Unnamed Occurrence (ARDF - TR002; head of Boundary Creek), Juneau Mining District, Juneau, Alaska, USAi

Regional Level Types
Unnamed Occurrence (ARDF - TR002; head of Boundary Creek)	- not defined -
Juneau Mining District	Mining District
Juneau	City Borough
Alaska	State
USA	Country

Location: 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.
Geology: 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 dikelike 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), 3 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 3-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% molybdenum.
Workings: There are no surface or underground workings and exploration has been limited.
Age: 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: Silicification is coincident with the mineralization. Iron staining is due to weathering of accessory pyrite and pyrrhotite (Clough,1990).

Commodities (Major) - Mo; (Minor) - Ag, Cu, W
Development Status: No
Deposit Model: Porphyry Mo (Cox and Singer, 1986; model 21b)

Other Databases

Link to USGS - Alaska:	TR002

Other Regions, Features and Areas containing this locality

References