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 Primary deposits |
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 The ground is blue in the volcanic
cones. Two modes of mining exist: the open-cast (or open-pit) and the underground mine. |
The open-cast mine
This type of miningn is
very much used, especially in South Africa where there is the famous Kimberley mine called « Big Hole ». The mining
is done by extracting the subsoil from the pipe using large hydraulic shovels. Hard
rock is drilled and blasted with explosives so the broken material can be removed.
The pipe is dug in tiers from which the materials to treat is put into trucks. |
The underground mine
The underground mine can today
reach depths of more than 1,000 meters.  The
content of diamonds is decreasing with the depth. Underground mining is more expensive
than open-pit mining and requires more complex management and machinery. Two techniques
of extractions are used: |
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 Block Caving: block caving is an inexpensive
method of mining in which large blocks of ore are blasted, causing the ore to break or
cave under its own weight. This method is largely depending upon the action of gravity
and is considerably less expensive than the traditional method of mining copper porphyry
deposits.Underground mining in tiers: it is a mixed
method which is used at the Premier Mine in South Africa. |
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| Secondary deposits eluvial and alluvial |
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- Eluvial deposit: the ground is yellow and near to the primary deposit.
- Alluvial deposit: this type of deposit is down in river beds over long distance.
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Several types of
mining exist: artisanal mining until it becomes industrial mining.  The extraction is generally done in the terraces of rivers where diamonds are
extracted from the sediments which cover them. they are then separated from the
gravel which was collected from the river beds. Dredges are used and also powerful pumps sucking sediments
and gravels. |
The industrial
mining uses large machines  (hydraulic shovels, dragline,
etc...) or explosives to reach the diamantiferous deposits. |
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| Marine littoral deposits |
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For this type of mining powerful equipemnts
and explosives are used to reach the  diamantiferous
gravel. The removal of the diamonds from the beaches requires the removal of a very large quantity of sand
before being able to reach the diamantiferous gravel, and it is not rare to dig more than
20 meters below the sea level before reaching the diamantiferous gravels. There are enormous
problems of watertightness. People work day and night. For the marine
mining, the operations are rather delicate and require specific equipements. De
Beers is the leader in this field and has boats and equipments unequalled, they have
concessions in Angola, Namibia, etc... |
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Mining
