BHP Billiton reported its first-quarter diamond production fell 32 percent year on year to 313,000 carats for the three months that ended on September 30.

Diamond production was lower than all comparable periods and reflected temporarily restricted mining conditions and unscheduled maintenance at the group's Ekati mine in Canada.

BHP expects that diamond production will recover in the fourth quarter and is then forecast to remain constrained for the midterm as the operation extracts lower-grade material, consistent with the mine plan, according to the group.

The sale of BHP Billiton’s 37 percent non-operated interest in Richards Bay Minerals (South Africa) to Rio Tinto was completed during the quarter. An overall review of BHP Billiton’s diamond business is continuing.