Leeville's resources & reserves continue to grow

Mar 18, 2023

Leeville Senior Geologist Chris Mack talks about the geological maps showing the progress at Leeville from 2019 to 2022. He said the maps show not only the increase in the resources and reserves, which are colored blue, yellow and red, but also how big the footprint for exploration potential at Leeville has grown.

A Boart Longyear drill was drilling at Leeville last fall. A surface to underground cased borehole will be installed to deliver paste backfill to the Four Corners area. The target for the drill is 1,700 feet down, beneath the dewatering settling ponds which can be seen in the background on the left. This is a big project because surface to underground boreholes at Leeville are relatively long and challenging to get in.

Shaft #2 at Leeville is a big elevator that transports people, materials and ore in and out of the mine. For a recent tour of the mine a group of people went down more than 1,500 feet.

William Newman, Leeville engineering superintendent, brasses in at the mine's shaft. Anyone going into the mine puts their lock onto the board to provide a record of their presence in the mine. The blasting key is only accessible if the board is free of locks so that the rack can be slid over to provide access to the key. This acts as a physical lockout of the blasting system which prevents blasting while anyone is still underground.

A Cat AD30 underground mining truck, which has a payload of just under 30 tons, sits in a bay in the main shop at the Leeville Underground Mine. Almost all the work on the mine's mobile equipment is done in this underground shop. The mine has two underground shop locations.

Walking through the Leeville Mine 1,500 feet underground.

Michael Beyer, Leeville superintendent of geology, talks about a Sandvik reverse circulation drill which is being used for exploration in the Four Corners area of the mine. He said that since the drill head can swivel, this drill makes it possible to define the orebody more quickly with drill angles that are optimal for the area being explored. "This is a really cool rig," Beyer said.

Dan Kough points out some Nevada bolts holding the wire mesh panels in place on a wall of the Leeville Mine. Nevada bolts are 32 thread, 8-foot-long high-capacity bolts that were designed for the challenging ground at Leeville. The bolts can handle up to six inches of stretch and still maintain full capacity.

Michael Beyer, Leeville superintendent of geology, visits with lead driller Jesus Romero.

Leeville bolter operator Juan Vera talks about the cut sheet maps for the area he is working on. The maps are developed by engineers and provide information about the ground and the drill patterns required as Vera drills bolts to hold up the wire mesh panels that keep the mine walls in place.

Leeville Engineering Superintendent William Newman talks about one of the eight-foot-long bolts which are drilled into the walls to hold up the wire mesh. When a bolt is in place high-pressure water is pumped in to expand the end of the bolt to anchor it. Leeville Operations Superintendent David Byrnes is on the left.

The Leeville Mine is part of the Carlin Complex north of Carlin, Nevada Gold Mines’ and Barrick's largest gold-producing complex.

When you’re driving through a tunnel 1,500 feet below the Earth's surface as you make your way to your destination at the Leeville mine, you are deep inside the heart of one of the richest gold deposits in the United States.

The Leeville deposit was discovered by Newmont Corp. in 1992, and the first ore was produced in 2005. Since then, Leeville has become a key asset in the Nevada Gold Mines portfolio. NGM is a joint venture formed in 2019 with 61.5% owned by Barrick Gold Corp. and 38.5% by Newmont Corp.

Leeville employs around 7% of NGM's 7,000 employees and is part of the world-renowned Carlin Complex – NGM and Barrick's largest gold-producing complex. The complex, which consists of a series of open pit mines, underground mines, and processing facilities, is located approximately 45 minutes west of Elko, Nevada in the northeast corner of Eureka County.

"Leeville is one of the largest underground mines in NGM's portfolio right now," said Leeville Operations Superintendent David Byrnes. "Currently, we’re sitting at just over 520 employees and move anywhere from seven to eight thousand tons of total material per day, with four to five thousand of that being hoisted ore. It's a large, complex operation with a lot of fast-moving parts, employees, and equipment."

"Leeville is a massive ore body," said Michael Beyer, the mine's superintendent of geology. "The size of Leeville and the potential that we have here is quite unique."

And after 17 years of full production, this rich and complex deposit still has a lot to offer.

During a visit to the mine, we started the day with geologists reviewing maps and talking about the current resource and growth opportunities identified since the formation of the joint venture. Geologic maps of the site highlight how drilling has upgraded the resources and expanded the exploration potential to the north, east and south of Leeville. A fresh look at the exploration data in combination with knowledge from the mine geologists has improved the understanding of the mineralization controls and informed exploration targets along key structures.

Much of the mining at Leeville now is 1,500 to 2,000 feet beneath the surface, which is around 4,000 feet above sea level, with some of the new targets trending deeper, up to 2,500 or more feet beneath the surface. These targets continue to grow, with several new high-grade intercepts reported each quarter.

"The big takeaway from the comparison maps is that you see not only the increase in our resources and reserves, but also the increased size of the exploration footprint. Much of that is due to the great work of our exploration team and the drilling that has been done to add to the resource," said Carlin Growth Superintendent Chris Mack.

"As geologists, one of the helpful aspects of the joint venture is that we are able to look at each site's data. Now we have a much better understanding of our structural trends as a region, as opposed to just an isolated area at a specific site."

