I’m really not very current on the question of U-234 content related to mines. However, I can speak to general issues of geological occurrence and isotope and uranium chemistry.

Wolfsthal’s analysis is correct and overlaps with what I posted on WhirledView earlier. His observation that the Pu on the containers could come from overpacks adds to the uncertainty as to origin.

I wasn’t aware that the U-234 content was known to vary within mines, but this would not be surprising. Content of practically everything varies within mines, sometimes within a few tens of feet.

In any case, the U-234 measurement is one-dimensional. It is a single number, which can depend on numerous factors and can be changed in processing, although probably not by much in a conversion to UF6. It’s also a small number and a fairly difficult analysis, so it can be subject to large uncertainties. I wouldn’t consider it enough to identify a mine; I’d probably look for trace elements, although they might disappear in the UF6 conversion.

The question of how many reference samples were available is a good one. I’ll repeat the possibility that uranium from different mines may be mixed at a mill (where the ore is converted to yellowcake). This was common practice in the Soviet Union. The Sillamäe plant in Estonia received ore from Central Asia, Czechoslovakia, Hungary, Romania, Poland, and East Germany, and the relative amounts differed from time to time. A recent article in Science noted that a mill in Kyrgyzstan received ore from as far away as Hungary. Doesn’t make much sense for a capitalist, but that’s the way the Soviets did it.