Hidden Creek: Grable and Blackburn Mine

The Hidden Creek: Grable and Blackburn Mine is a silver and gold mine located in Alaska.

About the MRDS Data:

All mine locations were obtained from the USGS Mineral Resources Data System. The locations and other information in this database have not been verified for accuracy. It should be assumed that all mines are on private property.

Mine Info

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Site Name

Primary: Hidden Creek: Grable and Blackburn Mine

Commodity

Primary: Silver
Primary: Gold
Secondary: Bismuth
Secondary: Tin
Secondary: Tungsten
Secondary: Thorium

Location

State: Alaska
District: McGrath

Land Status

Not available

Holdings

Not available

Workings

Not available

Ownership

Not available

Production

Not available

Deposit

Record Type: Site
Operation Category: Past Producer
Operation Type: Unknown
Years of Production:
Organization:
Significant:

Physiography

Not available

Mineral Deposit Model

Model Name: Sn-polymetallic vein

Orebody

Not available

Structure

Not available

Alterations

Alteration Type: L
Alteration Text: Auriferous gravels partially cemented with ferricrete, due to ground water oxidation.

Alteration Type: L
Alteration Text: Sericite and tourmaline.

Rocks

Not available

Analytical Data

Not available

Materials

Ore: Bismuth
Ore: Cassiterite
Ore: Gold
Ore: Scheelite
Ore: Thorianite
Gangue: Magnetite
Gangue: Zircon
Gangue: Hematite
Gangue: Ilmenite

Comments

Comment (Exploration): Status = Inactive

Comment (Geology): Age = Quaternary

Comment (Deposit): Model Name = Placer Au-PGE (Cox and Singer, 1986; model no. 39c)

Comment (Production): Production Notes = Hidden Creek contributed about 50 percent of the placer gold production from the Nixon Fork area. Placer gold was first discovered on Hidden Creek in 1917 (Herreid, 1966). In 1922, F.A. Matthews and Louis Blackburn initiated placer gold production, which continued every season until 1932. Production resumed in 1935 and continued until 1938. Total production from 1922 to 1938 is estimated to be 4,435 ounces (138 kg) of gold and 230 ounces (7 kg) of silver. Production on Hidden Creek from 1938 to 1960 has not been accurately determined, but is not thought to be significant (Ted Almasy and Margaret Mespelt, personal communication, 1998).

Comment (Workings): Workings / Exploration = From 1922 to 1932, placer deposits were developed with hydraulic mine methods. A scraper was used to move large monzonite boulders in the mine cuts; these boulders frequently ranged from 2 to 6 feet (0.6-2 m) in diameter. In 1922 , 274 ounces of placer gold were recovered from 4,000 cubic yards of pay; i.e., this mine cut contained a recovered grade of 0.06 oz/cubic yard (2.78 g/ cubic meter) gold. A dragline was first used in 1935 and was used until mine shutdown in 1938. After World War II, Birch Creek and its tributaries continued to produce on a small scale until about 1960.

Comment (Reference): Primary Reference = Brown, 1926

Comment (Deposit): Other Comments = See also Encio (Riddle) Gulch (MD063) Birch Gulch (MD073), and Holmes Gulch (MD072). The Hidden Creek: Grable and Blackburn Mine is on land selected or conveyed to Doyon Ltd. For further information, contact Doyon Ltd. at 210 1st Ave., Fairbanks, Alaska, 99701.

Comment (Geology): Geologic Description = The productive portion of Hidden Creek lies along a third order stream with an average gradient of 120 feet/mile. Bedrock in most of the area that was placer mined is part of the Nixon Fork monzonite pluton which has yielded a K-Ar age of 68.0 Ma (Bundtzen and Miller, 1997). Most of the stream gravels consisted of monzonite float. Limestone underlies Hidden Creek Valley about 2 miles downstream from the head of the drainage. A copper-bearing pyroxenite dike that intrudes the limestone was found in one placer mine cut, which was thought to be a local source for placer gold. (Cobb, 1978; Herreid, 1966). ? Unconsolidated overburden above monzonite bedrock was 10-12 feet (3.0-3.7 m) thick, and auriferous gravels averaged about 4 feet (1.2 m) thick. The paystreak width varied from 75 to 125 feet (23 to 38 m) wide and averaged about 60 feet (18 m) in width. Below Birch Gulch, the Quaternary fill quickly thickens to as much as 200 feet (60 m); this abrupt thickening of Quaternary valley fill is probably related to the change of underlying bedrock from monzonite to limestone; chemical weathering, karsting, and cavern formation in the limestone was noted by Brown (1926).? Fourteen gold fineness determinations from placer gold mined in Hidden Creek ranged from 912 to 962 and averaged 928 (Mertie, 1936; Smith, 1941; Glover, 1942). Silver was the major impurity in the placer gold, which exhibits some of the highest fineness values of any Alaskan placer gold. In addition, substantial quantities of native bismuth occurs, frequently intergrown with native gold, magnetite, ilmenite, and brown scheelite. Minor to trace amounts of barite, cassiterite, zircon, and thorianite were found in heavy mineral concentrates during mine production, however, no other minerals other than placer gold were commercially recovered. Other placer streams such as Holmes, Riddle, and Birch Gulches, which presumably have similar if not identical lode sources for the placer gold, yield significantly different fineness values, which has mystified previous workers (i.e., Smith, 1941). Such data suggests significantly different lode sources for the placer gold in these areas.

Comment (Geology): Age = Age of mineralization is probably Upper Cretaceous, based on isotopic age of Nixon Fork pluton (Moll and others, 1981).

References

Reference (Deposit): Smith, P.S., 1930, Mineral industry of Alaska in 1928: U.S. Geological Survey Bulletin 813-A, p. 1-72.

Reference (Deposit): Mertie, J.B., Jr., 1936, Mineral deposits of the Ruby-Kuskokwim region, Alaska: U.S. Geological Survey Bulletin 864-C, 115-245.

Reference (Deposit): Smith, P.S., 1930, Mineral industry of Alaska in 1927: U.S. Geological Survey Bulletin 810-A, p. 1-64.

Reference (Deposit): Smith, P.S., 1930, Mineral industry of Alaska in 1928: U.S. Geological Survey Bulletin 813, p. 1-72.

Reference (Deposit): Smith, P.S., 1926, Mineral industry of Alaska in 1924: U.S. Geological Survey Bulletin 783-A, p. 1-39.

Reference (Deposit): Cobb, E.H., 1974, Synopsis of mineral resources and geology of Alaska: U.S. Geological Survey Bulletin 1307, 53 pages.

Reference (Deposit): Brown, J.S., 1926, The Nixon Fork country: U.S. Geological Survey Bulletin 783. p. 97-144.

Reference (Deposit): Herreid, G.H., 1966, Geology and geochemistry of the Nixon Fork area, Medfra quadrangle, Alaska: Alaska Division of Mines and Minerals Geologic Report 22, 34 p., 1 sheet, scale 1:40,000.

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