Cape Darby

Occurrence, Inactive

Commodities and mineralogy

Main commodities U; W
Other commodities REE
Ore minerals allanite; monazite; scheelite
Gangue minerals biotite; epidote; fluorite; hematite; ilmenite; magnetite; zircon

Geographic location

Quadrangle map, 1:250,000-scale SO
Quadrangle map, 1:63,360-scale B-2
Latitude 64.385
Longitude -162.796
Nearby scientific data Find additional scientific data near this location
Location and accuracy This occurrence is on the east coast of Golovin Bay. It is on a sea cliff 3.3 miles southeast of Golovin Mission and 4.1 miles northeast of Cape Darby. This is occurrence 136 of Cobb (1972, MF 445; 1978, OF 78-181).

Geologic setting

Geologic description

West (1953) collected slope wash or detrital material from a small drainage at this locality. A heavy mineral concentrate obtained from the sample material (concentration ratio approximately 1,200:1) contained 0.049 percent equivalent uranium. The minerals identified in this concentrate included allanite, scheelite, monazite, fluorite, hematite, ilmentite, magnetite, epidote, biotite, and zircon. The bedrock here is an amphibolite facies, metasedimentary assemblage that forms a regional selvage between the Darby pluton to the east the the Kachauik pluton to the west (Miller and others, 1972; Till and others, 1986). The Darby pluton, is a large mid-Cretaceous granodiorite and granite body that has elevated background levels of uranium and thorium (Miller an Bunker, 1976; Johnson and others, 1979; Till and others, 1986). The Kachauik pluton is a composite syenite to granodiorite body, locally cut by nepheline syenite dikes, that is slightly older than the Darby pluton (99.9 +/- 3 Ma; Miller and others, 1972; Miller, 1972; Miller and Bunker, 1976). Parts of the Kachauik pluton contain U, Th, and REE mineralization near nepheline syenite dikes (Miller and others, 1976). Many of the minerals identified in the heavy mineral concentrate from this location are known accessory minerals in the Darby pluton.
Geologic map unit (-162.798575823382, 64.3842653759781)
Mineral deposit model Disseminated; the heavy mineral concentrate is from a sample of detrital materials.
Age of mineralization Mid-Cretaceous?; K/Ar ages for the Darby pluton are 88.3 +/- 1.5 and 92.8 +/- 2.6 Ma (Berry and others, 1976). A K/Ar age for the Kachauik pluton is 99.9 +/- 3 Ma (Miller and others, 1972; Miller and Bunker, 1976).

Production and reserves

Workings or exploration The reconnaissance sampling by West (1953) is the only work known in the area.
Indication of production None

References

MRDS Number D002606

References

Miller, T.P., 1972, Potassium-rich alkaline intrusive rocks of western Alaska: Geological Society of America Bulletin, v. 83, p. 2111-2128.
Reporters Travis L. Hudson (Applied Geology)
Last report date 8/19/1999