Unnamed (in upper Miller Gulch)

Occurrences, Undetermined

Commodities and mineralogy

Main commodities Au; Ir; Os; Pt
Ore minerals gold; osmiridium; tetraferroplatinum

Geographic location

Quadrangle map, 1:250,000-scale MH
Quadrangle map, 1:63,360-scale A-2
Latitude 63.1765
Longitude -144.8226
Nearby scientific data Find additional scientific data near this location
Location and accuracy The dikes, sills, and plugs that are described in this record are scattered widely at the head of Miller Gulch. Their center is at an elevation of about 4,800 feet in Miller Gulch and about 0.5 mile south-southwest of the center of section 14, T. 20 S., R. 15 E.

Geologic setting

Geologic description

Bittenbender and others (2007) summarized the occurrences of lode platinum group elements (PGE) and gold in the so-called 'dikes' in upper Miller Gulch. They are in Upper Jurassic to Cretaceous, black slatey argillite (Matteson, 1973; Summers, 1990; Nokleberg and others, 1992 [MF]; 1992 [Open-File]). The 'dikes' include dikes, sills, and plugs of gabbro, dunite, peridotite, hornblendite, and diorite that were intruded in several episodes. Matteson (1973) dated a mafic-ultramafic body nearby at the head of Quartz Creek (MH379) by K/Ar methods at a minimum age of 120-123 Ma.
Foley and Summers (1990) identified tetraferroplatinum, osmiridium, and native gold in the mafic and ultramafic rocks and in the argillite nearby. They believe that the platinum and at least part of the gold in the Miller Creek placer (MH296) that drains drains this area came from the mafic and ultramafic rocks. However, analyses of a considerable number of samples collected both by Foley and Summers (1990) and by Bittenbender and others (2007) failed to show significant amounts of the PGE or gold in these rocks in spite of the physical identification of PGE minerals and native gold in them. One reason may be their erratic distribution, i.e., the 'nugget' effect. In the samples collected by Bittenbender and others (1970), the maximum values in any of them was 7 parts per billion (ppb) gold, 0.2 part per million (ppm) silver, 479 ppm copper, 0.685 ppm mercury, 24 ppb palladium, and 19 ppb platinum.
Geologic map unit (-144.824829075973, 63.1761044263148)
Mineral deposit model PGE and gold mineralization in mafic to ultramafic dikes, sills, and plugs.
Age of mineralization Associated with dikes, sills, and plugs that may be older than 120-123 Ma mafic-ultramafic rocks nearby but younger than the Upper Jurassic to Cretaceous argillite host rock.
Alteration of deposit Not noted.

Production and reserves

Workings or exploration Only sampling by state and federal agencies.
Indication of production None
Reserve estimates None.
Production notes None.

References

References

Alaska thesis, 66 p.
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.
Matteson, C., 1973, Geology of the Slate Creek area, Mt Hayes (A-2) quadrangle, Alaska: Fairbanks, unpublished University of
Reporters D.J. Grybeck (Contractor, USGS)
Last report date 5/13/2012