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Unnamed (head of Boundary Creek)

Occurrence, Inactive

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Commodities and mineralogy

Main commodities Mo
Other commodities Ag; Cu; W
Ore minerals molybdenite; pyrite; pyrrhotite

Geographic location

Quadrangle map, 1:250,000-scale TR
Quadrangle map, 1:63,360-scale C-6
Latitude 58.6443
Longitude -133.8515
Nearby scientific data Find additional scientific data near this location
Location and accuracy This occurrence is at the head of Boundary Creek about midway between the Antler Peaks and the Bacon Glacier. It is in about the center of the east side of section 21, T.37 S., R.70 E. of the Copper River Meridian. This is location T002 of Wells and others (1986). The map location is the approximate center of several reported occurrences and is accurate within 1/4 mile.

Geologic setting

Geologic description

This occurrence is in the Coast Range plutonic-metamorphic complex which consists of high-grade schist and gneiss intruded by Cretaceous and Tertiary granodiorite. The metamorphic rocks are derived from volcanic, pelitic and minor carbonate strata of unknown protolith age (Brew and Ford, 1974, 1984).
Molybdenite was first reported in the Boundary Creek area by the U.S. Geological Survey in 1967 (Brew and Ford, 1969). Later investigations were conducted by the U.S. Geological Survey in 1985 (Koch and others, 1987) and the U.S. Bureau of Mines in 1987 (Clough, 1990). The USGS work identified a 100-foot-wide zone of highly altered and intensely iron-stained, north to northeast-trending aplite that contains pyrite and molybdenite. The mineralized zone was exposed for a slope distance of 300 feet. The host rock is a large dike-like body of aplite and granodiorite at least 2 miles long and 2000 feet thick. The country rocks include Mesozoic (?) schistose, biotite hornfels, hornblende hornfels, calc-silicate hornfels, and minor marble. The rocks are deformed into north to west-trending folds and are cut by Cretaceous (?) tonalite, a large dike of Tertiary aplite, and altered granodiorite (Brew and Ford, 1969). Silicification is coincident with the mineralization, and the rocks are iron-stained due to weathering of accessory pyrite and pyrrhotite (Clough,1990). K/Ar dating of hydrothermal muscovite at the geologically similar Boundary Creek 2 occurrence (TR003), three miles to the southeast, indicates that the molybdenite formed at or after 59.7 Ma (Miller and others, 1997).
U.S. Geological Survey sampled a 6- by 12-foot area with visible molybdenite (Brew and Ford, 1969). A COMPOSITE CHIP SAMPLE OF IRON-STAINED molybdenite-bearing ROCK contained 1000 ppm molybdenum, 9.6 ppm silver, and 300 ppm copper; another sample contained 1000 ppm molybdenum, 0.9 ppm silver, and 7 ppm copper. The U.S. Bureau of Mines sampled more widely (Clough 1990). A three-foot sample of garnet skarn contains 1000 ppm molybdenum, 45 ppm copper, and 300 ppm zinc; a 2-foot sample of syenite contains 33 ppm copper, 57 ppm molybdenum, and 400 ppm tungsten; a float sample of siliceous alaskite contains 1.0 percent molybdenum.
Geologic map unit (-133.853255145167, 58.6439900031687)
Mineral deposit model Porphyry Mo (Cox and Singer, 1986; model 21b)
Mineral deposit model number 21B
Age of mineralization K/Ar dating of hydrothermal muscovite at the geologically similar Boundary Creek 2 occurrence (TR003), 3 miles to the southeast, indicates that the molybdenite formed at or later than 59.7 Ma (Miller and others, 1997).
Alteration of deposit Silicification is coincident with the mineralization. Iron staining is due to weathering of accessory pyrite and pyrrhotite (Clough,1990).

Production and reserves

Workings or exploration There are no surface or underground workings and exploration has been limited.
Indication of production None

References

MRDS Number A012522

References

Brew, D.A., and Ford, A.B., 1969, Boundary Creek molybdenum-silver occurrence: U.S. Geological Survey Circular 615, p. 12-15.
Brew, D.A., and Ford, A.B., 1974, Geology of the Juneau Icefield and adjacent areas, in Carter, Claire, ed., U. S. Geological Survey Alaska Program, 1974: U.S. Geological Survey Circular 700, p. 63.
Brew, D.A., and Ford, A.B., 1984, The northern Coast plutonic-metamorphic complex, southeastern Alaska and northwestern British Columbia, in Coonrad, W.C., and Elliott, R.L., eds., The United States Geological Survey in Alaska--Accomplishments during 1981: U.S. Geological Survey Circular 868, p. 120-124.
Clough, A.H., 1990, Bureau of Mines mineral investigations in the Juneau mining district, Alaska, 1984-1988, Volume 2, Detailed mine, prospect, and mineral occurrence descriptions, Section E, Coast Range subarea: U.S. Bureau of Mines of Mines Special Publication, 44 p.
Koch, D.K., Brew, D.A., and Ford, A.B., 1987, Newly discovered molybdenum occurrence near Boundary Creek, Coast Mountains, southeastern Alaska, in Hamilton, T.D., and Galloway, J.P, eds, Geologic Studies by the U.S. Geological Survey in Alaska, 1986: U.S. Geological Survey Circular 998, 1987, p. 124-125.
Miller, L.D., Goldfarb, R.J., Snee, L.W., McClelland, W.C., and Klipfel, P.D., 1997, Paleocene molybdenum mineralization in the eastern Coast Batholith, Taku River region, and new age constraints on batholith evolution, in Dumoulin, J.A., and Gray, J.E., eds., Geologic studies in Alaska by the U.S. Geological Survey, 1995: U.S. Geological Survey Professional Paper 1574, p. 125-135.
Wells, D.E., Pittman, T.L., Brew, D.A. and Douglass, S.L., 1986, Map and description of the mineral deposits in the Juneau, Taku River, Atlin, and part of the Skagway quadrangles, Alaska: U.S. Geological Survey Open-File Report 85-717, 332 p., 1 sheet, scale 1:250,000.
Reporters J.C. Barnett and L.D. Miller (Juneau, Alaska)
Last report date 11/27/2001