The rough-diamond miner extracted about 11.6 million carats in Q3, or 20% more than in the same period last year. However, it could only sell 4.9 million carats.
The $3.15 billion project will tap into the world’s largest and highest grade deposit of polyhalite, used as a fertilizer, inside the North York Moors National Park.
Prices for the precious rocks have fallen almost 12% in the past year, amid weakening diamond jewellery demand from China, the second largest consumer after the U.S.