Diamond production at BHP Billiton saw a 11 percent drop to 676,000 carats in the quarter ending December 31, 2010. The company attributes this fall to: decrease in ore processed and lower average grade. The company conducts a mix of open pit and underground mining at its Ekati diamond mine in Canada. For the first fiscal half, diamond production slid by 10 percent to 1.379 million carats.