Science for Decision Making on Uranium Mining in Arizona
Research on the Genesis of Uranium Deposits—Clues to Defining the Region Where Deposits May Exist
The uranium ore deposits in the breccia pipes of the Grand Canyon region are unusual, perhaps unique, and their genesis (processes that created them) remains mostly speculative. This study provides an opportunity to piece together a scientific puzzle, a model that explains their step-by-step creation. Constructing this model is not only an academic exercise but can also assist in the management of federal lands by improving understanding of where and why deposits can occur in the region. This allows land management agencies to plan for areas that have the potential for future exploration, discovery, and mining.
Study several aspects of the breccia pipes of northern Arizona and their ore deposits to build a logical model that explains their formation, including the consideration of:
Processes that created the host structures and set the stage for the deposition of the uranium and metallic minerals. Modern studies on the formation of collapse features provide insights that can help explain the creation of the vertical, pipe-like, solution-collapse structures ("breccia pipes") that host these uranium deposits. The regional geologic processes of the past that combined to create the geology of northern Arizona will be linked to the formation of the breccia pipes and their mineral deposits.
Distinct assemblages of minerals in these deposits provide important clues into the source of the uranium and metals. Previous studies suggest that more than one phase of mineral deposition may have occurred, and these different phases may have occurred under different geologic conditions. Detailed microscopic studies utilizing scanning electron microscope analyses will determine the mineral phases present and examine their spatial, shape, size, and intergrowth relations in fine detail.
Age(s) of the uranium deposition determined by isotopic analyses of the uranium minerals. Samples from different mines will be analyzed.1
Analyses of sulfur isotopes and fluid inclusions in ore minerals will provide insights into the character of the fluids that formed the assemblages of metal-rich minerals that occur with the uranium minerals.
Ore bodies in these breccia pipe deposits consistently occur in the same rock units (formations). This observation provides another clue to the factors that influenced their formation.
Geographic distribution of the known uranium-bearing breccia pipes will be analyzed, providing a view of the geologic factors that influenced their formation on a regional scale.
Barton, I.F., Barton, M.D., and Van Gosen, B.S., 2021, U-Pb age determinations of uraninite by electron microprobe analyses of ore samples from two solution-collapse breccia pipe uranium deposits, Grand Canyon region, northwest Arizona, USA: U.S. Geological Survey data release, https://doi.org/10.5066/P95CPDAD.
Bradley S. Van Gosen
Central Mineral Resources Team