Foldstein, S.; Luo, S.; Ku, R. & Murrell, M. Uranium-Series Constraints on Radionuclide Transport and Groundwater Flow Beneath the Nopal I Uranium Deposit, Sierra Pena Blanca, Mexico, article, April 27, 2006; (https://digital.library.unt.edu/ark:/67531/metadc880494/m1/1/: accessed November 15, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; .