Nabesna Mine, Chisana District, Valdez-Cordova Borough, Alaska, USA
|Latitude & Longitude (WGS84):||62° 22' 28'' North , 143° 0' 54'' West|
|Latitude & Longitude (decimal):||62.37444,-143.01500|
|Köppen climate type:||ET : Tundra|
The mine is in the Wrangell-St. Elias National Preserve.
Location: This mine is on the low, southeast flank of White Mountain at an elevation of about 3,600 feet, 1,000 feet north of Nabesna. The mine is about 0.1 mile northwest of the center of section 21, T. 7 N., R. 13 E. of the Copper River Meridian. This is locality M3 of Lowe and others (1982), locality 13 of Richter and others (1975), and National Park Service locality WRST-14 (unpublished data). Cobb and Richter included this mine under the name 'Nabesna (Mining Corp.)'. It is located to within about 100 feet.
Geology: Pyrite-rich ore bodies in tactite peripheral to a granitic stock were mined for their gold content at the Nabesna mine. The initial discovery was made in 1925 where a bear dug a hole that exposed the Bear vein that was to become the principal ore body in the mine (Wayland, 1943). A mill was in operation by 1931 and several ore bodies were developed over six levels of underground workings. There were 368 feet of surface cuts, 9,224 feet of drifts, and 6,209 feet of raises, in 650 vertical feet of mine workings (Wayland, 1943). Year-around operations were underway by 1935 when 60 tons per day were being milled. Most of the known ore bodies were mined out by 1939; total production was about 53,400 ounces of gold assuming a gold price of $35.00 per ounce. This recovery was from 72,994 tons of ore that varied in grade from 0.46 to 2.58 ounces of gold per ton. The ore had a weighted average grade of 0.93 ounce of gold per ton; 15,228 tons of tailings had a weighted average grade of 0.39 ounce of gold per ton (Wayland, 1943, p. 194). The average recovery for the life of the mine was 73 percent. The ore concentrate was shipped to the Tacoma smelter and some copper and silver credits were obtained. The gold-rich ore bodies were discontinuous sulfide veins and replacements along marble-front contacts and crosscutting fissures (Wayland, 1943; Newberry and others, 1997). Pyrite was the most common sulfide but it was accompanied by lesser amounts of sphalerite, galena, and chalcopyrite, especially in upper parts of the mine. Arsenopyrite and stibnite were also reported and magnetite occurs locally at the margins or within some ore bodies. Sphalerite and galena occur in pockets and stringers cutting pyrite and along the edge of pyrite stringers, whereas chalcopyrite tends to be disseminated through the pyrite. Gold was with or near the later sulfides including chalcopyrite and galena. The principal gangue minerals are coarsely crystalline calcite and quartz. Oxidation extends a few tens of feet to as much as 350 feet below the surface; anglesite, cerussite, and a little sulfur were identified in oxidized portions of the veins (Pilgrim, 1931, p. 60-62; Wayland, 1943). The individual ore bodies range in thickness from a few inches to 35 feet and average 5 to 7 feet thick. The Bear vein extends 320 feet horizontally, 250 feet vertically, and has a maximum thickness of 35 feet. The 'No. 49 stope' vein had a maximum horizontal length of 250 feet, a vertical length of 320 feet, and an average width of 4 to 5 feet. Other ore bodies were smaller irregular, pipelike, or tabular deposits. With the exception of the galena-rich 'No. 49 stope' vein, the ore bodies at lower levels had lower gold values, erratic mineralization, irregular shapes, and lesser amounts of sphalerite, chalcopyrite, and galena (Wayland, 1943). A five-foot sample across the Bear vein assayed 10.39 ounces of gold per ton 12.70 ounces of silver per ton, 1.67 percent lead, and 0.15 percent copper. A five-foot sample along the limestone/intrusive contact assayed 0.10 ounce gold per ton, 1.8 ounce silver per ton, and 4.2 percent copper (Pilgrim, 1931). The deposits are in the contact zone of a mid-Cretaceous granodiorite and quartz diorite stock that intrudes Triassic limestone and dolomite (Lowe and others, 1982). Skarn assemblages are well developed in the general area and include calcic skarn with abundant garnet and pyroxene and magnesian skarn with magnetite and serpentine (Weglarz, 1991; Newberry and others, 1997). Minerals identified in the skarn assemblages include andradite, apatite, brookite, diopside-hedenbergite, calcite, chlorite, epidote, gypsum, magnetite, quartz, specular hematite, serpentine, spinel, sphene, vesuvianite, and wollastonite (Wayland, 1943). Massive magnetite bodies containing pyrite, calcite and a little gold are present at all levels of the mine and are up to 200 feet in maximum dimension; some are localized at marble contacts (Wayland, 1943; Weglarz, 1991; Newberry and others, 1997). Sulfide minerals are common in the calcic skarn and magnetite is common in the magnesian skarn. Chalcopyrite and other sulfide minerals are common in the calcic skarn and Newberry and others (1997) consider the deposits in the area to be gold-rich copper skarns. The gold-bearing sulfide-rich pods, lenses, and veins are commonly localized in marble-front replacements and crosscutting shears (Newberry and others, 1997, figure 9). A concordant biotite/hornblende K/Ar date for nearby intrusive rocks is 114 +/- 3.4 Ma (Richter, Lanphere, and Matson, 1975).
