Explained by David A. Lindsey
On the choice of deposit models
Deposits in this tract are small, lenticular bodies of reduced rock in permeable gray sandstone, siltstone, and shale. Most host rocks contain organic plant remains and some contain pyrite. The small mineralized bodies occur in reduced zones preserved in red beds. Anomalous concentrations of uranium are commonly present. These features match those of other red-bed-type copper deposits.
On the delineation of permissive tracts
Deposits and occurrences are in two areas in the Colorado Plateau. Permissive units include the Hermosa Group and Cutler Formation in Utah, and the Naco Formation in Arizona.
Important examples of this type of deposit
A cluster of small mines and occurrences in the Naco Formation in Arizona and scattered occurrences in Utah are the only evidence of red-bed-type copper deposition.
On the numerical estimates made
Because production and reserves from the largest deposits in this age group in this region are much smaller than the median red-bed deposit tonnage, and because of the lack of known deposits in this tract, for the 90th, 50th, 10th, 5th, and 1st percentiles, we estimated 0, 0, 0, 1, and 3 or more deposits consistent with the grade and tonnage model. Our estimate focused primarily on the highly-explored (for uranium), near-surface rocks, and may not accurately reflect the presence of undiscovered deposits in deeper parts of the tract.