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News Release, Kansas Geological Survey, Oct. 29, 1999

Survey Discovers Three New Volcanic Features in Northeast Kansas

LAWRENCE--Three previously unknown volcanic features in Riley and Marshall counties of northeastern Kansas have been located and studied by researchers at the Kansas Geological Survey, based at the University of Kansas.

Known as kimberlites, these deep pipes of volcanic material exploded to the surface about 90 million years ago. Nine other kimberlites in Riley County have long been known to geologists. Kimberlites are scientifically important because they provide information about the deep subsurface and because they are composed of the type of igneous rock that is the source of diamonds.

Unlike volcanoes, kimberlites do not pour out lava. Instead, they explode violently to the surface, forming small craters and leaving behind a mixture of igneous and sedimentary rock that often contains garnets, a dark red semi-precious stone. One of the previously known kimberlites, near the small town of Winkler in northern Riley County, produced a shallow crater several hundred feet in diameter that is visible on aerial photography. All of the newly discovered kimberlites are covered with soil, 15 to 20 feet below the ground surface. All are on private property.

Survey geologists located the new kimberlites by making very detailed magnetic surveys of the earth's surface. Because kimberlites are composed of igneous rock, and are surrounded by sedimentary rocks, the kimberlites produce unusual magnetic readings, or "signatures."

During the past summer, Survey researchers Tom Weis and Kevin Dobbs conducted detailed magnetic surveys on the ground at locations where previous aerial surveys had been conducted in the early 1980s by Cominco American, a mining company. Cominco's work identified several unusual magnetic signatures that indicated possible kimberlites. The new work showed that kimberlites were probably present at three of those locations. This fall the Survey drilled those three locations and confirmed the presence of the three kimberlites.

By drilling several hundred feet into the kimberlites, the Survey obtained core samples of the rock, which can then be analyzed for information about the deep subsurface geology in the area. The cores may also hold clues explaining why the kimberlites popped to the surface in northeastern Kansas, and not at some other location.

"These three new kimberlites are important, especially because the one in Marshall County extends the range of these features outside of Riley County," said Survey geologist Pieter Berendsen. "The magnetics and core samples from these kimberlites will tell us more about the deep underground geologic conditions that resulted in these features."

Chemical analysis and other lab work on the samples should provide more information about their potential for holding diamonds. In the 1980s, several Kansas kimberlites were explored for diamonds by Cominco. After sifting through tons of kimberlite, the company did not report any diamonds. Diamond mines in other parts of the world generally sort through many tons of kimberlite to produce one carat of diamond.

Research on the kimberlites is part of a larger Survey study of the geology of the area around Manhattan. That study involves mapping the area's bedrock geology, analyzing the deep subsurface, and looking at geologic hazards such as landslides.

Kevin Dobbs, one of the researchers involved in the project, has completed an undergraduate degree in environmental studies from KU, and is now a special student preparing for graduate school. His work on the project was supported by a grant from the Association of American State Geologists, as part of a field research program that mentors young students. The project gave Dobbs hands-on experience in the field, particularly related to mapping, geology, and geophysics.

Story by Rex Buchanan, (785) 864-3965

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