dazzaa, thanks. Extracted from The Journey of Botswana’s...

dazzaa,  thanks.

Extracted  from The  Journey  of  Botswana’s  Diamonds,   from   P14
Fully  realising  most  of  the  long  holders  know  all  this,  I  am  a  newby  and  there
are  probably  others  this  may  prove  helpful  to.

The middle part, the diatreme, is usually the richest in diamonds and is known as a
tuffisitic kimberlite breccia or TKB. These first two parts of the kimberlite profile were
termed “yellow ground” by Kimberly, South Africa mineworkers in the 19th Century.
The final part, the root zone, or “blue ground”, is usually much harder and mining
difficulties may be experienced due to the irregular shapes of the intrusion.
The presence and degree of preservation of these three different zones depends upon
the level of erosion, the volatile content of the erupting magma and the stability and
nature of the country rock surrounding the intruded kimberlite. The large, economically
important kimberlites at Orapa and Jwaneng have suffered very little erosion, and their
crater facies were preserved.
Volcanic eruptions pass through the diamond bearing rocks deep under the Earth at
depths of between 100 and more than 200 Kilometers and sometimes transport
the diamonds to the surface.

In Botswana, the eight diamond mines grades range from 8.5 cpht at B/K11 in the
Orapa kimberlite field to a massive 140cpht at Jwaneng Mine, which is by far the richest
diamond mine in the world with mostly gem quality diamonds.