“I’m highly skeptical of the real impact of the announcement this week,” says Gareth Hatch, cofounding principal of Technology Metals Research, a firm that advises rare earth metals stakeholders. “We’re being asked to take it on faith that it will happen, but it doesn’t work like that.”

The motivation may relate to the U.S. Department of Energy’s December 2010 Critical Materials Strategy report, which expresses concern about a short-term supply disruption. The announcement asserting the discovery of four of the report’s critical rare earth metals reassures manufacturers that the elements will be available to the supply chain at reasonable prices until other western suppliers start producing them in the next few years. Such a discovery also minimizes the need for engineers to redesign products so they won’t require problematic components.

Molycorp appears to have faith in its light rare earths: it’s spending $781 million to overhaul its equipment and expand potential production to 40,000 tons a year. But the 8-K statement filed with the U.S. Securities and Exchange Commission last week makes no promises as to what it will find once it starts drilling for the heavier varieties: “Molycorp must do extensive test drilling to determine the quantity and quality of the deposit. Accordingly, there can be no assurance as to the quantity or quality of such rare earth deposit or that such deposit will become proven or probable reserves.”