Le Roy

Site Name

Primary: Le Roy
Secondary: A. L. Parker
Secondary: Pet (after about 1975)

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Commodity

Primary: Gold
Secondary: Silver
Secondary: Arsenic
Secondary: Lead
Secondary: Zinc
Secondary: Cadmium
Secondary: Copper

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Location

State: Alaska
District: Juneau

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Land Status

Not available

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Holdings

Not available

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Workings

Not available

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Ownership

Not available

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Production

Not available

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Deposit

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

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Physiography

Not available

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Mineral Deposit Model

Model Name: Low-sulfide Au-quartz vein

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Orebody

Not available

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Structure

Not available

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Alterations

Alteration Type: L
Alteration Text: Rossman (1959, B 1058-B. p. 43) notes intense alteration that locally extends to 10 or 15 feet on each side of the vein, and is marked on the surface by rust-red staining. Alteration products almost certainly include ankerite and chlorite.

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Rocks

Role: Host
Age Type: Host Rock
Age Young: Cretaceous

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Analytical Data

Not available

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Materials

Ore: Arsenopyrite
Ore: Chalcopyrite
Ore: Galena
Ore: Pyrite
Ore: Sphalerite
Ore: Gold
Ore: Silver
Gangue: Ankerite
Gangue: Quartz

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Comments

Comment (Reserve-Resource): Reserves = Only a very small reserve is indicated with the present data. There are only about 260 ounces indicated in the floor of the lower adit by assuming 50 x 25 x 2-feet, a tonnage factor of 12 cu-ft/ton and grade of 1.25 oz/ton based on sampling reported by Holdsworth (1955).? Several narrow quartz veins are rich; the potential for discovering at least as much ore as was produced is good.

Comment (Deposit): Model Name = Similar to low-sulfide gold-quartz vein (Cox and Singer, 1986; model 36a). Low-sulfide gold-quartz vein, grading into a medium-sulfide type.

Comment (Production): Production Notes = Production was estimated by the U.S. Bureau of Mines (Kimball and others, 1978) to be from $130-170 thousand with gold at $35.00/ounce, or about 3700-4900 ounces of gold. During the main period of mining, the ore was crushed and ground in a mill on site. The ground ore was tabled; the dense table cut was amalgamated. The low-density table cut was then treated by flotation. The flotation concentrate was shipped to a smelter, presumably at Tacoma. The grinding limits are not known, so it is not possible to tell how much gold would have been liberated with very fine grinding. The owners reported only about 25 percent of the ore as free-milling (Kimball and others, 1978, p. C203). the main period of mining was from 1941-45 (Twenhofel and others, 1949, p. 32-34; Rossman, 1959, B 1058-B. p. 38-39).

Comment (Commodity): Ore Material = Gold (native)

Comment (Commodity): Ore Material = Silver (native)

Comment (Workings): Workings / Exploration = The discovery of the LeRoy occurred rather late in the history of the district. It was found in 1938 by A. L. Parker and his son, Leslie F. Parker. The Parkers mined and milled the ore on a small scale until Mr. Parker's death in 1941 (Rossman, 1959, B 1058-B, p. 38). The most extensive mining was done on lease between 1941 and 1945 by the LeRoy Mining Co. ? the LeRoy vein system has been explored by three main adits with more than 600 feet of workings. The upper LeRoy level is at a reported elevation of 987 feet; the lower LeRoy level is at about 950 feet. The workings on the Pet vein are at about 950 feet. The LeRoy vein was stoped above the upper Leroy level for about 100 feet. The vein was stoped below that level, but It has not been developed below the lower Leroy level. A 2-foot wide zone in the floor of the Lower level is reported to average 1.25 oz/ton gold for a distance of 50-feet.? the Pet vein is narrower. As exposed it generally ranges from 3-8 inches in thickness. It is about 1.5 feet thick in the face of the Pet drift. Most samples are in the 0.01 to .01 oz/ton gold range, but MacKevett obtained 0.44 ounce per ton gold on a narrow north-striking vein near the portal of the tunnel, and the Territorial Dept. of Mines found 0.22 ounce per ton gold in a raise near the face of the Pet. (MacKevett and others, 1971, p. 56-59, Pl. 9) the Pet probably was drilled in the 1970s, but the location of drill logs is unknown. ? the Leroy mine was examined by several territorial engineers, including Roehm (1942), Fowler (1950) and Holdsworth (1955).

Comment (Geology): Age = The granodiorite host rock is Cretaceous in age; mineralization is inferred to be Late Cretaceous or younger.

Comment (Geology): Age = Host rock is Cretaceous.

Comment (Exploration): Status = Inactive

Comment (Reference): Primary Reference = Rossman, 1959 (B 1058-B); Kimball and others, 1978

Comment (Deposit): Other Comments = There was minor activity at the LeRoy (Pet) in the 1970s by Jeannie Trump, the daughter of A. L Parker, and associates. Reportedly mineralization was sufficiently good to uphold the validity of two unpatented claims. The deposit is in Glacier Bay National Park and Preserve and the property is believed to be inactive.? the LeRoy deposit was the most productive mine in the Reid Inlet gold area, as defined by Kimball and others, 1978).

