The 1,111 carat diamond, which is yet to be analysed and valued, is the second biggest stone ever to be mined. Around the size of a tennis ball it is beaten only by the 3,106-carat Cullinan diamond found in South Africa in 1905 which was cut into nine separate stones, many of which are in the British Crown Jewels.
I was particularly interested and pleased to read on MEI Online that the stone was recovered by an X-ray sorter manufactured by Physical Separation '15 sponsor TOMRA Sorting Solutions. The sorter was only installed in May of this year, replacing conventional heavy medium separation. It is unlikely to be the last of big stones recovered by electronic sorting as the development of multiple sensors and rapid computing is making this technology an increasingly important feature particularly for reducing energy consumption in comminution circuits.
It must be remembered that although diamonds are the hardest minerals known they are also very brittle and many large stones must have been shattered in diamond crushing circuits. The Cullinan diamond might have suffered that fate if it had not been spotted in the wall of the mine itself and prised out by the mine manager using his pen-knife. It was part of a much larger stone which had been sheared off during mining. I remember visiting the mine in 1978 and seeing the new x-ray sorter, crude and low capacity by the standards of the modern TOMRA machine, but only a few months earlier it had recovered the Premier Rose, then the largest since the Cullinan, at 137 carats.
Expect to hear much more of the electronic sorting of many ore types in future.