pairs or small groups, following veins of gold with shoulder-hefted jackleg drills, compressed-air slushers and hand-dump ore cars.

They work in narrow timbered stopes, they clamber through unlit flats too low to stand up in, enter holes blasted through into adjacent excavations, and climb wooden ladders placed in stages up and down the dripping manways between levels.

But Sigma is nostalgia with a high-tech face. Modern steel arches are replacing timber for support in new stopes, a newly developed compact long-hole drill that can move through 8×8-ft. drifts is being introduced, and the mill has just been modernized and improved.

Hydro-Quebec no longer supplies 25Hz-volt electric power to industrial customers so Sigma has completed a $10-million program to convert to 60 Hz-volt, involving changing close to 100 motors in the mill. A visit underground demonstrates this is a complex mine. Without Roger Lacroix, project engineer, as guide, it would be “lost city.” Going down 6,000 ft. beneath the streets of Val d’Or, there are 300 miles of tunnels, drifts, flats and stopes. No two stopes are the same and up to 50 are likely to be active at the same time. It takes a miner an average of 30 minutes to get from surface to workplace at the start of a shift and 30 minutes to get back at the end of the day.

The tunnels and openings are man-size, not machine-size; so you walk, often in darkness lit by your miner’s lamp. In a typical stope we meet mine captain Andre Guay, a 29-year veteran of Sigma, himself built as square and compact as the rock he hews. He is supervising a miner, Joel Riviere, checking out the ore veins in the rock above their heads for visible gold. Although Lacroix says “Our high grade would be regarded often as waste at Campbell mine,” small nuggets and “corn flakes” of native metal are often seen in the veins. At Sigma, most of the gold is found in micro-fractures within pyrite crystals in the ore.

Mining methods depend on the individual characteristics of the gold-bearing zones, a mixture of cut-and-fill, irregular room and pillar, and long-hole mining. Broken ore is moved to ore passes by scrapers in the small confines, or is trammed along 18-inch gauge tracks by battery locomotives. On surface, the mill and related buildings have that 1930s look, but inside, the technology is 1990s. Mill superintendent Jean-Guy St. Jean relates how in modernizing the mill, the grinding circuit was replaced, a new leach tank and cyclones were installed and programmable logic controls added. The mill can treat 1,600 tons per day but runs at an average 1,525 tons per day. The standard cyanidation process installed in 1937 as new technology still accounts for 96% of gold recovery. The gold-bearing precipitate is fluxed and melted to make 15-lb. gold buttons which are melted again and poured into dore bars.

Employee loyalty at the mine is high and turnover is low. Employees are represented by the Syndicat des Employes de les Sigma Mines (Quebec), a small independent union. There has never been a strike or lockout. Of 430 employees, 40 have worked 25 years or more.

General manager Andre Carrier says he has the most competent mine workforce in Canada: “The challenge in the immediate future is to reduce our costs of production by improving productivity. I am sure I will enjoy support for that, and Sigma will continue to be Queen of the Valley of Gold.” Sigma and Val d’Or grew up together. Gold in a quartz vein was discovered under a blown-down tree in 1934. The mine has operated continuously since 1937.

From the magazine Prospect, a quarterly publication of Placer Dome.