Workings: The initial discovery was made in 1925 where a bear dug by a bear exposed the Bear vein, the principal ore body in the mine (Wayland, 1943). A mill was in operation by 1931 and several deposits were developed over six levels of underground workings. An aerial tramway transported the ore to the mill. There were 368 feet of surface cuts, 9,224 feet of drifts, and 6,209 feet of raises in over 650 vertical feet of mine workings (Wayland, 1943, p. 192). A total of 9,999 feet of diamond drilling supported exploration and development of the mine. Year-around operations were underway by 1935 when 60 tons per day were being milled. Most of the known ore bodies were mined out by 1939 and the last recorded production was in 1940 (Wayland, 1943). Exploration of the Nabesna mine area took place several times in the last half of the 20th century but the results have not been made public.
Age: Mid-Cretaceous. A concordant biotite/hornblende K/Ar date for the adjacent intrusive rocks is 114 +/- 3.4 Ma (Richter, Lanphere, and Matson, 1975).
Alteration: Oxidation was effective to a depth of several tens of feet and locally extends to more than 350 feet. Calc-silicate, magnetite, and sulfide replacement.
Production: Production is recorded from 1931 to 1940. Assuming a gold price of $35.00 per ounce, total production was about 53,400 ounces of gold. This was recovered from 72,994 tons of ore that ranged in grade from 0.46 to 2.58 ounces of gold per ton. The ore had a weighted average grade of 0.93 ounce of gold per ton; 15,228 tons of tailings had a weighted average grade of 0.39 ounce of gold per ton (Wayland, 1943, p. 194). The average recovery over the life of the mine was 73 percent. The ore concentrate was shipped to the Tacoma smelter and some copper and silver credits were obtained.
Commodities (Major) - Au; (Minor) - Ag, Cu, Fe, Pb, Zn
Development Status: Yes; medium
Deposit Model: Cu skarn (Cox and Singer, 1986; model 18b)
29 valid minerals.
This geological map and associated information on rock units at or nearby to the coordinates given for this locality is based on relatively small scale geological maps provided by various national Geological Surveys. This does not necessarily represent the complete geology at this locality but it gives a background for the region in which it is found.
Click on geological units on the map for more information. Click here to view full-screen map on Macrostrat.org
2.588 - 23.03 Ma
|Igneous: extrusive; Extrusive: undivided|
Age: Neogene (2.588 - 23.03 Ma)
Description: Okhotsk, Bering Sea, Pacific Alaska, Alaska Range
Comments: Orogen, magmatic arc/suite; Wilson & Hults, unpublished compilation, 2007-08
Lithology: Volcanic rocks; lava flows, pyroclastic debris
Reference: J.C. Harrison, M.R. St-Onge, O.V. Petrov, S.I. Strelnikov, B.G. Lopatin, F.H. Wilson, S. Tella, D. Paul, T. Lynds, S.P. Shokalsky, C.K. Hults, S. Bergman, H.F. Jepsen, and A. Solli. Geological map of the Arctic. doi:10.4095/287868. Geological Survey of Canada Map 2159A. 
|Carnian - Late Triassic|
228 - 237 Ma
|Chitistone and Nizina Limestones and Kamishak Formation|
Age: Late Triassic (228 - 237 Ma)
Description: Upper Part: thin-bedded, fine-grained limestone, interbedded with thin beds of argillite and carbonaceous shale. Minor beds of calcareous sandstone and grit Lower Part: fine-grained, massive limestone with chert lenses
Reference: Wilson, F.H., Hults, C.P., Mull, C.G, and Karl, S.M. (compilers). Geologic map of Alaska. doi: 10.3133/sim3340. U.S. Geological Survey Scientific Investigations Map 3340, pamphlet 196.