How diamonds are mined: Secondary deposits

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How diamonds are mined: Secondary deposits

After the volcanic eruption a diamond-bearing kimberlite or lamproite pipe reaches the surface of the earth. The kimberlite - which is also called blue ground- is now exposed to the open air and different weather types. Rain, wind and different temperatures cause erosion and the kimberlite has turned into yellow ground.

The diamonds are now released from the eroded rock and carried away from the pipe by rivers and streams. Some diamonds remained in dried up rivers or streams for even millions of years. The first river diamonds were discovered in India more than 2000 years ago!

Diamonds can even be found on beaches covered by sand and in offshore tidal zones. These are called marine deposits. Like here in Namibia where the onshore mining is one of the world’s largest earthmoving operations that takes place. Sand and gravel are excavated and removed by giant earthmovers and later processed to extract the diamonds.

To hold back the sea and expose the seabed (which can be 20 meters below sea level !), the miners build large dams in the surf zone to make the recovery easier. Mining operations involve giant vacuum systems which are mounted on trailers as heavy as 10 ton. The vacuums follow the earthmoving equipment and pick up the diamond bearing material which goes into a pipe and is  directly transported to the ore processing section.

Recovery of diamonds from the ocean floor  is a huge challenge! The deposits can be divided into two different zones. This is based on the depth of the water, at about 15 meters, divers can mine diamonds with  a hose which is attached to a suction pump located on the shore or on a ship. They vacuum the gravel of the ocean floor. This gravel is sieved and the remaining ore is sent to the procession section.

In deep areas however, the mining operation is more challenging and complex. At depth of about 40 m. the divers have to wear special heated diving suits and use very powerful vacuum systems to gravel of the ocean floor. They can only work for short periods.

Another more sophisticated method is the use of automated crawlers which are equipped with a suction device to vacuum the seafloor. This method is more efficient and also less risky.

Namibia is the richest marine diamond sources of the world and the diamonds from Namibia are 95% of gem quality !



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