Explained by Alan R. Wallace
On the choice of deposit models
Zinc-lead skarn deposits form by the replacement of carbonate rocks by base-metal sulfides (especially sphalerite and galena) and silicate skarn assemblage minerals, in close proximity to felsic- to intermediate-composition intrusive bodies.
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 zinc-lead skarn deposits in Texas is that area where carbonate rocks are present at or within a kilometer of the surface in the area of Tertiary felsic igneous rocks.
Important examples of this type of deposit
No deposits or prospects of this type are known.
On the numerical estimates made
This is a very rare type of deposit worldwide. Relatively few intrusions are known in the Texas carbonate terrane, and they are given a low estimate for porphyry copper deposits, which are most commonly associated with copper skarn deposits. Thus, the chance for there being an undiscovered zinc-lead skarn deposit is considered to be even less. 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 zinc-lead skarn deposits (Mosier, 1986).
Mosier, D.L., 1986, Grade and tonnage model of Zn-Pb skarn deposits, in Cox, D.P., and Singer, D.A., eds., Mineral deposit models: U.S. Geological Survey Bulletin 1693, p. 90-93.