Crystal Mine, Juneau Mining District, Juneau, Alaska, USAi

Regional Level Types
Crystal Mine	Mine
Juneau Mining District	Mining District
Juneau	City Borough
Alaska	State
USA	Country

Location: The Crystal Mine is about about 0.5 mile east-northeast of where it is shown on the USGS 1:63,360-scale topographic map. The mine is actually about 0.3 mile west-northwest of the center of section 17, R.45 S. R., 72 E. The mine workings are shown on figure D-221 of Redman and others (1989).
Geology: The Crystal Mine was discovered in 1895 and in 1901, a ten-stamp mill was installed (Spencer, 1906; Redman and others, 1989). By 1905, there were 1,000 feet of underground workings and about 1,210 ounces of gold had been mined. In 1909, the mill processed about 750 tons of ore. Work continued intermittently until 1925. When operations ceased, the mine had 2,350 feet of underground workings, 5 stopes, and a 175-foot upper adit with a stope. There are no production data after 1905 but some additional amount of gold was produced. The deposit at the Crystal Mine is a quartz vein that lays along a low-angle fault. The fault is 1 to 10 feet thick and cuts amphibolite near the Snettisham ultramafic complex. The fault strikes S30-50E and dips 8-35E. The quartz vein undulates and varies in character along the plane of the fault. Where the fault does not contain quartz, it consists of sheared and altered amphibolite. Orange-weathering calcite is common as stringers and as a major component of the fault zone. Much of the fault contains a few inches to 10 feet of quartz. Some portions of the vein may have up to 60 percent silicified amphibolite associated with the quartz; some portions may be entirely quartz. Gouge zones 1 to 4 inches thick are common in the vein structure. The amphibolite host rock is commonly silicified and chloritized for 1 inch to 2 feet from the vein. The vein contains numerous open spaces which are often filled with quartz and calcite crystals up to 6 inches long. Pyrite is common in the quartz and may comprise up to 60 percent of the vein. Locally pyrite cubes up to 2 inches across are common and Spencer (1906) reported euhedral gold crystals growing on the pyrite. The Smithsonian Institution had or has on display a stunning cubic, pyrite crystal from the Crystal Mine that is about 3 inches on a side and has abundant terminated crystals of gold growing on the surface of the pyrite (Donald Grybeck, personal observation, 1983). Chalcopyrite is the only other sulfide and it is rare. Based on similarity with other gold deposits in the Juneau Gold Belt, the mineralization at the Crystal Mine is probably about 54 to 56 Ma and the hydrothermal fluids were generated by metamorphic processes. (Goldfarb and others, 1997). Redman and others (1989) collected 45 samples of the vein. A weighted average of the samples is 7.2 parts per million gold across an average width of 1.7 feet. They calculated an indicated resource of 9,000 tons of material with 0.21 ounce of gold per ton.
Workings: The Crystal Mine was discovered in 1895 and in 1901 a ten-stamp mill was installed (Spencer, 1906; Redman and others, 1989). By 1905, there were 1,000 feet of underground workings and about 1,210 ounces of gold had been mined. In 1909, the mill processed about 750 tons of ore. Work continued intermittently until 1925. When operations ceased, the mine had 2,350 feet of underground workings, 5 stopes, and a 175-foot upper adit with a stope. There are no production data after 1905 but some additional amount of gold was produced.
Age: Based on similarity with other gold deposits in the Juneau Gold Belt, the mineralization at the Crystal Mine is probably about 54 to 56 Ma and the hydrothermal fluids were generated by metamorphic processes. (Goldfarb and others, 1997).
Alteration: The amphibolite host rock is commonly silicified and chloritized for 1 inch to 2 feet from the vein.
Production: In 1909, the mill processed about 750 tons of ore. Work continued intermittently until 1925. There is no production data after 1905 but some addition amount of gold was produced.
Reserves: Redman and others (1989) collected 45 samples of the vein. A weighted average of the samples is 7.2 parts per million gold across an average width of 1.7 feet. They calculated an indicated resource of 9,000 tons of material with 0.21 ounce of gold per ton.

Commodities (Major) - Au; (Minor) - Cu
Development Status: Yes; small
Deposit Model: Gold-quartz vein in amphibolite.

Other Databases

Wikipedia:	https://en.wikipedia.org/wiki/Crystal_Mine
Wikidata ID:	Q5191292
Link to USGS - Alaska:	SD005

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References