For the first time in more than 25 years, drilling is being conducted in southeast Nebraska to determine how much of a valuable and rare heat-resistant element lies hidden underground.

The drilling that began Thursday night is part of a Canadian mining company's exploration of the site. Quantum Rare Earth Developments is trying to determine whether to build a mine to retrieve niobium and possibly other rare elements from more than 500 feet underground.

The U.S. currently imports nearly all the niobium that's used in this country to harden steel and make it more heat-resistant for industrial uses. It hasn't been produced in America in significant amounts since the 1950s. The U.S. Geologic Survey estimates 8.5 million kilograms of niobium worth roughly $330 million was imported into the U.S. in 2010.

The agency also says the underground carbonatite formation near Elk Creek has the potential to become one of the world's largest sources of niobium and other rare earth elements used in cell phones, wind turbines, hybrid car batteries and other applications.

Earlier this year, Quantum released a new geology report confirming that a large deposit of niobium is present underground near Elk Creek, which is about 70 miles southwest of Lincoln.

The core samples Quantum is drilling now will help the company determine the boundaries of the carbonatite formation. Company officials estimate the drilling will continue for at least three months, but it could be longer if Quantum secures money to drill additional samples.

An underground niobium mine could employ as many as 400 to 500 people, but the project would likely cost between $300 million and $400 million to get started. Quantum has mineral-rights leases on about 9,500 acres of rural land near Elk Creek that are good for about four more years.

Quantum is not starting from scratch at the site because Colorado-based Molycorp drilled about 100 samples there during the 1970s and 1980s.

During the 1990s, Molycorp abandoned the Elk Creek site because it didn't appear that it would be profitable to build a niobium mine there. Niobium prices have since increased enough to prompt Quantum's interest.