A new major shareholder and plans to invest in a rare earth mining operation have sent shares in ISR Capital rocketing. But the background of the transaction may give investors pause.

ISR Capital has seen its share price rise a blistering 1,583% this year, making it the best-performing stock in the market by a long way. The second-best performers are China Essence Group and China Mining International, which are up 600% and 281%, respectively.

The rally unfolded as a new major shareholder named David Rigoll emerged, and as ISR Capital revealed plans to invest in a rare earth minerals project. But Rigoll, who was recently appointed an executive director of the company, has not been the only player in the changes unfolding at ISR Capital. According to ISR Capital’s filings, he accumulated his stake in ISR Capital just as a Cayman Islands-based fund managed by Value Capital Asset Management had been converting bonds issued by ISR Capital into new shares.

Meanwhile, the stake in the rare earth minerals project that ISR Capital is acquiring was previously held by a company substantially owned by Rigoll called Tantalus Rare Earths, which was once listed on the Frankfurt Stock Exchange. Yet, ISR Capital isn’t buying the rare earth project from Tantalus Rare Earths but from a privately held, Singapore-based company called REO Magnetic. Moreover, ISR Capital is paying a price that might give some of its shareholders pause.