Ann: Large Kimberlitic Signature Defined at L259, page-83

I am uninitiated when it comes to geology and whatnot.
I have several questions:
Obviously a great find no doubt, but arent they currently mining alluvials that sit on top of this structure? So wouldnt a fair proportion of those diamond bearing alluvials that are atop have come from a more upstream source and come to rest here? Wouldnt a fair proportion of alluvials from the erosion of this new found structure be located further downstream?
Healthy comments please. Just trying to learn and get some clarification from those more learned in this area.