It’s hard to believe that it’s been more than five years since Michael Gravelle, Ontario’s Minister of Northern Development and Mines, broke ground at the Young-Davidson mine in Matachewan to mark the start of renewed construction on what today is one of the country’s larger underground gold mines.
In fact, since that ceremonial shovel went into the ground on September 10, 2010, the site has been transformed from a local landmark containing a few remnants from of the original Young-Davidson/Matachewan Consolidated mine (mined from the mid-1930s to the mid-1950s) to now, where a small city of administrative buildings, head frame, mill, an open pit, tailings ponds, and a network of roadways criss-cross the 11,000-acre property.
Located approximately 60km west of Kirkland Lake on Highway 66, the mine is centrally located between Timmins, Kirkland Lake, North Bay and Sudbury, and for the past five years, Alamos Gold Inc. has been building on, and extensively expanding the underground workings at the 85-year-old site.
To say that Alamos has taken its work seriously is an understatement because as the mine’s General Manager Luc Guimond explains, “The Young-Davidson project was a challenge from the start because it involved the implementation of new technologies with original designs and underground workings and anytime you combine the two, the old with new, there’s always a chance the two don’t get along.”
By that, Guimond explains, is that anytime you pick up where someone else left off, especially underground involving historic shafts and stopes, there’s always a question about stability and especially the safety for the miners entering the existing mine.
In the case of the Young-Davidson Mine, however, Guimond said the teams of miners from his company, plus those from both of the main contractors, Dumas and Cementation, worked extremely carefully when expanding the mine and today, he proudly oversees the accident-free and productive mine.
As mentioned earlier, one of the main contractors involved with the Young-Davidson mine is Dumas, a company that Guimond says was involved long before the official ‘go-ahead’ was given to put the mine back into operation.
In fact, Dumas has been onsite continuously since 2006 when it was hired by Northgate Minerals (owners of the mine at the time), to dewater and rehabilitate the mine’s historic shaft, and replace the shaft bearings, as well as replace all timber sets with steel from surface to the 700-m level.
Dumas was also responsible for completing the installation of services, the hoist installation, and rehabilitation of the existing head frame.
During shaft rehabilitation, Dumas also undertook a concur-rent lateral development program that included portal construction, ventilation raises, and associated mine construction.
One of those construction phases involves an ore pass and ramp work that has involved more than 30,000m of ramp and lateral development to ore zones and ventilation drifts involving the excavation of approximately 7200m per year.
Perhaps one of the more ambitious and innovative mining techniques used during the construction of the Young-Davidson mine was the raise-boring of a 5.5-m-diameter production shaft.
Cementation, also a long-time contractor at Young-Davidson, having been on site since 2010, was responsible for the shaft’s engineering and design, plus underground development and construction.
Dennis Martin, Raise Boring Manager, Cementation, explains in more detail by saying: “The technical challenge for raise boring Alamos’s Young-Davidson production hoisting shaft was drilling the pilot hole straight and reaming it out to 5.5m in diameter.
“The vertical tolerance used for the engineering design was 300mm over the entire length of the shaft barrel, and completed at less than 100mm. The final shaft diameter of 5.5m was completed without an in-hole hardware failure, medical aid or lost time.”
He added; “This technical raise-boring challenge was accomplished due to three main elements and heavy capital investment by Cementation.
1. Tooling to drill vertical pilot holes with high accuracy;
2. Large diameter raise drills, rods, bottom hole assemblies, reamers; and
3. Very well-trained personnel.”
Martin further explains that a detailed risk assessment was completed prior to starting work, and a methodology put in place for the main work activities.
Here’s a look at the methodology used by the company.
Pre-mobilization: Prior to the equipment arriving, Cementation had a representative on site from time to time to ensure the site preparations and requirements where on schedule.
Site Preparation: The drilling site, raise drill foundation, underground reamer connecting site, and site services required for the raise boring operation of the project was completed by the Client as per Cementation drawings.
Mobilization: First truck load arrived on site one day after the last of the client’s site specific workforce orientation requirements where completed. Off-loading the majority of the drilling equipment took place prior to the drill set up but continued during drill set up. It required a forklift capable of 5+ tonne and a 100+ tonne crane working on day shift only.
Setting Up: Took approximately 10 days, was done on day shift only until the earliest opportunity 24/7 activity could take place.
Drilling the Pilot Hole: This was a critical activity as mentioned above and strict operational procedures were in place. Time was not a factor, accuracy was and the results exceeded design tolerance by a wide margin.
Breakthrough Area: The breakthrough area of the pilot hole is also the shaft bottom and this area was completed prior to completing the pilot hole. Shotcrete was applied to the back to keep the brow from peeling and provide a safe working area at the brow.
Reamer Installation: The reamer assembly had six major components that took two days to assemble and attach to the drill string.
Reaming the Raise: The reaming averaged 5.0 m/day and mucking the cuttings was completed with a remote loader.
Reamer Removal, Tear Down: It took 5 days to remove the raise drilling equipment from the top of the shaft and pull the reamer out the top with a crane.
In addition to Cementation’s raise-bored shaft, the underground is also accessed via a second shaft and main ramp. The raise boring of the Northgate shaft was completed down to the mid-shaft loading pocket in 2013, which accesses the first eight years of mine production.
Luc Guimond explains that work continues on developing vertical access in the underground mine below that of the mid-shaft loading pocket, to an eventual depth of 1500 metres. The existing shaft is expected to reach its ultimate depth this year to provide for the hoisting of personnel, materials, ore and waste.
The mine operates Scooptrams to load, haul and transfer stope production to the ore-pass system from where it is hoisted to the surface by 18-tonne skips.
There’s also the ramp that is being extended to the bottom of the mine from the existing exploration camp, currently at the 900-m level.
Once in the mill, both underground ore and stockpiled open-pit (closed in June, 2014) ore is processed through an 8,000 tpd single-stage semi-autogenous grinding circuit with a grinding circuit followed by flotation.
Guimond explains that the flotation concentrate is further ground and leached in a conventional carbon-in-leach system with flotation tailings also being leached in a carbon-in-leach circuit.
The gold is recovered from the carbon followed by electro-winning and pouring dore bars.
First gold was poured at the Young-Davidson Mine in April 2012.