After the volcanic eruption, the diamonds are settled in the kimberlite or lamproite pipe. Geologist call this a “primary deposit “. Mining a primary deposit starts with so-called “open-pit mining”.
This starts with the removal of all the materials ,so-called overburden, in and around the kimberlite or lamproite pipe. This is done with heavy equipment including explosives. The overburden, like sand, gravel and different types of rock, is now loaded into huge truck for processing the ore containing diamonds. The open-pit mine develops into a deep cone shaped hole following the contours of the pipe. This pipe is made up of terraces that can provide roadways around the mine’s perimeter so that the trucks can move the diamond ore to the processing plants.
Just imagine that 250 tons of ore has to be removed to find a diamond of 0.2 gram !
Like for example the Diavik mine in Canada’s Northwest Territories which is located at 64°29’46” N and110°16’24” W, on a small island in Lac de Gras, about 300 km northeast of Yellowknife (the capital of the Northwest Territories), and 220 km south of the Arctic Circle. It is one of the most remoted areas in the world!
This is one of the world’s most important diamond mines and consists of 4 kimberlite pipes, the 4th is in development and expected to produce the first diamonds at the end of 2018.
In the mid-1990’s the first diamond crystal ( with a weight of 2.5 ct. ) was discovered during the start of drilling the kimberlite pipe. The largest diamond this mine produced was discovered in 2015, the gem quality stone had a weight of 187.7 ct. and was named the Diavik Foxfire.
When an open-pit mine reaches a depth where it is no longer economical and to dangerous like 430 meters, but there are still diamonds in the pipe worth retrieving, the mining operation goes underground.