Explained by Alan R. Wallace
On the choice of deposit models
Tertiary felsic intrusive rocks were emplaced into Paleozoic carbonate rocks in western Texas, and the coincidence of the two rock types requires that this deposit type be considered. Einaudi and others (1981) distinguished two types of copper skarns, those related to porphyry copper deposits (Cox, 1986) and those related to barren intrusions (Cox and Theodore, 1986). Because porphyry copper deposits are uncommon in Texas, we used the grade and tonnage model of Jones and Menzie (1986).
On the delineation of permissive tracts
These deposits form where intermediate to felsic intrusive rocks, which are the principal sources of the metals, are emplaced into carbonate rocks. Therefore, the permissive tract for copper skarn deposits in western Texas is that area where carbonate rocks are present at or within a kilometer of the surface in areas where Tertiary felsic igneous rocks are also found. Skarn-type mineralization associated with alkaline intrusions is accounted for by the assessment for alkaline porphyry copper-gold deposits.
Important examples of this type of deposit
No deposits of this type are known; there is a small prospect in the Infiernito caldera (Price and others, 1983).
On the numerical estimates made
Relatively few intrusive bodies are known in the carbonate terrane, and the chance for the existence of undiscovered copper skarn deposits was considered to be less than the possibility for porphyry copper deposits. For the 90th, 50th, 10th, 5th, and 1st percentiles, the team estimated 0, 0, 0, 0, and 1 or more deposits consistent with the grade and tonnage model for copper skarn deposits of Jones and Menzie (1986).
Cox, D.P., 1986, Descriptive model of porphyry Cu, skarn-related deposits: Descriptive model of Cu skarn Deposits, in Cox, D.P., and Singer, D.A., eds., Mineral deposit models: U.S. Geological Survey Bulletin 1693, p. 82-85.
Cox, D.P., and Theodore, T.G., 1986, Descriptive model of Cu skarn deposits, in Cox, D.P., and Singer, D.A., eds., Mineral deposit models: U.S. Geological Survey Bulletin 1693, p. 86-89.
Einaudi, M.T., Meinert, L.D., and Newberry, R.J., 1981, Skarn deposits, in Skinner, B.J., ed., Economic Geology Seventy-Fifth Anniversary Volume, 1905–1980: Lancaster, Pennsylvania, Economic Geology Publishing Company, p. 317-392.
Jones, G.M., and Menzie, W.D., 1986, Grade and tonnage model for Cu skarns, in Cox, D.P., and Singer, D.A., eds., Mineral deposit models: U.S. Geological Survey Bulletin 1693, p. 86-89.
Price, J.G., Henry, C.D., and Standen, A.R., 1983, Annotated bibiliography of mineral deposits in Trans-Pecos Texas: Bureau of Economic Geology, Mineral Resource Circular, no. 73, 108 p.