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News Release, Kansas Geological Survey, Jan. 24, 1996

Diamonds in Riley County? Maybe

LAWRENCE--About 10 years ago, a mining company explored the hills northwest of Manhattan for diamonds.

Now, according to reports from a mining industry journal, the hills may have yielded two very small diamonds, each about the size of a pinhead.

But don't bet on a diamond rush in the Flint Hills just yet, says a geologist at the Kansas Geological Survey, based at the University of Kansas. Survey geologist Pieter Berendsen is skeptical about the reported diamonds.

"It's possible the diamonds came from Riley County, but it's hard to be certain," said Berendsen.

An article about U.S. diamond mining in a recent edition of the trade journal Mining Engineering reports the discovery of the two small diamonds in Riley County.

Riley County has long been known as the site of more than a dozen rock formations called kimberlites, a type of rock that yields diamonds in other parts of the world. Kimberlites are volcano-like pipes of once-molten rock that exploded to the surface of Riley County about 90 million years ago. Several of the Riley County kimberlites are barely exposed at the earth's surface. Others cover as much as ten acres.

Until now, searches for diamonds in Riley County kimberlites came up empty.

The Mining Engineering article traces the two diamonds to a kimberlite in a pasture northeast of Randolph, in north-central Riley County, near the Fancy Creek arm of Tuttle Creek Lake. In the 1980s, the mining company Cominco American leased several Riley County kimberlites, including the one near Fancy Creek, and used backhoes to dig trenches, about eight feet deep, through the soft, dark blue-green rock. The material pulled from the trenches was taken to a quarry near Junction City, where the kimberlite was sifted and concentrated, then shipped to a plant near Fort Collins, Colorado.

There the kimberlite was sifted by weight, then the heavier rock material was x-rayed at a wave-length set for diamonds. The published report says that two diamonds, each about three millimeters in diameter, came from the kimberlite near Randolph.

"It wouldn't surprise me if the diamonds are from Riley County kimberlite," said Berendsen. "The potential is there. But the samples could have been mixed up with kimberlite from other sources."

Most diamonds are located by panning small streams that drain the land around kimberlites, a process similar to panning for gold, says Berendsen. No diamonds have been found previously in Riley County because little panning has taken place there, says Berendsen. Or the Riley County kimberlite may contain no diamonds.

"There are lots of kimberlites, all over the world," said Berendsen. "But only a small percentage contain diamonds."

Because kimberlites in other parts of the world have produced large, high-quality diamonds, companies have conducted limited exploration in Riley County. In addition to mines in South Africa, discoveries in Canada, Australia, the former Soviet Union, and Asia have produced many gem-quality diamonds over the past decade.

"It takes lots of money and time to explore and mine for diamonds," said Berendsen. "If you're hunting for elephants, you go where you know there are elephants. The trouble with diamond exploration is that you know there are elephants in Canada and Australia. There's too much of a chance that these elephants don't live in Kansas."

Story by Rex Buchanan, (785) 864-3965

Kansas Geological Survey, Publications and Public Affairs