Uranium ore concentrates (UOCs) from around the world were measured for both 238U/235U and 235U/234U ratios. These isotopic signatures can reveal the type of geologic environment in which the uranium was deposited (238U/235U), as well as the extent of modern water/rock interactions (235U/234U). The pairing of these two systems on the same sample allows the a mine to develop a uranium isotope "fingerprint" which can be useful in cases of illicit smuggling of nulcear material.