By Warren I. Finch, Charles T. Pierson, and Hoyt B. Sutphin
COMMENTS All the deposits in this grade and tonnage compilation are from the Grand Canyon region of northwestern Arizona. From the many mineralized solution-collapse breccia pipes in the region, we have chosen eight deposits that contain mostly primary, unoxidized minerals and have complete, reliable grade and tonnage data. Other mineralized breccia pipes are deeply eroded, strongly weathered, depleted in uranium, and enriched by supergene processes to minable grades of copper, vanadium, and other metals. These remnant deposits are not considered here to be a separate, distinct class of deposits. Furthermore, grade and tonnage data of these remnant deposits (Chenoweth, 1988) are too incomplete to graph meaningfully either separately or combined with the primary deposits.
During the 1950-70 period when the Orphan Lode was mined, the cutoff grades were around 0.10 percent U3O8. Few, if any, breccia pipes were mined in the 1970's. In the 1980's, the cutoff grade was 0.20~.35 percent U3O8 for the remaining seven pipes. The average grade of the Orphan Lode ore mined in the early period was 0.43 percent U3O8 (Chenoweth, 1986), whereas ores mined from other pipes in the 1980's averaged about 0.65 percent U3O8 (Mathisen, 1987). The grade and tonnage data used to plot the graphs in figures 21 and 22 are based on premining reserves calculated at a cutoff grade of 0.05 percent U3O8. Energy Fuels Nuclear, Inc., operators of all deposits but the Orphan Lode, kindly permitted the use of data from their properties. See appendix B for locality abbreviations. See introduction for explanation of the grade and tonnage model as shown in figures 21 and 22.
Figure 21. Tonnages of solution-collapse breccia-pipe uranium deposits.
Figure 22. Uranium-oxide grades of solution-collapse breccia-pipe uranium deposits.
DEPOSITS                            DEPOSITS
Name               Country          Name                 Country
Canyon              USAZ           Kanab North       USAZ
Hack No. 1        USAZ          Orphan Lode       USAZ
Hack No. 2        USAZ           Pigeon                USAZ
Hack No. 3        USAZ           Pinenut                USAZ
The scatter plot of the logarithms (to base 10) of grade and tonnage is shown in figure 23. This plot and the correlation coefficient of -0.122 suggest that the log-tonnage and log-grade are not correlated. Neither probability plots nor histograms of the grade and tonnage data demonstrate either normality or lognormality. Skewness is 0.13 for log-tonnages and -0.90 for log-grades. The mean tonnage and grade are 269,600 metric tons and 0.57 percent U3O8, with standard deviations of 157,370 metric tons and 0.07 percent U3O8, respectively.
Trace-element contents of five of the eight pipes are shown in table 9. Because the selected samples were high graded, these data do not represent the average grade for a given deposit. Hence, grade curves cannot be constructed from the data. Nevertheless, they do show that the mean value of the elements As, Co, Cu, Ni, Pb, U. and Zn are high locally within breccia pipe primary orebodies. Copper, vanadium, gold, and silver have been produced from some highly oxidized breccia pipe uranium ores (Chenoweth, 1986, 1988).
Figure 23. Scatter plot of logarithms of average uranium-oxide grade vs tonnage of uranium ore.
Table 9. Summary statistics of chemical analyses of one selected sample from each of the five solution-collapse breccia pipe uranium deposits (based on analyses by Wenrich and Sutphin, 1989, and their unpublished data)
Element        Mean         Standard deviation
                   (ppm)                (ppm)
Ag                 34                    22
As            8,340               6,981
Ba               139                  109
Cd                31                    40
Ce              102                    94
Co           2,044               3,795
Cr                 51                    68
Cu          11,440               9,340
Fe                   4.7                    3.7
Ga                 21                      9
La                 17                      7
Li                  20                    16
Mo              403                  312
Ni             4,760               5,998
Pb             2,978               2,042
Sr                 372                  494
U             77,400             65,569
V                  121                    99
Y                  124                  112
Zn              9,584             11,469
  1. Fe values are in percent.