August 2009

Engineering Exchange

Sinking to new depths: Close coordination and clever scheduling helped Dumas sink a winze shaft without interrupting production

By M. Eisner

The Clam (air-powered mechanical excavator) suspended from the underside of the shaft sinking platform (galloway), during the excavation of the 257 station

Four years ago, Agnico-Eagle decided to dig deeper at its LaRonde mine. In production since 1988 and currently the largest operating gold mine in Canada in terms of reserves, the site is located in the Abitibi-Témiscamingue region of northwestern Quebec, approximately 650 kilometres northwest of Montreal. Of the mine’s three shafts, the 2,250-metre deep shaft #3, the Penna shaft, is believed to be the deepest single-lift shaft in the Western Hemisphere. It is used to hoist LaRonde’s ore production of approximately 7,200 tonnes per day. The mining method is predominantly transverse longhole stoping with delayed cemented backfill.

In May 2006, Agnico-Eagle decided to sink a winze shaft close to its Penna shaft in order to reach ore reserves of gold-copper and zinc-silver mineralization that until then had been inaccessible below level 245 (2,450 meters below surface) to a depth of approximately 3,110 metres. They engaged mine shaft specialists Dumas Contracting to sink the new winze.

Sinking a shaft below the surface starting at the 2,056-metre level “is a project that even from the beginning has its own unique set of challenges,” said  Jos Deschênes, Dumas general manager, Quebec and eastern Canada. One of the very first challenges Dumas faced was bringing the excavation equipment down via the surface ramp to the 215 level. This time-consuming process had to be executed with meticulous care because each bit of equipment had to be dismantled and lowered in the Penna shaft piece by piece and then put together before excavation of the winze could begin.

The situation was further complicated by the ongoing production at the mine. Twenty-four hours a day, seven days a week, ore is being hoisted to the surface via the Penna shaft. The Dumas team needed to find a solution whereby the daily ore needs were met, without delaying their schedule to sink the winze. They collaborated with Agnico-Eagle to coordinate shaft-sinking activities with the production imperatives of the operating mine.

The winze is lined with concrete and built to custom size specifications, which presented yet another challenge for Dumas. Plans called for the winze to be large, measuring 5.5 metres in diameter and 835 metres in depth, in order for it to accommodate the needs of the new mine. It had to be roomy enough for two skips, a double-deck cage and an auxiliary cage (sometimes referred to as a Marianne).The broken muck generated by the sinking of the shaft would be scooped out with a mechanical shovel, dumped into a bucket to bring it up to the 215 level, transferred to the Penna shaft, and then brought to the surface.

The design of the winze included the construction of three large stations and approximately 40 metres of lateral development per station. When the winze is completed, the miners will be able to commence production drilling from these workstations. Dumas is currently working on the second station at 2,780 metres.

Sinking the winze with ongoing mining activity presented another challenge to Dumas with regard to blasting, a potentially dangerous situation. Meticulous coordination with Agnico-Eagle was again needed so that blasting was done only in between shifts when no one was underground.

And finally, ventilation and heat in the shaft were initially a problem, but large fans were installed into ventilation raises to remedy the situation. “Agnico-Eagle put a lot of time in this to make sure there was the right amount of air circulation,” remarked Deschênes. “We began at the 215 level and heat was an issue until they commissioned a 4.6 MW cooling plant on 146 level to ensure that the sinking crew would have comfortable working conditions. It didn’t interfere with us, and we continued to do our work.”

With less than a year to go to complete the winze, Deschênes said the project will be finished on time. The shaft depth is now at 2,792 metres, not too far from the planned 2,840 metres. “We don’t expect any slowdowns or any major issues,” he said. “We are on target.”

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