(Bloomberg) -- Prices for some rare-earth minerals, which have soared in the past year after China restricted exports, will plunge as additional output creates an oversupply, according to a company developing a rare-earth mine in Wyoming.

"We're going to see a collapse of some of the prices," said Don Ranta, chief executive officer of Vancouver-based Rare Element Resources Ltd.

So-called light rare earths, including lanthanum, which is used in oil refining, and cerium, used in glass polishing, will "come down substantially," he said today in an interview at Bloomberg headquarters in New York. "Those are going to be in oversupply."

Rare earths are 17 chemically similar elements utilized in applications ranging from electric cars to missiles. Lanthanum oxide has increased fivefold in the last 12 months and cerium oxide more than sevenfold, according to data from China's Shanghai Steelhome Information.

Mining companies outside China, which accounts for more than 90 percent of global supplies, are responding to the rally in prices. Rare Element Resources plans to begin producing rare earths in 2015, while Greenwood Village, Colorado-based Molycorp Inc. plans to increase output to 40,000 tons a year by the end of 2015.

Still, not all rare earths will be in surplus, Ranta said.

"Neodymium, europium, terbium, dysprosium are going to be in shortage it sounds like forever," Ranta said. "They can't predict a time when we're going to have an adequate supply to meet all the potential needs for it."

Rare Element Resources' Bear Lodge project near Sundance, Wyoming, which includes a mine and a mill, will be ready for production in 2015, Ranta said.

Rare Element Resources dropped 35 cents, or 3.6 percent, to $9.27 as of 3:32 p.m. in New York Stock Exchange composite trading. The shares have declined 42 percent this year.