GOLCONDA — Staff at Newmont Mining Corp.’s Twin Creeks Mine will stay busy this year with new projects and pilot programs.
The mine is north of Golconda in Humboldt County and work has begun on cut 23, a layback on the north end of the Mega Pit.
Cut 23 is “a huge success story for the site,” said Twin Creeks Mine Manager Steve Johnson.
Operationally it is supported by the existing equipment and personnel. Twin Creeks has more than 500 employees, Johnson said.
Mining on the layback began late in the fourth quarter of last year. To begin Cut 23, Newmont employees had to shift the access road for better visibility, redesign the storm water collection points and reconfigure them, and re-route the power to the layback and move substations, Johnson said.
Johnson said the first ore should be reached in 2015 and the layback will be mined through 2017. The miners must remove the overburden or non-ore bearing rock first to reach the ore.
Johnson said they expect to recover 527,000 ounces of gold from the layback.
“It’s a source of higher grade refractory ore that will be recovered through our Sage Mill,” Johnson said.
The refractory ore goes through an on-site autoclave.
Life of mine runs out in 2022, Johnson said.
“Keep in mind going through an extensive exploration drilling program, and there are plenty of opportunities to expand both in Mega Pit and Vista Pit,” he said.
“We have a robust mine life,” Johnson said. “We have opportunities in both the Mega Pit and Vista Pit.”
The mine moves about 175,000 tons of material a day out of the Mega and Vista pits. The waste rock is mined in 40-foot benches and the ore is mined in 20-foot benches.
Twin Creeks has 18 Caterpillar 793 haul trucks that are 240-ton, said Mine Superintendent Mike Lester. The mine also has two hydraulic Hitachi shovels and a P&H 2800 electric shovel with a 41-yard bucket. The Hitachi shovels include a 5500 with a 41-yard bucket and a 3600 with a 30-yard bucket.
The electric P&H is the main shovel for Cut 23, Lester said. The support equipment fleet is mainly Caterpillar.
“About two-thirds of our production will come out of Cut 23,” Lester said.
The site also has four Atlas Copco drills — two Pit Vipers and two DMLs. The Pit Vipers are single pass drills.
“Those two drills (Pit Vipers) will be able to support the Cut 23 layback,” Lester said.
The Pit Vipers are more efficient for the bench height, he said. They can go down a further distance without having to add to the drill length.
Twin Creeks General Manager Mark Evatz said he has “a tremendous amount of pride” for his staff and what they are doing at the mine. He said the Twin Creeks Mine leads the industry in a couple of areas.
“Everything we do out here is built around the foundation of safe work performance,” Evatz said. “So, all the successes, and we have a multitude of successes that we celebrate over the course of the year. … Those are only as good as us getting safety right.
“You’ll see there is a tremendous amount of effort put into safety, because we are trying to move our culture toward a culture where zero harm is not just a catch phrase, but it is something that people believe in and work hard to achieve.”
After getting safety right, Evatz said the mine tries to be a good neighbor to the surrounding areas.
“It’s real easy to be community stewards because we’re doing it for ourselves, and our family and friends,” Evatz said.
The hierarchy is checked at the gate, from the manager to the truck drivers, so everyone works together for a safe mine, he said.
Part of that safety culture includes starting a traffic control system using lights. Steve Johnson said the mine has a red light, green light system.
“It’s efficient from a safety standpoint,” Johnson said.
The program began last year for efficiency and safety between the haul trucks and light equipment. The light system is still in a pilot program stage.
“We have a sensor on each truck that tells the light they’re coming,” Johnson said.
As a haul truck approaches an intersection, the light switches from red to green so the haul truck is given priority over any smaller equipment.
“We’re getting a lot of positive feedback from operators,” Johnson said.
Twin Creeks added a pre-aeration tank to the beginning of its carbon in leach circuit.
“We’re using air from air compressors to oxidize the iron in the ore,” said Project Manager Dean DeCock. “After that stage it goes on to the leach circuit, and we add the cyanide. By oxidizing the iron we are able to use significantly less cyanide.”
One of the byproducts of an autoclave process is ferrous iron, which is a cyanide consumer, said Twin Creeks Chief Metallurgist Greg Thies.
“When that’s consuming cyanide, obviously, you have to add more cyanide in order to compensate,” Thies said. “With pre-aeration that oxidizes that ferrous to a ferric iron, which does not interact with cyanide, so we can overall lower our cyanide consumption.”
The concept for the tank was “home grown,” Thies said.
“Metallurgist Rich Neu came up with the concept and it was tested and implemented on site,” he said.
Neu said he came up with the idea from different processes he worked with at other mine sites.
“This is much easier to do,” Neu said.
A pilot or test program ran for more than a year at Twin Creeks before the full size tank was approved for construction.
The new tank cost was estimated at $6.3 million but came in under budget, DeCock said.
Thies said while the process does not affect recovery, it does reduce the amount of cyanide consumed, so it is cost effective. Before the pre-aeration tank, cyanide use varied, but the staff is no longer seeing “big swings” in cyanide consumption.
“It’s already paying for itself,” he said.
The field work for the tank began in April and it was started up at the end of 2013. Construction took more than 27,000 man hours, with zero incidents. TIC, Schmueser and Great Basin Industrial were the main contractors.
The tank is 76 feet tall from the surface and about 52 feet in diameter. It holds about 850,000 gallons, said DeCock. When standing at the top of the tank, the brown slurry looks similar to a mud bath. The liquid churns and bubbles as agitators move the slurry to help it oxidize.
This new tank was built next to the CIL tanks and is the first step in the process, said Don Wilhite, process manager.
“We process 3.8 million tons from Sage and 1.4 million tons a year from Juniper,” Wilhite said.
The Juniper Mill processes the oxide ore. Some of the ore that goes through the mills comes from Turquoise Ridge and Newmont’s Carlin site. Turquoise Ridge is owned jointly by Newmont and Barrick Gold Corp.
The new tank has been running about three weeks, Wilhite said.