Gem Diamonds' shares dipped today after the miner revealed disappointing production in the first half of 2017.
The London-listed company reported it recovered 50,478 carats at its Letseng mine in the six months to the end of June, down one per cent from the second half of 2016.
Shares in the company edged down 1.92 per cent to 81.18p in afternoon trading.
The firm warned the market for rough and polished diamonds remained cautious during the period, but it said strong demand for Letseng's large, high-quality, white rough diamonds continued.
Gem Diamonds found four diamonds greater than 100 carats during the period, which chief executive Clifford Elphick said was encouraging.
The company's 70 per cent-owned Letseng mine in southern Africa is renowned for producing large, top colour exceptional white diamonds.
The market for Letseng's high-quality diamonds has remained firm over the period with the last tender of the period achieving over $2,200 per carat (£1,683).
This positive trend has continued with the most recent July tender achieving an average price of $2,385 per carat.
Elphick said a group-wide externally supported cost efficiency and bench-marking review has started at the company and has already identified opportunities that are being actively pursued.