Bird Beak Prospect, Valdez Creek Mining District, Southeast Fairbanks Census Area, Alaska, USAi

Regional Level Types
Bird Beak Prospect	Prospect
Valdez Creek Mining District	Mining District
Southeast Fairbanks Census Area	Census Area
Alaska	State
USA	Country

Location: The Bird Beak occurrence is at an elevation of about 5,900 feet, about 1,600 feet southwest of peak 6120, and about three-quarters of a mile west of lower Eureka Glacier. It is in the SW1/4SW1/4 section 27, T. 18 S., R. 7 E., Fairbanks Meridian. The occurrence corresponds to locality A7 of Kurtak and others (1992).
Geology: The Bird Beak prospect is in Upper Triassic ultramafic and mafic rocks that are enclosed in a Tertiary to Cretaceous composite granitic to dioritic pluton (Nokleberg and others, 1991). Rose (1966 [ADMM GR 20, figure 3]) mapped dunite bodies within diorite, quartz diorite, and gabbro in this area. The Broxson Gulch thrust appears to form the hanging wall of the intrusive series, and it has been inferred that dunite bodies formed a well-lubricated layer in the footwall of the thrust (Kurtak and others, 1992, p. 94). The hanging wall of the thrust consists of schist. Olivine melagabbro and serpentinized dunite are the predominant ultramafic rock types that host sulfide mineralization (W.T. Ellis, unpublished data, 2001). The U.S. Bureau of Mines collected samples of dunite and gabbro at the locality (Kurtak and others, 1992, table A7). Sample 3038 of olivine gabbro containing disseminated pyrrhotite and chalcopyrite assayed 0.15 percent copper, 0.21 percent chromium, 0.36 percent nickel, 550 parts per billion (ppb) palladium, and 80 ppb platinum. Sample 2644 of limonite-stained serpentine contained 0.13 percent copper, 896 parts per million (ppm) nickel, 280 ppb palladium, and 570 ppb platinum. A pentlandite(?) -bearing pyroxenite sample assayed 0.2 percent nickel and 25 ppb platinum.
Workings: The prospect was sampled by the U.S. Bureau of Mines (Kurtak and others, 1992). A sulfide-bearing olivine gabbro sample contained 0.36 percent nickel and 550 parts per billion (ppb) palladium. The highest platinum concentration (570 ppb) was in sample 2644 of limonite-stained serpentinite. Foley (1992) reported similar concentrations in a red, iron-oxide-stained, sulfide-rich, olivine gabbro; microprobe examination of the gabbro showed minute particles of moncheite (PtTe) along grain boundaries between chalcopyrite and ferromagnesian silicate minerals. The occurrence is on active MAN Resources claims (W.T. Ellis, unpublished field notes, 2001).
Age: Late Triassic, synchronous with emplacement of the mafic-ultramafic rocks.
Alteration: All of the ultramafic rock units are moderately to strongly serpentinized.

Commodities (Major) - Ni, Pd, Pt; (Minor) - Cr, Cu
Development Status: None
Deposit Model: Ni-Cu-PGE in differentiated mafic-ultramafic sill.

Other Databases

Link to USGS - Alaska:	MH094

Other Regions, Features and Areas containing this locality

References