Sheep Hill; Dust Mountain Prospect (west), Nelchina Mining District, Valdez-Cordova Census Area, Alaska, USAi

Regional Level Types
Sheep Hill; Dust Mountain Prospect (west)	Prospect
Nelchina Mining District	Mining District
Valdez-Cordova Census Area	Census Area
Alaska	State
USA	Country

Location: This prospect is near the summit of hill 5,140, on the divide between Bernard and Dust Creeks. It is in the NE1/4 section 26, T. 3 S., R. 2 E., of the Copper River Meridian. This prospect is approximately located, perhaps to within one-half mile. It is locality 43B of Winkler and others (1981 [OFR 80-892-B]).
Geology: Dunite, pryoxenite, and peridotite of the Tonsina ultramafic complex (Winkler and others, 1981 [OFR 80-892-A]; Burns, 1985; Foley and others, 1988) contain disseminated chromite, some podiform chromite, and local anomalous concentrations of nickel and platinum-group metals. At Sheep Hill, two low-grade, high-iron deposits with 5 percent chromite contain some PGE values (Foley and Barker, 1985; Foley and others, 1986; Dahlin and others, 1985; Foley and others, 1988, 1989). Samples from a 210- by 300-foot area contain as much as 927 ppb PGEs, including 515 ppb platinum (Pt) and 412 ppb palladium (Pd); Pt/Pt+Pd ratios range from 0.57 to 0.75. The PGEs are commonly associated with chromium spinel (Foley and others, 1988). The Tonsina ultramafic complex may be a deep part of large gabbroic plutons in the root zones of the Jurassic Talkeetna arc (Winkler and others, 1981 [OFR 80-892-A]; Burns, 1985). Because the Tonsina ultramafic complex contains granulites and tectonized harzburgite and dunite, it may have some mantle components and may in part be older than Jurassic mafic and ultramafic intrusives of the region (Burns, 1985).
Workings: Considerable reconnaissance surface oberservations and sampling have been carried out.
Age: The Tonsina ultramafic complex may be deep parts of large gabbroic plutons in the root zones of the Jurassic Talkeetna arc (Winkler and others, 1981 [OFR 80-892-A]; Burns, 1985). Because the Tonsina ultramafic complex contains granulites and tectonized harzburgite and dunite, it may have some mantle components and may in part be older than Jurassic mafic and ultramafic intrusives of the region (Burns, 1985).
Alteration: Minor serpentinization is probably present.

Commodities (Major) - Cr; (Minor) - Ni, PGE
Development Status: None
Deposit Model: Podifrom chromite (Cox and Singer, 1986; model 8a)

Other Databases

Link to USGS - Alaska:	VA015

Other Regions, Features and Areas containing this locality

References