One of China's biggest securities firms, Guotai Junan Securities Co. has announced the decision on Wednesday to return its Chairman and Chief Executive Officer, Yim Feng to active duty.

In a statement issued on Wednesday, the company said Yim had been assisting investigations by mainland authorities in a personal capacity.

It said neither Yim nor the company was the target of the investigations.

The brokerage appointed provisional replacements last month after losing contacts with the 52-year-old Yim for several days.

The shares of company then suffered a 12 percent sharp slide.

Some media outlets speculated the investigation was related to Yao Gang, former vice chairman of China's Securities Regulatory Commission, who was suspected of "serious violation of discipline".