The State Line Mining District where I have the diamond claims staked is related to an impact crater-like formation called the Virginia Dale Ring Dike Structure. The remnant ring dike rims that are still visible create a crater like expression at least 12 miles across. This structure has similar characteristics to the larger Vredefort Ring in South Africa. Several diamond mines had been developed around the Vredefort Ring long before it was confirmed as an impact crater. As yet, I have been unable to find firm evidence of impact at Virginia Dale due to the extreme erosion, but interestingly, the old Kelsey Lake diamond mine sits squarely in one of the rings!
It was amazing to me to see the kimberlite pipes emplaced into the deep granite crust west of Fort Collins and I was curious as to why it occurred there and not everywhere else that there was an ancient thick granite crust. I've developed a theory that diamonds were being brought up by the ancient impacts of large meteorites/comets and I have mapped many diamond areas around the globe that were located within or near impact craters. My thinking is that the over-pressure put upon the crust during an asteroid or comet impact has allowed for kimberlite magma to be ejected through the crater ring "cracks" generated as a result from a reflex shock wave generated during the hyper-velocity impact. I would say it is kind of like putting your finger tightly to an orange peel and watching the juice "erupt" from the skin. Kimberlite emplacement is always from deep sources and it is fast and quick...not prolonged like normal volcanism. As it turns out, the Russians had also observed this phenomenon and have made diamond discoveries near craters within the past few decades. The Virginia Dale Precambrian Ring-Dike Complex was first recognized by W. A. Braddock in 1962. In 1968, D. H. Eggler researched the structure and wrote his thesis on his findings. In 1970, R. S. Wing and L. F. Dellwig thought the structure may have had an influence on the Ferris-Aultman and other known Paleozoic age diatremes in the State Line vicinity.
Many scientists had dismissed the potential for meteorite/comet creation of the Vredefort Ring. The same thing has happened with Virginia Dale, in my opinion. Please consider my advice here...if you are prospecting an area near a known impact crater, I'd suggest that you also look for diamonds that may be associated with the crater. If the initial impact didn't bring diamonds to the surface, the resulting fractures in the granite may have allowed for later intrusive events to find a way up to the surface. In fact, many kimberlite pipes have shown multiple emplacements within the same diatreme. This makes sampling even more important since some parts of the pipe are too lean yet other intrusions have plenty of diamonds.
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