This report is the result of a limited investigation—led by the CGS during 2018 and 2019—into beach placers deposited within the Fox Hills Sandstone along the eastern flank of the Denver Basin. The primary purpose is to provide additional information on the nature of these critical mineral deposits, including critical mineral concentrations of rare earth elements (REEs), and the stratigraphy of an exposed paleoshoreline in the Fox Hills Sandstone. Digital PDF download. RS-48D
Beach placers deposited within the Fox Hills Sandstone along the eastern flank of the Denver Basin contain minerals deemed critical in 2018 by the U.S. Department of the Interior. These marine beach placers, or paleoplacers, were deposited in the Late Cretaceous along the western edge of the retreating Western Interior Seaway (WIS). Preliminary investigations determined that these deposits contain potential critical mineral resources including titanium, zirconium, hafnium, and rare earth elements (REE). This report contains the results of a limited investigation conducted by the CGS in this area to provide additional information on the nature of these mineral deposits. The following tasks were completed during this investigation: review and summary of publicly available documents and publications; collection of samples and stratigraphic analysis of accessible outcrops; mineralogical analysis of select samples; and laboratory analysis of samples for select critical mineral concentrations. This report may assist with future mineral exploration efforts in this area and provide insight into the retreat of the WIS during the Late Cretaceous.