I spent a good portion of my time, for several years, prospecting for diamonds in the Green River Basin. never found a diamond, but found lots of kimberlite-indicator minerals, like chromum diopside, pyrope garnet, and others. I met a guy from South Africa who was over here looking for diamonds. He now has several k-pipes claimed in the area you mentioned, and also near the old Kelsey Lake diamond mine. He had, at one time, the rights to the Sloan Ranch diamondiferous kimberlites, too. Don't know if he still has those rights. I left 2 sluices in drywashes in the basin. Haven't checked them for 3 years. Need to get that done next summer. Sluices aren't much good for gems, but work to some extent, and you can leave them in remote locations to do their work. Figured it was worth a try.:-)
Jim