Before going down into the mine we stopped at an overlook site and viewed some settling ponds in the distance. About 1,700 feet underneath those ponds is Four Corners, the underground zone where we would soon be visiting.

Right below us, a drill rig was drilling in preparation for the installation of a cased surface-to-underground borehole, designed to deliver paste backfill to the Four Corners area. Paste backfill is a pumpable concrete used to fill in mined-out voids.

"Surface to underground boreholes at Leeville are relatively challenging to drill compared to the other mines in the Carlin Trend, so this is a big project," said Leeville Engineering Superintendent William Newman.

"You would imagine if you were to drill a hole it would turn out perfectly straight," Newman said. "But a hole this size never ends up that way, it deviates. We’ll drill the hole approximately two-thirds of the way down, survey it, and find out exactly where it's deviated to. That way we’ll be able to position our access drift underneath it, so that we break into it perfectly."

In the distance we could see the paste plant where the paste backfill is mixed.

"To deliver paste backfill, we use a large two-cylinder piston pump to move it from the paste plant to the borehole collar," Newman said. "Once it's at the borehole collar, everything else is done by gravity."

From the overlook, we made our way to the headframe and used the service cage to travel down into the mine. We made our first stop at the main mechanic shop where most of the service work is done on the underground equipment. While there we saw a Caterpillar AD30 underground haul truck being serviced.

At this point in our tour, we finally reached the Four Corners zone to see the work that's being done there. Four Corners is one of the original three orebodies identified at the Leeville mine over 20 years ago and is the most recent one to be accessed for mining.

"It's the newest zone that we’ve been developing, and it will be our most important mining zone for at least the next three years," said Newman. "Four Corners will be the predominant gold producer for Leeville. There are several large-scale projects that we are working on to ensure we can deliver the ounces in our business plan. These projects include paste delivery, truck load outs, and vent raises."

"Truck load outs offset the truck and loader elevations so the loader can work on a level that's uncongested and can directly load trucks with an operator in the cab, or semi-autonomously with the operator stationed on surface," said Byrnes.

"Truck load outs are more efficient. Our sister mines at the Portals have them and they work well, so we’re excited to get them implemented at Leeville. We’re in the final stages of getting the second of five Four Corners truck load outs constructed and commissioned."

Next, we stopped by an area where bolter operator Juan Vera was installing short-term ground support, a process that involves wire mesh and eight-foot-long expandable rock bolts. The expandable bolts are installed inside a drill hole and then inflated using high-pressure water.

"Once inflated, the friction between the bolt steel and rock surface is what creates the anchorage that holds everything in place," Newman said.

Additional long-term ground support is installed in all drifts with longer lifespans. Long-term ground support consists of grouted or resin bolts. At Leeville, a modified hollow rebar is used.

"We call them Nevada bolts," said Dan Kough, a senior geotechnical engineer for Leeville. "They were specifically designed for Leeville ground by Leeville employees."

"As the ground moves after initial excavation, the Nevada bolt can handle up to six inches of stretch and still maintain its full strength," Kough said. "This has allowed us to mine through some of the most challenging ground in the world."

Installing the ground support is part of the process of progressing a new drift, which can advance anywhere between 6 and 12 feet at a time. Miners working on development crews follow the design guidelines developed by the engineering team.

"Juan will be done in about three hours," Byrnes said. "We will then bring in a loader to clean up so we can move a jumbo drill, and depending on how abrasive the rock is, the jumbo will take anywhere from an hour and a half up to three hours to drill a round out; they’ll drill holes in the face. Once drilled off, a powder crew will load explosives into the drill holes, and we will initiate the blast remotely from surface during shift change while no personnel are underground, and start the cycle over again."

Newman said they generally create about eight to nine miles of new drifts every year at Leeville. However, that doesn't mean the total miles of open drift increases by that much, because older drifts that no longer serve a purpose are backfilled.

On the last stop of our tour, we visited an Aries B exploration drill which was being used to collect samples of rock. These samples are sent to an assay lab where they are analyzed to determine the gold content of the orebody.

"This drill has become very useful for us the last few years by helping us better predict what we’re going to be mining. We can drill out 300 feet in a shift, which is a lot for a rig like this," Beyer said.

Beyer added that any drill rig is only as good as its operator, and he said that Jesus Romero, who was leading the drilling crew, is one of the best. At the time of our visit, the drillers were dealing with a challenging section of ground.

"There are some faults here that we’re drilling into, which take a little bit more effort to drill," Romero said.

"Four Corners has difficult ground conditions but they say the gold is where the ground is bad," Beyer added.

Leeville is poised to continue to be a top producing site for NGM and Barrick for many years to come, with a current mine life extending through 2036 and promising exploration potential.

Nevada Gold Mines says Leeville's world-class workforce of 520 is focused on safely producing along with implementing the company's refreshed Journey to Zero safety program. The program includes an emphasis on "Stop Unsafe Work Responsibility," encouraging employees to stop, speak up, and make it right when they see unsafe work or behavior. The team also takes pride in embracing NGM's mission and core values, also known as the company's DNA ─ and are dedicated to achieving their goals as one team with one mission through effective communications and collaboration across the site. 

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