Unnamed (on Sukakpak Mountain)

Prospect, Inactive

Commodities and mineralogy

Main commodities Ag; Au; Sb
Other commodities Hg; Mo
Ore minerals cinnabar; gold; molybdenite; stibnite; tetrahedrite
Gangue minerals calcite; quartz

Geographic location

Quadrangle map, 1:250,000-scale CH
Quadrangle map, 1:63,360-scale C-6
Latitude 67.5957
Longitude -149.7334
Nearby scientific data Find additional scientific data near this location
Location and accuracy The main vein at this prospect extends for almost 600 feet; the center is at an elevation of about 3,500 feet, about 0.6 mile south-southeast of the summit of Sukakpak Mountain. It is about 0.6 mile east-southeast of the center of section 15, T. 32 N., R. 10 W. The location is accurate. Kurtak and others (2002, figure C-6) ) include a detailed map of the prospect.

Geologic setting

Geologic description

Mineralization is exposed in two places at this prospect: the main 'upper vein' (at the coordinates), and a 'lower vein' about a half mile to the southwest. The veins do not appear to be continuous but they have the same general trend (Kurtak and others, 2002). Lode claims were staked in 1977 but they were invalid because the prospect is in the Trans-Alaska Pipeline corridor which is closed to mineral entry. There is a small prospect pit on the upper vein and some trenching on the lower vein.
This prospect is near the contact of marble of the Devonian Skajit Limestone and Cambrian muscovite-albite-quartz schist (Huber 1988; Dillon and Reifenstuhl, 1990; Kurtak and others, 2002). The mineralization is mainly in the marble but the trend of the veins parallels and is very close to the contact.
The upper vein is exposed for 120 feet, varies from 1 to 6 feet wide, and averages about two feet thick (Huber 1988; Kurtak and others, 2002). It strikes N55E, dips steeply to vertical, and can be traced for 570 feet in float and discontinuous exposures. The upper vein is entirely in marble about 50 feet from the contact with the schist. There are two generations of quartz; an early, nearly barren generation with traces of tetrahedrite, and a later generation with stibnite and gold. The stibnite often makes up 50 percent of the vein. There is minor arsenopyrite and the stibnite weathers to stibiconite and kermesite. (The red kermesite has been misidentified as cinnabar.) The stibnite contains native gold which is difficult to detect. The gold occurs as small cubes and as wire and flakes in fractures in the veins, with stibnite, quartz, and graphite. There is no evidence of alteration adjacent to the vein. The vein is banded with evidence of repeated movement during and after mineralization. The vein show open-space filling with crystalline stibnite and cockscomb quartz crystals. Huber (1988) collected 11 samples along the vein; they averaged 15.52 parts per million (ppm) gold and 20.8 percent antimony. Kurtak and others (2002) collected 9 continuous chip samples and 3 float samples from the upper vein. The samples average 39.59 ppm gold and 22.74 percent antimony, but the values were erratic along strike. Dillon (1982) reported mercury and molybdenum in samples from the vein. However, in the samples collected by Kurtak and others (2002), the highest mercury value was 2.9 ppm and the highest molybdenum value was 8 ppm.
The lower quartz vein at an elevation of about 2,500 feet is mineralized for about 50 feet and quartz-vein material can be traced in float and rubble for about 350 feet (Huber 1988; Kurtak and others, 2002. The mineralization is similar to the upper vein. Stibnite occurs sporadically in quartz-carbonate gangue. The vein strikes N70E to N70W with a variable dip. The vein is in marble near the schist contact. Kurtak and others (2002) collected a spaced-chip sample; it contained 25.23 ppm gold and 21.22 percent antimony.
Dillon (1982) suggests that the mineralization is Albian (middle Cretaceous). Huber (1988) concluded that the mineralization is no older than the end of the Neocomian (Early Cretaceous), Brooks Range Orogeny.
Kurtak and others (2002) estimated an 'inferred resource' of 31,000 tons with 'weighted average grades' of 1.22 ounces of gold per ton and 18.44 percent antimony.
Geologic map unit (-149.736157112211, 67.5952880585346)
Mineral deposit model Gold-stibnite-quartz vein.
Age of mineralization Dillon (1982) suggests that the mineralization is Albian (Middle Cretaceous). Huber (1988) concludes that the mineralization is no older than the end of the Neocomian (Early Cretaceous) Brooks Range Orogeny.
Alteration of deposit There is little gossan or other weathering associated with the veins and almost no wallrock alteration. The stibnite weathers to yellow stibiconite (Sb3O6(OH)) and red kermesite (Sb2S2O).

Production and reserves

Workings or exploration A small prospect pit and some trenching by industry. Mapped and sampled by government agencies. The occurrence was first reported in print in the early 1980s, although there are older workings on outcrops of the veins and evidence of drift mining nearby on Discovery Creek (CH077). Lode claims were staked in 1977 but they were invalid because the prospect is in the Trans-Alaska Pipeline corridor, which is closed to mineral entry.
Indication of production None
Reserve estimates Kurtak and others (2002) estimated an 'inferred resource' of 31,000 tons with 'weighted average grades' of 1.22 ounces of gold per ton and 18.44 percent antimony.
Production notes None.

Additional comments

This prospect is in the Alaska pipeline inner corridor which is not open to mineral entry. It probably is the source of placer Au in Discovery Creek (CH077).
MAS No. 0020310071

References

MRDS Number A012160

References

Huber, J.A., 1988, The geology and mineralization of the Sukakpak Mountain area, Brooks Range, Alaska: Fairbanks, University of Alaska, M.Sc. thesis, 81 p.
Kurtak, J.M., Klieforth, R.F., Clark, J.M., and Maclean, E.A., 2002, Mineral investigations in the Koyukuk mining district, northern Alaska, 2 vols.: Bureau of Land Management, Alaska Technical Report 50, 845 p.
Reporters J.M. Britton (Anchorage, Alaska); D.J. Grybeck (Contractor, U.S. Geological Survey)
Last report date 4/18/2010