Diamond mines can be categorized into two main groups. Most of the significant diamond mines around the world target the primary diamond deposits – the volcanic rocks called kimberlites (and in rare cases closely related volcanic rocks called lamproites) that brought the diamonds to surface. The second type of mine targets the diamonds that have been eroded from these primary sources. At the Batovi project our main focus is discovering the primary kimberlite source of the alluvial diamonds found in the rivers.
The recovery of diamonds from kimberlite is based upon the physical differences of diamond and the kimberlite. As diamond is relatively dense the first steps in a recovery plant are typically designed to produce a dense concentrate. A dense media separator is used to remove the light material, leaving in most cases less than 3% of the material as a heavy concentrate. This concentrate contains diamond and other dense minerals (including many of the diamond indicator minerals discussed in the exploration section). Diamond is then recovered from this concentrate using two additional properties of diamond. When diamonds are exposed to x-rays most will fluoresce. An x-ray sorter recovers any minerals that fluoresce from the concentrate. Diamonds are also hydrophobic (and lipophyllic) – they repel water but are attracted to grease. Thus grease tables are commonly used as a final recovery step. The concentrate is passed over a table coated in grease. Diamonds will adhere to the grease while other minerals continue to pass over the table. Periodically the grease table is scraped off – recovering any diamonds.
As described above the recovery of diamonds has a minimal impact on the environment. Kimberlite itself is relatively benign, and the chemicals used in the recovery process are inert.