Geology
Diamonds formed billions of years ago in the Earth's mantle, more than 150kms below the surface. Carbon subjected to very high pressure and temperature crystallized to form diamonds.
Much later - between 90 and 120 million years ago - melted down rock and magma, forced its way through the Earth's crust and burst through to the surface in volcanic eruptions.
The magma carried diamonds with it - and when it eventually cooled in the pipes, the diamonds became known as Kimberlite, named after the city of Kimberly, South Africa.
Over Millions of years the diamonds trapped in these pipes have eroded into secondary deposits like ancient river beds and beaches.
Early History
Diamonds were first discovered in India more than 3000 years ago and it wasn't until 1725 when discoveries in Brazil eclipsed those in India.
In the 1860's, in faraway South Africa, the modern diamond era began with the discovery of the 21 carat "Eureka" diamond, followed shortly thereafter by the 83 carat " Star of South Africa."
South Africa and diamond mining would never be the same again.
For the first time extinct volcanic pipes were identified as the primary source for diamonds.
Worldwide, only a fraction of volcanic pipes yield diamonds, yet Southern Africa, by some geological anomaly has an unusual number of extremely rich diamond bearing pipes.
Early Small Scale Mining
The early mining days were marked by inefficiencies, duplication of effort and great hardships.
Small claims were originally connected by access roads that often collapsed as each digger exploited his claim to the limit, causing their "big holes" to deepen rapidly.
Rope-ways, connecting each claim to the edges of the mines, were then rigged to haul the diamond-bearing ground to the surface.
Eventually the surface mining was exhausted and the only place to go was down.
The first shafts were sunk. It wasn't until several large companies consolidated, bringing efficiency and order to this wild industry, that large scale efficient mining became possible.
Opencast Mining
Diamond pipes decrease in size with depth.
Generally below 600 meters they become fragmented and irregular.
There is an overall tendency for ore grade to decrease with depth making it too expensive at some point to continue to mine.
Open cast mining at the surface is far more efficient and economical than underground mining, which only starts when the surface area becomes too restricted.
Block Cave Mining
Once a service shaft is sunk along side the pipe, a series of concrete lined tunnels are punched through it, side by side, beneath a solid block of kimberlite about 180 meters high.
From various draw points, cones are cut into the still solid block of kimberlite to a height of 9 meters.
The block above the cones are then undercut, causing the solid mass of kimberlite to cave and break up under its own weight.
Broken ground is drawn through the draw-points into a collection area, crushed into manageable sizes for removal to the surface.
Alluvial and Deep Sea Mining
Generally speaking the gem content of the diamond ore in alluvial mines is higher than in primary deposits.
This is because the higher grade rough has a purer and therefore stronger crystal structure better able to withstand the diamonds long grinding journey downstream.
These mining operations involve the removal of large amounts of "overburden" to get access to the ancient diamond bearing bedrock.
In the erosion process over the millennia, diamonds have been washed out to sea.
Probably the world's most important sea-mining operations take place off the western coastline of South Africa and Namibia.
Southern Africa - A Sparkling History
The bigger and the more spectacular the diamond the more likely that it originated in Southern Africa.
Of all the world's most famous and notable diamonds approximately 2/3 are of Southern African origin.
From the world's largest diamond, the 3,106 carat Cillinan diamond discovered in 1902 to the 599 carat Centenary diamond discovered in 1986, its mines are noted for the large and often extremely rare qualities it produces.
Just one of its mines, the Premier diamond mine, has produced 1/4 of all know diamonds larger than 400 carats.
