Generally, kimberlites occur in clusters of up to five or more, in close proximity to each other. They are not necessarily all the consequence of a single volcanic event. Indeed, they may have resulted from several different events over a period of time, adding to the complexity of sampling and proving their economic potential.
Geologists use many methods to explore for kimberlites, including satellite remote sensing, geophysics and reconnaissance sampling. Any kimberlites discovered can then be drilled to establish whether or not they contain economic quantities of diamonds.
The first step is generally to investigate areas with a history of diamond recovery, and then to follow up with stream or deflation sampling for evidence of kimberlite indicators such as garnets. Thereafter, the use of geophysics to search for magnetic anomalies is applied. Sampling and drilling are then used to confirm whether the anomalies are indeed kimberlites.
Once an anomaly has been confirmed as a kimberlite, HMA sampling of representative material is carried out as a quick and efficient method of assessing whether the kimberlite has the potential to be diamondiferous. Micro-diamond and mini-bulk sampling are then used to establish if there is the potential for those kimberlites prioritised by HMA sampling to host an economic concentration of diamonds.
If positive results are achieved through the initial processes mentioned above, then a company will be in a position to commence bulk sampling material by drilling the deposit and extracting core for analysis. The aim is here to establish the economics for mining a particular kimberlite, and will give indications of grade, cost per tonne and average value per carat. From here, a production decision can be made.