Sukakpak Mountain Prospect, Koyukuk Mining District, Yukon-Koyukuk Census Area, Alaska, USAi

Regional Level Types
Sukakpak Mountain Prospect	Prospect
Koyukuk Mining District	Mining District
Yukon-Koyukuk Census Area	Census Area
Alaska	State
USA	Country

This prospect is in the Alaska pipeline inner corridor and is not open to mineral entry. It probably is the source of placer Au in Discovery Creek (CH077). Analytical results from assay of selected high-grade grab samples: 5 to 38 ppm Cu, less than 1 to 30 ppm Pb, 2 to 109 ppm Zn, as much as 27.2 ppm Au, as much as 4.5 ppm Ag, as much as 17,000 ppm Mo, 0.35 to 62 percent Sb, and up to or more than 5,000 ppm Hg, (Dillon, 1982, table 2, p. 17).
Location: The Sukakpak Mountain prospect is at an elevation of about 3,600 feet on the south flank of Sukakpak Mountain about 1/2 mile south of the summit (SE1/4 sec. 15, T. 32 N., R. 10 W., of the Fairbanks Meridian). The location is accurate within a 1/4-mile radius.
Geology: The Sukakpak Mountain prospect consists of 2 or 3(?) quartz-stibnite-gold veins exposed intermittently for 1 kilometer in and near a high-angle fault at the contact between Devonian and Silurian(?) Skajit Limestone and underlying Ordovician to Cambrian(?) graphitic quartz-, chlorite-, calcareous schists intruded by metabasite dikes (Dillon, 1982). The veins occur in the Skajit Limestone along thin schist layers or along the contact between marble and the underlying schist unit. The veins consist of early sulfide-poor (traces of chalcopyrite and tetrahedrite) and later stibnite- and gold-bearing quartz. The stibnite occurs as euhedral crystals in amounts ranging from less than 10 percent to more than 50 percent of the vein. Stibnite crystals as long as 8 inches are present. Gold occurs as small cubes and as wire and flakes in fractures within the veins along with stibnite, quartz, and graphite. The veins exhibit characteristics of open-space filling that include crystalline stibnite and cockscomb quartz crystals. Eleven channel samples of the veins (Huber, 1988) showed values of 0.1 to 43 ppm Au, less than 1 to 16.5 ppm Ag, and 0.23 percent to 34 percent Sb. Thirteen additional channel samples (Dillon and Reifenstuhl, 1990) showed an average grade of 0.44 ounce of gold per ton and 17.4 percent Sb. Nokleberg (1987) reported grab samples (presumably of vein material) with as much as 560 grams of gold per ton, 4.5 grams of silver per ton, 54 percent Sb, and 1.7 percent Mo; 0.5 percent Hg was also reported. Some reports (Dillon, 1982; Nokleberg, 1987) have suggested the presence of cinnabar and possibly molybdenite, but Huber's analyses showed little evidence of elements other than Au and Sb. Huber also noted the presence of kermesite (Sb2S2O), a red mineral that resembles cinnabar, as a weathering product of the stibnite. Huber described two veins and referred to them as the lower and upper veins. The lower vein, exposed by trenching on the schist-marble contact, consists of an 8-inch vein and eight small veinlets that trend N70W and dip 45 degrees northeast. They are exposed along strike for a distance of approximately 20 feet and terminate at both ends in black clay- and calcite-rich fault gouge. The veinlets, 1/2 to 4 inches in width and 1 to 3 feet in length, are in thin schist layers in the marble. The footwall of the lower vein is pyritic, graphite-quartz schist, and the hangingwall is black graphitic marble. The upper vein is entirely within the Skajit Limestone. It strikes N56E and dips 70 degrees to 90 degrees southeast. It is 1 to 6 feet in width and is exposed for nearly 400 feet along strike and for 150 vertical feet.
Workings: Surface sampling with some trenching. The occurrence was recognized in the early 1980s, although apparently there are old workings on vein outcrops and evidence of drift mining on Discovery Creek (CH077).
Age: Middle Cretaceous(?) based on arguments by Dillon (1982) that the age of emplacement of the gold-bearing quartz veins of the Koyukuk and Chandalar districts was between the Neocomian metamorphism of the Devonian host rocks and their erosional unroofing and cooling in Albian time.
Alteration: There is little gossan or other weathering associated with the veins and almost no wallrock alteration. The stibnite weathers to yellow stibconite (Sb3O6(OH)) and red kermesite (Sb2S2O).

Commodities (Major) - Ag, Au, Sb; (Minor) - Hg(?), Mo(?)
Development Status: None
Deposit Model: Sb-Au vein deposit (Nokleberg and others, 1987)

Other Databases

Link to USGS - Alaska:	CH076

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References