This is a cost-effective method where a carrot shaped hole is dug in the ground. Nor ore is missed this way, but the feasibility of this type of mining derives from the amount of rock or host material on top of the kimberlite.
This type of mining is done after an open pit mine is no longer feasible to extend. The most common method blocks caving, where a large tunnel is dug at a shallow angle to the ore, after which a large void is extracted underneath the target kimberlite. This type of mining can extend the life of the mine by 10 to 20 years.
This type of mining happens in areas where diamond-bearing kimberlite rocks have been transported to other locations. This makes these diamonds easier to access, extract and process, without the need for explosives or crushing.
This is carried out through ships vacuuming the seabed with long hoses at a depth of 500 feet. The mix of water and gravel is moved to land-based facilities where the diamonds are recovered.