Johnson

Prospect, Active

Alternative names

Johnson and Martin

Commodities and mineralogy

Main commodities Sb
Other commodities W
Ore minerals arsenopyrite; pyrite; scheelite; stibnite
Gangue minerals quartz

Geographic location

Quadrangle map, 1:250,000-scale LG
Quadrangle map, 1:63,360-scale A-1
Latitude 65.0637
Longitude -147.4577
Nearby scientific data Find additional scientific data near this location
Location and accuracy The Johnson prospect is near the mouth of Willow Creek, a headwater tributary of Cleary Creek. It is in the NW1/4NE1/4 sec. 25, T. 3 N., R. 1 E., of the Fairbanks Meridian. The location is accurate to within 1,000 feet.

Geologic setting

Geologic description

Note: As of 2008, this site and several others in the vicinity are being explored as a single entity by Freegold Ventures Inc. (Freeman, 2008) Considerable new mineralization has been discovered that indicates this prospect is part of a larger mineralized system that is described as a separate ARDF site (LG207).
In 1942, a placer cut on Willow Creek exposed high-grade stibnite in several parts of a shear zone (Joesting, 1943). The stibnite is in a vertical vein with occasional quartz and other sulfides; it is 6 to 8 inches wide and was traced N40E for 75 feet (Killeen and Mertie, 1951). Nearby in 1912, a shaft was sunk 16 feet on a narrow quartz stringer carrying stibnite (Killeen and Mertie, 1951). Massive stibnite and coarse grained scheelite were identified on the dumps at the Johnson and Martin prospect (Byers, 1957). The prospect was examined by Metz and Robinson (1980) who noted that massive stibnite and scheelite were in quartz muscovite schist that strikes N60E and dips 25NW. Ore exposed in a 28-inch-thick horizon in a small pit contained abundant coarse- to fine-grained stibnite, discrete bands of coarse scheelite grains to 0.8 inch across, and minor pyrite and arsenopyrite. By volume, stibnite constitutes 95 percent of the lens, scheelite 4 percent, and arsenopyrite and pyrite about 1 each.
In 1986 the prospect was examined by Fairbanks Exploration Inc. (Fairbanks Exploration Inc., unpublished report, 1986). They reported disseminated to massive coarse-bladed stibnite with scheelite crystals disseminated in the stibnite. Gold values ranged from 420 parts per billion (ppb) to 2,450 ppb; silver values ranged from a trace to 2.21 ounces of silver per ton, antimony values were greater than 10,000 parts per million (ppm), and arsenic values ranged from 600 to 800 parts per million. Extensive trenching was conducted by the Yukon Tanana Mining Company in the vicinity of the Johnson and Martin prospect in 1988 but the results of this work are not known (Freeman, 1992).
Geologic map unit (-147.460147667721, 65.0632765363783)
Mineral deposit model Stibnite vein (Cox and Singer, 1986; model 27d).
Mineral deposit model number 27d
Age of mineralization About 90 Ma based on analogy with similar gold deposits nearby.
Alteration of deposit Not stated.

Production and reserves

Workings or exploration In 1912, a shaft was sunk 16 feet on a narrow quartz stringer carrying stibnite (Killeen and Mertie, 1951). Extensive trenching was conducted by the Yukon Tanana Mining Company in the vicinity of the Johnson and Martin prospect in 1988 (Freeman, 1992).
Indication of production Undetermined

References

MRDS Number A015429; D002656

References

Freeman, C.J., 1992, 1991 Golden Summit project final report, volume 2: Historical summary of lode mines and prospects in the Golden Summit project area, Alaska: Avalon Development Corp., 159 p. (Report held by Freegold Recovery Inc. USA, Vancouver, British Columbia.)
Freeman, C.J., 2008, Executive summary report for the Golden Summit project, Fairbanks Mining District, Alaska: Unpublished Technical Report for Freegold Ventures Ltd., 112 p. (posted on www.sedar.com, March 31, 2008).
Reporters C.J. Freeman, J.R. Guidetti Schaefer (Avalon Development Corporation); D.J. Grybeck (Port Ludlow, WA)
Last report date 6/5/2008