| The report that identified these rocks was based on surface rock collection by government scientists in 1954. It was a GSC memoir (author?) that investigated alkaline volcanic centres in the NWT. In fact the identity of the rocks at the time was as ijolites and magnetite sovites. Looking back on the chemistry published in these "later-to-be-found -diamond-centres", it can be seen that from Mitchell at least, that the magnesium chemistry (+30%), potassium +3%, calcium (low) and aluminum (low), that the intrusive breccia rocks were clearly diatreme facies kimberlites by major element chemistry and not even alnoites, which are higher in aluminum and calcium. So it is a retrospective ID as kimberlite by major element chemistry and not other methods admittedly. Mitchell has said that major element chemistry is NOT the preferred way to ID kimberlite, but it should be minor phenocryst content and phenocryst chemistry (micas, garnets, ilmenite, diallage or pyroxene.) and macrocrysts that ID the rock. I have to say that to be definitive this is probably the case. But alnoite looks almost identical, but is different in major element chemistry and has few non faceted garnets or high chrome pyrope. The jury is definitely out on the newest rock to contain significant diamonds, in Wawa, a lamprophyre. Still hardly a sensation yet in geological circles, the discovery alleged by Mitchell that the diamond bearing rocks at this Ontario location are in fact lamprophyres, which have never previously been accused of containing diamonds, should be front page news. It is a sign of the extreme moribundity of the Canadian exploration industry that neither the sensational staking rush in the Coronation Gulf in 2001 nor the fact of new diamond bearing rocks in Ontario, seem to have awoken more than a yawn from investors. |
