Diamonds are the most valuable mineral. Diamond’s clarity and brightness make it highly attractive for jewellery while it’s high conductivity, extreme hardness and other physical attributes make it indispensible to industry.
The value of diamonds is in part due to its extreme rarity. Workers in diamond mines have often never seen one in the rock themselves. The exploration for diamonds requires specialized techniques, in many cases different from those used to explore for other commodities.
Principal Exploration Techniques
Exploration for diamondiferous kimberlites makes use of a number of different exploration techniques. These include geochemical surveys and geophysical surveys which define and prioritize targets to be tested. Then comes the exciting stage of testing these anomalies to determine whether they are diamond bearing kimberlites.
Perhaps the most important technique in the discovery of diamondiferous kimberlites is the geochemistry of indicator minerals. This technology is initially used to identify vast regions which could host diamond bearing kimberlites, with more detailed surveys determining where the kimberlites occur at a property scale. At this point exploration licenses can be acquired. More detailed geochemical surveys are then undertaken to ascertain where within the license the most prospective kimberlites are likely to occur. All of this work has been conducted at the Batovi project.
Once a kimberlite has been discovered the geochemistry of the contained indicator minerals (along with its micro diamond content) is used to assess its diamond potential.
At each phase identified above the surveys are searching for and identifiying minerals that grow with diamond at depth. These minerals are termed Diamond Indicator Minerals (DIM) Even in a diamond mine diamond is extremely rare (typically far less than 1 ppm) and as such one explores for DIM which are often 100 times more common than diamond, and are thus much more likely to be found.
Collecting a heavy mineral sample to be analyzed for diamond indicator minerals.
Charles Fipke is widely regarded as the leading expert on diamond indicator mineral geochemistry. Through extensive research he has developed a proprietary method of interpreting the compositions of minerals which grew with diamonds. He used this technology to discover the Ekati Diamond Mine and since then has greatly refined it for use on projects such as Batovi.
- The river at right flows from the bottom of the page to the top
- Upstream from where the 300ct diamond was found the abundance of diamond indicator minerals increases to the bend in the river
- Thereafter the numbers decrease markedly, suggesting that a kimberlite is located near this location
Geophysical surveys are used to pinpoint the potential kimberlite sources of the diamond indicator minerals. For kimberlites the survey technologies typically used are magnetic, electromagnetic and gravity.
The surveys are designed to detect the physical properties of the ground below. As the kimberlite pipes intrude the surrounding rocks they may have different physical properties than the surrounding rocks. They could be strongly or weakly magnetic, more conductive or more resistive and may have a density contrast to the surrounding rocks. The term “geophysical anomaly” refers to a location where one of the above cases occurs; where there is an area where the physical properties differ from the surroundings.
A helicopter borne electromagnetic survey
Geophysical surveys covering large areas are typically conducted from the air, with instruments carried by either planes or helicopters. For more detailed or follow up work the surveys are typically undertaken on the ground.
A fixed wing geophysical survey.
Having located geophysical anomalies they now need to be tested. Depending on the conditions at the site anomalies can be tested by pitting, augering or drilling. In each case the goal is to determine whether the underlying rocks are in fact kimberlite.
If a kimberlite is located a sample of it is collected to recover any contained diamond indicator minerals and microdiamonds. Should these results be positive additional drilling is undertaken to evaluate the target. If the results warrant a bulk sample is then collected to allow the recovery of a parcel of diamonds. The minimum parcel size is typically 1,000 carats as one needs at least this many stones to model the expected diamond grade and average diamond value should the pipe be mined.
This is a video from Geotech – who have flown the survey on the project.
Results of Electromagentic Survey
Now read how we extract the diamonds.