Explained by Donald Grybeck, Thomas D. Light, Warren J. Nokleberg, William J. Keith, Dennis P. Cox, Gregory K. Lee, and Jeffrey D. Phillips.
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 permissive area for polymetallic veins is considered to be the entire extent of the Yukon-Tanana Upland and the Kokrine-Hodzana Highlands of Wahrhaftig (1965), which comprise the southern and western portions of east central Alaska and the northern portion of south-central Alaska. This area is predominately Paleozoic metamorphic and sedimentary units intruded by Late Cretaceous and early Tertiary granitic plutons, dikes, and sills of the Kluane arc. Geophysical and geochemical data may support the permissive classification of large areas where no polymetallic vein deposits are known. This tract is contiguous to the permissive tract in east-central Alaska.
Important examples of this type of deposit
The Banjo and Quigley Ridge deposits in the Mount McKinley quadrangle (Nokleberg and others, 1987), as well as many of the veins in the Fairbanks area can be classified as polymetallic veins. Insufficient information precludes a more detailed classification in many cases.
On the numerical estimates made
No estimates of the undiscovered polymetallic veins in this tract was attempted because of the lack of detailed geologic information.
Nokleberg, W.J., Bundtzen, T.K., Berg, H.C., Brew, D.A., Grybeck, Donald, Robinson, M.S., Smith, T.E., and Yeend, Warren, 1987. Significant metalliferous lode deposits and placer districts of Alaska: U.S. Geological Survey Bulletin 1786, 104 p.
Wahrhaftig, Clyde, 1965, Physiographic Divisions of Alaska: U.S. Geological Survey Professional Paper 482, 52 p.