Unnamed Occurrence (ARDF - SO039; tributary to Clear Creek), Koyuk Mining District, Nome Census Area, Alaska, USAi

Regional Level Types
Unnamed Occurrence (ARDF - SO039; tributary to Clear Creek)	- not defined -
Koyuk Mining District	Mining District
Nome Census Area	Census Area
Alaska	State
USA	Country

Location: This occurrence is on the first north tributary to Clear Creek upstream from the confluence of Clear Creek and the Tubutuluk River. It is about 0.2 miles upstream from the confluence of the tributary and Clear Creek and at an elevation of about 125 feet. This is sample location 2974 of West (1953, Plate 1) and locality 131 of Cobb (1972, MF 445; 1978, OF 78-181).
Geology: A heavy-mineral concentrate (concentration ratio of 600:1) from stream gravels at this locality contained 0.023% equivalent uranium (West, 1953). Minerals identified in this concentrate include pyrite, ilmenite, magnetite, anatase, hornblende, topaz, allanite, biotie, and sphene. This drainage crosses the eastern contact of the Darby pluton with metasedimentary rocks (Till and others, 1986). 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 to the north, 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 some of these have been derived from the Darby pluton. 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 are probably accessory pha

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Link to USGS - Alaska:	SO039

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References