Clear Creek Occurrence, Koyuk Mining District, Nome Census Area, Alaska, USAi

Regional Level Types
Clear Creek Occurrence	Occurrence
Koyuk Mining District	Mining District
Nome Census Area	Census Area
Alaska	State
USA	Country

Location: This occurrence is on Clear Creek, a main west tributary to the Tubutuluk River, is at about 275 feet elevation. It is approximately sample locality 3016 of West (1953, Plate 1). This is locality 133 of Cobb (1972, MF 445; 1978, OF 78-181).
Geology: Heavy-mineral concentrates from stream sediments in the Clear Creek drainage commonly contain 0.01 to 0.02% equivalent uranium (West, 1953). The source of this uranium is mostly an unidentified titanium niobate mineral. The widespread elevated Nb values in stream sediments (Miller and Grybeck, 1973) and in heavy -mineral concentrates (West, 1953) of the Clear Creek-Vulcan Creek area may indicate specific mineralized zones or disseminations in late, felsic phases of the Darby pluton (Miller and Grybeck, 1973). Other minerals common in the heavy mineral concentrates are magnetite, hematite, ilmenite, topaz, allanite, and sphene. Clear Creek and its north tributaries have headwaters in the Darby pluton. Many of the heavy minerals in the concentrates from stream sediments in the area are known accessory minerals in the Darby pluton. The widespread elevated Nb values in stream sediments (Miller and Grybeck, 1973) and in heavy -mineral concentrates (West, 1953) of the Clear Creek-Vulcan Creek area may indicate specific mineralized zones or disseminations in late, felsic phases of the Darby pluton (Miller and Grybeck, 1973). The Darby pluton is a mid-Cretaceous granodiorite and granite that has elevated background levels of uranium and thorium (Miller and others, 1972; Miller and Bunker, 1976; Johnson and others, 1979). This pluton is considered the bedrock source of uranium that was mobilized and deposited in the Death Valley sandstone uranium deposit during the Eocene (Dickinson and others, 1987). K/Ar ages for the Darby pluton are 88.3 +/- 1.5 and 92.8 +/- 2.6 Ma (Berry and others, 1976).
Workings: There are no known workings; exploration in the region may have included reconnaissance stream sediment sampling and radiometric surveys.
Age: The heavy mineral concentrates are from Holocene surficial materials but these have been primarily derived from the nearby bedrock of the Darby pltuton. The Darby pluton is mid-Cretaceous; K/Ar ages for the Darby pluton are 88.3 +/- 1.5 and 92.8 +/- 2.6 Ma (Berry and others, 1976).

Commodities (Major) - REE, U
Development Status: None
Deposit Model: Disseminated uranium and rare-earth-bearing minerals may be accessory phases in

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Link to USGS - Alaska:	SO037

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References