MOSCOW - Russia’s central bank probed on Thursday a flurry of unusual trades that saw shares in one of the country’s largest miners nearly halve in minutes on no apparently significant public news.

The stock price of Mechel plunged on Wednesday by 47.2 percent to 50.7 rubles on the Moscow Exchange before making a slight recovery.

Shares in the metals and coal and steel conglomerate traded at around 61.5 rubles on Thursday afternoon.

The central bank’s financial markets regulator said it was paying “close attention” and examining “the actions of several traders” who sold shares of Mechel in a 30-minute span starting at 5:00 pm (1300 GMT). Mechel has been weighed by $9.4 billion (7.0 billion euros) in debt from an acquisition drive that directly preceded the 2008-2009 global financial crisis.

The global miner has spent months in debt restructuring negotiations and its susceptibility to commodity price weakness has been an open secret to both traders and analysts. Spokesman Arseny Palagin said that Mechel’s talks with creditors were proceeding smoothly and called the stock decline “speculative in nature”.

“There are no negative events happening inside the company,” Palagin said in an emailed statement.

But the central bank on Thursday still decided to correct the value of Mechel’s bonds “to a coefficient of zero”—effectively ruling them out of any future refinancing deal. Many in the financial media pointed to the irony of Mechel shares suffering another precipitous drop.

Vladimir Putin in July 2008 managed to shave $6 billion off the company’s market value by noting the absence of Mechel chief executive Igor Zyuzin at an industry conference. Putin accused Mechel of exporting raw materials at half the price at which it sold them on the domestic market and demanded to know why Zyuzin was not present at the meeting to explain himself. Zyuzin “suddenly got sick,” Putin then told the meeting. He “should get better as quickly as possible,” Putin continued. “Otherwise we will have to send him a doctor.” Investment banks and traders said there was no such obvious explanation for Mechel’s decline this time around.

Credit Suisse said in a note to clients that there were “unsubstantiated reports” of Mechel having problems reaching an agreement with creditors about debts coming due next year. But the Swiss bank noted that those rumours have been denied by one of Mechel’s largest creditors and that it believed “other creditors may also confirm that negotiations are also going as planned.”