The one thing that hits me is how fast they are saying this is a kimberlite. I am not saying it isn't and I do not know exactly when the hole was drilled, or what tests have been done, but Mitchell tells me that it takes a few weeks of xenocrystic microscope lab tests and maybe a whole rock analysis to positively identify a rock as kimberlite. There are a lot of tuffisitic breccia intrusives that resemble kimberlite but aren't. Sovite, Ijolite, Carbonatite, Lamproite, Lamprophyre, Alnoite, Peridotite, Minette and a few more, are often mistaken for kimberlite upon visual examination and even sometimes with further work. They can look identical. Kimberlites themselves may vary widely in texture, colour and composition. They may be coarse of fine grained, have plentiful macrocrysts, or not, have many visible xenocrysts, and xenoliths or none, be gray, green, blue, black, yellow or red. They may have lots or magnetite or hardly any. Loads of pyrope or none. How to tell? Lab tests and lots of them are the only way.
I will admit that if I saw a blue-grey tuffisite breccia with rounded purple pyrope, green diallage, zircons, ilmenites, and micas, and it tested 3 per cent potassium and 30 percent magnesium and the pyrope were high chrome, low calcium I would be tempted to say it was a kimberlite too.
DeBeers has made mistakes. They possessed Crater of Diamonds park in Arkansas, and also the pipe at the argyle in Australia and called them kimberlites for years. They are not. They are lamproites. Their composition is entirely different. Canabrava called the rocks they were finding in Wawa kimberlites for at least 4 years. They were examined by mineralogists and were found to be lamprophyres. BTW, the Wawa lamprophyres are the first such rocks of this kind in the world to be found to be diamondiferous, although in Kalimantan and other areas, lamprophyres have been postulated as a possible source rock of diamonds but it has never been proven. The Minettes of Alberta and Montana are also suspect diamond sources, but no adequate testing has been done.
There is some disagreement in these areas. Nicolas Rock of Britain postulates lamprophyre, carbonatite and kimberlite as a related series of gradational ultramafic intrusives, other petrologists, notably Mitchell strongly disagree and say that the rocks are unrelated and compositioally not from similar sources. In other words the demarcation of the rocks is sharp, compositionally.
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