Precious gem departs the Sibanye-Stillwater mine

Chief geologist Mike Koski punches out after 39-year career
Marlo Pronovost
Thursday, August 23, 2018

SCN photo by Mikaela Koski
Mike Koski works on a water-color painting on his newly constructed gazebo. The longtime Columbus resident retired as the Sibanye-Stillwater Mine’s head geologist after a 39-year career.

Photo courtesy of Mike Koski

Mike Koski works at his desk at the start of his long career.

Photo courtesy of Mike Koski

The Brass Monkey gang on Iron Mountain.

Koski and Brent LaMoure at their joint retirement party.

Mike Koski has been a part of the Sibanye-Stillwater Mine since before the internationally known company even had a name.

The Columbus man was a geological intern still in college when in 1979, he was put to work on what is now called the Stillwater Complex by the John Manville Corp., conducting diamond and surface drilling during what was considered an early exploration stage.

In 1983, while working full time for the merged company called Tri Ventures, Koski was one of nine geologists tasked with a mining feasibility mission — meaning was there enough ore present in the Stillwater Complex to be financially worth mining.

The answer was yes and the Stillwater Mining Company opened for operation in 1986.

Koski, 60, retired from the company in July as the head geologist, bringing to an end a 39-year career and becoming the longest employee at the mine.

“I had an exceptional career due to the cooperative team efforts of everyone involved,” said Koski, declining to take sole credit for his success. “I enjoyed working. It is very hard to walk away from.”


The John Manville Corp. — after which the J-M Reef is named — first started searching for PGMs (platinum group metals) in the area in 1965. Ten years later, the company found them.

“They found a taste of it,” said Koski.

In late 1979, the Manville Corp. formed a joint venture with the Chevron Corporation, which controlled everything along the reef except for the Stillwater Valley. The valley belonged to the Anaconda Company. When Koski went to work full-time, a Tri Venture had been formed, consisting of Chevron, Anaconda and Manville. This, explains Koski, was the beginning of the Stillwater Mining Company.

The nine geologists tasked with the mining feasibility research came from all three companies. Koski’s group was called the Brass Monkeys and had a field camp on Iron Mountain.

As his group “proved out minablity in the Stillwater Valley,” the rest of the Manville group continued to work on surface exploration on the rest of the complex outside of the Stillwater Valley.


Geologists are involved in nearly every aspect of business at the Sibanye-Stillwater Mine. After all, the mine exists because of the PGMs found in the ore throughout what is called the Stillwater Complex. And more specifically, in the J-M Reef.

As Koski explains, the Stillwater Complex is an old magma chamber that sits six to nine miles below the earth’s surface. Present in the complex are palladium and platinum, as well as other valuable metals. The J-M Reef is the only known significant source of PGMs in the United States and has the highest-grade PGM deposit in the world.

Sibanye-Stillwater is the third largest producer of those two PGMs in the world.


It took geologists to determine if the PGM grade was rich enough to support the costly venture of mining. And because of the high cost of mining operations, it still takes geologists to make sure the company stays on the most valuable ore it can.

“And it’s not easy,” said Koski. “It’s a lot of responsibility.”

That requires geologists to work “at the face,” which means underground, at the site where the actual ore is being harvested. Geologists also direct underground blasting.

“We’re very involved in the actual mining activities,” said Koski.


The success of the mine, and the opportunities it is giving people, is something Koski singles out as high points in his career. Koski said he had no idea how big the company would become. He notes how there are now third generation miners.

“Which is big,” Koski said with a smile.

Koski also stresses that the company has always focused on clean mining and never wavered from that commitment.


Koski himself is a story of a local boy from Red Lodge working hard and rising to the top of his profession. Before he became the head geologist, Koski worked “at the face” for 10 years, spent time in the engineering department to learn how to design stopes, ran the Development Section for eight years and then spent the last eight years as the head geologist. Along the way, Koski helped develop new ways of mining.

But he is quick to defer taking full credit for his success.

“It’s amazing what talented people can do…one step at a time,” said Koski.

Although he technically retired in July, Koski continues to help the company with the transition of his replacement, who he hand selected. Also retiring was Koski’s boss, Brent LaMoure, who also is assisting with the transition of his replacement.


An avid fisherman and developing watercolor painter, Koski has already delved into his new life, although he does consider not working to be out of his comfort zone. But it’s a feeling he is embracing.

He’s already built a gazebo at his house.

Koski’s wife, Lorrie, retired from the Columbus School System two years ago. The couple has two children, Mikaela, who is a reporter at the SCN, and Ryan, who starts his senior year at the University of Montana next week.