Mining efforts resumed at BSG Resources Ltd.'s Koidu diamond operation in Sierra Leone after being halted for almost a year, though the company still faces challenges in running the mine.

The Koidu operation has suffered setbacks since late 2014 when the Ebola virus started to hit mines in Sierra Leone.

BSG Resources has been working to resume mining at Koidu and spent about US$50 million to extend the life of the mine by converting it to an underground operation, Bloomberg News reported May 14, citing Dag Cramer, an adviser to Beny Steinmetz, who controls BSG Resources.

"We've injected additional resources," Cramer said. "That was tough, that's why we fell behind with creditors."

Koidu can now produce about 400,000 carats per year, which could be increased to 650,000 carats per year.