Unnamed Occurrence (ARDF - SO044; on Rock Creek), Koyuk Mining District, Nome Census Area, Alaska, USAi

Regional Level Types
Unnamed Occurrence (ARDF - SO044; on Rock Creek)	- not defined -
Koyuk Mining District	Mining District
Nome Census Area	Census Area
Alaska	State
USA	Country

Location: Rock Creek is a west tributary to the Tubutuluk River. This occurrence is at an elevation of about 900 feet along the main drainage; it is about 4.3 miles upstream from the north boundary of the Solomon D-1 quadrangle. It is sample location 3052 of West (1953, Plate 1) and locality 126 of Cobb (1972, MF 445; 1978, OF 78-181).
Geology: A heavy-mineral concentrate (concentration ratio 2,250:1) from stream gravels at this locality contained 0.036% equivalent uranium (West, 1953). Minerals identified in the concentrate included allanite, hematite, ilmenite, magnetite, anatase, garnet, topaz, kyanite, epidote, and sphene. An unidenitied uraniferous titanium niobate mineral is present in many heavy-mineral concentrates from the eastern part of the Darby pluton (West, 1953). The Rock Creek drainage is primarily within the Darby pluton but headwater areas cross the western contact of the pluton to areas of metasedimentary rocks (Till and others, 1986). 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 much of these materials 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:	SO044

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References