UM Landslide

Prospect, Active

Alternative names

Dunite Diatreme

Commodities and mineralogy

Main commodities Au; Cu; Ni; Pd; Pt
Other commodities Hg
Ore minerals cinnabar; gold; magnetite; pyrite

Geographic location

Quadrangle map, 1:250,000-scale MH
Quadrangle map, 1:63,360-scale B-5
Latitude 63.3054
Longitude -146.2795
Nearby scientific data Find additional scientific data near this location
Location and accuracy This mile-long and half-mile-wide prospect is on the west side of an southeast-flowing tributary of Eureka Creek that is informally called Landslide Creek. It is about 5.1 mile northwest of the junction of Eureka Creek and Broxson Gulch, about 0.7 mile southeast of the center of section 31, T. 17 S., R. 8 E, and about 0.3 mile southeast of peak southeast of peak 5460. The site includes not only conglomerate outcrops on the 5460 ridge but also a large landslide that flows down to the east from peak 5460.

Geologic setting

Geologic description

The geology of this prospect has been variously interpreted. Most early workers have interpreted it as a sedimentary conglomerate composed mostly of clasts of peridotite and dunite and lesser gabbro in a serpentine matrix with hematite. (Moffit, 1912; Rose, 1966, Stout, 1976; Foley, 1992; Nokleberg and others, 1992 ([MF]; Nokleberg and others, 1992 [Open-File]) . The conglomerate caps the ridge of hill 5460 and is the source of landslide material below it to the east. The landslide covers an area about a mile long and one-half mile wide. Conglomeratic material in the slide consists of angular to subrounded boulders, cobbles, and pebbles of ultramafic rocks, mainly dunite, in a sand-size serpentine matrix rich in magnetite. The magnetite particles are as much as an inch in diameter. However, L.D. Hulbert (oral communication, 2000) interpreted the conglomerate as a diatreme that contains as much as 700 parts per billion (ppb) platinum and palladium.
Grab samples of the conglomerate and heavy-mineral concentrates produced by panning pulverized conglomerate and regolith overlying the conglomerate contained traces of gold and platinum-group minerals (Foley and others, 1989; Foley and Summers, 1990). The panned samples contained up to 102 ppb gold, 150 ppb palladium, and 240 ppb platinum. Panned concentrates from the creek to the east of peak 5640, informally named Landslide Creek, contained abundant pyrite and cinnabar and gold particles as heavy as 4 milligrams.
Bittenbender and others (2007) visited and resampled the prospect and concluded that it is in a conglomerate. Samples contained up to 9 ppb gold, 132 parts per million (ppm) copper, 1,810 ppm nickel, 70 ppb platinum, and 52 ppb palladium.
Geologic map unit (-146.281764332125, 63.3049762186494)
Mineral deposit model Placer Au-PGE (Cox and Singer, 1986; model 39a); conglomerate with precious metal values.
Mineral deposit model number 39a
Age of mineralization The landslide and associated placer deposits are Holocene. The source of the mafic and ultramafic rocks in the conglomerate are probably the Late Triassic, Eureka ultramafic-mafic complex that is widely exposed in the vicinity.
Alteration of deposit The ultramafic clasts in the conglomerate are remarkably fresh looking and essentially unaltered (L. Hulbert, oral communication, 2000).

Production and reserves

Workings or exploration Examined and sampled by a succession of companies and government agencies from before 1912 into the 2000s.
Indication of production None
Reserve estimates None.
Production notes None.



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.
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