The ages are interesting aren't they?
You are absolutely right VAUGHN, they are.
As you probably know, to get preserved over time, older rocks have to be burried under other rocks. If not, they will be eroded and diseappear for the eternity!!!!!!!
If you study the geology of the Superior craton in Québec, you will surely note that these rocks were formed a long time ago (between 1,8 and 3,1 billion years). And that during the last 1,8 billions years, they were for most of the time, exposed and eroded (except a small period during the ordovician transgression, 500 million years ago).
This is a very important fact. It means that if the kimberlite are very old (between 1 and 3 billion years), they have probably been deeply eroded since they were not buried for most of that period.
However, if they are younger (less than 250 million years), they may have been much more well preverved, even less eroded if they were not buried, as the ones found in some kimberlite fields in Québec, Ontario, NWT and Nunavut.
Up to now, only 3 kimberlites (and minor dykes) have been in the Otish (Beaver lake, Renard 1 and 2). Their facies (deep roots and hypabyssal) suggests they are old and deeply eroded. Note that no aging is available yet. Some studies suggests they have the same age that the Desmaraisville field (1,1 billions years old), others says they are even older.
This fact has serious implications on tonnage and grade. We all know that hypabyssal facies have much less tonnage potential (and higher mining costs) and that diamonds size and numbers tend to be smaller in such facies.
I would love to have a sample of one of these kimberlites. I would not send it to Lakefield for diamonds and trace minerals analysis. I would just try to find its age!!!!!!!!!!!!!!
But it's a long «Ski-Doo» ride from my home!!!!!!!!!!!!!
Regards
JP |
