Hundreds of Chinese investors protested outside of the Fanya Metal Exchange, in the south of the country last week, after finding that the minor rare earth metals exchange was unable pay out on investment products.

The bone of contention is an asset management product guaranteed by Fanya, called Ri Jin Bao, which promised retail investors yearly returns of at least 10%, and the right to withdraw such funds at any time, Financial Times reported (subs. required).

However, a sustained fall of rare metals prices forced the trading platform-turned-asset manager to freeze those funds in April, when Fanya ran into “liquidity problems.”

The bourse, which owes investors the equivalent of US$6.4bn, said it plans to pay them off by buying back some metals on a regular basis.

Until 2010, China controlled around 97% of the supply of the coveted metals, used in advanced electronics. But when it sought to impose export controls to give an advantage to domestic electronics producers, prices soared by up to 20 or 30 times previous levels. That encouraged investment in the sector in the U.S., Australia and other places outside China. But, at the same time, it fired up smuggling from China and a consequent drop in prices.