Explained by Jeanine M. Schmidt, Thomas D. Light, and Bruce M. Gamble
On the choice of deposit models
Two Mississippi Valley type (MVT) deposits are described in Cox and Singer (1986). The differences between Southeast Missouri Pb-Zn (model 32a; Briskey 1986b) and Appalachian Zn (model 32b; Briskey, 1986a) are subtle enough that the grade and tonnage models for the two deposit types are plotted together with no differentiation between types (Mosier and Briskey, 1986). In Alaska, the lack of detailed geologic information prevents distinguishing between the two deposit types, and a generic Mississippi Valley type model has been used.
This tract is permissive for Mississippi Valley type deposits because it locally contains platform carbonate rocks, which in west-central Alaska, host deposits thought to be Mississippi Valley type.
On the delineation of permissive tracts
This tract includes the Nixon Fork and Minchumina terranes, both of which locally contain lower Paleozoic platform carbonate rocks (Patton and others, 1994), in the Mt. McKinley quadrangle.
Important examples of this type of deposit
The Reef Ridge deposit in the Medfra quadrangle of west-central Alaska is an example of a Mississippi Valley type deposit (Andrews and Rishel, 1982).
On the numerical estimates made
No estimate of the number of undiscovered deposits was attempted.
Andrews, T., and Rishel, John, 1982, 1981 Annual Report-Reef Ridge I-XIII project areas, Kuskokwim Block, Volume 1 of 3: unpublished report, Patino Inc., Anchorage, Alaska, 49 p.
Briskey, J.A., 1986a, Descriptive model of Appalachian Zn, in Cox, D.P., and Singer, D.A., eds., Mineral deposit models: U.S. Geological Survey Bulletin 1693, p. 222-223.
Briskey, J.A., 1986b, Descriptive model of southeast Missouri Pb-Zn, in Cox, D.P., and Singer, D.A., eds., Mineral deposit models: U.S. Geological Survey Bulletin 1693, p. 220-221.
Cox, D.P., and Singer, D.A., eds., 1986, Mineral deposit models: U.S. Geological Survey Bulletin 1693, p. 130.
Mosier, D.L., and Briskey, 1986, Grade and tonnage model of southeast Missouri Pb-Zn and Appalachian Zn deposits, in Cox, D.P., and Singer, D.A., eds., Mineral deposit models: U.S. Geological Survey Bulletin 1693, p. 224-226.
Patton, W.W., Jr., Box, S.E., Moll-Stalcup, E.J., and Miller, T.P., 1994, Geology of west-central Alaska, in Plafker, George, and Berg, H.C., eds., The Geology of Alaska: Boulder, Colorado, Geological Society of America, The Geology of North America, v. G-1, p. 241-269.