Some Learning, page-5

WangChung,

Kimberlite is not the only source but it is by far the most important source accounting for about 70% of world diamond production (as measured in 2004) and there are several hundred diamondiferous kimberlite pipes known in the world. The other important diamond carrying magma is olivine lamproite, an ultramafic, ultrapotassic rock similar in certain respects to kimberlite. In 2007 lamproites accounted for ~5% by value (20% by weight) of world diamond production.

A famous source of lamproite diamonds is the Argyle mine in Western Australia. If my recent reading memory serves me correctly the lamproites at Argyle are formed off-craton in a mobile belt (see the schematic drawing in my original post).

There is also a third variety, lamprophyres. Lamprophyres are rarely diamondiferous. They are only of petrological interest as hosting the world’s oldest erupted diamonds, which occur at Wawa in Ontario.

I can only guess that the other magmas don't erupt with enough velocity to allow the diamonds to survive the trip to the surface.

I'll try and explain the conditions needed for the emplacement of a kimberlite in my next post.

Eshmun