Foggy Day

Prospects, Inactive

Alternative names


Commodities and mineralogy

Main commodities None
Other commodities Ag; Pb; U
Ore minerals galena; zeunerite
Gangue minerals complex mineralogy characterizes assemblages

Geographic location

Quadrangle map, 1:250,000-scale TE
Quadrangle map, 1:63,360-scale C-5
Latitude 65.519
Longitude -167.156
Nearby scientific data Find additional scientific data near this location
Location and accuracy Several mineral occurrences are located on west-facing slopes peripheral to the Brooks Mountain granite stock in the headwaters of a southeast tributary to the Mint River. Mint River flows northward from its headwaters along the continental divide in the York Mountains. This prospect area is downslope to the west of the continental divide at an approximate elevation of 1,750 feet. Prospects included in this area are Foggy Day, Cameron, Read, and Paigite (West and White, 1952, plate 1). This area was shown as locality 11 of Cobb and Sainsbury (1972) and Cobb (1975) summarized relevant references 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).
The mineralization in this area is associated with contact metamorphic rocks developed in Ordovician limestone peripheral to the southwest contact of the Brooks Mountain granite stock. Complex mineralogy characterizes the occurrences here. Tactite forms seams and irregular masses in crystalline marble; idocrase, garnet, diopside, augite, hedenbergite, phlogopite, and fluorite are present in the tactite. Sulfide minerals, dominately galena, include pyrrhotite, stannite, sphalerite, pyrite, arsenopyrite, chalcopyrite, chalcocite, and bornite. Other minerals include scapolite, chondrodite, siderophyllite, tourmaline, scheelite, ludwigite, magnetite, hematite, limonite, cerussite, azurite, malachite, pageite, and hulsite. Zuenerite is locally present in association with hematite in oxidized granite adjacent to marble.
This is primarily an area of interesting mineral occurrences although selected samples of galena-rich material assayed 34% lead and 11 opt silver (Knopf, 1908, p. 42-43) and zuenerite-rich material contained up to 2.14% eU (West and White, 1952, p. 4).
Geologic map unit (-167.158727921187, 65.5182281016377)
Mineral deposit model This is an approximate 1,500 by 3,000 foot area of variable contact metamorphism of Ordovician limestone near the contract of 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 Primarily calc-silicate tactite development but with significant associated boron metasomatism.

Production and reserves

Workings or exploration Several surface pits and some dozer trenches have been completed here.
Indication of production None
Reserve estimates Not defined


MRDS Number 10308419


Reporters Travis L. Hudson (Applied Geology)
Last report date 5/10/1998