Grant

Mine, Inactive

Commodities and mineralogy

Main commodities Au
Other commodities Ag; Pb; Sb; W
Ore minerals arsenic and antimony oxides; arsenopyrite; galena; gold; scheelite
Gangue minerals goethite; muscovite

Geographic location

Quadrangle map, 1:250,000-scale FB
Quadrangle map, 1:63,360-scale D-2
Latitude 64.882
Longitude -147.957
Nearby scientific data Find additional scientific data near this location
Location and accuracy The Grant mine is located in the SE1/4 sec. 28, T. 1 N., R. 2 W., Fairbanks Meridian. The Grant mine is marked on the Fairbanks D-2 topographic map on the southeast side of Ester Dome on the east side of Saint Patrick road. It is about 2.6 miles east of the top of Ester Dome and about three-quarters of a mile from the junction of the Saint Patrick road and the Ester Dome road. This mine is locality 21 of Cobb (1972 [MF 410]).

Geologic setting

Geologic description

The Grant mine consists of two, structurally controlled, gold-bearing vein-fault deposits, hosted in polymetamorphic schist and quartzite: the Irishman zone (FB057) and the O'Dea zone. From December 1980 to June 1981, Bundtzen and Kline (1981) spent 25 days mapping the underground workings at the Grant mine, and the following is a summary of their work. At the Irishman vein-fault system, late-stage silica injection was accompanied by free gold, arsenopyrite, lead-antimony sulfosalts and rare scheelite. Ore fluids were emplaced along a fault zone trending sinuously N20-40E and dipping steeply to the southeast. On the 150-foot and 200-foot levels, the vein-fault dips from 58 to 72 degrees, but it flattens out to 15 to 35 degrees in raises above the 100-foot level, where it intersects incompetent graphite-muscovite schist. Vein widths vary from 3 to more than 22 inches and average about 13 inches wide on the 100-foot and 150-foot levels. By 1982, underground exploration and development had shown that the Irishman vein was more than 400 feet long and had not bottomed out in the lowest workings. The deposit probably continues beyond the southwest end of the ore body that has been explored, but the northeast end is cut by a north-northwest-striking joint-fault system.
The O'Dea breccia zone consists of auriferous quartz breccia cemented by iron, arsenic, and antimony oxides, broken schist fragments, mylonite, and minor sulfides. The width of the vein-fault system varies from 6 inches to more than 6 feet. Multiple injections of silica also occurred along the O'Dea breccia zone, but unlike the Irishman system, recurrent movement along the vein-fault zone resulted in heavily oxidized, broken, and brecciated zones.
The first recorded exploration at this site occurred in 1929, when lode gold mineralization was found at the bottom of an old shaft that was sunk for placer prospecting. The shaft was sunk through muck and gravel to bedrock which dipped east at a steep angle (Hill, 1933, p. 150). This original shaft was continued in bedrock to a depth of 240 feet and had 280 feet of drifts on the 200-foot and 240-foot levels. The 5- to 6-foot-wide quartz vein was said to strike N40E and dip 65 E. (Hill, 1933). Before 1931, approximately 500 to 600 tons of ore was milled from this vein. Exploration and development at the mine has been intermittent since the 1920s. Prior to 1950, about 6,000 tons of ore were mined from the Irishman vein (Eakins and others, 1985, p. 16).
From 1979 to 1981, Tri-Con Mining, operator for Silverado Gold Mines, Ltd., at the Grant gold mine, engaged in an aggressive exploration and development program on the Irishman, O'Dea, and other gold-bearing shear zones on the Grant property (Eakins and others, 1985, p. 16). Underground workings consisted of 3,600 feet of drifts, crosscuts, and raises on and above the 200-foot level of the O'Dea zone (Bundtzen and Kline, 1981). During 1984, a $1.9 million exploration program was completed at the Grant mine (Eakins and others, 1985, p. 16). The drilling program defined an ore system on the O'Dea zone that extends 4,000 feet on strike and is as much as 1,000 feet deep. In 1985, the Grant mine recovered 1,563 ounces of gold and 1,178 ounces of silver from 5,036 tons of ore (Bundtzen and others, 1986, p. 26). During the seven weeks of mine production in 1989, the mill processed 8,000 tons which yielded 732 ounces of gold and 138 ounces of silver. From December 1987 to February 1989 when the mine closed, the Grant mine produced a total of 9,454 ounces of gold and 3,658 ounces of silver from 96,555 tons of ore at an average grade of 0.098 ounce of gold per ton (Bundtzen and others, 1990, p. 36-37).
Geologic map unit (-147.959431110042, 64.8815646056462)
Mineral deposit model Structurally controlled, auriferous vein-fault deposit hosted in polymetamorphic schist and quartzite.
Age of mineralization Gold-bearing quartz veins cut Fairbanks Schist host rocks that are considered to be pre-Devonian and probably Proterozoic in age (Newberry and others, 1996).
Alteration of deposit The O'Dea vein-fault zone is heavily oxidized; it consists of gold-bearing quartz breccia cemented by iron, arsenic and antimony oxides, broken schist fragments, mylonite, and minor sulfides (Bundtzen and Kline, 1981).

