Unnamed (on western side of Brooks Mountain)

Prospect, Inactive

Commodities and mineralogy

Main commodities None
Other commodities Pb; U
Ore minerals galena
Gangue minerals calcite; idocrase; tourmaline

Geographic location

Quadrangle map, 1:250,000-scale TE
Quadrangle map, 1:63,360-scale C-5
Latitude 65.529
Longitude -167.153
Nearby scientific data Find additional scientific data near this location
Location and accuracy This area is along the west contact zone of the Brooks Mountain granite stock, about 0.8 mile north of the prospects on the southwest side of the stock (TE055). The prospect area is at an elevation of about 2,500 feet along and immediately west of the continental divide. This locality was not shown separately by Cobb and Sainsbury (1972) but some relevant references were summarized by Cobb (1975) under the name 'Brooks Mtn.'.

Geologic setting

Geologic description

Brooks Mountain granite stock is a 1 by 2 mile composite intrusion just south and east of Brooks Mountain (elevation 2,898 feet), the highest part of the York Mountains. The country rocks to the Late Cretaceous (77.0 +/- 3.0 my; Hudson and Arth, 1983, p. 769) Brooks Mountain granite are Ordovician limestone and locally fine-grained, carbonaceous metaclastic rock of unknown but probable Paleozoic age. Tactite is common in marble nearby to the granite contact on the northwest and southwest sides of the stock (Sainsbury, 1969, plate 1). Hornfels is developed in the nearby metaclastic rocks. The granite is dominately seriate and porphyritic types (Hudson and Arth, 1983, p. 770) that are not known to be directly linked with significant tin metallization in the western Seward Peninsula tin belt; they are instead precusor-type granites (Hudson and Reed, 1997, figure 3).
Tactite here contains much idocrase and some tourmaline. It forms irregular masses and green-colored seams along fractures in marble. Small cubes of galena are present in open vugs in the tactite. About 700 feet to the southeast, the Brooks Mountain granite contains 1 to 4 inch wide quartz-tourmaline veins along joints. Uranium (to 1% eU) is present in zuenerite associated with hematite coatings on vein and fracture surfaces (West and White, 1952).
Geologic map unit (-167.155729855029, 65.5282289990064)
Mineral deposit model This is an area of variable contact metamorphism of Ordovician limestone by the Brooks Mountain granite stock. Possibly tin skarn (Cox and Singer, 1986; model 14b)
Mineral deposit model number 14b
Age of mineralization The age of the mineralization is assumed to be similar to the age of the Brooks Mountain granite (77.0 +/- 3.0 my; Hudson and Arth, 1983, p. 769).
Alteration of deposit Tactite in carbonate rocks, quartz-tourmaline veining in granite, and secondary oxide development.

Production and reserves

Workings or exploration Some surface pits have been dug here.
Indication of production None
Reserve estimates Not defined

References

MRDS Number 10308420

References

Hudson, T.L., and Arth, J. G., 1983, Tin granites of Seward Peninsula, Alaska: Geological Society of America Bulletin, v. 94, p. 768-790.
Hudson, T.L., and Reed, B.L., 1997, Tin deposits of Alaska, in Goldfarb, R.J., and Miller, L.D., eds., Mineral Deposits of Alaska: Economic Geology Monograph 9, p. 450-465.
Patton, T.L., and Robinson, M.S., 1975, Bedrock geology, geochemistry, and geophysics of Brooks Mountain, Seward Peninsula, Alaska: Fairbanks, University of Alaska, M.Sc. thesis, 106 p.
Reporters Travis L. Hudson (Applied Geology)
Last report date 5/10/1998