Granite

Mine, Inactive

Commodities and mineralogy

Main commodities Ag; Au
Other commodities Cu; Pb; Zn
Ore minerals arsenopyrite; chalcopyrite; galena; gold; pyrite; sphalerite; stibnite
Gangue minerals calcite; chlorite; graphite; quartz

Geographic location

Quadrangle map, 1:250,000-scale SR
Quadrangle map, 1:63,360-scale D-4
Latitude 60.9704
Longitude -148.2111
Nearby scientific data Find additional scientific data near this location
Location and accuracy The mine is located in the SE1/4 section 9, T. 10 N., R. 7 E., of the Seward Meridian. The mine and mill complex extend from sea level to 700 feet elevation, just inland from the shore of Port Wells between Harrison Lagoon and Hobo Bay. This is location 117 of Condon and Cass (1958), location 71 of Cobb and Richter (1972), location 77 of MacKevett and Holloway (1977), location 120 of Cobb and Tysdal (1980), location 77 of MacKevett and Holloway (1977), and location S-147 of Jansons and others (1984). This location is accurate to within a quarter of a mile.

Geologic setting

Geologic description

The Granite mine is hosted in slate and graywacke of the Valdez Group of Late Cretaceous age that has been cut by a large mass of Tertiary biotite granite. The granite is altered near the main vein to a light-gray to greenish-gray rock (Hoekzema and Sherman, 1983).
Most of the production has come from the main vein, which has a general strike of N50W to N70W and a dip of 43 to 55 N, although there is considerable variation in strike and dip in the workings (Johnson, 1915). The main vein is cut in numerous places by small normal faults. The main vein ranges from 3.5 inches to more than 14 feet in width and averages about 3.5 feet wide. The character of the vein varies with the country rock. In the sedimentary rocks, it consists of shattered slate, graywacke, and argillite cemented by veins and networks of sulfide-bearing, porous white crystalline quartz, accompanied by minor graphite, calcite, and chlorite. In the granite, the vein is a single structure, although at its widest part it consists of numerous shattered masses of altered granite cemented by quartz veinlets (Johnson, 1915).
The ore minerals consist of arsenopyrite, chalcopyrite, galena, pyrite, sphalerite, stibnite, and gold. Gold occurs as flakes and nuggets associated with graphite bands in the quartz veins (Roehm, 1936 [PE 95-6]). Generally the veins appear to have been higher in grade and more extensively stoped where hosted by metasedimentary rocks than by granite (Hoekzema and Sherman, 1983).
Total production from this mine was 31,919 tons of ore that contained 24,440 ounces of gold and 2,492 ounces of silver (Jansons and others, 1984).
Geologic map unit (-148.213173619866, 60.9698234697259)
Mineral deposit model Low-sulfide Au-quartz veins (Cox and Singer, 1986; model 36a)
Mineral deposit model number 36a
Age of mineralization Tertiary or younger; the veins cut Tertiary granite.
Alteration of deposit Granite is altered to a light-gray to greenish-gray rock (Johnson, 1915).

Production and reserves

Workings or exploration
The Granite mine consists of about 8,200 feet of workings that produced 31,919 tons of ore that contained 24,440 ounces of gold and 2,492 ounces of silver (Jansons and others, 1984). Most of the production occurred between 1914 and 1922. The ore was crushed in a 17-stamp mill to minus 40 mesh and passed over an amalgamator plate and concentrated on Wilfley and Deister tables. Power to the mine was provided originally by an oil-fired steam boiler that furnished steam for a 180-horsepower electric generator (Smith, 1917 [BMB 142, BMB 153]).
In 1982, the 350-foot-level adit was accessible, but the 200-foot-level adit was caved at the portal. The U.S. Bureau of Mines collected 25 samples from the mine and two samples of tailings (Hoekzema and Sherman, 1983). The mine samples contained from nil to 6.1 ppm gold. The tailing samples contained 0.18 and 0.19 ounce of gold per ton. The tailing samples were tested both by fire assay and cyanide bottle rolls. Bottle rolls and simulated heap leach tests indicated that 80 percent of the gold could be recovered by cyanidation.
Indication of production Yes; medium
Reserve estimates The U.S. Bureau of Mines estimated a resource of 1,860 tons of ore containing a grade of 0.78 ounce of gold per ton and 30,000 tons of tailings containing 0.18 to 0 0.19 ounce of gold per ton (Hoekzema and Sherman, 1983).
Production notes
The U.S. Bureau of Mines visited the Granite mine on several occasions during the RARE II study in the early 1980's (Hoekzema and Sherman, 1983). On the basis of past mining history and on low but persistent gold values present in samples collected by the Bureau, additional work appears to be warranted. The existing workings, however, appear to have nearly exhausted the deposit. Additional work thus should include drilling to identify possible vein extensions. Generally, the veins appear to have been higher in grade and more extensively stoped where hosted by metasedimentary rocks rather than by granite. However, high values were identified in samples of a granite-hosted portion of the vein located at the face of the 350-foot level (sample 5740A).
A 200-pound sample of the tailings was collected in 1982. This sample was sent to the Bureau of Mines laboratory in Juneau and to Helner Lindstrom Associates Inc. in Nevada. Both labs analysed the tails and obtained assays of about 0.18 to 0.19 ounce of gold per ton. The Bureau lab attempted to recover gold by amalgamation, but only 29 percent was recovered. Heiner Lindstom Associates Inc. performed bottle roll and simulated heap leach tests of the tailings. Both tests indicated that about 85 percent gold recovery could be obtained by cyanidation. The simulated heap leach test recovered 80 percent of the gold after 7 days. Apparently, amalgamation alone would not be sufficient to recover gold from the tailings, possibly because much of the gold is stained due to oxidation of sulfides.
The Bureau concluded that there is moderate mineral development potential for small to medium-size lode operation and high potertial for a cyanide leaching operation (Hoekzema and Sherman, 1983).

References

MRDS Number A010534

References

Hoekzema, R.P., and Sherman, G.E., 1983, Mineral investigations in the Chugach National Forest, Alaska (Peninsula study area): U.S. Bureau of Mines in-house report; held at U.S. Bureau of Land Management Alaska State Office, Anchorage, 524 p.
Smith, S.S., 1917, The mining industry in the Territory of Alaska during the calendar year 1915: U.S. Bureau of Mines Bulletin 142, 65 p.
Smith, S.S., 1917, The mining industry in the Territory of Alaska during the calendar year 1916: U.S. Bureau of Mines Bulletin 153, 89 p.
Reporters Jeff A. Huber (Anchorage)
Last report date 1/9/2000