Boundary Creek 2

Occurrence, Inactive

Commodities and mineralogy

Main commodities Ag; Mo
Other commodities Au; Cu; Pb; W
Ore minerals molybdenite

Geographic location

Quadrangle map, 1:250,000-scale TR
Quadrangle map, 1:63,360-scale C-6
Latitude 58.6206
Longitude -133.7795
Nearby scientific data Find additional scientific data near this location
Location and accuracy This occurrence is on the crest of the ridge between Boundary Creek and Bacon Creek, 5.5 miles north of the Taku River, and 1.5 miles west of the Canadian border. It is in the SE1/4NW1/4 section 36, T.37 S., R.70 E.; the NE1/4 section 2, T.38 S., R.70 E.; and the N1/2 section 31, T.37 S., R.71 E. of the Copper River Meridian. 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 (TR002) by the U.S. Geological Survey in 1967 (Brew and Ford, 1969). 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).
This occurrence, which is geologically similar to the one at the head of Boundary Creek (TR002) is in Tertiary or younger, iron-stained alkali granite and aplite. It consists of disseminations of fine- to coarse-grained flakes of molybdenite in miarolitic cavities in the granite and aplite (Clough, 1990). Pyrite and pyrrhotite accompany the molybdenite. Widely spaced, narrow, pyrite-bearing quartz veins cut the granite and aplite, but they do not contain molybdenite (Koch and others, 1987). The U.S. Bureau of Mines collected a 4-foot sample of molybdenite-bearing aplite that contained 4,800 ppm molybdenum, 1,600 ppm lead, 250 ppm silver, and 0.210 ppm gold (Clough, 1990). Molybdenite occurrences in this area are localized along sets of fractures that strike northeast and east-northeast, and dip steeply. The molybdenite forms rosettes that are associated with muscovite on fracture surfaces. The fracture surfaces are also coated with epidote (Miller, and others, 1997). There is pervasive silicification throughout the mineralized area. The area is intensely iron-stained due to the weathering of pyrite and pyrrhotite (Clough, 1990). K/Ar dating of hydrothermal muscovite from a biotite-rich, molybdenite-bearing granite dike indicates that the molybdenite formed at after 59.7 Ma. (Miller, and others, 1997).
Geologic map unit (-133.781250314168, 58.6202896064132)
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 from a biotite-rich, molybdenite-bearing granite dike indicates that the molybdenite formed at after 59.7 Ma. (Miller, and others, 1997).
Alteration of deposit There is pervasive silicification throughout the mineralized area. The rocks are intensely iron-stained due to the weathering of 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

Reporters J.C. Barnett and L.D. Miller (Juneau, Alaska)
Last report date 11/27/2001