Unnamed Occurrences (ARDF - MH163; southwest of upper Ann Creek); East Rainy skarn, Delta River Mining District, Southeast Fairbanks Census Area, Alaska, USAi

Regional Level Types
Unnamed Occurrences (ARDF - MH163; southwest of upper Ann Creek); East Rainy skarn	Skarn
Delta River Mining District	Mining District
Southeast Fairbanks Census Area	Census Area
Alaska	State
USA	Country

Location: These occurrences are at an elevation of about 4,200 feet on a southwest tributary to the north fork of Ann Creek. They are in the SE1/4NE1/4 section 29, T. 18 S., R. 10 E., Fairbanks Meridian. The site is the same as Foley's (1992) upper Ann Creek occurrence.
Geology: At the east end of the Rainy ultramafic-mafic complex intrusion of Late Triassic age, carbonate beds and serpentinized dunite are intruded by a Cretaceous (?) diorite (quartz-bearing gabbro?) (Foley, 1992). Garnet-pyroxene skarn, marble, basalt, diorite, gabbro, and serpentinite contain disseminated and nearly massive pods of pyrite, pyrrhotite, chalcopyrite, and sphalerite. In this area the ultramafic body thins rapidly to less than 1,000 feet thick. Airborne magnetic data indicate that the Rainy intrusion may connect with the Ann Creek ultramafic body 3 miles to the east (MH166) (W.T. Ellis, oral communication, 2001). This skarn mineralization was discovered by the U.S. Bureau of Mines (Foley and others, 1989). Their samples contained as much as 1.3 percent nickel, 2.65 percent copper, 0.07 percent cobalt, 450 parts per billion (ppb) palladium, and 130 ppb platinum. American Copper and Nickel Company sampled skarn mineralization that contained as much as 0.17 percent nickel, 0.9 percent copper, 0.04 percent cobalt, 4.6 percent zinc, 126 ppb palladium, and 55 ppb platinum. The Rainy ultramafic-mafic complex is a steeply north dipping tablular intrusion of dunite, peridotite, and gabbro that varies from less than 100 feet thick to more than 6,000 feet thick and extends for more than 12 miles in length (W.T. Ellis, oral communication, 2001). Discontinuous marginal gabbro extends along most of the southern (lower) contact and is less continuous along the northern (upper) contact. The complex intrudes the Slana Spur Formation of Pennsylvanian age (Nokleberg and others, 1991). Magmatic mineralization is synchronous with emplacement of the Rainy complex, which is part of a 120-mile-long belt of mafic-ultramafic and associated rocks in the east-central Alaska Range.
Workings: The skarn mineralization at this site was discovered by the U.S. Bureau of Mines (Foley and others, 1989). Their samples contained as much as 1.3 percent nickel, 2.65 percent copper, 0.07 percent cobalt, 450 parts per billion (ppb) palladium, and 130 ppb platinum. American Copper and Nickel Company sampled skarn mineralization that contained as much as 0.17 percent nickel, 0.9 percent copper, 0.04 percent cobalt, 4.6 percent zinc, 126 ppb palladium, and 55 ppb platinum. The occurrences are on active claims of MAN Resources.
Age: Late Triassic or Cretaceous (?).
Alteration: Garnet-pyroxene skarn has replaced marble beds, and the dunite is strongly serpentinized adjacent to the diorite intrusion.

Commodities (Major) - Cu, Ni, Zn; (Minor) - Co, Pd, Pt
Development Status: None
Deposit Model: Cu skarn (Cox and Singer, 1986; model 18b).

Other Databases

Link to USGS - Alaska:	MH163

Other Regions, Features and Areas containing this locality

References