McGonogill; McGonagall Prospects, Kantishna Mining District, Denali Borough, Alaska, USAi

Regional Level Types
McGonogill; McGonagall Prospects	Group of Prospects
Kantishna Mining District	Mining District
Denali Borough	Borough
Alaska	State
USA	Country

The upper and lower McGonogill prospects are in Denali National Park and Preserve.
Location: This site represents two prospects. The upper McGonogill prospect (Cobb, 1980 [OFR 80-363]) is at an elevation of about 3400 feet at the head of the north fork of upper Glacier Creek, a fork locally called McGonogill Gulch. The prospect is about on the north border of the SW1/4 SW1/4 section 35, T. 15 S., R. 17 W., Fairbanks Meridian. The lower McGonogill (sometimes spelled McGonagall) prospect is about a half-mile to the west, at an elevation of about 2700 feet (Davis, 1923). It is in the SE1/4 section 34, T. 15 S., R. 17 W. The location is for the upper prospect and is accurate within 300 feet. The upper McGonogill prospect corresponds to number 13 of Cobb (1972 [MF 366]), 44 of Bundtzen, Smith, and Tosdal (1976), 51 of Bundtzen (1981), 64 of Thornsberry, McKee, and Salisbury (1984), and 218 of Hawley and Associates (1978). The lower prospect has not been cited in published reports since about 1970.
Geology: The country rocks in the area of the McGonogill prospects are schists correlated with the upper Precambrian Birch Creek Schist (Bundtzen, 1981). Wells (1933, p. 372) reported that an adit at the upper prospect was driven in graphitic schist. Thornsberry, McKee, and Salisbury (1984, v. 2, occurrence 64) reported that the country rock is mainly micaceous quartzite that strikes NNW and dips SW at a low angle. The upper McGonogill deposit is a mineralized shear zone as much as 8 feet thick. It contains polymetallic quartz-sulfide veins, strikes about N 58 E, and dips 34 SW (Wells, 1933, p. 372). The quartz contains disseminated and veinlet pyrite and arsenopyrite, and smaller amounts of galena, stibnite, chalcopyrite, boulangerite, and sphalerite. The sulfides locally are oxidized to limonite, scorodite, and stibiconite (Bundtzen, 1981; Thornsberry, McKee, and Salisbury, 1984, v. 2). The deposit was explored by a 40-foot adit. Davis (1923) reported that the vein exposed at the face of the adit assayed about 0.6 ounce of gold per ton and 63 ounces of silver per ton. Typical ore is much lower in grade. Bundtzen (1981) reported that quartz vein material containing abundant arsenopyrite and rarer boulangerite and galena assayed as much as 2. 2 percent lead and 8.51 percent arsenic, but only about 0.1 ounce of gold per ton and 1 ounce of silver per ton. Other veins in the area include one that crops out northeast of the workings. It assayed 3.5 percent lead, 1.5 percent zinc, 0.13 ounce of gold per ton, 3 ounces of silver per ton, 2800 ppm antimony, and 89 ppm mercury (Hawley and Associates, 1978, sample 218). At the lower McGonogill prospect, a quartz vein containing free gold is offset by a shear zone impregnated with tetrahedrite, stibnite, and chalcopyrite (Davis, 1923, p. 131-132). Samples of the mineralized shear zone assayed as much as 52 ounces of silver per ton.
Workings: The McGonogill deposits were discovered and prospected before 1916 (Capps, 1919, p. 100). By about 1930, the upper deposit was explored by a 40-foot tunnel (Davis, 1923; Wells, 1933). Apparently not much work was done after that.
Age: The deposits are assumed to be Eocene (see record MM091). At the lower McGonogill prospect, a polymetallic, mineralized shear zone postdates a low-sulfide gold-quartz vein.
Alteration: Silcification and sulfidization of shear zones. Oxidation of iron, arsenic, and antimony minerals.
Production: About 1 ton of gold-bearing quartz was shipped for testing purposes from the lower McGonogill prospect.

Commodities (Major) - Ag, Au; (Minor) - Cu, Hg, Pb, Sb, Zn
Development Status: Yes; small
Deposit Model: Polymetallic veins and low-sulfide Au-quartz veins (Cox and Singer, 1986; model

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Link to USGS - Alaska:	MM073

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References