It issued 29.2 million ordinary shares at 1.2p per new share to be admitted to trading on AIM on or around June 6. After the placement, the company's share capital will comprise 202.3 million ordinary shares.

The company said it expected to start mining at Pipe 1 in the September quarter and its development was ahead of schedule, with 107,000 tonnes of waste already mined and the first kimberlite blast expected in the next month.

Pipe 1 is similar in geology and size to Pipe 2, where mining operations began in 2015, but its inferred grade was 40% higher at 6.3 carats per hundred tonnes.

BlueRock's last fundraising for £500,000 in March allowed it to upgrade its crushing and processing plants to increase efficiencies and reliability.

It said the crushing circuit was averaging around 1,350t per day — equivalent to over 28,000t a month — and daily volumes were expected to increase further once the company completed the final changes to the crushing plant in June.

BlueRock CEO Adam Waugh said the company was continuing to look for ways to increase production levels.

"We are excited about beginning to mine K1 with the prospect of a significant increase in grade," he said.

BlueRock kept its 2018 guidance unchanged at 275,000t at an average grade of 3.5-4.5cpht and revenue of US$362 per carat.

The Kareevlei mine has five known diamondiferous kimberlite pipes, with the inferred mineral resource based on three of the pipes, K1, K2 and K3, while the remaining two pipes were smaller.

BlueRock's shares were down 18.03% Thursday to 1.25p.