Explained by Frederic H. Wilson, Stanley E. Church, Richard W. Saltus, Lawrence J. Drew, and W. David Menzie.
On the choice of deposit models
Polymetallic vein deposits can be associated with intrusive rocks of any age and a wide range of compositions (Cox, 1986). Polymetallic veins may also be spatially related to a large number of other types of deposits, thus making their permissive area quite extensive. This model also serves as somewhat of a catch‑all for deposits of unknown type that, given minimal information, do not appear to fit into other similar categories
On the delineation of permissive tracts
The tract is defined as all areas that lie within approximately 5 km of known or inferred volcanic and hypabyssal intrusions of Tertiary and Quaternary age in the Chignik subterrane of the Alaska Peninsula. Geochemical data support the permissive classification of large areas where no polymetallic vein deposits are known. Many areas of hydrothermally altered volcanic or sedimentary rocks occur within this tract and sparsely distributed geochemical sampling shows that a number of these are anomalous in multiple metals, including copper, lead, and or zinc. Polymetallic vein deposits are permissive around porphyry copper-type occurrences; the large number of potential porphyry copper-type occurrences in this tract suggest high potential for polymetallic veins. Areas that are not considered permissive are predominantly where there is sufficiently detailed geologic information to indicate that deposits do not exist.
Important examples of this type of deposit
Of a total of 210 occurrences in this tract (Wilson and others, 1988), 52 of the occurrences are classified as possible polymetallic veins. Renshaw Point is an example of a possible polymetallic vein. Many other small occurrences of this type of deposit are known and additional deposits are expected.
On the numerical estimates made
The minimum number of undiscovered polymetallic vein deposits, consistent with the tonnage and grade model of Bliss and Cox (1986), expected to occur in this tract is estimated as:
Percentile 90 50 10 5 1
Estimated number of deposits 10 40 90 90 90
Bliss, J.D., and Cox, D.P., 1986, Grade and tonnage model of polymetallic veins, in Cox, D.P., and Singer, D.A., eds., Mineral deposit models: U.S. Geological Survey Bulletin 1693, p. 125-129.
Cox, D.P., 1986, Descriptive Model of polymetallic veins, in Cox, D.P., and Singer, D.A., eds., Mineral deposit models: U.S. Geological Survey Bulletin 1693, p. 125.
Wilson, F.H., White, W.H., and DuBois, G.D., 1988, Brief descriptions of mines, prospects, and mineral occurrences in the Port Moller and Stepovak Bay quadrangles, Alaska Peninsula: U.S. Geological Survey Open‑File Report 88‑666, 128 p., scale 1:250,000, 1 map sheet.