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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

January 24, 2020

This data release compiles the major and trace element analytical results of drill core samples that typify the uranium-copper ore bodies of the Canyon deposit, located about 6.1 miles (10 km) south-southeast of Tusayan, Arizona. The Canyon deposit lies from about 750 to 2,000 ft (230 to 610 m) below the surface at latitude 35.88333 North, longitude -112.09583 West (datum WGS 1984). Energy Fuels, owners and operators of the property, has conducted extensive drilling into the Canyon deposit, which has defined the extent and characteristics of the ore bodies, leading to mine development. 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, focused primarily on intervals of high-grade uranium and associated mineralization. This data release provides the analytical results of 35 samples of drill core collected during the visit by the authors. Additionally, X-ray Diffraction analyses were performed on 28 of these samples to examine their mineralogy.

These samples and their geochemistry reflect the variation of base-metal sulfide and uranium oxide mineralization within ore zones of the Canyon deposit. The ore mineralogy, and thus rock chemistry, can vary over short intervals (centimeters). However, although their concentrations vary, the group of metals that occur together is generally consistent.

The 35 samples were analyzed for 63 elements by a laboratory contracted by the USGS. Concentrations for 58 elements were measured by Inductively Coupled Plasma-Optical Emission Spectrometry (ICP-OES) and Inductively Coupled Plasma-Mass Spectrometry (ICP-MS). Additionally, total carbon, carbonate carbon (inorganic carbon), total sulfur, mercury, and selenium concentrations were determined using other element-specific analytical techniques (described below). From this suite of 35 samples, 28 were analyzed by X-ray Diffraction to determine their mineralogy. The X-ray Diffraction scan results are provided in the data file named "Canyon_deposit_drill_core_samples_XRD.csv".

The Canyon uranium-copper deposit occurs within a matrix-supported column of breccia (a "breccia pipe") that is similar to numerous other uranium-bearing breccia pipes of the Grand Canyon region of northwest Arizona. These uranium deposits occur in unusual features described as solution-collapse breccia pipes, or simply breccia pipes (Wenrich, 1985; Alpine, 2010). The regions north and south of the Grand Canyon host hundreds of breccia pipes that were formed by solution and collapse (Van Gosen and others, 2016). Breccia refers to the broken rock that fills these features, and pipe refers to the vertical, pipe-like shape of these features. 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 breccia fragments that form the pipes are consistently blocks and pieces of rock units found below their normal position in the wall rock; that is, all rocks within the breccia column have fallen downward and are never found above their original level. In contrast to many other types of breccia pipes, there are no igneous rocks associated with the northwestern Arizona breccia pipes, nor have igneous processes contributed to their formation.

Many of these breccia pipes contain concentrated deposits of uranium, arsenic, copper, silver, lead, zinc, cobalt, and nickel minerals (Wenrich, 1985), as is reflected in this data set. Subsequent to the primary episodes of solution and collapse (breccia pipe formation), base-metal mineralization was deposited in the breccia pipes, primarily as sulfide phases, and principally in the stratigraphic levels of the Coconino Sandstone, Hermit Formation, and Esplanade Sandstone (Wenrich, 1985; Alpine, 2010). In the Canyon breccia pipe, the base-metal sulfides are most concentrated around the outer several meters of the breccia column forming a halo of mineralization, but not extending into the enclosing host country rock. Detailed microscopy studies of the ores indicate that the uranium mineralization, in the form of uranium oxide (uraninite), was deposited after sulfide mineralization was in place. Microscopic textures and relationships suggest that uranium, carried by oxidized waters, reacted with pre-existing sulfide minerals within the breccias; this interaction reduced the uranyl ions, thereby depositing microscopic uraninite in voids between the sulfide minerals and breccia clasts. Finally, there is evidence of subsequent episodes of internal collapse within the Canyon pipe that followed sulfide and uranium mineralization.

The Canyon deposit is most thoroughly described by Mathisen and others (2017), a NI 4301 report prepared for Energy Fuels. 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, Measured Resources of 6,000 tons at an average grade of 0.43 percent U oxide for a total of 56,000 pounds U oxide; Indicated Resources 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 Inferred Resources 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 be Measured Resources of 6,000 tons at an average grade of 9.29 percent Cu for a total of 1,203,000 pounds Cu; Indicated Resources of 94,000 tons at an average grade of 5.70 percent Cu for a total of 10,736,000 pounds Cu; and Inferred Resources 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.

Several breccia pipes of the Grand Canyon region have been mined for their uranium deposits (Wenrich, 1985; Alpine, 2010; Van Gosen and others, 2016). While hundreds of breccia pipes in the region have been identified, exploration across the region for six decades has discovered that most are not mineralized; only a small percentage of the breccia pipes contain economic uranium deposits (Van Gosen and others, 2016). To date (2019), 13 breccia pipes in the region have been mined for uranium from the 1950s to present (Alpine, 2010; Van Gosen and others, 2016). In 2018, Energy Fuels completed a mine shaft and other mining facilities at the Canyon deposit in preparation for mining. In the foreseeable future, the Canyon deposit may join the list of northwest Arizona breccia pipes that have been mined for their uranium ore, and this time with potentially the co-production of copper.

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 4301 Report, prepared by Roscoe Postle Associates Inc. for Energy Fuels Resources (USA) Inc., dated October 6, 2017, 139 p. Accessed December 20, 2019, at https://www.energyfuels.com/pinyon-plain-mine

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