Explained by David A. Lindsey
On the choice of deposit models
Deposits in this tract are small, lenticular bodies of reduced permeable sandstone, siltstone, and shale, within a larger red-bed sequence. 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 occur in Middle Pennsylvanian (DesMoinesian) through Lower Permian (Wolfcampian) clastic rocks derived from erosion of the Ancestral Rocky Mountains. Stratigraphic units include Minturn, Madera, Bursum, Naco, Sangre de Cristo, Abo, Yeso, Supai, and Cutler Formations, and these rocks constitute the permissive tract. Within these, the red bed-over-gray bed transition (Sangre de Cristo to Minturn or Madera; Abo to Bursum; Supai to Naco) is the best target.
Important examples of this type of deposit
The Scholle district, in New Mexico (Hatchell and others, 1982) is the best example.
On the numerical estimates made
Although more than a dozen districts and occurrences are known (Soule, 1956), the largest production of any district (Scholle, New Mexico) has been 12,340 metric tons of ore (Hatchell and others, 1982); reserves in most districts are almost nil. Because production and reserves are much smaller than the median red-bed deposit tonnage, an estimate of 0, 1, 2, 4, and 5 or more deposits was made for the 90th, 50th, 10th, 5th, and 1st percentiles, consistent with the grade and tonnage model (Mark 3 no. 97).
Hatchell, W.O., Blagbrough, J.W., and Hill, J.M., 1982, Stratigraphy and copper deposits of the Abo Formation, Abo Canyon area, central New Mexico, in Grambling, J.A., and Wells, S.G., eds., Albuquerque Country II, New Mexico Geological Society Guidebook, 33rd Annual Field Conference, p. 249-260.
Soule, J.H., 1956, Reconnaissance of the "Red Bed" copper deposits in southeastern Colorado and New Mexico: U.S. Bureau of Mines Information Circular 7740, 74 p.