There is one aspect of the Mining Quarterly editor’s job that has stayed consistent since the earliest days of the magazine, and that is touring the different mines that dot the Nevada landscape. I recently received my formal introduction to a working gold mine courtesy of Nevada Gold Mines, which arranged for a guided tour of its Cortez Gold Mine at the end of July.
For someone whose previous experience underground comes from enjoying the stalagmites and stalactites of Virginia’s Luray Caverns, it was quite the eye-opening experience. After the roughly 90-minute drive out to the mine site with Natacia Eldridge, NGM communications specialist, we arrived at Cortez.
After officially checking in and suiting up, we were ready to go underground. We met up with Cortez General Manager Henri Gonin, who took the wheel for our descent into Cortez Hills Underground.
During our ride down to the mine’s 3880 level, I was struck with how complex the underground tunnel system is. As someone who is decently good at directions, I have to admit I was glad to have a guide who knew how to navigate underground. Another aspect I found interesting was the flow of mine traffic underground, and just how many vehicles were operating at once.
After reaching our destination at the 3800 level, Gonin began to explain the process of drift and fill mining, which is one of the mining techniques utilized by Cortez Underground.
“We mine the first level at the top, the A level, and then B, C, D and E levels. Typically by the time you get to E, if the ore-body keeps on extending down, there is another A-level there, so you are really in the gravy train, because you have got backfill all around,” Gonin said.
Gonin explained that in other parts of the world, overhand cut and fill mining is more common.
“In other parts of the world they will go overhand cut and fill mining, but in our case, this backfill is a stronger composition of rock than the virgin rock in the ground,” he said. “We can make it safer to be under than being on top of it.”
“It is just safer and more efficient,” Gonin added.
Eighteen-year mine employee Jason Bundrock was operating a jumbo drill during the tour, and said that after spending two years on the surface, he is happy to be back working underground.
“I enjoy it. A lot of people don’t like it, they say underground is more dangerous. I disagree,” Bundrock said from the cab of his jumbo.
Working underground gives a miner more control over their immediate environment, and eliminates any weather complications or outside influences, he said.
“You are in your own world, so you take care of your heading, you are good,” Bundrock said.
Gonin said that after the jumbo drills a pattern of holes into the rock wall, it will then be charged with explosives and later, after everyone has left the mine, the explosives will be detonated.
After the lockbox is clear, signaling everyone who was underground that day has officially returned to the surface, then and only then will the explosives set that day blast from a central location above ground.
It is now time for the mucker to come in and remove the blasted rock material, where it will be taken above ground to an awaiting haul-truck. After cleaning out the immediate area, roof vaults are installed as well as ceiling mesh.
Another underground mining method utilized by Nevada Gold Mines is known as longhole stope mining, which is when a drift is developed, along with a second drift between 45-60 feet below the first one. A longhole drill rig is then brought in and used to drill holes in the rock from top down before it is charged with explosives and shot.
“It falls to the ground and on the bottom level you bring in your mucker and you load all that stuff,” Gonin said. “Now you have got this big open slot and you can blast again, and again and again, and then we backfill it.”
Gonin said these mining methods are not necessarily the most efficient, but the mining method used at a mine site is determined by just how big an opening a company can make without ground falling in.
“In Northern Nevada, where we are, the ground is typically fairly weak. We get places that have really good hard ground, too, but in general fairly weak compared to other parts of the world,” he said.
Gonin said the practice of lining a mine’s walls and ceiling with backfill is not used by all mines throughout the world, but in Nevada, a mine must ensure ground stability.
“There are mines in the world that they would look up at us and ask, why would you use that wire, what is that for? They wouldn’t know,” he said.
“We need to use a lot of ground supports, which is the vaults and the mesh and stuff. We don’t get to mess around with that, safety depends on that,” Gonin added.
After leaving the Cortez Underground 3880 level, we made our way to the mine’s Range Front Declines, where we toured the new feeder-breaker system that will allow Cortez Underground to expand its daily ore production from between 3,600 to 3,800 tons to 5,00 tons each day over time.
Gonin said that about 60 feet above the new system, there is a location where ore will be dumped into bins from above. It will then be fed through feeder breakers to reduce its size and then be dropped onto the new conveyor belt system and out of the mine.
“Right now we are using haul trucks to drive all the way out, dump the load and come back in again,” he said. “Once this is up and running we will use the trucks in the mine only, and not need to send them all the way out of the mine.”
The Range Front Declines project at Cortez has been a work in progress since 2017, and Gonin says it has presented some challenges, but they have found solutions and expect to have the new conveyor system operating by the end of August of this year.
After making our way back above ground, the tour continued on to the Cortez open pit mine, located on the other side of the property. I was struck by the vastness of the Cortez complex, and how much time can be spent just driving around to the different areas of the mine.
Upon arriving at an overlook of the open pit I was greeted by Acting Open Pit Mine Manager Danny Donnelli, who gave me the rundown on the open pit mining process.
Donnelli said the mine had about 125 employees working in the open pit that day, and roughly 52 ore-trucks operating. One of my first questions after seeing the open pit mine was about how the trucks and heavy equipment are managed to eliminate congestion and downtime.
Gonin said that each piece of equipment is tracked via satellite and wifi systems, and Nevada Gold Mines is able to keep track of exactly where each of its trucks is at all times. The dispatch systems use algorithms to determine how many trucks are needed for a particular shovel loading ore.
The algorithms are designed to help eliminate what the mines call standing time, or when a truck is just waiting its turn to be loaded with ore.
“That is standing time, that truck is not making any money right now,” Gonin said. “Conversely, when there are no trucks and the shovel is just standing there, it is called hanging time.”
Donnelli said that in open pit mining their safety concerns include fatigue, as well as accidents that can happen when mounting and dismounting from the heavy equipment.
After leaving the open pit mine, our next stop was the mine’s oxide mill and lab, and then it was time for the drive back to Elko. The mine tour made for quite the interesting day, and I would like to extend a thank you to the crew at Nevada Gold Mines for taking the time to explain the mining process to this industry newcomer.
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