Grizzly Bear

Mine, Inactive

Alternative names

Yellow Jacket

Commodities and mineralogy

Main commodities Ag; As; Au; Sb
Other commodities Cu; Pb; Te; W
Ore minerals arsenopyrite; covellite; digenite; gold; jamesonite; pyrite; stibnite
Gangue minerals quartz

Geographic location

Quadrangle map, 1:250,000-scale BD
Quadrangle map, 1:63,360-scale B-1
Latitude 64.3512
Longitude -144.2093
Nearby scientific data Find additional scientific data near this location
Location and accuracy The Grizzly Bear mine is situated on a ridge of Black Mountain separating the headwaters of Antimony Creek, a tributary of Tibbs Creek (BD040), and Summit Creek, a tributary of Boulder Creek (BD004). The mine is about 0.3 mile east of the center of section 32, T. 6 S., R. 18 E., of the Fairbanks Meridian. The Yellow Jacket deposit is nearby (The Grizzly Bear Mine is misplaced on the USGS 1:63,360-scale topographic map.).

Geologic setting

Geologic description

The Grizzly Bear mine and Yellow Jacket deposit are situated the ridge of Black Mountain that is largely underlain by Cretaceous granodiorite (Weber and others, 1978). Augen gneiss, gneissic schist, and schist are the west of Black Mountain. There is intense shearing and faulting in the contact between the metamorphic and intrusive rocks. This shearing is observed in the underground workings and at the surface as pronounced saddle-like depressions across the spurs separating the westward-flowing tributaries of Tibbs Creek. This shear zone trends roughly N 15 E and dips 65 degrees NW. The lode deposits in the area are mostly gold-bearing quartz veins in the shear zone, although some are in the granodiorite. The veins contain gold and a variable assemblage of sulfides, including arsenopyrite, covellite, digenite, jamesonite, pyrite, and stibnite. Typically, gold content decreases as sulfides increase. Veins are commonly 2 to 3 feet in width, with some as wide as 8 feet (Thomas, 1970). When gold is present, it is usually extremely fine grained. However, other near veins such as in the Blue Lead Mine (BD003) contain relatively coarse gold, which is easily visible in hand specimen.
The Grizzly Bear Mine was developed on an 18-inch-wide quartz vein. Based on underground workings, the vein dips steeply to the south (Reed, 1937). Much of the ore is on the hanging wall (Thomas, 1970). Thomas (1970) shows the Yellow Jacket prospect as a vein exposed at the surface approximately one third of a mile southwest of the Grizzly Bear Mine. Glover (1950) reported a range in gold fineness of 766 to 780 for the Grizzly Bear Mine.
The Goodpaster region was first explored for placer gold in 1915. In the early 1930s, gold-bearing quartz veins were discovered in the upper Tibbs Creek area. By the winter of 1936, the first underground workings were being installed. A 450-foot tunnel was driven following a small vein, termed the Blue Lead Extension (BD003). After disappointing results, the work was stopped. In the summer of 1936, five men drove a 300-foot tunnel at the outcrop of the Blue Lead vein (Reed, 1937). During the winter of 1937, a 300-foot tunnel was driven at the Grizzly Bear Mine (BD018) and a 50-ton mill was constructed. In the summer of 1938, the mill was moved to the Blue Lead Mine and operated for a year and a half until the fall of 1939 (Joesting, 1938). There was limited exploration in the 1970s. The mill was still on site and the mine shaft was accessible in 1970, but blocked by ice (Thomas, 1970). It is reported that 350 tons of ore was produced from the Grizzly Bear mine and processed at the mill at the Blue Lead mine. Another 150 tons was produced from the Blue Lead mine (Reed, 1937). No ore was mined from the Yellow Jacket vein (Thomas, 1970).
From 1995 to 1999, The Stone Boy Joint Venture (Sumitomo Metal Mining and WGM) spent more than $1.3 million exploring in the area; they did extensive surface mapping and sampling, surface and airborne geophysics. They drilled 26 holes in the area that totaled 16,215 feet in 26 holes. The location of the holes is vague but one or more of these holes was at the Grizzly Bear Mine.
In 2002, Freegold Ventures optioned a large block of claims that covered the Grizzly Bear Mine and several others deposits nearby that are described separately: the Blue Lead (BD003), Michigan Lode (BD025), Gray Lead (BD017), Wolverine (BD057), Upper Trench/ Lower Trench (BD058) and O'Reely (BD059). Freegold has continued the exploration through early 2012 as the Rob project. (Flanders, 2010; Freegold Ventures Ltd., 2012). The work has included extensive geologic mapping, surface sampling, and geochemical and geophysical surveys.
Freeman (2004) and Flanders (2010) consider the deposit to be Au ± base metal, ± Ag ± W ± Bi intrusion-hosted mineralization with a possible
genetic relationship between the precious metal mineralization and the emplacement of the intrusion.
Geologic map unit (-144.211624818353, 64.3508350947743)
Mineral deposit model Silver-gold-quartz veins and stockwork, +/- arsenic, copper, lead, antimony, tellurium, and tungsten (Cox and Singer, 1986; model 22c).
Mineral deposit model number 22c
Age of mineralization Probably genetically related to a nearby Cretaceous granodiorite intrusive.

Production and reserves

Workings or exploration
The Goodpaster region was first explored for placer gold in 1915. In the early 1930s, gold-bearing quartz veins were discovered in the upper Tibbs Creek area. By the winter of 1936, the first underground workings were driven. A 450-foot tunnel was driven following a small vein called the Blue Lead Extension. After disappointing results, the work was stopped. In the summer of 1936, five men drove a 300-foot tunnel at the outcrop of the Blue Lead vein (Reed, 1937). During the winter of 1937, a 300-foot tunnel was driven at the Grizzly Bear Mine (BD018) and a 50-ton mill was constructed. In the summer of 1938, the mill was moved to the Blue Lead Mine and operated for a year and a half until the fall of 1939 (Joesting, 1938). The mill was still on site and the mine shaft openings were accessible in 1970, but blocked by ice (Thomas, 1970).
From 1995 to 1999, The Stone Boy Joint Venture (Sumitomo Metal Mining and WGM) spent more than $1.3 million exploring in the area; they did extensive surface mapping and sampling, surface and airborne geophysics, and 16,215 feet of diamond drilling. They drilled 26 holes; one or more of these hole may have been at the Grizzly Bear Mine but the details are obscure. In 2002, Freegold Ventures optioned a large block of claims that covered the Grizzly Bear and several other nearby deposits that are described separately: the Blue Lead (BD003), Michigan Lode (BD025), Gray Lead (BD017), Wolverine (BD057), Upper Trench/ Lower Trench (BD058) and O'Reely (BD059). They continued to explore them as a unit as the Rob project through early 2012 (Flanders, 2010; Freegold Ventures Ltd., 2012). The work has included extensive geologic mapping, surface sampling, and geochemical and geophysical surveys.
Indication of production Yes; small
Production notes The Grizzly Bear Mine has produced 350 tons of ore and processed them at the mill at the Blue Lead mill (Reed, 1937). No ore was mined from the Yellow Jacket vein (Thomas, 1970).

References