Molycorp Inc. (MCP) said that President and Chief Executive Mark A. Smith has left the company and the rare-earth mining company has named Director Constantine Karayannopoulos to fill the roles as it seeks a permanent successor.

The company's shares were down 5.6% at $10.68 in recent after-hours trading.

Molycorp--which manufactures and sells rare-earth products used in high-tech gadgets--didn't provide details about why Mr. Smith has departed and a company spokesman wasn't immediately available to comment.

The company is on the verge of a transformative year after a costly rare-earth mining-facility upgrade, but the company's shares may remain volatile until investors get greater clarity about production contracts and cash needs for next year.

Chairman Ross R. Bhappu in a statement said Mr. Smith's "significant contributions and leadership over the past four years that have brought Molycorp to this natural transition into an ongoing operating business, and we wish him well in his future endeavors."

Mr. Karayannopoulos is a professional engineer. His prior experience includes serving as president and CEO of Neo Material Technologies, a position he held from 2005 until this year.

Write to Tess Stynes at Tess.Stynes@dowjones.com

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