Comment (Geology): Geologic Description = The LeRoy mine is within a large sheared roof pendant within a granodiorite pluton of Cretaceous age (Brew and others, 1978). The pendant, strikes northerly to north-northeast in the vicinity of the mine; to the south, strike is north-northwest. Rocks within the pendant include graphitic schist and crystalline schist that Rossman (1959, B 1058-B, p. 45) proposed was metasedimentary. Thin section studies by MacKevett and others (1971, p. 56) show, however, that much of the schistose crystalline rock is intensely sheared (cataclastic) granodiorite. South of the mine a major fault lies within and is subparallel to the cataclastic zone (Rossman, 1959, B 1058-B, pl. 4). This fault is locally mineralized, as at the Highland Chief (MF030). A mafic dike that strikes northeast crops out east of mine; it appears to form the vein wall rock in the south part of the mine. ? the LeRoy vein is the thickest and most continuous of a swarm of about 15 quartz veins exposed at the mine. The veins strike north-northeast and are almost vertical. At least two other veins may have had some gold production; one is a vein developed in a short drift 25 feet east of the main workings. The so-called Pet vein was developed in a subparallel drift 100 feet northwest of the main LeRoy workings. ? the LeRoy vein consisted mainly of quartz and ankerite and averaged about 2 feet thick. Locally it was as much as 4.5 feet thick. The veins of the area are banded. Typically they contain 3-5 percent, occasionally more, sulfide minerals, which in approximate order of abundance are, arsenopyrite, pyrite, sphalerite, galena, and chalcopyrite. Gold occurred both in relatively coarse native form, also finely divided within the sulfide minerals. About one-third of the gold was recovered at the mine as native gold in gravity circuit or on amalgam plates. The rest was recovered from sulfide concentrate shipped to the smelter at Tacoma. The mine was rich, averaging about 3 ounces of gold per ton. Vein material exposed in the floor of the lower LeRoy workings averages about 1.25 ounce per ton gold in a remaining unmined shoot (Holdsworth, 1955). The vein appears to terminate or lose strength in the mafic dike host, but the vein system has not been well explored to the south.

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References

Reference (Deposit): Cobb, E.H., 1972, Metallic mineral resources map of the Mount Fairweather quadrangle, AK: U.S. Geological Survey Miscellaneous Field Study Map MF-436, 1 sheet, scale 1:250,000.

Reference (Deposit): Cobb, E.H., 1978, Summary of references to mineral occurrences (other than mineral fuels and construction materials) in the Mt. Fairweather and Skagway quadrangles, Alaska: U.S. Geological Survey Open-File Report 78-316, 123 p.

Reference (Deposit): Smith, P.S., 1942, Mineral industry of Alaska in 1940: U.S. Geological Survey Bulletin 933-A, p. 1-102.

Reference (Deposit): Twenhofel, W.S., Reed, J. C., and Gates, G.O., 1949, Some mineral investigations in southeastern Alaska: U.S. Geological Survey Bulletin 963-A, p. 1-45.

Reference (Deposit): Roehm, J.C., 1942, LeRoy Mining Company gold lode: Alaska Territorial Department of Mines Examination Report 111-2A, 7 p.

Reference (Deposit): Rossman, Darwin, 1959, Geology and ore deposits in the Reid Inlet area, Glacier Bay, Alaska: U.S. Geological Survey Bulletin 1058-B, p. 33-58.

Reference (Deposit): Fowler, H.M., 1950, Memorandum report on the Leroy Mine, Glacier Bay: Alaska Territorial Department of Mines, Prospect Evaluation 111-4, 2 p., 1 sheet, scale 1 inch = 20 feet.

Reference (Deposit): Holdsworth, P.R., 1955, Mt. Parker area, Mt. Fairweather quadrangle: Alaska Territorial Department of Mines Preliminary Examination Report 111-5, 3 p.

Reference (Deposit): MacKevett, E.M., Jr., Brew, D.A., Hawley, C.C., Huff, L.C., and Smith, J.G., 1971, Mineral resources of Glacier Bay National Monument, Alaska: U.S. Geological Survey Professional Paper 632, 90 p., 12 plates, scale 1:250,000.

Reference (Deposit): Kimball, A.L., Still, J.C., and Rataj, J.L., 1978, Mineral resources, in Brew, D. A., and others, Mineral resources of the Glacier Bay National Monument wilderness study area, Alaska: U.S. Geological Survey Open-File Report 78-494, p. C1-C375.

Reference (Deposit): Brew, D.A., Johnson, B.R., Grybeck, D., Griscom, A., Barnes, D.F., Kimball, A.L., Still, J.C., and Rataj, J.L., 1978, Mineral resources of the Glacier Bay National Monument Wilderness Study Area, Alaska: U.S. Geological Survey Open-File Report 78-494, 670 p.

Reference (Deposit): Smith, P.S., 1942, Mineral Industry of Alaska in 1940: U. S. Geological Survey Bulletin 933-A, p. 1-102.

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