CARLIN – Despite plans to finish mining at Exodus this year, Newmont Mining Corp. will not leave that underground any time soon.
The company has begun an expansion called Northwest Exodus.
“We’re treating it essentially like a new mine, but utilizing the Exodus equipment and manpower,” said Operations Superintendent Gus Friesen.
The discovery hole for Exodus was drilled in 1996 and underground exploration drifting began in September 2008. The first stope was completed with a transition to full production in 2011. The expansion into Northwest Exodus received full approval in 2016 from Newmont.
“In 2017, Exodus proper is scheduled to mine its last ounce, and then subsequently in 2018, we’ll pick right up and start mining Northwest Exodus,” Geology Manager Tyson Gibbs said.
Laterally there is about 1,200 feet between the edges of the ore body, said Mark Brazier, operations general foreman. The lowest level planned for Northwest Exodus will be about 1,900 feet below the surface, but the ore body is still open below that.
Northwest Exodus will be an 800,000 ounce expansion of Exodus, said Senior Engineer Jenessa Haarala. It extends the mine life until 2028. The new development will enable Newmont to use the mine’s existing workforce and continue to use the Exodus decline, which is accessed through a portal at the bottom of the Lantern Pit.
Exodus and its expansion is part of the Carlin Trend. It is refractory ore associated with arsenic-rich pyrite, Gibbs said. The deposition differs from other deposits on the Carlin Trend in that the gold follows a vertical sense along structural features rather than stratigraphic contacts.
“As the rock folds, it kind of forms a cup and has a really good geologic environment for gold deposition,” Gibbs said.
The first ore production out of Northwest Exodus was in 2016, Haarala said. Commercial production will begin in 2018. In 2015, the average grade was 0.27 ounces per ton and estimated reserve and resource was 807,000 ounces, Haarala said.
Since 2015, Northwest Exodus had 17,000 feet of drift development completed, 720 feet of vent raises and 615 feet of shaft development.
“We have 25,000 feet of capital drift planned over the life of the mine,” she said. “Some has already been developed. We have 1,700 feet of vertical rises planned and expense waste around 19,000 feet.”
Miners will develop the ore headings and start stoping the north end of the orebody from the 4145 level up. The mining method in the expansion will be the same as in Exodus proper – mechanized longhole stoping. They plan on mining 1,250 ore tons per day.
In preparation of moving to commercial production in Northwest Exodus, Newmont had to drill a new ventilation shaft.
In January, Thyssen Mining was sinking the 1,000-foot shaft that will serve as the fresh-air intake. Two fans will be on the surface.
“We’re planning to finish our shaft and then commission the new fans this year, which is pretty exciting,” Haarala said. “We’re going to continue developing the decline down towards the bottom of the mine.”
The contractors bored an eight-foot diameter hole from the bottom up to start the shaft, Friesen said. It isn’t a blind sink, but a bore and slash method. The slashing makes the hole bigger from the top down.
“You have to have an underground working to use that method,” Friesen said.
Changes in Operations
“One thing that we’re doing a little bit differently at Northwest Exodus is we’re putting in an underground shop,” Haarala said.
All of Exodus’s shop facilities are on the surface. Since Northwest Exodus is even farther from the surface, Newmont decided to relocate maintenance to the underground. It will decrease the amount of time spent waiting on equipment since the vehicles won’t have to travel as far. The underground shop will also include a wash bay and a fuel and lube bay. It should be done by the end of this year.
Northwest Exodus will also have ore passes and backfill transfer raises.
“These are a series of vertical raises that we’ll use to move material from up in the mine to down where we need it for placing backfill,” Haarala said.
Ore will be dropped down a raise and into a chute. The trucks will be loaded and then head out of the mine, Brazier said.
It decreases the number of haul truck traffic on levels, Haarala said.
“When you have several haul trucks trying to queue up on a level, there’s a lot of congestion,” she said. “It will decrease their cycle time and they’ll get loaded a lot faster, getting loaded from a chute versus having a mucker get a few buckets.”
It also will improve efficiency with autonomous mucking.
Automated Stope Drilling
“Another way that we’re looking at automating at Northwest Exodus, is we’re going to use a new stope drill,” Haarala said.
The Atlas Copco Simba drill has “some significant safety improvements” over the Cubex drill used currently, she said.
The first improvement is the operator will be in an enclosed cab, rather than being in the heading, which means they will have less exposure to noise and silica.
The Cubex drill also forces miners to work in the heading and handle drill rods, which means they have more potential to trip or fall since they are on uneven terrain.
The Simba drill rods are automated so the operator doesn’t have to leave the cab to change them and there is less chance of getting muscle strain since the rods don’t have to be moved manually. This automation also makes the Simba drills more efficient and faster than the Cubex, Friesen said. In a Cubex, the miner has to physically reposition the drill for each hole, but the Simba moves the boom mechanically.
Despite the automation of machines in the underground, the mine will keep all of its workforce.
“This uses the same number of people, it just removes a lot of that physical work,” Haarala said.
“We’re actually increasing our headcount with the execution of Northwest Exodus,” Friesen said.
Exodus is budgeted for 98 hourly positions, which increases the current workforce by 12.
In September 2016, Exodus hit a milestone of three years of zero harm.
The mine won first place in 2016 from the Nevada Mining Association for medium sized underground mine. Pete Bajo won third place for small underground mine, and Small Mine Development, which operates in the Chukar underground won first place in the contractor category.
“A couple of things we’ve implemented through our safety journey really is employee-based or employee-driven safety programs,” Brazier said. “Rather than the company just dictating everything, we want the employees involved in the discussion.”
Each crew has a vital behaviors representative and the employees make suggestions. Every Monday morning the staff reviews them and implements solutions.
“The program is intended to prevent injuries, rather than just being reactive and looking backwards. We’re looking forward,” Brazier said.