Emerick; Rainbow Ridge; Miller Creek Prospect, Delta River Mining District, Southeast Fairbanks Census Area, Alaska, USAi

Regional Level Types
Emerick; Rainbow Ridge; Miller Creek Prospect	Prospect
Delta River Mining District	Mining District
Southeast Fairbanks Census Area	Census Area
Alaska	State
USA	Country

Platinum group element minerals identified by the U.S. Bureau of Mines using a scanning-electron microprobe include merenskyite, palarstanide, and irarsite.
Location: This prospect is at an elevation of 2,900 feet at the north end of Rainbow Ridge. It is about a mile southeast of Millers Roadhouse on the Richardson Highway and in the SE1/4NE1/4 section 18, T. 18 S., R. 11 E., Fairbanks Meridian. Access to the property is by a dirt road (not shown on the 1984 topographic map) from the east side of the highway (at mile 213.5) approximately a mile south of the roadhouse. The prospect is described by Rose (1965, figure 4) and corresponds to locality 13 of Cobb (1979 [OFR 79-238]) and locality S99 in table 2 of Nokleberg and others (1991).
Geology: This prospect consists of a sheared and mineralized gabbronorite dike and serpentinized peridotite (Barker, 1988). The rocks are adjacent to the Broxson Gulch Fault near its intersection with the Denali Fault (Barker, 1988). The ore minerals occur as disseminations and lenses of pyrrhotite, pentlandite, chalcopyrite, bornite, garnierite, and pyrite in serpentinized gabbronorite and peridotite. The copper minerals are locally oxidized to malachite. Sanders (1962 [PE 68-08]) described nine mineralized lenses as much as 20 feet long and 10 feet wide. They generally strike approximately parallel to the northwest trend of the peridotite (Hanson, 1963; Rose, 1965). The rocks adjacent to the lenses are strongly sheared and brecciated and are part of the Upper Triassic ultramafic-mafic complex that intrudes the Slana Spur Formation of Pennsylvanian age (Nokleberg and others, 1991). Mineralization is Late Triassic, synchronous with emplacement of a 120-mile-long belt of mafic-ultramafic and associated rocks in the east-central Alaska Range. Samples from the northernmost prospect pit averaged 0.91 percent copper and 3.4 percent nickel; those from the southernmost pit averaged 1.0 percent copper and 2.6 percent nickel. (Saunders, 1961 [PE 68-07). Samples of three other showings between the two pits averaged 1.1, 2.6, 0.6 percent copper and 7.6, 8.1, and 2.6 percent nickel respectively (Saunders, 1961 [PE 68-07]). U.S. Bureau of Mines samples from the Emerick property averaged about 1.0 percent copper and nickel each and 0.02 percent cobalt, 193 parts per billion (ppb) gold, 977 ppb palladium, 989 ppb platinum, and minor amounts osmiridium, osmium, and rhodium (Barker, 1988).
Workings: The prospect was discovered in the early 1950's by Rollie Emerick of Delta Junction, Alaska (Saunders, 1962 [PE 68-08]). Newmont Mining Company conducted dozer trenching, mapping, and sampling at the prospect in 1962. Inco examined the property in the early 1970's and completed a magnetic survey. COMINCO staked the property in 1989 and also completed a magnetic survey. Northeast Mining acquired the claims in 1994 and optioned the claims to Falconbridge in 1997. Falconbridge completed an airborne magnetic and electromagnetic survey and a large-loop ground electromagnetic survey and drilled two core holes. The property continues (in 2002) to be actively explored by Northeast Exploration. Samples from the northernmost prospect pit averaged 0.91 percent copper and 3.4 nickel; those from the southernmost pit averaged 1.0 percent copper and 2.6 percent nickel (Saunders, 1961 [PE 68-07]). Samples of three other showings between the two pits averaged 1.1, 2.6, and 0.6 percent copper and 7.6, 8.1, and 2.6 percent nickel respectively (Saunders, 1961 [PE 68-07]). U.S. Bureau of Mines samples from the Emerick property averaged about 1.0 percent copper and nickel each and 0.02 percent cobalt, 193 parts per billion (ppb) gold, 977 ppb palladium, 989 ppb platinum, and minor amounts of iridium, osmium, and rhodium (Barker, 1988).
Age: Late Triassic or younger.
Alteration: The peridotite and gabbronorite are sheared and serpentinized. Copper minerals are oxidized.

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

Other Databases

Link to USGS - Alaska:	MH209

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References