Selenium and molybdenum enrichment in uranium roll-front deposits of Wyoming and Colorado, USA

Liam A. Bullock, John Parnell

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Sandstone uranium (U) roll-front deposits of Wyoming and Colorado (USA) are important U resources, and may provide a terrestrial source for critical accessory elements, such as selenium (Se), molybdenum (Mo), and tellurium (Te). Due to their associated toxicity, Mo-Sesingle bondTe occurrences in roll-fronts should also be carefully monitored during U leaching and ore processing. While elevated Mosingle bondSe concentrations in roll-fronts are well established, very little is known about Te occurrence in such deposits. This study aims to establish Mo-Sesingle bondTe concentrations in Wyoming and Colorado roll-fronts, and assess the significance of these deposits in an environmental and mineral exploration context.

Sampled roll-front deposits, produced by oxidized groundwater transportation through a sandstone, show high Mosingle bondSe content in specific redox zones, and low Te, relative to crustal means. High Se concentrations (up to 168 ppm) are restricted to a narrow band of alteration at the redox front. High Mo content (up to 115 ppm) is typically associated with the reduced mineralized nose and seepage zones of the roll-front, ahead of the U orebody. Elevated trace element concentrations are likely sourced from proximal granitic intrusions, tuffaceous deposits, and local pyritic mudstones. Elevated Mosingle bondSe content in the sampled roll fronts may be regarded as a contaminant in U in-situ recovery and leaching processing, and may pose an environmental threat in groundwaters and soils, so extraction should be carefully monitored. The identification of peak concentrations of Mosingle bondSe can also act as a pathfinder for the redox front of a roll-front, and help to isolate the U orebody, particularly in the absence of gamma signatures.
Original languageEnglish
Pages (from-to)101-112
Number of pages12
JournalJournal of Geochemical Exploration
Early online date19 Jun 2017
Publication statusPublished - Sept 2017

Bibliographical note

The authors wish to thank Cal VanHolland, Jim Bonner and John Cooper of Ur-Energy (Casper, Wyoming) for their assistance with sampling, data provision and feedback. We are grateful to Adrian Boyce and Alison McDonald of the Isotope Community Support Facility at SUERC for technical support with isotope sample preparation and analyses. Critical comments that greatly improved the manuscript from Samuel Spinks and Marat Abzalov are gratefully acknowledged.

This research was supported by a grant from the Natural Environment Research Council (NERC) (NE/M010953/1).


  • Selenium
  • Molybdenum
  • Roll-fronts
  • Tellurium
  • Uranium
  • Wyoming


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