Emerick

Prospect, Active?

Alternative names

Rainbow
Talnakh

Commodities and mineralogy

Main commodities Cu; Ni; Pd; Pt
Other commodities Au; Co; Ir; Os; Rh
Ore minerals bornite; chalcopyrite; garnierite; malachite; pentlandite; pyrite; pyrrhotite

Geographic location

Quadrangle map, 1:250,000-scale MH
Quadrangle map, 1:63,360-scale B-4
Latitude 63.3564
Longitude -145.701
Nearby scientific data Find additional scientific data near this location
Location and accuracy The Emerick prospect is at an elevation of about 2,900 feet south of the terminus of the Canwell Glacier and about 1.1 mile southeast of Millers Roadhouse on the Richardson Highway. It is about 0.6 mile east-northeast of the center of section 18, T. 18 S., R. 11 E. Figure 23 in Bittenbender and others (2007) is a geologic map of the prospect.

Geologic setting

Geologic description

The Emerick prospect is in a fault-bounded sliver of Triassic serpentinized dunite, peridotite, and gabbro (Nokleberg and others, 1992 [MF]; 1992 [Open-File]]; Bittenbender and others, 2007). The prospect is in sheared and mineralized body of gabbronorite that was initially thought to be a dike (Barker, 1988; Foley and others, 1989; Foley, 1992), but is more likely a fault block within the ultramafic rocks (Wells, 1998; Bittenbender and others, 2007). The prospect is adjacent to the Broxson Gulch fault near its intersection with the Denali fault.
The prospect was discovered in 1955 by Rollie Emerick (Saunders, 1962; Bittenbender and others, 2007). Through the late 1950s, the property was examined by several individuals, the Alaska Alaska Department of Mines, and the U.S. Bureau of Mines (Saunders, 1961, 1962). Newmont Mining Company optioned the claims and dug a 1,600-foot road cut along the deposit. In 1971, the U.S. Bureau of Mines reexamined the property (Barker and others, 1985). Cominco Alaska re-staked the property in 1980s as the Rainbow claims, dug several long trenches with a dozer in 1988, and mapped and sampled them. Falconbridge Exploration U.S., Inc. staked the Talnakh claims over the property in 1990. They mapped the geology, did ground and aerial geophysical surveys over the claims, and drilled one hole 350 meters deep. Northridge Exploration re-excavated the old trenches and dug more trenches from 2000 to 2002.
The mineralization consists of several massive sulfide lenses in the ultramafic rocks and gabbro 'dike', and disseminated sulfides. (Figure 23 in Bittenbender and others (2007) is a geologic map of the prospect.) The ore minerals are mainly pyrrhotite and pentlandite with minor chalcopyrite and pyrite; bornite and garnierite have been noted and the copper minerals are locally oxidized to malachite. Saunders (1962) described nine mineralized lenses up to 20 feet long and 10 feet wide. They generally parallel the northwest trend of the ultramafic and mafic rocks (Hanson, 1963; Rose, 1965). The rocks adjacent to the lenses are strongly sheared and brecciated.
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). Samples of three other showings between the two pits respectively averaged 1.1, 2.6, 0.6 percent copper and 7.6, 8.1, and 2.6 percent nickel. U.S. Bureau of Mines samples from the Emerick property averaged about 1.0 percent copper and nickel and 0.02 percent cobalt, 193 parts per billion (ppb) gold, 977 ppb palladium, 989 ppb platinum, and minor amounts of osmiridium, osmium, and rhodium (Barker, 1988). Samples collected by the U.S. Bureau of Mines contained merenskyite, palarstanide, and irarsite which were identified with a scanning-electron microprobe. Samples collected by Bittenbender and others (2007) from the peridotite contained up to 6.31 percent nickel, 2.5 percent copper, 1,175 parts per billion (ppb) platinum, and 2.280 ppb palladium. Samples from the gabbro contained up to 8,050 parts per million (ppm) copper, 1.38 percent nickel, 1,175 ppb platinum, and 1,330 ppb palladium. Samples consistently show high chromium values, some more than 2,000 ppm.
Geologic map unit (-145.703256408122, 63.3559882760192)
Mineral deposit model Nickel-copper-PGE mineralization in a differentiated mafic-ultramafic dike or fault silver.
Age of mineralization Probably genetically related to the emplacement of a Triassic mafic-ultramafic complex.
Alteration of deposit The peridotite and gabbronorite are sheared and serpentinized. Copper minerals are oxidized.

Production and reserves

Workings or exploration The prospect was discovered in 1955 by Rollie Emerick (Saunders, 1962; Bittenbender and others, 2007). Through the late 1950s, the property was examined by several individuals, the Alaska Alaska Department of Mines, and the U.S. Bureau of Mines (Saunders, 1961, 1962). Newmont Mining Company optioned the claims and dug a 1,600-foot road cut along the deposit. In 1971, the U.S. Bureau of Mines reexamined the property (Barker and others, 1985). Cominco Alaska re-staked the property in the 1980s as the Rainbow claims, dug several long trenches with a dozer in 1988, and mapped and sampled them (Hinderman, 1989). Falconbridge Exploration U.S., Inc. staked the Talnakh claims over the property in 1990. They mapped the geology, did ground and aerial geophysical surveys, and drilled one hole 350 meters deep. Northridge Exploration re-excavated the old trenches and dug more from 2000 to 2002.
Indication of production None
Reserve estimates None.
Production notes None.

References

MRDS Number A011793

References

Barker, J.C., 1988, Distribution of platinum-group elements in an ultramafic complex near Rainbow Mountain, east-central Alaska Range, IN Vassilou, A.H., Hausen, D.M., and Carson, D.J.T, eds, Process Mineralogy VII, Applications to mineral beneficiation: Proceedings of the Metal Society SME/AIME Joint [Annual] Meeting, Denver, Colo., p. 197-220.
Bittenbender, P.E., Bean, K.W., Kurtak, J.M., and Deininger, James Jr., 2007, Mineral assessment of the Delta River Mining District area, east-central, Alaska: U.S. Bureau of Land Management, Alaska Technical Report 57, 675 p.
Wells, K., 1998, Report on the 1997 work program for Falconbridge Exploration U.S., Inc. on the Forbes Nickel Project (PN 5-998)-Mt. Hayes quadrangle, Alaska: Unpublished report, Falconbridge Exploration U.S., Inc., 41 p.
Reporters W.T. Ellis (Alaska Earth Sciences), C.C. Hawley (Hawley Resource Group), and W.J. Nokleberg (USGS); D.J. Grybeck (Contractor, USGS)
Last report date 5/13/2012