Grizzly Bear; Yellow Jacket Mine, Goodpaster Mining District, Southeast Fairbanks Census Area, Alaska, USAi

Regional Level Types
Grizzly Bear; Yellow Jacket Mine	Mine
Goodpaster Mining District	Mining District
Southeast Fairbanks Census Area	Census Area
Alaska	State
USA	Country

Location: 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 located in the SW1/4NE1/4 section 32, T. 6 S., R. 18 E., of the Fairbanks Meridian, approximately 54 miles north of Delta Junction. The Yellow Jacket deposit is located nearby in the SW1/4SE1/4 section 32, T. 6 S., R. 18 E., of the Fairbanks Meridian. A winter trail from the South Fork of the Goodpaster River provides access up Divide Creek. The mine entrance was still accessible in 1970 (Thomas, 1970). There are numerous surface workings at and surrounding the site. Note: The Grizzly Bear Mine is incorrectly labeled on current U.S.G.S. maps. It is locality 4 of Cobb and Eberlein (1980), who summarized relevant references under the name 'Grizzly Bear'.
Geology: The Grizzly Bear mine and Yellow Jacket deposit are 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. The area is characterized by rounded hills and flat-topped ridges (Thomas, 1970). The most prominent ridge is Black Mountain, which trends about 12 miles in a northerly direction and is underlain by Cretaceous granodiorite (Weber and others, 1978). Several creeks flow westward off Black Mountain in steep, parallel, V-shaped valleys to form the headwaters of Tibbs Creek. A combination of augen gneiss, gneissic schist, and schist are to 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 N15E and dips 65 degrees NW. The lode deposits in the area are gold-bearing quartz veins in the shear zone. Most of the veins are in the shear zone, although some are in the intrusive rocks. 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 veins such as the Blue Lead mine (BD003) contain relatively coarse gold, which is easily visible in hand specimen. The Grizzly Bear mine is centered 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 as a vein exposure at the surface approximately one third of a mile southwest of the Grizzly Bear mine. Foster and others (1978) cite the following emission spectroscopy assay of a rock sample from the area surrounding the Grizzly Bear mine: sample 74WR-180e contained greater than 10,000ppm As, 15 ppm B, 100 ppm Ba, 1.5 ppm Cr, 100 ppm Cu, 2 ppm Sr, 5 ppm V, 10 ppm Zr, and 0.3 ppm Au. 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 1930's, gold-bearing quartz veins were discovered in the upper Tibbs Creek area. By the winter of 1936, the first underground workings were being installed. The original base camp was on Summit Creek. A 450-foot tunnel was driven following a small vein, termed 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 outcropping 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 Blue Lead mine and Blue Lead Extension have approximately 775 feet of underground workings. There was limited exploration in the 1970's. The mill was still on site and the mine shaft openings were 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).
Workings: The Goodpaster region was first explored for placer gold in 1915. In the early 1930's, gold-bearing quartz veins were discovered in the upper Tibbs Creek area. By the winter of 1936, the first underground workings were being installed. The original base camp was on Summit Creek. A 450-foot tunnel was driven following a small vein, termed 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 outcropping 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 Blue Lead mine and Blue Lead Extension have approximately 775 feet of underground workings. There was limited exploration in the 1970's. The mill was still on site and the mine shaft openings were accessible in 1970, but blocked by ice (Thomas, 1970).
Age: Postdates Cretaceous granodiorite intrusion
Production: 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).

Commodities (Major) - Au; (Minor) - Ag, Cu, Pb, Sb
Development Status: Yes; small
Deposit Model: Shear-hosted, magmatic-hydrothermal vein

Other Databases

Link to USGS - Alaska:	BD018

Other Regions, Features and Areas containing this locality

References