Mineralogical analyses of drill core samples from the Canyon uranium-copper deposit, a solution-collapse breccia pipe, Grand Canyon area, Coconino County, Arizona, USA

This data release compiles the X-ray diffraction and electron microscopy analyses of drill core samples collected by the U.S. Geological Survey that were selected to typify the uranium-copper ore bodies of the Canyon deposit. The deposit is hosted by a solution-collapse breccia pipe, in which mineralization exists from about 650 to 2,100 ft (200 to 640 m) below the surface (Mathisen and others, 2017), located about 6.1 miles (10 km) south-southeast of Tusayan, Arizona, at latitude 35.88333 North, longitude -112.09583 West (datum WGS 1984). Energy Fuels Inc., owner and operator of the property, has conducted extensive drilling into the Canyon deposit that delineated the extent and uranium and copper content of the ore bodies. Mining facilities, including a shaft, have been developed by Energy Fuels at the deposit. As of October 2020, they await favorable economic conditions to resume mining operations and recover the ore.
On a site visit in February 2018, Energy Fuels generously allowed the authors (U.S. Geological Survey geologists) to examine and sample drill cores of mineralized portions of the Canyon deposit. Thirty-five samples were collected, which were chosen primarily as representative intervals of high-grade uranium, copper, and associated sulfide mineralization. An earlier-published data release (Van Gosen and others, 2020) provides the geochemical analyses of the 35 samples for 63 elements. X-ray diffraction (XRD) analyses were performed on 28 of these samples to examine their mineralogy. The raw data from these XRD analyses are also provided in Van Gosen and others (2020). This data release provides a mineralogical interpretation of the XRD data. 
This data release summarizes the mineralogy of the drill core samples, based on interpretation of the XRD analyses (28 samples) and observations by scanning electron microscopy. From the XRD data, mineralogy was determined using specialized software and user interpretation of the software's selections, which are detailed in the section on process description below. Polished thin sections cut from 21 of the Canyon drill core samples were examined using a scanning electron microscope equipped with an energy dispersive spectrometer (SEM-EDS) to identify the ore minerals and observe their relationships at high magnification. The EDS vendor's auto identification algorithm was used for peak assignments; the user did not attempt to verify every peak identification. The spectra for each EDS measurement are provided in separate documents in Portable Data Format (pdf), one document for each of the 21 samples that were examined by SEM-EDS. The interpreted mineral phase(s), which is based solely on the judgement of the user, is given below each spectrum. XRD and SEM-EDS analyses identified uraninite (U oxide) as the uranium ore mineral, which is intergrown with at least a dozen identified sulfide minerals, within a gangue matrix of mainly quartz and lesser amounts of clay minerals, dolomite, calcite, barite, and potassium feldspar.
The Canyon deposit is similar to numerous other uranium deposits hosted by solution-collapse breccia pipes in the Grand Canyon region of northwest Arizona. The uranium-copper deposits occur within matrix-supported, vertical columns of breccia (a "breccia pipe") that formed by solution and collapse of sedimentary strata (Wenrich, 1985; Alpine, 2010). The breccia pipes average about 300 ft (90 m) in diameter and can extend vertically for as much as 3,000 ft (900 m), from their base in the Mississippian Redwall Limestone to as stratigraphically high as the Triassic Chinle Formation. The regions north, south, and east of the Grand Canyon host hundreds of solution-collapse breccia pipes (Van Gosen and others, 2016). Six decades of exploration across the region has found that most of these breccia pipes are not mineralized or substantially mineralized, and only a small percentage of the breccia pipes contain ore-grade uranium deposits. The mineralized breccia pipes contain concentrations of uranium, arsenic, copper, silver, lead, zinc, cobalt, and nickel minerals (Wenrich, 1985), which is reflected in this data set of Canyon deposit samples.
The geology of the Canyon deposit is most thoroughly described by Mathisen and others (2017), a NI 43-101 report prepared for Energy Fuels. The Canyon pipe has an average diameter of about 200 ft (61 m), but narrows to about 80 ft (24 m) in the primary ore zones, which are at the horizons of the Coconino Sandstone and the Hermit Formation. The uranium oxide-copper sulfide mineralization has its highest concentrations at these stratigraphic horizons and in concentric zones of fractures that bound the breccia column along its contact with the intact sedimentary strata. Based on 130 diamond holes totaling nearly 80,000 ft of drilling, Mathisen and others (2017) calculated a mineral resource estimate for the Canyon deposit (effective date of June 17, 2017) as uranium resources, with a Measured Resource of 6,000 tons at an average grade of 0.43 percent U oxide for a total of 56,000 pounds U oxide; an Indicated Resource of 132,000 tons at an average grade of 0.90 percent U oxide for a total of 2,378,000 pounds U oxide; and an Inferred Resource of 18,000 tons at an average grade of 0.38 percent U oxide for a total of 134,000 pounds U oxide. Additionally, the breccia pipe contains copper resources, determined by Mathisen and others (2017) to contain a Measured Resource of 6,000 tons at an average grade of 9.29 percent Cu for a total of 1,203,000 pounds Cu; an Indicated Resource of 94,000 tons at an average grade of 5.70 percent Cu for a total of 10,736,000 pounds Cu; and an Inferred Resource of 5,000 tons at an average grade of 5.90 percent Cu for a total of 570,000 pounds of Cu. While the high uranium content of the Canyon deposit is not unusual for the orebodies of the breccia pipe deposits of the Grand Canyon region, the copper content of the Canyon deposit appears to be anomalously high. Energy Fuels is investigating methods to recover both the copper and the uranium during the processing of the Canyon deposit ores.
References cited above:
Alpine, A.E., ed., 2010, Hydrological, geological, and biological site characterization of breccia pipe uranium deposits in northern Arizona: U.S. Geological Survey Scientific Investigations Report 2010-5025, 353 p., 1 plate, scale 1:375,000, available at http://pubs.usgs.gov/sir/2010/5025/
Mathisen, M.B., Wilson, Valerie, and Woods, J.L., 2017, Technical report on the Canyon mine, Coconino County, Arizona, U.S.A.: NI 43-101 Report, prepared by Roscoe Postle Associates Inc. for Energy Fuels Resources (USA) Inc., dated October 6, 2017, 139 p., accessed December 20, 2019, at http://www.energyfuels.com/canyon-mine
Van Gosen, B.S., Benzel, W.M., and Campbell, K.M., 2020, Geochemical and X-ray diffraction analyses of drill core samples from the Canyon uranium-copper deposit, a solution-collapse breccia pipe, Grand Canyon area, Coconino County, Arizona: U.S. Geological Survey data release, https://doi.org/10.5066/P9UUILQI
Van Gosen, B.S., Johnson, M.R., and Goldman, M.A., 2016, Three GIS datasets defining areas permissive for the occurrence of uranium-bearing, solution-collapse breccia pipes in northern Arizona and southeast Utah: U.S. Geological Survey data release, https://dx.doi.org/10.5066/F76D5R3Z
Wenrich, K.J., 1985, Mineralization of breccia pipes in northern Arizona: Economic Geology, v. 80, no. 6, p. 1722-1735, https://doi.org/10.2113/gsecongeo.80.6.1722

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