Molycorp (NYSE: MCP) has appointed an interim president and CEO, the rare-earth mining company said in an official news release. Constantine Karayannopoulos will occupy the two positions as a replacement for Mark Smith.

Karayannopoulos, who served as the vice president of the firm's board, is to continue in that role during his temporary stay as president and CEO. Molycorp said in its statement that he will "immediately" begin a search for a replacement.

The departure of Smith and ascendancy of Karayannopoulos come barely over a month after Molycorp revealed that the SEC was investigating it over, "among other things, the accuracy of the company's public disclosures."