Production and reserves

Workings or exploration
The first recorded exploration at this site occurred in 1929, when lode gold mineralization was found at the bottom of an old shaft that was sunk for placer prospecting. The shaft was sunk through muck and gravel to bedrock, which dipped east at a steep angle (Hill, 1933, p. 150). This original shaft was continued in bedrock to a depth of 240 feet and had 280 feet of drifts on the 200-foot and 240-foot levels. Exploration and development at the mine has been intermittent since the 1920s.
From 1979 to 1981, Tri-Con Mining, operator for Silverado Gold Mines, Ltd., at the Grant gold mine, engaged in an aggressive exploration and development program on the Irishman, O'Dea, and other gold-bearing shear zones on the Grant property (Eakins and others, 1985, p. 16). Underground workings consisted of 3,600 feet of drifts and crosscuts and raises on and above the 200-foot level of the O'Dea zone (Bundtzen and Kline, 1981). The principal levels at the Irishman vein were at the 100-foot, 150-foot and 200-foot levels (Bundtzen and Kline, 1981). During 1984, a $1.9 million dollar exploration program was completed at the Grant mine (Eakins and others, 1985, p. 16). The drilling program defined an ore system on the O'Dea zone that extends 4,000 feet along strike and is as much as 1,000 feet deep. Late in 1989, Silverado Gold Mines, Ltd., signed an option agreement with American Copper and Nickel (ACNC) to explore and develop Silverado mining properties on Ester Dome, including the Grant mine property (Bundtzen and others, 1990, p. 37). In 1990, ACNC drilled 17,434 feet of core in the O'Dea vein system and on the Ethel vein system 2,000 feet to the north (Swainbank and others, 1991). ACNC also conducted an aerial geophysical survey of the area that same year (Bundtzen and others, 1991).
Indication of production Yes; medium
Reserve estimates The results of the 1990 ACNC drilling on a portion of the O'Dea vein system show a resource of 212,000 tons of material that contains 0.36 ounce of gold per ton (Swainbank and others, 1991, p. 11).
Production notes
Prior to 1950, about 6,000 tons of ore were mined from the Irishman vein (Eakins and others, 1985, p. 16). In 1985, the Grant mine recovered 1,563 ounces of gold and 1,178 ounces of silver from 5,036 tons of ore (Bundtzen and others, 1986, p. 26). During the seven weeks of mine production in 1989, the mill processed 8,000 tons, which yielded 732 ounces of gold and 138 ounces of silver. From December 1987 to February 1989 when the mine closed, the Grant mine produced a total of 9,454 ounces of gold and 3,658 ounces of silver from 96,555 tons of ore at an average grade of 0.098 ounce of gold per ton (Bundtzen and others, 1990, p. 36-37).
In early 1989, after the 100,000-ton tailings pond filled up at the Grant mine, the company decided that the costs for construction and permitting of a new tailings facility was prohibitive, and mining was shut down (Bundtzen and others, 1990, p. 37).

References

MRDS Number A010696; A015285

References

Reporters J.R. Guidetti Schaefer and C.J. Freeman (Avalon Development Corporation)
Last report date 7/31/2001