Apex-El Nido

Mines, Active

Commodities and mineralogy

Main commodities Ag; Au; Cu; Pb; W; Zn
Ore minerals arsenopyrite; chalcopyrite; galena; gold; pyrite; scheelite; sphalerite; tetrahedrite
Gangue minerals quartz

Geographic location

Quadrangle map, 1:250,000-scale SI
Quadrangle map, 1:63,360-scale D-7
Latitude 57.949
Longitude -136.2936
Nearby scientific data Find additional scientific data near this location
Location and accuracy The Apex and El Nido mines are at the head of Cann Creek on northwest Chichagof Island, and are named on the USGS D-7 topographic map (1997 ed.). The mines are about 0.4 mile apart. The Apex Mine is at an elevation of about 1,050 feet, 0.3 mile south-southwest of the center of sec. 23, T. 45 S., R. 56 E.; the El Nido Mine is about at the same elevation, 0.4 mile southeast of the center of sec. 23. For this record, the site is plotted about midway between the mines. It is location P-17 of Bittenbender and others (1999), location 6 of Cobb (1972, 1978), and MAS no. 0021140008 (U.S. Bureau of Land Management, 2002). The location is accurate.

Geologic setting

Geologic description

Johnson and Karl (1985) map the rocks in the area of the Apex and El Nido mines as a stock of Cretaceous or Jurassic diorite. The stock is cut by diverse faults, the most prominent of which is the Peril Strait Fault, a regional-scale, northwest-striking, steeply-dipping fault that truncates the stock on the northeast.
The deposits at the mines are auriferous, sulfide-bearing quartz veins and stockworks (Buddington, 1925; Reed and Coats, 1941; Twenhofel and others, 1949; Rossman, 1959). The country rocks are a mixture of diorite, gabbro, pyroxenite, hornblendite, and aplitic dike rock. The rocks near the veins are intensely altered to quartz, calcite, and sericite. The veins, which locally display ribbon structure, are mostly quartz, but in places contain up to 50 percent sulfides. The sulfides, which also are disseminated in the wallrocks, are arsenopyrite, pyrite, sphalerite, chalcopyrite, and sparse tetrahedrite; gold and scheelite are also present. The veins pinch and swell from a few inches to about 7 feet. The stockwork at the El Nido Mine occurs at an abrupt change in orientation of the principal vein or where the vein is offset. A vertical fault separates the Apex and El Nido veins, which are symmetrical on either side of the fault.
Assays of the Apex lode averaged about 1.9 ounces of gold per ton in underground workings and about 4.57 ounces of gold per ton in surface outcrops. Assays of the El Nido vein were a little lower, but some outcrop samples ran as much as 24.2 ounces of gold per ton. The mines were in production from 1919-1920, when the veins were discovered, until 1939, when the mines closed (Cobb, 1978). Incomplete data record production of between 10,000 and 50,000 ounces of gold and about the same amount of silver. There were a total of about a mile of workings. The Apex Mine had 4 levels and about 3,600 feet of workings; the El Nido had about 1,800 feet of workings.
Bittenbender and others (1999), citing Holmes (1941) and Kimball (1982), report that the Apex and El Nido mines produced a cumulative total of about 17,000 ounces of gold and 2,400 ounces of silver in the periods 1924-28, 1934-35, and 1937-39. They describe the deposits as 1- to 4-foot-thick, steeply-dipping, gold-bearing quartz veins in diorite and amphibolite. Scheelite is erratically distributed in the veins. The main Apex vein strikes northeast and dips about 50 northwest; the El Nido vein strikes N70E and dips 30-80SE. The two vein systems are separated by about 2,000 feet of country rock. The U.S. Bureau of Mines examined the mines in 1978-79 (Kimball, 1982), sampled the underground workings, and collected outcrop samples of the veins over a strike length of 800 feet. Their samples contained a trace to 3.8 ounces of gold per ton across 0.2- to 3.8-foot-thick veins, and a trace to 0.4 ounce of gold per ton in aplite dikes. They identified an indicated resource of 26,633 tons of material with an average grade of 0.945 ounce of gold per ton. According to Bittenbender and others, the claims are active.
Isotopic studies indicate that the gold-quartz veins in coastal southern and southeastern Alaska are Eocene, about 50 Ma in age (Haeussler, 1995; Goldfarb, 1997; Goldfarb and others, 1997).
Geologic map unit (-136.295433751969, 57.9486172405845)
Mineral deposit model Polymetallic veins (Cox and Singer, 1986; model 22c).
Mineral deposit model number 22c
Age of mineralization Isotopic studies indicate that the gold-quartz veins in coastal southern and southeastern Alaska are Eocene, about 50 Ma in age (Haeussler and others, 1995; Goldfarb, 1997; Goldfarb and others, 1997).
Alteration of deposit The rocks near the veins are intensely altered to quartz, calcite, and sericite.

Production and reserves

Workings or exploration There were a total of about a mile of workings. The Apex Mine had 4 levels and about 3,600 feet of workings; the El Nido had about 1,800 feet of workings. The U.S. Bureau of Mines examined the mines in 1978-79, sampled the underground workings, and collected outcrop samples of the veins over a strike length of 800 feet.
Indication of production Yes; large
Reserve estimates The U.S. Bureau of Mines examined the mines in 1978-79 (Kimball, 1982), sampled the underground workings, and collected outcrop samples of the veins over a strike length of 800 feet. They identified an indicated resource of 26,633 tons of material with an average grade of 0.945 ounce of gold per ton.
Production notes According to Cobb (1978), incomplete data for the Apex and El Nido mines recorded the production of between 10,000 and 50,000 ounces of gold and about the same amount of silver from 1919 to 1939. Bittenbender and others (1999), citing Holmes (1941) and Kimball (1982), report that the Apex and El Nido mines produced a cumulative total of about 17,000 ounces of gold and 2,400 ounces of silver in the periods 1924-28, 1934-35, and 1937-39.

References

MRDS Number A010690; A013241; A013242

References

Bittenbender, P., Still, J.C., Maas, K., and McDonald, M., Jr., 1999, Mineral resources of the Chichagof and Baranof Islands area, southeast Alaska: Bureau of Land Management, BLM-Alaska Technical Report 19, 222 p.
Goldfarb, R J., 1997, Metallogenic evolution of Alaska, in Goldfarb, R.J., and Miller, L.D., eds., Mineral Deposits of Alaska: Economic Geology Monograph 9, p. 4-34.
Goldfarb, R.J., Miller, L.D., Leach, D.L., and Snee, L.W, 1997, Gold deposits in metamorphic rocks in Alaska, in Goldfarb, R.J., and Miller, L.D., eds., Mineral Deposits of Alaska: Economic Geology Monograph 9, p. 151-190.
Haeussler, P J., Bradley, D., Goldfarb, R., Snee, L., and Taylor, C., 1995, Link between ridge subduction and gold mineralization in southern Alaska: Geology, v. 23, no. 11, p. 995-998.
Holmes, G.L., 1941, Report on the Apex-EI Nido Mine: Unpublished report, 20 p. (Report held by the Mineral Information Center, Bureau of Land Management, Juneau, Alaska.)
U.S. Bureau of Land Management, 2002, Alaska mineral locations database report (Sitka quadrangle), July 2, 2002, 205 p. [http://imcg.wr.usgs.gov/dem.html]
Reporters H.C. Berg (U.S. Geological Survey)
Last report date 10/16/2004