Lilian, further to your post, I have some more info for any interested.
Oolites and oolitic deposits occur worldwide. They share the same basic system of formation, i.e., concretionary accumulation of minerals around some sort of seed grain -- could be sand, could be shell, but something acts as the seed to start the ball rolling.
According to the illustrious Tom Bryant, it is the nature of the seed grains that makes the Clear Hills so interesting. They have been confirmed as kimberlitic. This seems to be a real exception to the oolite family. In analyzing samples from the Clear Hills, what made them stand out was the strange geochemistry beyond the very obvious iron, as in, things that just wouldn't be in your standard iron rich sedimentary deposit. Having said that, it hasn't yet been ruled out that the high iron in the system may have been as a result of volcanic activity pumping soluble iron into the area. So the iron may be the result of volcanic activity, ... indirectly.
In short what is being dealt with is reported to look like a sandstone made from kimberlitic sand grains - the iron and the oolites are more a character of the deposit and not associated with the kimberlite at all - - then again ? . . . more study is needed, of course!
Cheers,
-j
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