One of the largest diamonds in North America has been unearthed at a mine in the backcountry of northern Colorado that some companies previously had rejected as too expensive to develop.
The 28.3-carat yellow stone, which is about the size of a thumb-nail, was found Wednesday in a cylindrical field of kimberlite ore at the Kelsey Lake mine, which sits at 8,000 feet on a rugged mountain about 45 miles northwest of Fort Collins.It was the fifth-largest stone in North America. The largest was the "Uncle Sam," a 40.23-carat gem recovered in Arkansas in 1924.
Howard Coopersmith, a tall, thin geologist who works at the open-pit mine, said Friday that the find was exciting, but he expects larger gems to turn up in the future.
"It's safe to say we didn't find the biggest stones in the first two years," said Coopersmith.
Pete Modreski, a geologist with the U.S. Geological Survey in Denver, on Friday called the find extraordinary.
"This is certainly exciting to find a stone like that," he said, adding that the geologists' hopes of finding stones up to 60 carats at the site are "not unreasonable."
Redaurum Ltd., which owns the mine, plans to offer the diamond at a Sept. 24 tender sale in Denver. Company officials said the stone could fetch up to $10,000 a carat, making it worth up to $280,000.
Areas in Colorado and Wyoming are known to have the right kind of geology for diamonds.
Coopersmith said miners walked over the site as they headed for Colorado's gold rush in the 1800s. "There was no gold in northern Colorado, and nobody was looking for diamonds," he said.
The geologist began a systematic search for diamonds in Colorado in 1975, narrowing down geological formations that could produce diamonds.
In 1987, Coopersmith discovered the Kelsey Lake deposits of kimberlite, the ore which contains diamonds.
Some companies looked at the area, but decided it was not economically feasible to develop into a mine.
Redaurum began production at the site last year, and already has uncovered a 14.2-carat stone and a 9.4-carat stone. Most of the diamonds recovered so far have been less than one carat.
The reserves are estimated to hold $153 million in diamonds.
The Kelsey Lake mine has 14 employees, and is the only commercial diamond mine in the United States.