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 Aleutian Islands are a poorly mapped area of volcanic and volcaniclastic rocks of Tertiary and Quaternary age intruded by plutons of Oligocene, Late Miocene, and possibly other ages. The geologic setting is permissive for polymetallic vein deposits and there are several small occurrences that possibly are polymetallic veins. In addition, polymetallic veins may be spatially related to other types of deposits, especially porphyry type systems, thus enlarging their permissive area. Very little geophysical and geochemical data are available to support or rule out the permissive classification of large areas where no polymetallic vein deposits are known. Areas 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
The Biorka prospect on Sedanka Island (Webber and others, 1946) and the Rootok Island prospect (Butherus and others, 1979) may both be polymetallic veins. In addition, a prospect reported by the Russians in the 18th or 19th century near Bornite Lake (Reinken or Bornite Lake prospect, Randolph, 1991) on Unalaska Island may also be a polymetallic vein.
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) has been estimated at:
Percentile 90 50 10 5 1
Estimated number of deposits 5 10 45 45 45
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.
Butherus, D.L., Gressitt, E.E., Pray, Jim, Corner, N.G., Lindberg, P.A., and Fankhauser, R.E., 1979, Exploration and evaluation of the Aleut Native Corporation Lands 1979: Unpublished Resource Associates of Alaska report prepared for Houston Oil and Minerals Corporation and available from The Aleut Corporation, 69 p., 1 appendix.
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.
Randolph, D.B., 1991, Unalaska project 1990 final report, Battle Mountain Exploration Company, Alaska District: unpublished report available from The Aleut Corporation, 62 p., 5 appendices, 15 plates, various scales.
Webber, B.S., Moss, J.M., and Rutledge, F.A., 1946, Exploration of Sedanka zinc deposit, Sedanka Island, Alaska: U.S. Bureau of Mines Report of Investigations 3967, 15 p.