ELK CREEK, Neb. (AP) — This summer’s drilling to explore a deposit of a rare heat-resistant element in southeast Nebraska prompted a Canadian mining firm to increase its estimate of the deposit’s size.

NioCorp Developments said Monday that the latest drilling results show that the niobium deposit near Elk Creek is even bigger than expected.

The company also said Monday that it plans to raise up to $16.5 million through private placement to support the Elk Creek project.

NioCorp previously estimated that more than 100 million tons of niobium rests several hundred feet below the ground. The company is trying to determine if it will be profitable to build a mine.

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.