A paradigm shift

Nestled between the snow-covered Cortez Mountains and the Shoshone Range, the Cortez gold mine has been synonymous with United States gold mining for decades. Cortez is Nevada’s longest continuously operated gold mine and the largest gold producer in the state, which is responsible for nearly 80 percent of all gold mined in the US. The Cortez area has been actively mined since the discovery of silver in 1862 and modern-day gold production started from the Cortez pit in 1969. Since 1997, the mine’s Pipeline open pit and Cortez Hills open pit and underground operations have produced more than 20 million ounces of gold. Cortez has consistently been one of the world’s top 5 gold producing operations, churning out 1.06 million ounces of gold in 2016. Production is expected to increase to between 1.25 and 1.29 million ounces in 2017, and although ore has historically been sourced primarily from open pits at Cortez, the mine is shifting its focus to an expanding underground operation while aiming to maintain annual production levels of more than a million ounces over at least the next decade.

Barrick chose mechanical cutting instead of traditional drill-and-blast to develop the new portals to its underground operation at Cortez, the first time a roadheader has ever been used at the mine. The company is also set to introduce a roadheader in ore production at its nearby Turquoise Ridge gold mine later in 2017. It’s a paradigm shift towards continuous mining that Barrick expects will bring significant economic and safety benefits to its Nevada operations. Roadheader does it better Jim Wieser is the safety manager for Drill Tech on the Cortez contract, the company’s lone mining job among more than 100 projects started in 2016. “Driving tunnels, sinking shafts, whether it’s for a water tunnel or for a gold mine it’s all the same,” Wieser says. “The principles don’t change a bit.” Despite spending nearly his entire 40-year career in drill-and-blast development, Wieser became an instant believer in the advantages of mechanical cutting during his first roadheader project tunnelling through high-pressure shale in Wyoming. “Our first 800 feet was drill-and-blast and we used a roadheader for the rest of the mile-long tunnel,” he says. “In 10 years we rehabbed the drill-blast section four times and the roadheader section looks like it was just cut and bolted yesterday. Roadheaders are definitely better for long-term development.”

You’re just carving it out and it gives you a much better profile to put your ground support in. Your grade is cut perfectly. It’s easier to keep your road beds in, keep your ramps in shape. There’s a lot of benefits to roadheader versus drill-blast – if you have a machine that can cut the rock.” ‘A great machine for the harder-type material’ Weighing 125 tonnes, the Sandvik MH620 cutting the Range Front declines at Cortez is one of the world’s largest roadheaders. A 300-kilowatt cutting motor drives twin rotating cutter heads that are manoeuvred by a large hydraulically-operated boom. Wieser, who’s operated smaller roadheaders from Sandvik predecessors Voest-Alpine and Dosco in previous projects, estimates some of the hardest black limestone Drill Tech has encountered at Cortez to be in the 12,000-15,000 PSI range. “The MH620 has no trouble cutting it,” Wieser says. “The roadheader itself stays stable and doesn’t move around and jump around and beat itself to death. It’s a great machine for the harder-type material.” Sandvik MH620 features the most modern version of the OEM’s automatic cutting system – nicknamed AutoCut – designed to enable a consistently accurate profile that reduces ground support costs. Improved roadway quality also helps reduce the risk of slip, trip and fall injuries. The AutoCut system guides the cutter boom to cut the required roadway section within a pre-given profile contour. The roadheader’s PLC calculates necessary boom cutting traces based on input parameters selected by an operator defining profile size and geometry. Wieser has worked with crew lead Darin Davison on three other roadheader projects.

Extending the life of Cortez The Range Front declines are expected to take three years to complete. Each decline is projected to be at least 7,200 feet (2,200 metres) long and Barrick plans to install a conveyor in the east decline to transport ore to the surface at a significantly cheaper cost than haul trucks, which will still be used underground for moving muck to the conveyor and for backfill. “The tunnels have to be straight,” Wieser says. “Extremely straight. If you’re off just a little bit that conveyor isn’t going to fit in that tunnel and come all the way out.” To develop the declines, Sandvik MH620 loads the cut material into Sandvik TH430 trucks for transport to surface. Metal ducting that will improve ventilation underground is installed section by section as the roadheader advances.

“We’re maybe one, two percent overbreak, or maybe under,” Wieser says. “It’s cutting a very, very nice tunnel.” Drill Tech celebrated six injury-free months at Cortez on March 17, 2017. “Nobody’s had so much as a scratch,” Wieser says. “We’re very proud of our workforce and the job they’re doing here. I believe Barrick’s very pleased with our performance, both health and safety-wise and production-wise. It’s a good marriage here. We’re having fun. We have a lot of fun here. We really do.”