An exchange traded fund that invests in rare earth and strategic metals has traded lower this week with top holding Molycorp weighing after the miner announced a secondary offering of shares.

Molycorp shares have fallen sharply after the company late Tuesday said certain of its selling stockholders intend to offer 10 million shares of comment stock, and have granted the underwriters an option to purchase up to an additional 1.5 million shares. It also proposed a $200 million offering of convertible senior notes.

Late Thursday, Molycorp priced the share offering at $51 each. The stock closed Thursday at $51.29.

“While the sale of $200 million of convertible notes may not be particularly worrisome, the fact that insiders are lining up to unload as much as 11.5 million shares of stock may be,” said Matt Koppenheffer at Motley Fool. The sell-off “could be a little overblown since the bulk of the shares being sold are coming from private equity companies,” he wrote.

Molycorp is a top-ten holding in Market Vectors Rare Earth/Strategic Metals ETF (NYSEArca: REMX). The ETF is down 7% over the past month, according to Morningstar.