North Rainy Occurrence, Delta River Mining District, Southeast Fairbanks Census Area, Alaska, USAi

Regional Level Types
North Rainy Occurrence	Occurrence
Delta River Mining District	Mining District
Southeast Fairbanks Census Area	Census Area
Alaska	State
USA	Country

Location: The North Rainy prospect is located at an elevation of 4,200 feet on the east valley wall of upper North Fork Rainy Creek. It is in the SW1/4NE1/4 section 24, T. 18 S., R. 9 E., Fairbanks Meridian.
Geology: At the North Rainy occurrence a cluster of eight airborne electromagnetic anomalies marks a subcircular magnetic high (W.T. Ellis, oral communication, 2001). The rocks in this area are variably serpentinized dunite near a fine-grained gabbro intrusion. There is a well-developed breccia zone at the dunite-gabbro contact that is locally mineralized. The breccia consists of angular dunite clasts of various sizes (and at least one large inclusion of hornfelsed Tetelna sedimentary rocks) in a fine-grained gabbro matrix. Mineralization consists of 2 to 4 percent pyrrhotite, chalcopyrite, and pentlandite (?) disseminated in the gabbro (W.T. Ellis, oral communication, 2001). Float of sulfide-bearing dunite, gossan, and copper-stained serpentine occur in a few places along the breccia contact. Rock samples contain as much as 0.18 percent nickel, 0.63 percent copper, 0.02 percent cobalt, 76 parts per billion (ppb) palladium, and 80 ppb platinum. The Rainy ultramafic-mafic complex is a Late Triassic 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: Exploration on the North Rainy property has been by American Copper and Nickel Company (ACNC) working with Fort Knox Gold Resources, Inc. Exploration from 1995 through 1998 included rock sampling, airborne and ground geophysical surveys, and completion of one diamond drill hole (W.T. Ellis, oral communication, 2001). The general area was staked by ACNC in 1995, but the North Rainy occurrence was not discovered until 1998 when the exploration followed up a reconnaissance large-loop geophysical survey. There is a moderately strong UTEM geophysical conductor that coincides with the occurrence. Rock samples contain as much as 0.18 percent nickel, 0.63 percent copper, 0.02 percent cobalt, 76 parts per billion (ppb) palladium, and 80 ppb platinum. The occurrence is on active claims of Fort Knox Gold Resources.
Age: Late Triassic.
Alteration: Irregular serpentinization; oxidization of iron and copper minerals.

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

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Link to USGS - Alaska:	MH153

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